In the oak forest of the introduction live oaks, deer, beetles and fungi, on soil that gets rain and sunlight.

Which of the following is a population?

1. A. ✓ The oaks of one kind in the forest
2. B. The oaks, deer, beetles and fungi of the forest together
   Several kinds of organism living in one place together are a community.
   A population is all the organisms of one species living in one place.
3. C. The oaks, deer, beetles and fungi together with the soil, rain and sunlight
   The living things of a place together with their non-living surroundings are an ecosystem.
   A population is one species in one place.

Why: A population is all the organisms of one species living in one place.
The oaks of one kind in the forest are one species in one place.
So they are a population.

Ecology is one branch of biology.

Which of the following is a question that ecology asks?

1. A. How the muscles in one trout’s tail push it through the water
   How one trout’s muscles work is the biology of one organism.
   Ecology asks how living things interact with one another and with their surroundings.
2. B. ✓ Why the trout in a stream gather where the water is coldest
3. C. How a town can cut the plastic it throws away
   Cutting plastic waste is something people do.
   Ecology is a branch of biology: the study of how living things interact.

Why: Ecology studies how living things interact with one another and with their surroundings.
Where the trout gather in the stream is a question about the trout and their surroundings.
So it is a question that ecology asks.

A biologist counts the pill bugs under fifty logs in a forest and records how damp the soil is under each log.

Which branch of biology is this biologist working in?

1. A. The study of how one cell works
   Counting pill bugs under logs and recording the soil studies a population and its surroundings.
   How living things interact with their surroundings is ecology, not the biology of one cell.
2. B. The study of how traits pass from parent to offspring
   Counting pill bugs under logs and recording the soil does not follow a trait from parent to offspring.
   It asks how a population and its surroundings go together: ecology.
3. C. ✓ Ecology

Why: The biologist is counting a population of pill bugs and recording its surroundings, the damp soil.
How living things interact with their surroundings is ecology.

Biology has several branches.

What is ecology?

1. A. The study of how one cell makes and uses the energy it needs to stay alive
   How a cell makes and uses energy is the biology of one cell.
   Ecology is about living things interacting with one another and with their surroundings.
2. B. ✓ The study of how living things interact with one another and with their surroundings
3. C. The care of the environment by people who recycle waste and save energy
   Caring for the environment is something people do.
   Ecology is a branch of biology: the study of how living things interact.

Why: Ecology is the study of how living things interact with one another and with their surroundings.

A large glass of juice raises a person’s blood glucose from 90 mg/dL to 140 mg/dL. Cells of the pancreas then release insulin, and the glucose falls back toward 90 mg/dL.

Which of the following is the stimulus?

1. A. ✓ The rise in blood glucose to 140 mg/dL
2. B. The release of insulin by cells of the pancreas
   Releasing insulin is what the body did about the rise.
   The stimulus is the change that moved the glucose away from its set point: the rise.

Why: A stimulus is a change that moves a regulated quantity away from its set point.
The rise to 140 mg/dL moved the glucose away from 90 mg/dL.
So the rise is the stimulus.

A lamp is switched on above an earthworm lying on the soil. The earthworm pulls back into its burrow.

Which of the following is the stimulus?

1. A. ✓ The light from the lamp
2. B. The earthworm pulling back into its burrow
   Pulling back into the burrow is what the earthworm did about the light.
   The stimulus is the change the earthworm detected: the light.

Why: The stimulus is the change the organism detects.
The earthworm detected the light from the lamp.
So the light is the stimulus.

Suppose a shadow passes over a cricket that is chirping. The cricket falls silent.

Which of the following is the response?

1. A. The shadow passing over the cricket
   The shadow is the change the cricket detected: the stimulus.
   The response is what the cricket did about it: falling silent.
2. B. ✓ The cricket falling silent

Why: The response is what the organism does about the change it detected.
The cricket detected the shadow and fell silent.
So falling silent is the response.

A finger touches a leaf of a sensitive plant (Mimosa). Within seconds the leaf folds up.

Which of the following is the stimulus?

1. A. The leaf folding up
   Folding up is what the plant did about the touch: the response.
   The stimulus is the change the plant detected: the touch.
2. B. ✓ The touch of the finger

Why: The stimulus is the change the organism detects.
The plant detected the touch of the finger.
So the touch is the stimulus.

A twig snaps behind a deer. The deer sprints into the trees.

Which of the following is the response?

1. A. ✓ The deer sprinting into the trees
2. B. The sound of the twig snapping
   The snap is the change the deer detected: the stimulus.
   The response is what the deer did about it: sprinting into the trees.

Why: The response is what the organism does about the change it detected.
The deer detected the snap and sprinted into the trees.
So the sprint is the response.

A person steps out of a warm house into cold air and starts to shiver.

Which of the following is the stimulus?

1. A. The shivering
   Shivering is what the person’s body did about the cold: the response.
   The stimulus is the change the person detected: the cold air.
2. B. ✓ The cold air

Why: The stimulus is the change the organism detects.
The person detected the cold air.
So the cold air is the stimulus.

Suppose the water at the surface of a lake warms through the afternoon. A trout near the surface swims down to deeper, cooler water.

Which of the following is the response?

1. A. The surface water warming
   The warming is the change the trout detected: the stimulus.
   The response is what the trout did about it: swimming down.
2. B. ✓ The trout swimming down to deeper water
3. C. The trout being cooler afterwards
   Being cooler is the result of the swim.
   The response is what the trout did: swimming down to deeper water.

Why: The response is what the organism does about the change it detected.
The trout detected the warmer water and swam down.
So the swim to deeper water is the response.

Suppose a cat hears a dog bark close by.

Which of the following is a physiological response?

1. A. The cat leaps onto the fence
   Leaping is something the whole cat does.
   A physiological response is a change inside the cat’s body.
2. B. The cat hisses at the dog
   Hissing is something the whole cat does.
   A physiological response is a change inside the cat’s body.
3. C. ✓ The cat’s heart beats faster

Why: A physiological response is a change inside the organism’s body.
A faster heartbeat is a change inside the cat’s body.
So the faster heartbeat is the physiological response.

As the morning sun comes up, a snake slides out onto a warm rock.

Which kind of response is this?

1. A. ✓ A behavioral response
2. B. A physiological response
   Sliding onto the rock is something the whole snake does.
   A response the whole organism does is a behavioral response.

Why: Sliding onto the rock is something the whole snake does.
So it is a behavioral response.

A bright light shines into a person’s eyes, and their pupils narrow.

Which kind of response is this?

1. A. A behavioral response
   The narrowing of the pupils is a change inside the person’s body.
   A change inside the body is a physiological response.
2. B. ✓ A physiological response

Why: The pupils narrowing is a change inside the person’s body.
So it is a physiological response.

A fox appears at the edge of a field, and a rabbit’s heart beats faster.

Which kind of response is this?

1. A. A behavioral response
   A faster heartbeat is a change inside the rabbit’s body.
   A change inside the body is a physiological response.
2. B. ✓ A physiological response

Why: A faster heartbeat is a change inside the rabbit’s body.
So it is a physiological response.

A hedgehog comes out to feed after dark.

Which kind of response is this?

1. A. ✓ A behavioral response
2. B. A physiological response
   Coming out to feed is something the whole hedgehog does.
   A response the whole organism does is a behavioral response.

Why: Coming out to feed is something the whole hedgehog does.
So it is a behavioral response.

The ground dries out, and a snail pulls back into its shell.

Which kind of response is this?

1. A. ✓ A behavioral response
2. B. A physiological response
   Pulling back into its shell is something the whole snail does.
   A response the whole organism does is a behavioral response.

Why: Pulling back into its shell is something the whole snail does.
So it is a behavioral response.

A person smells food cooking, and their mouth waters.

Which kind of response is this?

1. A. A behavioral response
   The mouth watering is a change inside the person’s body.
   A change inside the body is a physiological response.
2. B. ✓ A physiological response

Why: The mouth watering is a change inside the person’s body.
So it is a physiological response.

A student watches a person sweating in the sun and says: “Only movements count as responses, so sweating is something else.”

Is the student correct?

1. A. Yes
   Sweating is a change the body makes inside itself because of the heat.
   A change inside the body made about a stimulus is a physiological response.
2. B. ✓ No

Why: The heat is the stimulus.
The person’s body releases sweat because of the heat.
A change inside the body made about a stimulus is a response.
So sweating is a response, a physiological one, and the student is not correct.

Suppose a cat is out on a cold night. It curls up tightly, and its heart beats a little faster.

Which of the two responses is the physiological response?

1. A. ✓ The cat’s heart beating faster
2. B. The cat curling up tightly
   Curling up is something the whole cat does: a behavioral response.
   The change inside the cat’s body is the faster heartbeat.

Why: A physiological response is a change inside the organism’s body.
Curling up is something the whole cat does.
The faster heartbeat is a change inside the cat’s body.
So the faster heartbeat is the physiological response.

Three organisms each answer a stimulus.

Which of the following is a physiological response?

1. A. A dog running to the door when it hears a car
   Running to the door is something the whole dog does.
   A physiological response is a change inside the body.
2. B. ✓ A person’s face flushing red in the heat
3. C. A bee flying back to its hive as the light fades
   Flying back to the hive is something the whole bee does.
   A physiological response is a change inside the body.

Why: A physiological response is a change inside the organism’s body.
The face flushing red is a change in the blood flow inside the person’s body.
So the flushing is the physiological response.

In cold air, a person’s skin turns pale.

Which kind of response is this?

1. A. A behavioral response
   The skin turning pale is a change inside the person’s body.
   A change inside the body is a physiological response.
2. B. ✓ A physiological response

Why: The skin turning pale is a change inside the person’s body.
So it is a physiological response.

As evening comes, a frog begins to call from the edge of a pond.

Which kind of response is this?

1. A. ✓ A behavioral response
2. B. A physiological response
   Calling is something the whole frog does.
   A response the whole organism does is a behavioral response.

Why: Calling is something the whole frog does.
So it is a behavioral response.

On a hot afternoon, a cow walks to the water trough and drinks.

Which kind of response is this?

1. A. ✓ A behavioral response
2. B. A physiological response
   Walking to the trough and drinking are things the whole cow does.
   A response the whole organism does is a behavioral response.

Why: Walking to the trough and drinking are things the whole cow does.
So they are a behavioral response.

An organism answers a stimulus.

What is a behavioral response?

1. A. A change the organism’s body makes inside itself
   A change inside the body is a physiological response.
   A behavioral response is something the whole organism does.
2. B. ✓ Something the whole organism does, such as moving or calling

Why: A behavioral response is something the whole organism does about a stimulus, such as moving or calling.

A hand comes near a tortoise, and the tortoise pulls its head into its shell.

Which kind of response is this?

1. A. ✓ A behavioral response
2. B. A physiological response
   Pulling its head into its shell is something the whole tortoise does.
   A response the whole organism does is a behavioral response.

Why: Pulling its head into its shell is something the whole tortoise does.
So it is a behavioral response.

Cockles live buried in the sand of a seashore.

Which of the following is a question in ecology?

1. A. Which bases pair up with which in a cockle’s DNA?
   Which bases pair is a question about one molecule inside a cell.
   Ecology asks how living things interact with their surroundings.
2. B. How does a cell in a cockle’s gut make ATP?
   How a cell makes ATP is a question about the inside of one cell.
   Ecology asks how living things interact with their surroundings.
3. C. ✓ Why do cockles crowd where the sand stays wet at low tide?

Why: Ecology is the study of how living things interact with one another and with their surroundings.
Why cockles crowd where the sand stays wet asks how the cockles interact with their surroundings.
So it is a question in ecology.

Suppose a slug is on a garden path at dawn. The sun comes up and the path dries out. The slug crawls under a stone.

Which of the following is the stimulus?

1. A. ✓ The path drying out
2. B. The slug crawling under the stone
   Crawling under the stone is what the slug did about the change: the response.
   The stimulus is the change the slug detected: the path drying out.

Why: The stimulus is the change the organism detects.
The slug detected the path drying out.
So the drying of the path is the stimulus.

A student stands up to give a talk to the class, and her heart beats faster.

Which kind of response is this?

1. A. A behavioral response
   A faster heartbeat is a change inside the student’s body.
   A change inside the body is a physiological response.
2. B. ✓ A physiological response

Why: A faster heartbeat is a change inside the student’s body.
So it is a physiological response.

At the first light of dawn, a robin begins to sing.

Which of the following is the response?

1. A. ✓ The robin singing
2. B. The first light of dawn
   The first light is the change the robin detected: the stimulus.
   The response is what the robin did about it: singing.

Why: The response is what the organism does about the change it detected.
The robin detected the first light and began to sing.
So the singing is the response.

A student says: “Ecology means protecting the environment, so it is a job rather than a branch of biology.”

Is the student correct?

1. A. Yes
   Ecology is the study of how living things interact with one another and with their surroundings.
   That study is a branch of biology.
2. B. ✓ No

Why: Ecology is the study of how living things interact with one another and with their surroundings.
A study of living things is biology.
So ecology is a branch of biology, and the student is not correct.

A lizard sits on a rock in the sun. The rock gets hot, and the lizard walks into the shade.

Which of the following is the stimulus?

1. A. ✓ The rock getting hot
2. B. The walk into the shade
   The walk is what the lizard does about the change.
   The response is what the organism does; the stimulus is the change it detected.

Why: The stimulus is the change the organism detects.
The lizard detected the rock getting hot.
So the rock getting hot is the stimulus.

Three changes happen around and inside a frog.

Which of the following is an internal change?

1. A. The pond where the frog lives freezes over
   The pond froze in the frog’s surroundings, not inside its body.
   A change in the surroundings is an external change.
2. B. ✓ The frog’s blood glucose falls
3. C. Rain starts to fall on the frog’s pond
   The rain fell in the frog’s surroundings, not inside its body.
   A change in the surroundings is an external change.

Why: The frog’s blood is inside its body.
The fall in glucose happened inside the frog.
So the fall in blood glucose is an internal change.

A hare has not eaten all day. The glucose in its blood falls.

Which kind of change is the fall in glucose?

1. A. ✓ An internal change
2. B. An external change
   The glucose fell inside the hare’s own body, not in its surroundings.
   A change inside the body is an internal change.

Why: The glucose is in the hare’s blood, inside its body.
The fall happened inside the hare.
So the fall in glucose is an internal change.

In autumn the nights get longer over the forest where a deer lives.

Which kind of change is the lengthening of the nights?

1. A. An internal change
   The nights got longer in the deer’s surroundings, not inside its body.
   A change in the surroundings is an external change.
2. B. ✓ An external change

Why: The length of the night is part of the deer’s surroundings.
The change happened outside the deer.
So the lengthening of the nights is an external change.

A hawk’s shadow passes over a mouse feeding in a field.

Which kind of change is the passing shadow?

1. A. An internal change
   The shadow passed over the field, in the mouse’s surroundings.
   A change in the surroundings is an external change.
2. B. ✓ An external change

Why: The shadow fell on the field around the mouse.
The change happened outside the mouse.
So the passing shadow is an external change.

A dog chases a ball for ten minutes. Its body temperature rises.

Which kind of change is the rise in body temperature?

1. A. ✓ An internal change
2. B. An external change
   The temperature rose inside the dog’s own body, not in the air around it.
   A change inside the body is an internal change.

Why: The dog’s body temperature is a state of its own body.
The rise happened inside the dog.
So the rise in body temperature is an internal change.

A fox has drunk nothing since morning. The amount of water in its body falls.

Which kind of change is the fall in body water?

1. A. ✓ An internal change
2. B. An external change
   The water fell inside the fox’s own body, not in its surroundings.
   A change inside the body is an internal change.

Why: The water is inside the fox’s body.
The fall happened inside the fox.
So the fall in body water is an internal change.

Frost forms overnight on the grass where a rabbit feeds.

Which kind of change is the frost?

1. A. An internal change
   The frost formed on the grass, in the rabbit’s surroundings.
   A change in the surroundings is an external change.
2. B. ✓ An external change

Why: The grass is part of the rabbit’s surroundings.
The frost formed outside the rabbit.
So the frost is an external change.

A pill bug on the dry side of a dish walks until it reaches the damp side.

Which kind of response is the walk?

1. A. ✓ A behavioral response
2. B. A physiological response
   The walk is something the whole pill bug does.
   A change inside the pill bug’s body would be a physiological response.

Why: The whole pill bug walked.
So the walk is a behavioral response.

Suppose a snail sits on a dry stone in the sun for an hour.

What happens to the water in the snail’s body?

1. A. ✓ The snail loses water
2. B. The snail gains water
   Water leaves the snail through its skin into the dry air.
   No water comes in from dry air.
3. C. The amount of water stays the same
   In dry air water keeps leaving through the snail’s skin.
   So the amount of water in the snail falls.

Why: In dry air water leaves the snail through its skin.
Nothing replaces that water.
So the snail loses water.

A student watches the pill bug walk to the damp side and says: “The walk is worth having because the pill bug decides to do it.”

Is the student correct?

1. A. Yes
   The walk helps because it ends in damp air, where the pill bug loses less water.
   Whether the pill bug decided to walk does not change that.
2. B. ✓ No

Why: The walk ends in damp air.
There the pill bug loses less water.
So it survives.
The walk is worth having because it keeps the pill bug alive.
Whether the pill bug decided to walk does not change that.

On a hot afternoon the water at the surface of a lake warms. Less oxygen dissolves in warm water than in cool water. A trout swims down into the cooler, deeper water.

Which of the following does the swim into cooler water do for the trout?

1. A. ✓ The swim keeps the trout alive
2. B. The swim lets the trout reproduce
   No mate, eggs or offspring are part of this case.
   The swim changes how much oxygen the trout can take in.
3. C. The swim neither keeps the trout alive nor lets it reproduce
   In warm water the trout takes in too little oxygen and can die.
   In cool water it takes in enough oxygen to stay alive.

Why: Less oxygen dissolves in the warm surface water.
A trout that stays there takes in too little oxygen and can die.
More oxygen dissolves in the cooler, deeper water.
So the swim keeps the trout alive.

In spring a male stork stands at a nest and claps its bill in a display. A female joins him at the nest. The pair raises chicks.

Which of the following does the display do for the male stork?

1. A. The display keeps the stork alive
   The display brings no food and removes no danger.
   It brings the female, and the pair raises chicks.
2. B. ✓ The display lets the stork reproduce
3. C. The display neither keeps the stork alive nor lets it reproduce
   The pair raises chicks after the display.
   Chicks are offspring, so the display let the stork reproduce.

Why: The display brings a female to the nest.
The pair raises chicks, which are the male’s offspring.
So the display lets the stork reproduce.

On a cold night a squirrel’s body temperature falls.

Which kind of change is the fall in body temperature?

1. A. ✓ An internal change
2. B. An external change
   The temperature fell inside the squirrel’s own body, not in the air around it.
   A change inside the body is an internal change.

Why: The squirrel’s body temperature is a state of its own body.
The fall happened inside the squirrel.
So the fall in body temperature is an internal change.

A bat roosts by day and flies out at dusk to hunt. On a day it has not eaten, its hunger makes it leave the roost earlier. A student says: “Only a change outside the bat can be a stimulus, so the bat’s hunger is just a feeling.”

Is the student correct?

1. A. Yes
   A stimulus is a change the organism detects, inside the body or outside it.
   The bat detects its own hunger and answers it, so the hunger is a stimulus.
2. B. ✓ No

Why: A stimulus is a change the organism detects.
The change can happen inside the organism’s own body.
The bat detects its hunger and leaves the roost earlier.
So the hunger is a stimulus, an internal one.

A lizard sits on a rock at noon. The rock gets hot. The lizard walks into the shade.

Which of the following does the walk into the shade do for the lizard?

1. A. ✓ The walk keeps the lizard alive
2. B. The walk lets the lizard reproduce
   No mate, eggs or offspring are part of this case.
   The walk changes how hot the lizard’s body gets.
3. C. The walk neither keeps the lizard alive nor lets it reproduce
   In the shade the lizard’s body stops heating up.
   A lizard whose body gets too hot dies, so the walk does help.

Why: On the hot rock the lizard’s body heats up.
A lizard whose body gets too hot dies.
In the shade its body stops heating up.
So the walk keeps the lizard alive.

The stream a deer drinks from dries up in a drought.

Which kind of change is the drying of the stream?

1. A. An internal change
   The stream dried up in the deer’s surroundings, not inside its body.
   A change in the surroundings is an external change.
2. B. ✓ An external change

Why: The stream is part of the deer’s surroundings.
The drying happened outside the deer.
So the drying of the stream is an external change.

A student watches a lizard walk off a hot rock into the shade and says: “The walk helps the lizard because the lizard chooses to walk.”

Is the student correct?

1. A. Yes
   The walk helps because of what it does to the lizard’s body.
   In the shade the body stops heating up, so the lizard stays alive.
2. B. ✓ No

Why: In the shade the lizard’s body stops heating up.
A lizard whose body gets too hot dies.
So the walk keeps the lizard alive.
The walk helps for that reason, whether or not the lizard chose it.

A woodlouse on the warm half of a dish moves fast. On the cool half the woodlouse moves slowly.

Which of the following is the stimulus?

1. A. ✓ The warmth of the dish
2. B. The woodlouse’s fast movement
   The fast movement is what the woodlouse does.
   What the woodlouse does is the response.

Why: The stimulus is the change the woodlouse detects.
The woodlouse detects the warmth.
So the warmth is the stimulus.

Suppose an insect flies toward a lamp at night.

Which kind of movement is the insect’s flight?

1. A. ✓ A taxis
2. B. A kinesis
   A kinesis has no fixed direction.
   The insect’s flight has one: toward the lamp.

Why: The lamp is the stimulus.
The insect moves toward the lamp.
A movement toward or away from the stimulus is a taxis.

Suppose beetles walk fast in dry air and slowly in damp air, in no fixed direction.

Which kind of movement is the beetles’ walking?

1. A. A taxis
   A taxis has a direction, toward or away from the stimulus.
   These beetles change speed with no fixed direction.
2. B. ✓ A kinesis

Why: The dryness is the stimulus.
The beetles change their speed with no fixed direction.
A change in speed with no fixed direction is a kinesis.

Suppose a flatworm turns often in bright light and rarely in the shade, in no fixed direction.

Which kind of movement is the flatworm’s turning?

1. A. A taxis
   A taxis has a direction, toward or away from the stimulus.
   The flatworm’s turning has no fixed direction.
2. B. ✓ A kinesis

Why: The light is the stimulus.
The flatworm changes how often it turns, with no fixed direction.
A change in turning with no fixed direction is a kinesis.

Suppose a snail crawls away from a bright light.

Which kind of movement is the snail’s crawl?

1. A. ✓ A taxis
2. B. A kinesis
   A kinesis has no fixed direction.
   The snail’s crawl has one: away from the light.

Why: The light is the stimulus.
The snail moves away from the light.
A movement toward or away from the stimulus is a taxis.

Suppose a fish swims toward the smell of food.

Which kind of movement is the fish’s swim?

1. A. ✓ A taxis
2. B. A kinesis
   A kinesis has no fixed direction.
   The fish’s swim has one: toward the smell.

Why: The smell is the stimulus.
The fish moves toward the smell.
A movement toward or away from the stimulus is a taxis.

Suppose a fish swims fast in warm water and slowly in cool water, in no fixed direction, and ends up in the cool water.

Which kind of movement is the fish’s swim?

1. A. A taxis
   Ending up in the cool water does not give the movement a direction.
   No fish headed for the cool water; each fish slowed down there.
2. B. ✓ A kinesis

Why: The warmth is the stimulus.
The fish changes speed with no fixed direction.
The fish slows in the cool water, so it stays there longer.
A change in speed with no fixed direction is a kinesis, even when it ends somewhere better.

The two drawings below show the path of one small animal in a dish with a shaded patch.

Which drawing shows a taxis?

1. A. ✓ Drawing 1
2. B. Drawing 2
   In drawing 2 the path bends again and again, with no fixed direction.
   That movement is a kinesis.

Why: In drawing 1 the animal moves in one direction: toward the patch.
A movement toward the stimulus is a taxis.

Suppose fish in a tank swim fast at the warm end and slowly at the cool end, in no fixed direction. After an hour most of the fish are at the cool end. A student says: “They must have swum toward the cool end.”

Is the student correct?

1. A. Yes
   The fish do not head for the cool end.
   Each one slows down there and stays; at the warm end each one moves fast and soon leaves.
2. B. ✓ No

Why: Each fish moves fast at the warm end and slowly at the cool end.
A fish that reaches the cool end slows down.
So it stays there.
A fish at the warm end soon leaves it.
So the fish gather at the cool end without swimming toward it.

Suppose an insect speeds up in dry air, in no fixed direction.

Is the insect’s movement a taxis?

1. A. Yes
   A taxis has a direction, toward or away from the stimulus.
   This movement has no fixed direction.
2. B. ✓ No

Why: The insect changes speed with no fixed direction.
A change in speed with no fixed direction is a kinesis, not a taxis.

Suppose a beetle walks toward the smell of rotting fruit.

Is the beetle’s walk a taxis?

1. A. ✓ Yes
2. B. No
   The beetle moves toward the smell.
   A movement toward the stimulus is a taxis.

Why: The smell is the stimulus.
The beetle moves toward the smell.
So the walk is a taxis.

Suppose a snail turns more often in bright light, in no fixed direction.

Is the snail’s turning a kinesis?

1. A. ✓ Yes
2. B. No
   The snail changes how often it turns, with no fixed direction.
   That change is a kinesis.

Why: The snail changes how often it turns.
The turning has no fixed direction.
So the turning is a kinesis.

Suppose a fish swims away from a patch of cold water.

Is the fish’s swim a kinesis?

1. A. Yes
   A kinesis has no fixed direction.
   The fish’s swim has one: away from the cold water.
2. B. ✓ No

Why: The fish moves away from the cold water.
A movement away from the stimulus is a taxis, not a kinesis.

An animal responds to a stimulus by moving.

What is a taxis?

1. A. ✓ A movement toward or away from the stimulus
2. B. A change in speed or turning, with no fixed direction
   A change in speed or turning with no fixed direction is a kinesis.
3. C. A change inside the animal’s body
   A change inside the animal’s body is a physiological response, not a movement.

Why: A taxis is a movement toward or away from the stimulus.

An animal responds to a stimulus by moving.

What is a kinesis?

1. A. A change inside the animal’s body
   A change inside the animal’s body is a physiological response, not a movement.
2. B. A movement toward or away from the stimulus
   A movement toward or away from the stimulus is a taxis.
3. C. ✓ A change in speed or turning, with no fixed direction

Why: A kinesis is a change in speed or turning, with no fixed direction.

A shoot on a windowsill grows toward the light from the window.

Which kind of change is the light?

1. A. An internal change
   An internal change happens inside the plant’s own body.
   The light comes from the plant’s surroundings.
2. B. ✓ An external change

Why: An internal change happens inside the organism’s own body.
An external change happens in its surroundings.
The light comes from the window, in the plant’s surroundings.
So the light is an external change.

Suppose a potted plant on a shelf bends toward the room’s one window.

Which kind of response is the bend?

1. A. ✓ Phototropism
2. B. Photoperiodism
   Photoperiodism is a timing: when the plant flowers.
   This bend is a direction of growth.

Why: The light from the window is the stimulus.
The plant grows toward the light.
A shoot growing toward the light is phototropism.

Suppose a seedling in a dark box grows toward the box’s one small hole.

Which kind of response is the seedling’s growth?

1. A. ✓ Phototropism
2. B. Photoperiodism
   Photoperiodism is a timing of flowering.
   This seedling is growing in a direction: toward the light from the hole.

Why: Light comes through the hole.
The seedling grows toward the light.
A shoot growing toward the light is phototropism.

Suppose a plant flowers in spring, once the nights have grown short.

Which kind of response is the flowering?

1. A. Phototropism
   Phototropism is a shoot growing toward the light.
   This plant is timing its flowering by the length of the night.
2. B. ✓ Photoperiodism

Why: The length of the night is the stimulus.
The plant times its flowering by that length.
A plant timing its flowering by the length of the night shows photoperiodism.

Suppose a vine’s shoots grow toward the sunnier side of a garden.

Which kind of response is the shoots’ growth?

1. A. ✓ Phototropism
2. B. Photoperiodism
   Photoperiodism is a timing of flowering.
   These shoots grow in a direction: toward the sunnier side.

Why: The sunlight is the stimulus.
The shoots grow toward the sunlight.
A shoot growing toward the light is phototropism.

Suppose a plant flowers in autumn, once the nights have grown long.

Which kind of response is the flowering?

1. A. Phototropism
   Phototropism is a direction of growth, toward the light.
   Flowering once the nights grow long is a timing.
2. B. ✓ Photoperiodism

Why: The length of the night is the stimulus.
The plant flowers once the nights are long.
A plant timing its flowering by the length of the night shows photoperiodism.

A chrysanthemum flowers in autumn. A student says: “The plant flowers because it senses that the weather has turned colder.”

Is the student correct?

1. A. Yes
   The chrysanthemum responds to the hours of darkness each night, not to the temperature.
2. B. ✓ No

Why: The chrysanthemum responds to the length of the night.
In autumn the nights grow longer.
The longer nights are what the plant responds to, not the colder weather.

Suppose a sunflower seedling’s shoot bends toward the morning sun.

Is the bend phototropism?

1. A. ✓ Yes
2. B. No
   The shoot grows toward the light.
   A shoot growing toward the light is phototropism.

Why: The sunlight is the stimulus.
The shoot grows toward the sunlight.
So the bend is phototropism.

Suppose a plant flowers in early summer, once the nights have grown short.

Is the flowering photoperiodism?

1. A. ✓ Yes
2. B. No
   The plant times its flowering by the length of the night.
   That timing is photoperiodism.

Why: The plant flowers when the nights are short.
The length of the night sets the timing.
So the flowering is photoperiodism.

Suppose a plant flowers once the nights are longer than 11 hours.

Is the flowering phototropism?

1. A. Yes
   Phototropism is a shoot growing toward the light.
   This plant is timing its flowering by the length of the night.
2. B. ✓ No

Why: The plant times its flowering by the length of the night.
That timing is photoperiodism, not phototropism.

A plant responds to light.

What is phototropism?

1. A. ✓ A shoot bending to grow toward the light
2. B. A plant timing its flowering by the length of the day or night
   A plant timing its flowering by the length of the day or night shows photoperiodism.
3. C. A shoot growing faster in brighter light
   Phototropism is a direction of growth, not a speed of growth.

Why: Phototropism is a shoot growing toward the light.

A plant responds to light.

What is photoperiodism?

1. A. A shoot growing faster in brighter light
   Photoperiodism is a timing of flowering, not a speed of growth.
2. B. A shoot bending to grow toward the light
   A shoot bending to grow toward the light is phototropism.
3. C. ✓ A plant timing its flowering by the length of the day or night

Why: Photoperiodism is a plant timing its flowering by the length of the day or night.

Suppose a plant flowers as the winter nights shorten into spring.

Which of the following is this response?

1. A. Taxis
   A taxis is an animal moving toward or away from the stimulus.
   This plant is timing its flowering.
2. B. Kinesis
   A kinesis is an animal changing speed or turning with no fixed direction.
   This plant is timing its flowering.
3. C. Phototropism
   Phototropism is a shoot growing toward the light.
   This plant is timing when it flowers.
4. D. ✓ Photoperiodism

Why: The length of the night is the stimulus.
The plant times its flowering by that length.
That timing is photoperiodism.

Suppose an insect moves fast in dry air and slowly in damp air, in no fixed direction.

Which of the following is this response?

1. A. Taxis
   A taxis has a direction, toward or away from the stimulus.
   This insect’s movement has no fixed direction.
2. B. ✓ Kinesis
3. C. Phototropism
   Phototropism is a shoot growing toward the light.
   This is an animal changing its speed.
4. D. Photoperiodism
   Photoperiodism is a plant timing its flowering.
   This is an animal changing its speed.

Why: The dryness is the stimulus.
The insect changes speed with no fixed direction.
That change is a kinesis.

Suppose a shoot in a greenhouse bends toward the brightest pane of the glass roof.

Which of the following is this response?

1. A. Taxis
   A taxis is an animal moving toward or away from the stimulus.
   This is a shoot growing.
2. B. Kinesis
   A kinesis is an animal changing speed or turning.
   This is a shoot growing.
3. C. ✓ Phototropism
4. D. Photoperiodism
   Photoperiodism is a timing of flowering.
   This shoot is growing in a direction: toward the light.

Why: The bright light is the stimulus.
The shoot grows toward the light.
That growth is phototropism.

Suppose a fish swims away from a patch of cloudy water.

Which of the following is this response?

1. A. ✓ Taxis
2. B. Kinesis
   A kinesis has no fixed direction.
   This fish swims in one direction: away from the cloudy water.
3. C. Phototropism
   Phototropism is a shoot growing toward the light.
   This is an animal swimming.
4. D. Photoperiodism
   Photoperiodism is a plant timing its flowering.
   This is an animal swimming.

Why: The cloudy water is the stimulus.
The fish moves away from the cloudy water.
That movement is a taxis.

Suppose a millipede moves fast in bright light and slowly in the shade, in no fixed direction, and ends up in the shade.

Which of the following is this response?

1. A. Taxis
   Ending up in the shade does not give the movement a direction.
   The millipede did not head for the shade; it slowed down there.
2. B. ✓ Kinesis
3. C. Phototropism
   Phototropism is a shoot growing toward the light.
   This is an animal changing its speed.
4. D. Photoperiodism
   Photoperiodism is a plant timing its flowering.
   This is an animal changing its speed.

Why: The light is the stimulus.
The millipede changes speed with no fixed direction.
That change is a kinesis, even though the millipede ends up somewhere better.

Suppose a houseplant’s stem curves toward a skylight.

Which of the following is this response?

1. A. Taxis
   A taxis is an animal moving toward or away from the stimulus.
   This is a plant’s stem growing.
2. B. Kinesis
   A kinesis is an animal changing speed or turning.
   This is a plant’s stem growing.
3. C. ✓ Phototropism
4. D. Photoperiodism
   Photoperiodism is a timing of flowering.
   This stem is growing in a direction: toward the light.

Why: The light from the skylight is the stimulus.
The stem grows toward the light.
That growth is phototropism.

In Unit 3 a student compared catalase from potato and from liver. The source of the catalase was the condition she deliberately changed.

Which name does a fair test give to the condition the experimenter deliberately changes?

1. A. ✓ The independent variable
2. B. The dependent variable
   The dependent variable is the quantity measured to see the effect.
3. C. A control variable
   A control variable is a condition kept the same in every tube.

Why: The independent variable is the condition the experimenter deliberately changes.
She deliberately changed the source of the catalase.
So the source of the catalase was the independent variable.

A student covers the left side of a dish so it is dark and leaves the right side in the light. She tips in 12 woodlice and counts the woodlice on each side after 3 minutes.

Which is the independent variable?

1. A. The number of woodlice on each side
   The number of woodlice on each side is the result she measures.
   That count is the dependent variable.
2. B. The size of the dish
   The size of the dish is the same for both sides.
3. C. ✓ Dark or light on a side

Why: The independent variable is the condition the experimenter deliberately sets to two values.
She makes one side dark and leaves the other side in the light.
So light is the independent variable.

A student lays warm sand on the left side of a tray and cool sand on the right side. He tips in 12 mealworms and counts the mealworms on each side after 5 minutes.

Which is the independent variable?

1. A. The number of mealworms on each side
   The number of mealworms on each side is the result he measures.
   That count is the dependent variable.
2. B. ✓ Temperature
3. C. The size of the tray
   The size of the tray is the same for both sides.

Why: The independent variable is the condition the experimenter deliberately sets to two values.
He makes one side warm and the other side cool.
So temperature is the independent variable.

A student lays warm sand on one side of a tray and cool sand on the other side, and tips 12 mealworms into every tray he sets up.

Is the number of mealworms tipped in the independent variable?

1. A. Yes
   He tips 12 mealworms into every tray.
   A condition kept the same is not the condition he changes.
2. B. ✓ No

Why: The independent variable is the one condition the experimenter deliberately changes.
He keeps the number of mealworms at 12 in every tray.
So the number of mealworms is not the independent variable.
Temperature is.

A student lays damp cloth on one side of a board and dry cloth on the other side, tips in 15 snails and counts the snails on each side after 10 minutes.

Is dampness the independent variable?

1. A. ✓ Yes
2. B. No
   She deliberately sets one side damp and the other side dry.
   Dampness is the one condition she changes.

Why: The independent variable is the one condition the experimenter deliberately changes.
She sets one side damp and the other side dry.
So dampness is the independent variable.

In the Unit 3 enzyme tubes, the student collected the oxygen from each tube for 4 minutes and measured its volume.

Which name does a fair test give to the quantity measured to see the effect?

1. A. The independent variable
   The independent variable is the condition the experimenter deliberately changes.
2. B. ✓ The dependent variable
3. C. A control variable
   A control variable is a condition kept the same in every tube.

Why: The dependent variable is the quantity measured to see the effect.
She measured the volume of oxygen to see the effect of the tissue.
So the volume of oxygen was the dependent variable.

A student tips 20 fruit flies into a tube lit at one end and dark at the other end. She counts the flies at each end after 3 minutes.

Which is the dependent variable?

1. A. ✓ The number of flies at each end
2. B. Dark or light at an end
   Light is the condition she deliberately changes from one end to the other.
   Light is the independent variable.
3. C. The number of flies tipped in
   She sets the number of flies, 20, at the start.
   She does not measure it as the result.

Why: The dependent variable is the quantity measured to see the effect.
She counts the flies at each end after 3 minutes.
So the number of flies at each end is the dependent variable.

A student lays rough cloth on one side of a board and smooth cloth on the other side. He tips in 15 snails and counts the snails on each side after 10 minutes.

Which is the dependent variable?

1. A. The roughness of the cloth
   The roughness of the cloth is the condition he deliberately changes.
   Roughness is the independent variable.
2. B. The size of the board
   The size of the board is the same for both sides.
3. C. ✓ The number of snails on each side

Why: The dependent variable is the quantity measured to see the effect.
He counts the snails on each side after 10 minutes.
So the number of snails on each side is the dependent variable.

A student covers the left side of a dish so it is dark and leaves the right side in the light, then tips in 12 woodlice.

Is light the dependent variable?

1. A. Yes
   She sets one side dark and the other side light.
   Light is a condition she sets, not a result she measures.
2. B. ✓ No

Why: The dependent variable is the quantity measured to see the effect.
She sets the light on each side.
She does not measure it as the result.
So light is not the dependent variable.
Light is the independent variable.

A student lays warm sand on one side of a tray and cool sand on the other side, tips in 12 mealworms and counts the mealworms on each side after 5 minutes.

Is the number of mealworms on each side the dependent variable?

1. A. ✓ Yes
2. B. No
   He counts the mealworms on each side to see the effect of temperature.
   That count is the result he measures.

Why: The dependent variable is the quantity measured to see the effect.
He counts the mealworms on each side after 5 minutes.
So the number of mealworms on each side is the dependent variable.

In the Unit 3 enzyme tubes, one tube of hydrogen peroxide got the same treatment as the others but no tissue.

What is the control in an experiment?

1. A. A condition kept the same in every tube
   A condition kept the same in every tube is a control variable.
2. B. The condition the experimenter deliberately changes
   The condition the experimenter deliberately changes is the independent variable.
3. C. ✓ The tube that lacks only the factor under test

Why: The control is a whole tube.
It gets the same treatment as the other tubes but lacks the factor under test.
So it shows the result with that factor absent.

A student tests whether woodlice gather in the dark. Four dishes are drawn below, numbered 1 to 4, each with paper on both sides. The shaded paper is dark. Dishes 1, 2 and 4 hold 12 woodlice each; dish 3 holds 20.

Which dish is the control?

1. A. Dish 1
   Dish 1 has dark paper on one side and light on the other.
   The woodlice have a difference to choose between, so dish 1 is a test dish.
2. B. Dish 2
   Dish 2 has dark paper on one side and light on the other, the sides swapped.
   The woodlice still have a difference to choose between.
3. C. Dish 3
   Dish 3 has dark paper on one side and light on the other, with more woodlice.
   More woodlice does not remove the difference between the sides.
4. D. ✓ Dish 4

Why: The control is the dish given the same treatment but with no difference to choose between.
Dish 4 has dark paper on both sides.
So dish 4 is the control.

A student lays warm sand on one side of a tray and cool sand on the other side, tips in 12 mealworms, and sets up a second tray with warm sand on both sides and 12 mealworms. He says: “The control in this experiment is keeping 12 mealworms in every tray.”

Is the student correct?

1. A. Yes
   Keeping 12 mealworms in every tray is a condition kept the same: a control variable.
   The control is a whole tray.
2. B. ✓ No

Why: The control is a whole tray given the same treatment but with no difference to choose between.
Keeping 12 mealworms in every tray is a condition kept the same, a control variable.
So the student is not correct.
The control is the tray with warm sand on both sides.

A student lays damp cloth on one side of a board and dry cloth on the other side, tips in 15 snails and counts the snails on each side after 10 minutes.

Which of the following boards is the control for this experiment?

1. A. ✓ A second board with damp cloth on both sides
2. B. A second board with twice as many snails
   Doubling the snails leaves a damp side and a dry side.
   The snails still have a difference to choose between.
3. C. A second board left for twice as long
   Doubling the time leaves a damp side and a dry side.
   The snails still have a difference to choose between.

Why: The control is the board given the same treatment but with no difference to choose between.
A board with damp cloth on both sides has no difference in dampness.
So the board with damp cloth on both sides is the control.

In the Unit 3 enzyme tubes, a tube of hydrogen peroxide with no tissue sat beside the potato tubes.

What did the no-tissue tube show?

1. A. That the potato contains catalase
   The no-tissue tube on its own does not show what the potato does.
   Only the comparison with the potato tubes shows that.
2. B. ✓ How much oxygen the peroxide releases on its own
3. C. How much peroxide each tube held at the start
   The no-tissue tube does not measure the starting volume of peroxide.

Why: The tested factor was the tissue.
The no-tissue tube was the control, the tube lacking the tested factor.
So it showed how much oxygen the peroxide releases on its own.

A student tips 20 fruit flies into a tube lit at one end and dark at the other end. Beside it she sets up a second tube lit at both ends with 20 fruit flies.

What does the second tube show?

1. A. That the flies prefer the dark
   The second tube on its own does not show what light does to the flies.
   Only the comparison with the first tube shows that.
2. B. How many flies were tipped in
   The student sets the number of flies at the start.
   The second tube does not measure it.
3. C. ✓ How the flies spread when both ends are lit

Why: The second tube has no difference in light between its ends.
So it shows how the flies spread when there is nothing to choose between.

A student tips 20 fruit flies into a tube lit at one end and dark at the other end, and 20 fruit flies into a second tube lit at both ends. After 3 minutes, 17 flies sit at the dark end of the first tube. In the second tube, 17 flies sit at one end.

Can the lopsided count in the first tube be put down to light?

1. A. Yes
   In the second tube the flies bunched at one end with no difference in light.
   So bunching happens anyway.
2. B. ✓ No

Why: The second tube has no difference in light.
The flies still bunched at one end, 17 against 3.
So the flies bunch at one end anyway.
The lopsided count in the first tube cannot be put down to light.

A student covers one side of a box so it is dark and leaves the other side lit. She tips in 20 crickets and counts the crickets on each side after 5 minutes.

Which is the dependent variable?

1. A. ✓ The number of crickets on each side
2. B. Dark or light on a side
   Light is the condition she deliberately changes from one side to the other.
   Light is the independent variable.
3. C. The number of crickets tipped in
   She sets the number of crickets, 20, at the start.
   She does not measure it as the result.

Why: The dependent variable is the quantity measured to see the effect.
She counts the crickets on each side after 5 minutes.
So the number of crickets on each side is the dependent variable.

A student covers one side of a box so it is dark and leaves the other side lit, tips in 20 crickets, and sets up a second box lit on both sides with 20 crickets.

Is keeping 20 crickets in every box the control?

1. A. Yes
   Keeping 20 crickets in every box is a condition kept the same: a control variable.
   The control is a whole box.
2. B. ✓ No

Why: The control is a whole box given the same treatment but with no difference to choose between.
Keeping 20 crickets in every box is a condition kept the same, a control variable.
So it is not the control.
The control is the box lit on both sides.

A student covers one side of a box so it is dark and leaves the other side lit. She tips in 20 crickets and counts the crickets on each side after 5 minutes.

Which is the independent variable?

1. A. ✓ Dark or light on a side
2. B. The number of crickets on each side
   The number of crickets on each side is the result she measures.
   That count is the dependent variable.
3. C. The size of the box
   The size of the box is the same for both sides.

Why: The independent variable is the condition the experimenter deliberately sets to two values.
She makes one side dark and leaves the other side lit.
So light is the independent variable.

A student covers one side of a box so it is dark and leaves the other side lit, tips in 20 crickets, and sets up a second box lit on both sides with 20 crickets.

What does the box lit on both sides show?

1. A. That crickets prefer the dark
   The box lit on both sides on its own does not show what the dark does to the crickets.
   Only the comparison with the first box shows that.
2. B. How many crickets were tipped in
   The student sets the number of crickets at the start.
   The second box does not measure it.
3. C. ✓ How the crickets spread with no difference in light

Why: The box lit on both sides has no difference in light.
So it shows how the crickets spread when there is nothing to choose between.

A student covers one side of a box so it is dark and leaves the other side lit, tips in 20 crickets, and sets up a second box lit on both sides with 20 crickets. A classmate says: “The control is the box lit on both sides, and keeping 20 crickets in every box is one of the experiment’s control variables.”

Is the classmate correct?

1. A. ✓ Yes
2. B. No
   Keeping 20 crickets in every box is a condition kept the same in every box.
   A condition kept the same is a control variable; the control is a whole box.

Why: The control is a whole box with no difference to choose between.
A control variable is a condition kept the same in every box.
The student keeps 20 crickets in every box.
So it is a control variable and not the control, and the classmate is correct.

A student covers one side of a box so it is dark and leaves the other side lit, and tips in 20 crickets.

Which of the following boxes is the control for this experiment?

1. A. A second box with twice as many crickets
   Doubling the crickets leaves a dark side and a lit side.
   The crickets still have a difference to choose between.
2. B. ✓ A second box lit on both sides
3. C. A second box left for twice as long
   Doubling the time leaves a dark side and a lit side.
   The crickets still have a difference to choose between.

Why: The control is the box given the same treatment but with no difference to choose between.
A box lit on both sides has no difference in light.
So the box lit on both sides is the control.

In Unit 5 a breeder predicted a ratio from a Punnett square and counted the offspring.

Which of the following was the null hypothesis for the cross?

1. A. The offspring really differ from the predicted ratio, for a reason the breeder can name
   A claim that the counts really differ from the model is the alternative hypothesis.
   The null hypothesis claims no real difference.
2. B. ✓ The offspring occur in the ratio the model predicts, and any difference from it is due to chance

Why: The null hypothesis is the no-difference statement.
For a breeding cross, the no-difference statement is that the offspring fit the predicted ratio and any gap is chance.

A student tips 30 pill bugs into a chamber with a dark half and a light half.

Which of the following is the null hypothesis for the test?

1. A. ✓ The pill bugs have no preference, and any gap from 15 and 15 is due to chance
2. B. The pill bugs prefer the dark half, so the gap from 15 and 15 is real
   A preference is a real difference between the halves.
   A claim of a real difference is the alternative hypothesis.
3. C. Exactly 15 pill bugs sit on each half, with no straying at all
   The null hypothesis expects chance to make the counts stray from 15 and 15.
   The null hypothesis never promises exact counts.

Why: The null hypothesis is the no-difference statement.
No preference means an even spread of the 30 pill bugs: 15 on each half.
So the null hypothesis says the pill bugs have no preference, and the gap from 15 and 15 is chance.

A student tips 20 pill bugs into a chamber with a damp half and a dry half, and writes the null hypothesis as: “The pill bugs prefer the damp half.”

Is the student's statement the null hypothesis?

1. A. Yes
   A preference is a real difference between the halves.
   The null hypothesis claims no real difference.
2. B. ✓ No

Why: The null hypothesis is the no-difference statement.
A preference for the damp half is a real difference.
So the student has written the alternative hypothesis; the null hypothesis is that the pill bugs have no preference, and any gap from 10 and 10 is chance.

In a fruit-fly cross, every class has an observed count and an expected count.

Which of the following is chi-square?

1. A. The number of offspring whose class did not fit the ratio the model predicts
   Chi-square is a sum of squared gaps divided by expected counts.
   It is not a count of offspring.
2. B. ✓ For every class, the squared gap between o and e divided by e, added over the classes
3. C. The gap between the largest observed count and the smallest observed count
   Chi-square compares each observed count with its own expected count.
   It does not compare one observed count with another.

Why: For each class, chi-square takes the gap between o and e, squares it, and divides by e.
Then the classes are added.
So chi-square is the squared gaps divided by the expected counts, summed.

A chi-square test compares two classes. The table below is the formula sheet's.

Which of the following is the critical value at p = 0.05?

1. A. ✓ 3.84
2. B. 5.99
   5.99 is the p = 0.05 value for two degrees of freedom.
   Two classes give one degree of freedom.
3. C. 6.63
   6.63 is the p = 0.01 row's value for one degree of freedom.
   The 0.05 row is the row to read.

Why: Two classes give one degree of freedom: two minus one.
Go down the column for one degree of freedom and along the 0.05 row.
The cell reads 3.84.

Chi-square for a set of counts comes out larger than the critical value.

Which of the following is the verdict?

1. A. Accept the null hypothesis
   A chi-square test never accepts or proves a hypothesis.
   The verdict is written as reject, or fail to reject.
2. B. Fail to reject the null hypothesis
   Fail to reject is the verdict when chi-square is not larger than the critical value.
   Here chi-square is larger.
3. C. ✓ Reject the null hypothesis

Why: Chi-square is larger than the critical value.
So the gap between the counts and the model is too large to be chance.
The verdict is: reject the null hypothesis.

In another dark-and-light chamber, 13 pill bugs sat on the dark side and 7 on the light side, and chi-square against no preference is 1.8. The table below is the formula sheet's.

Which of the following is the verdict on the null hypothesis at p = 0.05?

1. A. Reject
   Chi-square, 1.8, is not larger than the critical value, 3.84.
   A gap this size is small enough to be chance.
2. B. ✓ Fail to reject

Why: Two sides give one degree of freedom, and the 0.05 row reads 3.84.
1.8 is not larger than 3.84.
So fail to reject the null hypothesis: 13 and 7 is consistent with no preference.

In another four-section chamber with 40 pill bugs, the counts are 18, 10, 8 and 4, and chi-square against no preference is 10.4. The table below is the formula sheet's.

Which of the following is the verdict on the null hypothesis at p = 0.05?

1. A. ✓ Reject
2. B. Fail to reject
   Four sections give three degrees of freedom, and the 0.05 row reads 7.81.
   10.4 is larger than 7.81.

Why: Four sections are four classes, so the degrees of freedom are three.
The 0.05 row at three degrees of freedom reads 7.81.
10.4 is larger than 7.81.
So reject the null hypothesis: the counts do not fit no preference.

In another light-and-dark chamber with 50 pill bugs, 36 sat on the dark side and 14 on the light side, and chi-square against no preference is 9.68. The table below is the formula sheet's.

Which of the following is the verdict on the null hypothesis at p = 0.05?

1. A. ✓ Reject
2. B. Fail to reject
   Two sides give one degree of freedom, and the 0.05 row reads 3.84.
   9.68 is larger than 3.84.

Why: Two sides give one degree of freedom, and the 0.05 row reads 3.84.
9.68 is larger than 3.84.
So reject the null hypothesis: the counts do not fit no preference.

A student tips 48 pill bugs into a chamber with four sections: damp and dark, dry and dark, damp and light, dry and light.

Which of the following is the null hypothesis for the test?

1. A. Exactly the same count sits in each section with no straying at all
   The null hypothesis expects chance to make the counts stray from 12 in each section.
   The null hypothesis never promises exact counts.
2. B. The pill bugs prefer the damp and dark section so the gap from an even spread is real
   A preference is a real difference between the sections.
   A claim of a real difference is the alternative hypothesis.
3. C. ✓ The pill bugs have no preference, and any gap from 12 in each section is due to chance

Why: The null hypothesis is the no-difference statement.
No preference means an even spread of the 48 pill bugs: 12 in each section.
So the null hypothesis says the pill bugs have no preference, and the gap from 12 in each section is chance.

In another warm-and-cool chamber with 24 pill bugs, 14 sat on the cool side and 10 on the warm side, and chi-square against no preference is 0.67. The table below is the formula sheet's.

Which of the following is the verdict on the null hypothesis at p = 0.05?

1. A. Reject
   Chi-square, 0.67, is not larger than the critical value, 3.84.
   A gap this size is small enough to be chance.
2. B. ✓ Fail to reject

Why: Two sides give one degree of freedom, and the 0.05 row reads 3.84.
0.67 is not larger than 3.84.
So fail to reject the null hypothesis: 14 and 10 is consistent with no preference.

In another damp-and-dry chamber with 36 pill bugs, 26 sat on the damp side and 10 on the dry side, and chi-square against no preference is 7.11. The table below is the formula sheet's.

Which of the following is the verdict on the null hypothesis at p = 0.05?

1. A. ✓ Reject
2. B. Fail to reject
   Two sides give one degree of freedom, and the 0.05 row reads 3.84.
   7.11 is larger than 3.84.

Why: Two sides give one degree of freedom, and the 0.05 row reads 3.84.
7.11 is larger than 3.84.
So reject the null hypothesis: the counts do not fit no preference.

In Unit 4, cells of the adrenal glands released epinephrine into the blood. Heart cells detected the epinephrine and beat faster.

Which of the following was the chemical signal?

1. A. The blood
   The blood carried the epinephrine from the adrenal glands to the heart.
   The chemical signal is the molecule the blood carried.
2. B. ✓ The epinephrine molecule
3. C. The faster heartbeat
   The faster heartbeat is the heart cells’ response after they detected the epinephrine.
   The chemical signal is the molecule they detected.

Why: A chemical signal is a molecule one cell releases that carries information to other cells.
The adrenal cells released the epinephrine.
The heart cells detected it.
So the epinephrine molecule is the chemical signal.

A male cricket chirps. A female cricket walks toward the chirping.

Which of the following is the signal?

1. A. The air that carries the chirp
   The air carries the chirp from one cricket to the other.
   The signal is the chirp the air carries.
2. B. The female cricket’s movement toward the male
   Walking toward the chirp is what the female cricket does after she detects it.
   The signal is the chirp she detected.
3. C. ✓ The chirp

Why: A signal is something one organism produces that another organism detects.
The male cricket produced the chirp.
The female cricket detected the chirp.
So the chirp is the signal.

Signals pass between organisms.

What is a signal between organisms?

1. A. Any change in the surroundings that an organism detects
   A change no organism produced, such as rain, is a stimulus but not a signal.
   An organism produces a signal.
2. B. What an organism does after it detects a change
   What the organism does afterwards is its response.
   The signal is the thing it detected.
3. C. ✓ Something one organism produces that another organism detects

Why: A signal is something one organism produces that another organism detects.

Rain falls on a leaf and on the snail sitting on it.

Is the rain a signal?

1. A. Yes
   No organism produced the rain.
   A signal is something an organism produces.
2. B. ✓ No

Why: The snail detected the rain.
But no organism produced the rain.
So the rain is not a signal.

A firefly flashes its light. A second firefly sees the flash.

Is the flash a signal?

1. A. ✓ Yes
2. B. No
   The first firefly produced the flash, and the second firefly detected it.
   That is what a signal is.

Why: The first firefly produced the flash.
The second firefly detected the flash.
So the flash is a signal.

A stork on its nest performs its courtship display. A second stork sees the display.

Is the display a signal?

1. A. ✓ Yes
2. B. No
   The first stork produced the display, and the second stork detected it.
   That is what a signal is.

Why: The first stork produced the display.
The second stork detected the display.
So the display is a signal.

Thunder rolls across a field. A horse in the field hears it.

Is the thunder a signal?

1. A. Yes
   No organism produced the thunder.
   A signal is something an organism produces.
2. B. ✓ No

Why: The horse detected the thunder.
But no organism produced the thunder.
So the thunder is not a signal.

A flower’s petals are brightly colored. A bee sees the color and lands on the flower.

Is the flower’s color a signal?

1. A. ✓ Yes
2. B. No
   The flower, a living organism, produced the color of its petals.
   The bee detected the color.

Why: The flower produced the color of its petals.
The bee detected the color.
So the color is a signal, even though a plant produced it.

A cold wind blows across a hillside. A sheep on the hillside turns its back to the wind.

Is the wind a signal?

1. A. Yes
   No organism produced the wind.
   A signal is something an organism produces.
2. B. ✓ No

Why: The sheep detected the wind.
But no organism produced the wind.
So the wind is not a signal.

A rabbit thumps its hind foot on the ground. A second rabbit in a nearby burrow hears the thump.

Which of the following is the signal?

1. A. ✓ The thump
2. B. The ground under the rabbit’s foot
   The ground is what the foot struck.
   The signal is the thump the second rabbit detected.

Why: The first rabbit produced the thump.
The second rabbit detected the thump.
So the thump is the signal.

A stork chick in its nest makes begging movements. The parent stork sees the movements and feeds the chick.

Which of the following is the signal?

1. A. The food the parent brings
   The food is what the parent brings after it detects the movements.
   The signal is the movements the parent detected.
2. B. ✓ The chick’s begging movements
3. C. The parent’s feeding of the chick
   Feeding the chick is what the parent does after it detects the begging movements.
   The signal is the movements.

Why: The chick produced the begging movements.
The parent stork detected the movements.
So the begging movements are the signal.

A firefly flashes its light at night. A second firefly sees the flash.

Which kind of signal is the flash?

1. A. ✓ A visual signal
2. B. An electrical signal
   An electrical signal is an electric pulse the receiver detects.
   The second firefly detected light.
3. C. A chemical signal
   A chemical signal is a chemical the receiver detects.
   The second firefly detected light, whatever the first firefly used to make it.

Why: The kind of signal is named from what the receiver detects.
The second firefly saw the flash: it detected light.
So the flash is a visual signal.

A bird sings at dawn. A second bird hears the song.

Which kind of signal is the song?

1. A. A visual signal
   A visual signal is one the receiver sees.
   The second bird heard the song.
2. B. ✓ An audible signal
3. C. A tactile signal
   A tactile signal is one the receiver detects as touch.
   The second bird heard the song.

Why: The kind of signal is named from what the receiver detects.
The second bird heard the song: it detected sound.
So the song is an audible signal.

One chimpanzee grooms another, picking through its fur with its fingers.

Which kind of signal is the grooming?

1. A. ✓ A tactile signal
2. B. A visual signal
   A visual signal is one the receiver sees.
   The groomed chimpanzee detected the touch of the fingers in its fur.
3. C. A chemical signal
   A chemical signal is a chemical the receiver detects.
   The groomed chimpanzee detected the touch of the fingers in its fur.

Why: The kind of signal is named from what the receiver detects.
The groomed chimpanzee detected the fingers in its fur: it detected touch.
So the grooming is a tactile signal.

An electric fish sends a weak electric pulse through the water. A second fish detects the pulse.

Which kind of signal is the pulse?

1. A. A tactile signal
   A tactile signal is one the receiver detects as touch.
   The second fish detected an electric pulse through the water, with nothing touching it.
2. B. An audible signal
   An audible signal is one the receiver hears.
   The second fish detected an electric pulse, not a sound.
3. C. ✓ An electrical signal

Why: The kind of signal is named from what the receiver detects.
The second fish detected an electric pulse.
So the pulse is an electrical signal.

A female moth releases a chemical into the night air. A male moth detects the chemical.

Which kind of signal is the chemical?

1. A. A visual signal
   A visual signal is one the receiver sees.
   The male moth detected a chemical in the air.
2. B. ✓ A chemical signal
3. C. A tactile signal
   A tactile signal is one the receiver detects as touch.
   The male moth detected a chemical in the air.

Why: The kind of signal is named from what the receiver detects.
The male moth detected a chemical.
So the chemical is a chemical signal.
It passed between two moths of the same species.
So it is also a pheromone.

A peacock fans its tail and gives a loud call. A peahen sees the tail and hears the call.

Which kinds of signal did the peacock send?

1. A. Visual only
   The peahen saw the tail, and she also heard the call.
   The call is a second signal, one she heard.
2. B. Audible only
   The peahen heard the call, and she also saw the tail.
   The fanned tail is a second signal, one she saw.
3. C. ✓ Visual and audible

Why: The kind of signal is named from what the receiver detects.
The peahen saw the fanned tail: a visual signal.
The peahen heard the call: an audible signal.
So the peacock sent both at once.

A rabbit thumps its hind foot on the ground. A second rabbit in a nearby burrow hears the thump.

Which kind of signal is the thump?

1. A. ✓ An audible signal
2. B. A tactile signal
   The rabbit’s foot touched the ground, not the second rabbit.
   The second rabbit heard the thump: it detected sound.
3. C. A visual signal
   A visual signal is one the receiver sees.
   The second rabbit heard the thump: it detected sound.

Why: The kind of signal is named from what the receiver detects.
The second rabbit heard the thump: it detected sound.
So the thump is an audible signal.

A student says: “A signal between organisms is always a sound.”

Is the student correct?

1. A. Yes
   A signal can travel as light, touch, an electric pulse or a chemical as well as sound.
   A firefly’s flash is a signal with no sound.
2. B. ✓ No

Why: A signal is something one organism produces that another organism detects.
The receiver may see it, hear it, detect it as touch, detect it as an electric pulse or detect it as a chemical.
So a signal is not always a sound.

A deer raises its white tail as it bounds away. A second deer sees the raised tail.

Which kind of signal is the raised tail?

1. A. An audible signal
   An audible signal is one the receiver hears.
   The second deer saw the raised tail: it detected light.
2. B. ✓ A visual signal
3. C. A chemical signal
   A chemical signal is a chemical the receiver detects.
   The second deer saw the raised tail: it detected light.

Why: The kind of signal is named from what the receiver detects.
The second deer saw the raised tail: it detected light.
So the raised tail is a visual signal.

Signals travel between organisms in five ways.

What is a visual signal?

1. A. ✓ A signal the receiver sees
2. B. A signal the receiver hears
   A signal the receiver hears is an audible signal.
3. C. A signal the receiver detects as touch
   A signal the receiver detects as touch is a tactile signal.

Why: A visual signal is a signal the receiver sees.

Signals travel between organisms in five ways.

What is an audible signal?

1. A. A signal the receiver sees
   A signal the receiver sees is a visual signal.
2. B. ✓ A signal the receiver hears
3. C. A signal the receiver detects as a chemical
   A signal the receiver detects as a chemical is a chemical signal.

Why: An audible signal is a signal the receiver hears.

Signals travel between organisms in five ways.

What is a tactile signal?

1. A. A signal the receiver hears
   A signal the receiver hears is an audible signal.
2. B. A signal the receiver detects as an electric pulse
   A signal the receiver detects as an electric pulse is an electrical signal.
3. C. ✓ A signal the receiver detects as touch

Why: A tactile signal is a signal the receiver detects as touch.

Signals travel between organisms in five ways.

What is an electrical signal?

1. A. ✓ A signal the receiver detects as an electric pulse
2. B. A signal the receiver detects as touch
   A signal the receiver detects as touch is a tactile signal.
3. C. A signal the receiver sees
   A signal the receiver sees is a visual signal.

Why: An electrical signal is a signal the receiver detects as an electric pulse.

Signals travel between organisms in five ways.

What is a chemical signal between organisms?

1. A. A signal the receiver hears
   A signal the receiver hears is an audible signal.
2. B. ✓ A signal the receiver detects as a chemical
3. C. A signal the receiver sees
   A signal the receiver sees is a visual signal.

Why: A chemical signal between organisms is a signal the receiver detects as a chemical.

Some chemical signals have a name of their own.

What is a pheromone?

1. A. A visual signal passed between organisms of the same species
   A visual signal is one the receiver sees.
   A pheromone is a chemical.
2. B. An audible signal passed between organisms of the same species
   An audible signal is one the receiver hears.
   A pheromone is a chemical.
3. C. ✓ A chemical signal passed between organisms of the same species

Why: A pheromone is a chemical signal passed between organisms of the same species.
The ant’s trail chemical, detected by other ants, is one.

A prairie dog town sits quiet at noon. One prairie dog stands on a mound and barks, and every prairie dog in sight stops feeding and runs to the mouth of its burrow.

Which of the following is the signal?

1. A. ✓ The bark
2. B. The mound
   The mound is where the prairie dog stands.
   No prairie dog produced the mound for another to detect.
3. C. The burrow
   The burrow is where each prairie dog goes.
   No prairie dog produced the burrow for another to detect.

Why: A signal is something one organism produces that another organism detects.
One prairie dog produced the bark.
The other prairie dogs detected it.
So the bark is the signal.

In a wolf pack, one wolf walks stiff-legged toward another, tail raised, staring. The second wolf drops its tail and looks away.

Which job did the posture do for the sender?

1. A. ✓ Shows dominance
2. B. Leads others to food
   No wolf fed after the posture.
   The second wolf gave way to the first.
3. C. Marks territory
   The posture marked no ground; the second wolf stayed in the pack.
   The second wolf gave way to the first.
4. D. Wins a mate
   The second wolf did not stay as the sender’s mate.
   The second wolf gave way to the first.

Why: The sender stared, and the second wolf gave way without a fight.
A signal after which a rival gives way shows dominance.
So the posture showed dominance.

A stork at its nest clatters its bill in a display. A second stork lands beside it and stays as its mate.

Which job did the clattering do for the sender?

1. A. Shows dominance
   The second stork did not give way; it stayed beside the sender.
2. B. Leads others to food
   No stork fed after the clattering; a second stork stayed as the sender’s mate.
3. C. Marks territory
   The clattering kept no stork away; a second stork landed beside the sender and stayed.
4. D. ✓ Wins a mate

Why: After the clattering, a second stork landed beside the sender and stayed as its mate.
A signal after which a mate joins the sender wins a mate.
So the clattering won the stork a mate.

A worker honeybee returns to the hive from a patch of flowers and dances on the comb. The other workers then fly out to the same flowers.

Which job did the dance do for the sender?

1. A. Shows dominance
   No worker gave way to the dancer; the other workers flew out to the flowers.
2. B. ✓ Leads others to food
3. C. Marks territory
   The dance kept no bee out of any ground; the other workers flew out to the flowers.
4. D. Wins a mate
   No bee stayed as the dancer’s mate; the other workers flew out to the flowers.

Why: After the dance, the other workers flew out to the flowers the dancer had found.
A signal after which others go to the food leads others to food.
So the dance led the other workers to food.

Suppose a fox leaves its scent on a fence post at the edge of the ground it hunts. A second fox smells the post and turns back.

Which job did the scent do for the sender?

1. A. Shows dominance
   The two foxes never came face to face, so neither gave way to the other; the second fox turned back at the post.
2. B. Leads others to food
   No fox fed after smelling the post; the second fox turned back.
3. C. ✓ Marks territory
4. D. Wins a mate
   No fox stayed as the sender’s mate; the second fox turned back at the post.

Why: The scent sat at the edge of the ground the sender hunts.
The second fox smelled it and turned back, so the sender kept that ground to itself.
A signal that keeps others out of the sender’s ground marks territory.
So the scent marked the fox’s territory.

Suppose an ant finds a pile of seeds and lays a scent trail from the seeds back to its nest. Other ants from the nest then follow the trail to the seeds.

Which job did the trail do for the sender?

1. A. Shows dominance
   No ant gave way to the sender; the other ants followed the trail to the seeds.
2. B. ✓ Leads others to food
3. C. Marks territory
   The trail kept no ant out of any ground; the other ants followed it to the seeds.
4. D. Wins a mate
   No ant stayed as the sender’s mate; the other ants followed the trail to the seeds.

Why: After the trail was laid, the other ants followed it to the seeds.
A signal after which others go to the food leads others to food.
So the trail led the other ants to food.

Suppose two male deer come face to face in a clearing. One lowers its antlers toward the other and roars. The other deer backs away, and no fight follows.

Which job did the lowered antlers and the roar do for the sender?

1. A. ✓ Shows dominance
2. B. Leads others to food
   No deer fed after the roar; the other deer backed away.
3. C. Marks territory
   The roar marked no ground; the other deer backed away from the sender itself.
4. D. Wins a mate
   The other deer did not stay as the sender’s mate; it backed away.

Why: After the lowered antlers and the roar, the other deer backed away without a fight.
A signal after which a rival gives way shows dominance.
So the antlers and the roar showed dominance.

Suppose a male firefly flashes its light at dusk. A female firefly flashes back and moves toward him, and the two pair.

Which job did the flash do for the sender?

1. A. Shows dominance
   No firefly gave way to the sender; a female moved toward him and the two paired.
2. B. Leads others to food
   No firefly fed after the flash; a female moved toward the sender and the two paired.
3. C. Marks territory
   The flash kept no firefly away; a female moved toward the sender and the two paired.
4. D. ✓ Wins a mate

Why: After the flash, a female firefly moved toward the sender and the two paired.
A signal after which a mate joins the sender wins a mate.
So the flash won the firefly a mate.

Suppose a male songbird sings every morning in spring from a post at the edge of his patch. When another male lands nearby, the singer flies at him and chases him off the patch.

Which job did the song do for the sender?

1. A. Shows dominance
   The other male did not give way to the singer face to face; the singer chased him off the patch.
2. B. Leads others to food
   No bird fed after the song; the singer chased the other male off the patch.
3. C. ✓ Marks territory
4. D. Wins a mate
   No bird stayed as the singer’s mate; the singer chased the other male off the patch.

Why: The singer sang from the edge of his patch and chased another male off it.
A signal that keeps others out of the sender’s ground marks territory.
So the song marked the singer’s territory.

Suppose a bat has caught nothing for two nights, and its stomach is empty.

Which kind of change is the empty stomach?

1. A. ✓ An internal change
2. B. An external change
   An external change happens in the animal’s surroundings.
   The empty stomach is inside the bat’s own body.

Why: An internal change happens inside the animal’s own body.
The bat’s stomach is inside its body.
So the empty stomach is an internal change.

In a wolf pack, the second wolf walks up close to the first. The first wolf then walks stiff-legged toward it, tail raised, staring.

Which of the following set the stare off?

1. A. ✓ The second wolf coming close
2. B. The first wolf’s empty stomach
   Nothing in the case says the first wolf was hungry.
   The second wolf came close, and the stare followed.
3. C. The first wolf’s tail rising
   The rising tail is part of the posture, the signal itself.
   The second wolf came close, and the stare followed.

Why: The second wolf came close.
The stare followed that approach.
So the second wolf coming close set the stare off.

In a wolf pack, the second wolf walks up close to the first, and the first wolf stares at it.

Is the cue for the stare internal or external?

1. A. Internal
   An internal cue is inside the sender’s body.
   The second wolf’s approach happened outside the first wolf’s body.
2. B. ✓ External

Why: The cue was the second wolf coming close.
That approach happened outside the first wolf’s body.
A cue outside the sender’s body is external.

Suppose a male songbird sings more each morning as the days lengthen in spring.

Is the cue for the singing internal or external?

1. A. Internal
   An internal cue is inside the sender’s body.
   The lengthening day is in the bird’s surroundings.
2. B. ✓ External

Why: The cue was the lengthening day.
Day length changes in the bird’s surroundings, outside its body.
A cue outside the sender’s body is external.

Suppose a female moth releases a scent into the air once the eggs inside her are ready to lay. Males detect the scent.

Is the cue for the scent release internal or external?

1. A. ✓ Internal
2. B. External
   An external cue is in the sender’s surroundings.
   The eggs becoming ready are inside the moth’s own body.

Why: The cue was the eggs inside the moth becoming ready to lay.
That change happened inside the moth’s body.
A cue inside the sender’s body is internal.

Suppose a dog growls when a stranger steps into its yard.

Is the cue for the growl internal or external?

1. A. Internal
   An internal cue is inside the sender’s body.
   The stranger stepped into the yard, in the dog’s surroundings.
2. B. ✓ External

Why: The cue was the stranger stepping into the yard.
The stranger is outside the dog’s body.
A cue outside the sender’s body is external.

Suppose a lamb bleats when its body is short of water. Its mother then leads it to the trough.

Is the cue for the bleat internal or external?

1. A. ✓ Internal
2. B. External
   An external cue is in the sender’s surroundings.
   The shortage of water is in the lamb’s own body.

Why: The cue was the shortage of water in the lamb’s body.
That change happened inside the lamb’s body.
A cue inside the sender’s body is internal.

Suppose a puppy whines when its stomach is empty. Its mother then feeds it.

Is the cue for the whine internal or external?

1. A. ✓ Internal
2. B. External
   An external cue is in the sender’s surroundings.
   The empty stomach is inside the puppy’s own body.

Why: The cue was the puppy’s empty stomach.
The stomach is inside the puppy’s body.
A cue inside the sender’s body is internal.

Suppose a ground squirrel whistles when a hawk’s shadow crosses the ground beside it. The other squirrels dive into their burrows.

Is the cue for the whistle internal or external?

1. A. Internal
   An internal cue is inside the sender’s body.
   The hawk’s shadow crossed the ground beside the squirrel, in its surroundings.
2. B. ✓ External

Why: The cue was the hawk’s shadow crossing the ground.
The shadow is outside the squirrel’s body.
A cue outside the sender’s body is external.

A male cricket chirps at night. A female cricket detects the chirping.

Which cricket is the receiver of the signal?

1. A. The male cricket
   The male cricket produced the chirping, so the male cricket is the sender.
2. B. ✓ The female cricket

Why: The receiver is the organism that detects the signal.
The female cricket detected the chirping.
So the female cricket is the receiver.

Suppose a blackbird feeding on a lawn gives a sharp call when a cat walks onto the grass. The other blackbirds on the lawn detect the call.

Which change is the call most likely to make in the other blackbirds’ behavior?

1. A. ✓ The other blackbirds fly up into the hedge
2. B. The other blackbirds fly toward the calling blackbird
   The blackbird called when the cat appeared, so the call warns of a predator.
   Receivers of a warning move to cover, not toward the sender.
3. C. The other blackbirds keep feeding on the lawn
   The call is a signal: one blackbird produced it and the others detected it.
   A signal changes what the receivers do.

Why: The blackbird called when the cat appeared, so the call warns of a predator.
A signal changes what the receivers do.
Receivers of a predator warning move to cover.
So the other blackbirds fly up into the hedge.

A student says: “A signal forces the receiver to act the same way every time.”

Is the student correct?

1. A. Yes
   Some receivers of one call move toward the caller, and some stay where they are.
   The call changed what most receivers did; it forced none of them.
2. B. ✓ No

Why: A signal changes what the receiver does.
Some receivers of one call move toward the caller, and some stay where they are.
So a signal makes one action more likely.
A signal does not force the receiver to act the same way every time.

Suppose a hen finds spilled grain and gives a soft, repeated call. Her chicks, scattered across the yard, detect the call.

Which of the following is the change the call makes in the chicks’ behavior?

1. A. The chicks move away from the hen
   The hen called when she found grain, so her call is a food signal.
   Receivers of a food signal move to the food, beside the sender.
2. B. The chicks stop moving and freeze in the grass
   Freezing is what receivers of a predator warning do.
   The hen called when she found grain, not when a predator appeared.
3. C. ✓ The chicks move toward the hen

Why: The hen called when she found grain.
So the call’s job is to lead the chicks to food.
Receivers of a food signal move to the food.
The grain is beside the hen, so the chicks move toward the hen.

In Unit 7, a small male guppy fathered 30 young that survived to reproduce, and a large male guppy fathered 12.

Which male has the higher evolutionary fitness?

1. A. ✓ The small male guppy
2. B. The large male guppy
   Evolutionary fitness is counted in offspring that survive to reproduce, not in size.
   The small male left 30 such offspring; the large male left 12.

Why: Evolutionary fitness is counted in offspring that survive to reproduce.
The small male left 30 and the large male left 12.
So the small male has the higher evolutionary fitness.

Suppose in a field of crickets, some males chirp for most of the night and others chirp for an hour. The table below shows how many females reach each kind of male over the summer.

Which crickets leave more offspring by the end of the summer?

1. A. The males that chirp for an hour
   5 females reach each male that chirps for most of the night; 1 reaches each male that chirps for an hour.
   More matings give more offspring.
2. B. ✓ The males that chirp for most of the night
3. C. Both kinds of male leave the same number
   Each female that reaches a male lays a clutch of eggs.
   5 clutches against 1 clutch is not the same number.

Why: 5 females reach each male that chirps for most of the night.
1 female reaches each male that chirps for an hour.
Each female that reaches a male mates with him and lays eggs.
So the males that chirp for most of the night leave more offspring.

In a pond of frogs, the loud callers father more tadpoles than the quiet callers. Every female at the pond mates with one male and lays one clutch. A student says: “The loud calls help the whole pond of frogs leave more offspring.”

Is the student correct?

1. A. Yes
   The females that reached the loud callers would otherwise have reached other males.
   The loud calls changed which males fathered the tadpoles, not how many tadpoles the pond produced.
2. B. ✓ No

Why: Each female lays one clutch whichever male she reaches.
The loud calls drew females to the loud callers and away from the quiet callers.
So the loud callers fathered more clutches and the quiet callers fewer.
The loud calls helped the loud callers, not the whole pond.

Suppose in one kind of bird, the females move toward the males with the brightest feathers.

Which males leave the most offspring?

1. A. ✓ The males with the brightest feathers
2. B. The males with the dullest feathers
   The females move toward the brightest males, not the dullest.
   A male that no female reaches leaves no offspring.
3. C. Every male leaves the same number
   More females reach the brightest males.
   Each female that reaches a male mates with him, so the brightest males father more offspring.

Why: The bright feathers are a signal the females detect.
More females move toward the brightest males.
Each female that reaches a male mates with him and lays eggs.
So the males with the brightest feathers leave the most offspring.

Suppose a raven finds a dead deer in the snow and gives a loud, repeated call. Other ravens far off detect the call.

Which change is the call most likely to make in the other ravens’ behavior?

1. A. The other ravens fly away from the caller
   The raven called when it found food, so the call is a food signal.
   Receivers of a food signal move to the food.
2. B. The other ravens stay where they are and call back
   A signal changes what the receivers do.
   The call was given at food, so the receivers move to the food.
3. C. ✓ The other ravens fly to the dead deer

Why: The raven called when it found the dead deer.
So the call’s job is to lead others to food.
Receivers of a food signal move to the food.
So the other ravens fly to the dead deer.

Suppose peahens choose among peacocks by the size of the tail fan each male displays. The table below shows how many peahens reach each kind of peacock over a season.

Which peacocks leave more offspring?

1. A. The peacocks with small tail fans
   1 peahen reaches each peacock with a small tail fan; 4 reach each peacock with a large tail fan.
   Each peahen that reaches a peacock lays a clutch of eggs.
2. B. ✓ The peacocks with large tail fans
3. C. Both kinds of peacock leave the same number
   4 peahens reach each peacock with a large tail fan and 1 reaches each peacock with a small tail fan.
   More matings give more offspring.

Why: 4 peahens reach each peacock with a large tail fan.
1 peahen reaches each peacock with a small tail fan.
Each peahen that reaches a peacock mates with him and lays eggs.
So the peacocks with large tail fans leave more offspring.

A student says: “A female frog that detects a male’s call is more likely to move toward him than a female that detects no call.”

Is the student correct?

1. A. ✓ Yes
2. B. No
   The call makes the move toward the caller more likely.
   A female that detects no call has no caller to move toward.

Why: A signal changes what the receiver does.
The call makes a move toward the caller more likely.
A female that detects no call has no caller to move toward.
So the female that detects the call is more likely to move toward him.

Suppose a large male toad fathers 3 clutches of eggs in a spring and a small male toad fathers 7 clutches. The same share of each clutch survives to reproduce.

Which toad has the higher evolutionary fitness?

1. A. The large male toad
   Evolutionary fitness is counted in offspring that survive to reproduce, not in body size.
   The small toad fathered 7 clutches; the large toad fathered 3.
2. B. ✓ The small male toad

Why: Evolutionary fitness is counted in offspring that survive to reproduce.
The small male toad fathered 7 clutches and the large male 3.
The same share of each clutch survives, so the small male leaves more offspring that survive to reproduce.
So the small male toad has the higher evolutionary fitness.

Suppose, in the mating season, a male grasshopper rubs its legs against its wings and makes a buzzing song. A female grasshopper nearby detects the song.

Which of the following is the change the song makes in the female’s behavior?

1. A. ✓ The female grasshopper moves toward the buzzing male
2. B. The female grasshopper moves away from the buzzing male
   A male’s song in the mating season is a mating signal.
   Receivers of a mating signal move toward the sender.
3. C. The female grasshopper freezes in the grass
   Freezing is what receivers of a predator warning do.
   The male sang in the mating season; no predator appeared.

Why: The male sang in the mating season, so the song’s job is to win a mate.
A signal changes what the receiver does.
Receivers of a mating signal move toward the sender.
So the female grasshopper moves toward the buzzing male.

In a pond, the quiet callers father few tadpoles. A student says: “A quiet male frog will call louder next spring because he needs more offspring.”

Is the student correct?

1. A. Yes
   A male frog does not change his call because he needs offspring.
   The loud callers drew more females this spring, so more tadpoles followed.
2. B. ✓ No

Why: A male frog does not change his call because he needs offspring.
The loud callers drew more females this spring, so more tadpoles followed.
The behavior came first, and the count of offspring followed from it.

A hawk’s shadow passes over a mouse. The mouse darts into a hole.

Which is the stimulus?

1. A. The mouse darting into the hole
   Darting into the hole is what the mouse does: the response.
   The stimulus is the change the mouse detected.
2. B. ✓ The hawk’s shadow passing over the mouse

Why: The stimulus is the change the organism detects.
The mouse detected the shadow passing over it.
So the shadow is the stimulus, and the dart into the hole is the response.

Three animals each do something.

Which of the following is an innate behavior?

1. A. A horse that trots to the fence at the sound of a feed bucket, after being fed there many times
   Being fed there many times changed what the horse does at the sound.
   A behavior changed by the individual’s experience is a learned behavior.
2. B. A parrot that says a word after hearing its owner say the word many times
   Hearing the word many times changed what the parrot says.
   A behavior changed by the individual’s experience is a learned behavior.
3. C. ✓ A newborn kangaroo that climbs into its mother’s pouch minutes after birth, with no joey to copy

Why: The newborn kangaroo climbs into the pouch minutes after birth, with no joey to copy.
So experience did not build the behavior.
A behavior present without experience is an innate behavior.

A newborn baby grips a finger placed in its palm on its first day. Every newborn grips the same way.

Which kind of behavior is the grip?

1. A. ✓ An innate behavior
2. B. A learned behavior
   The baby grips on its first day, with no experience of gripping.
   A behavior present without experience is an innate behavior.

Why: The baby grips on its first day, with no experience.
Nothing the baby went through shaped the grip.
So the grip is an innate behavior.

A dog sits when it hears the word sit, after weeks of being given food each time it sat.

Which kind of behavior is the sitting?

1. A. An innate behavior
   Weeks of food each time it sat changed what the dog does at the word.
   A behavior changed by the individual’s own experience is a learned behavior.
2. B. ✓ A learned behavior

Why: The food each time it sat is the dog’s own experience.
That experience changed what the dog does at the word.
So the sitting is a learned behavior.

Suppose a bird pecks open the foil top of a milk bottle after watching another bird do it.

Which kind of behavior is the pecking?

1. A. An innate behavior
   Watching the other bird is the bird’s own experience, and it changed what the bird does.
   A behavior changed by experience is a learned behavior.
2. B. ✓ A learned behavior

Why: The bird watched another bird open a bottle.
That experience changed what the bird does.
So the pecking is a learned behavior.

Suppose a spider raised alone spins a web of the same pattern as every spider of its kind.

Which kind of behavior is the web-spinning?

1. A. ✓ An innate behavior
2. B. A learned behavior
   The spider was raised alone, so no experience of other webs built the pattern.
   A behavior present without experience is an innate behavior.

Why: The spider spins the pattern with no web to copy.
Nothing the spider went through shaped the pattern.
So the web-spinning is an innate behavior.

Suppose a moth flies toward a lamp on its first night out of the cocoon, like every moth of its kind.

Which kind of behavior is the flight toward the lamp?

1. A. ✓ An innate behavior
2. B. A learned behavior
   The moth flies to the lamp on its first night, with no experience of lamps.
   A behavior present without experience is an innate behavior.

Why: The moth flies to the lamp on its first night, with no experience.
Nothing the moth went through shaped the flight.
So the flight toward the lamp is an innate behavior.

A prairie dog sounds an alarm call at human footsteps. After hearing footsteps many times with no harm following, it stops calling at them.

Which kind of behavior is the prairie dog’s silence at footsteps?

1. A. An innate behavior
   Hearing footsteps many times with no harm is the prairie dog’s own experience, and it changed the calling.
   A behavior changed by experience is a learned behavior.
2. B. ✓ A learned behavior

Why: The prairie dog heard footsteps many times with no harm.
That experience changed its calling.
So the silence is a learned behavior.

Suppose a gull chick pecks at a red spot on its parent’s bill on the day it hatches, and every chick of its kind pecks the same way. The chick pecks when the bill appears and stops when the bill is gone.

Which kind of behavior is the pecking?

1. A. ✓ An innate behavior
2. B. A learned behavior
   The bill sets the pecking off, but the chick’s experience did not build it.
   A behavior present without experience is an innate behavior.

Why: The chick pecks on its first day, with no experience.
Nothing the chick went through shaped the pecking.
So the pecking is an innate behavior.
The parent’s bill sets the pecking off; a trigger from outside does not make a behavior learned.

A sea turtle hatchling crawls straight to the sea on its first night, like every hatchling of its kind.

Which kind of behavior is the crawl to the sea?

1. A. ✓ An innate behavior
2. B. A learned behavior
   The hatchling crawls to the sea on its first night, with no experience of the sea.
   A behavior present without experience is an innate behavior.

Why: The hatchling crawls to the sea on its first night, with no experience.
Nothing the hatchling went through shaped the crawl.
So the crawl is an innate behavior.

A pigeon pecks a button more and more often after being given a seed each time it pecked.

Which kind of behavior is the pecking at the button?

1. A. An innate behavior
   A seed each time it pecked is the pigeon’s own experience, and it changed how often the pigeon pecks.
   A behavior changed by experience is a learned behavior.
2. B. ✓ A learned behavior

Why: The seed each time it pecked is the pigeon’s own experience.
That experience changed how often the pigeon pecks.
So the pecking at the button is a learned behavior.

A newborn calf stands and walks on its first day, with no experience of walking, like every calf.

Which kind of behavior is the walking?

1. A. ✓ An innate behavior
2. B. A learned behavior
   The calf walks on its first day, with no experience of walking.
   A behavior present without experience is an innate behavior.

Why: The calf walks on its first day, with no experience.
Nothing the calf went through shaped the walking.
So the walking is an innate behavior.

An animal does something.

What is a learned behavior?

1. A. ✓ A behavior changed by the individual’s own experience
2. B. A behavior present without experience, so not learned
   A behavior present without experience, not shaped by the individual’s own experience, is an innate behavior.

Why: A learned behavior is a behavior that the individual’s own experience has changed.

An animal does something.

What is an innate behavior?

1. A. A behavior changed by the individual’s own experience
   A behavior changed by the individual’s own experience is a learned behavior.
2. B. ✓ A behavior present without experience, so not learned
3. C. A behavior that nothing outside the animal can set off
   An innate behavior can be set off by something outside the animal.
   Innate means the pattern was not learned.

Why: An innate behavior is present without any experience: nothing the individual went through shaped it.

Unit 7 taught natural selection.

In natural selection, which phenotype becomes more common in later generations?

1. A. The phenotype an individual picks up during its own life
   A phenotype picked up during life is not heritable.
   Natural selection makes a phenotype more common only when it is inherited.
2. B. The phenotype of the largest and strongest individuals
   Size and strength are not counted.
   The phenotype whose owners survive or reproduce more becomes more common.
3. C. ✓ The heritable phenotype whose owners survive or reproduce more

Why: In natural selection, individuals with one heritable phenotype survive or reproduce more.
So that phenotype becomes more common in later generations.

Unit 7 taught evolutionary fitness.

What does an animal’s evolutionary fitness count?

1. A. ✓ The offspring it leaves that survive to reproduce
2. B. The number of years it lives before it dies
   Lifespan is not counted.
   Evolutionary fitness counts the offspring an animal leaves that survive to reproduce.
3. C. Its size and strength compared with the others
   Size and strength are not counted.
   Evolutionary fitness counts the offspring an animal leaves that survive to reproduce.

Why: Evolutionary fitness is the number of offspring an animal leaves that themselves survive to reproduce.

Suppose that on an open hillside some young hares lie still when a fox comes near, and other young hares bolt across the open ground. The fox chases what it sees.

Which young hares survive the fox more often?

1. A. The hares that bolt
   The fox chases what it sees, and a bolting hare is seen.
   A hare lying still is passed by.
2. B. ✓ The hares that lie still
3. C. Both kinds equally
   The fox sees the bolting hares and passes the still ones.
   So the two kinds do not survive equally.

Why: The fox chases what it sees.
A bolting hare is seen; a hare lying still is passed by.
So the hares that lie still survive the fox more often.

A student looks at the hillside hares and says: “Lying still spread through the hares because it is good for the hare species as a whole.”

Is the student correct?

1. A. Yes
   A behavior spreads because the individual hares that have it survive more and leave more offspring.
   Being good for the species is not what spreads it.
2. B. ✓ No

Why: The hares that lie still survive the fox more often.
So they leave more young, and their young lie still too.
Lying still spread because the hares that had it left more offspring, not because it helped the species as a whole.

Suppose a few crows in a city learn to drop nuts onto a road so that cars crack them. Young crows learn the trick from their parents. The crows with the trick find more food in winter and raise more young.

Over several generations, what happens to the share of the city’s crows that use the trick?

1. A. ✓ The share rises
2. B. The share falls
   The crows with the trick raise more young, and the young learn it.
   So the share rises.
3. C. The share stays the same
   The trick-users raise more young than the other crows, and their young learn the trick.
   So the share rises.

Why: The crows with the trick find more food and raise more young.
Their young learn the trick.
So each generation has a larger share of crows with the trick.

Suppose that on an island some lizards dart into rock cracks when a hawk’s shadow passes, and other lizards stay in the open. The hawk takes the lizards it can see.

Which lizards leave more offspring over their lives?

1. A. ✓ The lizards that dart into cracks
2. B. The lizards that stay in the open
   The hawk takes the lizards it can see, and a lizard in the open is seen.
   A lizard in a crack survives to breed.

Why: The hawk takes the lizards it can see.
A lizard in a crack is hidden; a lizard in the open is taken.
So the lizards that dart into cracks survive longer and leave more offspring.

A squirrel opens the lid of a bird feeder after many failed tries over several days.

Which kind of behavior is opening the lid?

1. A. An innate behavior
   Many failed tries are the squirrel’s own experience, and they changed what the squirrel does at the feeder.
   A behavior changed by experience is a learned behavior.
2. B. ✓ A learned behavior

Why: The squirrel’s many tries are its own experience.
That experience changed what the squirrel does at the feeder.
So opening the lid is a learned behavior.

Suppose darting into cracks has become common among the island’s lizards. A student says: “Darting became common because each lizard chose to protect its species.”

Is the student correct?

1. A. Yes
   Darting became common because the lizards that darted survived the hawk and left more offspring.
   A lizard’s choice for its species plays no part.
2. B. ✓ No

Why: The lizards that dart into cracks survive the hawk more often.
So they leave more offspring, and their offspring dart too.
Darting became common because the darting lizards left more offspring, not because any lizard chose to protect the species.

Suppose a kitten arches its back and hisses the first time a dog comes near, with no experience of dogs, and every kitten does the same. A student says: “The dog set the hissing off, but the hissing is still an innate behavior, because the kitten needed no experience to do it.”

Is the student correct?

1. A. ✓ Yes
2. B. No
   The kitten hisses with no experience of dogs.
   A trigger from outside does not make a behavior learned.

Why: The kitten hisses with no experience of dogs.
Nothing the kitten went through shaped the hissing.
So the hissing is an innate behavior.
The dog sets the hissing off; a trigger from outside does not make a behavior learned.

Suppose a cuckoo chick raised by birds of another species, with no cuckoo to copy, sings the cuckoo’s own song when it is grown.

Which kind of behavior is the song?

1. A. ✓ An innate behavior
2. B. A learned behavior
   The cuckoo had no cuckoo to copy, so experience did not build the song.
   A behavior present without experience is an innate behavior.

Why: The cuckoo sings the song with no cuckoo to copy.
Nothing the cuckoo went through shaped the song.
So the song is an innate behavior.

Suppose some gulls at a harbor learn to feed on scraps thrown from a road with fast traffic, and young gulls learn it from their parents. Cars kill the gulls that feed at the road more often than the other gulls.

Over several generations, what happens to the share of the harbor’s gulls that feed at the road?

1. A. The share rises
   Cars kill the gulls that feed at the road more often, so those gulls leave fewer young.
   The share falls.
2. B. ✓ The share falls
3. C. The share stays the same
   The gulls that feed at the road leave fewer young than the other gulls.
   So the share falls.

Why: Cars kill the gulls that feed at the road more often.
So those gulls leave fewer young, and fewer young learn the behavior.
So each generation has a smaller share of gulls that feed at the road.

A hawk appears over a meerkat colony. One meerkat on a mound gives a sharp call. The other meerkats hear the call and dive for cover.

Which of the following is the signal?

1. A. The hawk
   The hawk is the change the sentinel detected.
   The signal is the thing one organism produced and the others detected: the call.
2. B. ✓ The call
3. C. The dive for cover
   The dive is what the other meerkats did after they detected the call.
   The signal is the call they detected.

Why: A signal is something one organism produces that another organism detects.
The sentinel produced the call.
The other meerkats detected the call.
So the call is the signal.

A meerkat stands upright on a mound and watches for hawks while the others of its group dig for beetles.

Which of the following makes the standing guard cooperative behavior?

1. A. The whole group stands guard on the mound at the same moment
   Only one meerkat stands guard at a time.
   The test is a cost to the individual now and a help to the others.
2. B. ✓ It misses its digging while it stands, and its call sends the others to cover
3. C. Another meerkat in the group detects the guard’s call and responds
   Something another animal detects is a signal.
   Cooperative behavior is judged by its cost to the individual and its help to the group.

Why: The meerkat on the mound is not digging, so standing guard costs it its digging time now.
Its call lets the others reach cover, so it helps the others in its group.
So standing guard is cooperative behavior.

A ground squirrel stands up in the grass and watches for hawks while the others of its colony feed. When a hawk comes it whistles, and the others dive into their burrows.

Is the watching cooperative behavior?

1. A. ✓ Yes
2. B. No
   Watching costs the ground squirrel its feeding time now.
   The whistle it gives sends the others to their burrows in time.

Why: Watching costs the ground squirrel its feeding time now.
Watching helps the others in its colony: they hear the whistle and reach their burrows.
So the watching is cooperative behavior.

A lizard lies on a warm rock in the sun until its body warms.

Is the basking cooperative behavior?

1. A. Yes
   Basking warms the lizard itself and helps no other lizard.
   Cooperative behavior helps the others in the group.
2. B. ✓ No

Why: Basking warms the lizard’s own body.
Basking helps no other lizard.
So the basking is not cooperative behavior.

Wolves that hunted carry meat back to pack members that missed the hunt.

Is the carrying of meat cooperative behavior?

1. A. ✓ Yes
2. B. No
   Carrying the meat back costs the hunters meat they could have eaten now.
   The meat feeds the others in the pack.

Why: Carrying the meat back costs the hunters meat they could have eaten now.
The meat feeds the others in the pack.
So the carrying of meat is cooperative behavior.

Ten ants carry one leaf back to their nest together. The leaf feeds the whole colony.

Is the carrying of the leaf cooperative behavior?

1. A. ✓ Yes
2. B. No
   Carrying the leaf costs each ant its effort now.
   The leaf feeds the others in the colony.

Why: Carrying the leaf costs each ant its effort now.
The leaf feeds the others in the colony.
So the carrying of the leaf is cooperative behavior.

A robin sings from a branch to keep other robins out of its patch of garden.

Is the singing cooperative behavior?

1. A. Yes
   The song keeps the patch for the singer alone and helps no other robin.
   Cooperative behavior helps the others in the group.
2. B. ✓ No

Why: The song keeps the patch of garden for the singer.
The song helps no other robin.
So the singing is not cooperative behavior.

A school of small fish swims together. When a predator comes near, each fish turns with the school instead of darting off along its own escape route. A predator catches fewer fish from a school that turns together, so the fish around it are less likely to be caught.

Is turning with the school cooperative behavior?

1. A. ✓ Yes
2. B. No
   Each fish gives up its own escape route now, a cost to it.
   Fewer of the fish around it are caught, so the turning helps the others in its group.

Why: Cooperative behavior costs the individual now and helps the others in its group.
Each fish gives up its own escape route now: a cost.
Fewer of the fish around it are caught: a help to the others.
So the turning is cooperative behavior.

A bird in a flock gives a loud call when a fox appears. The call marks the caller out to the fox, and every other bird in the flock flies up out of reach.

Is the call cooperative behavior?

1. A. ✓ Yes
2. B. No
   The call marks the caller out to the fox, so it costs the caller its safety now.
   The call helps the others in the flock fly up in time.

Why: The call marks the caller out to the fox, so it costs the caller its safety now.
The call helps the others in the flock fly up in time.
So the call is cooperative behavior.

A cat washes its own fur with its tongue.

Is the washing cooperative behavior?

1. A. Yes
   Washing its own fur helps no other cat.
   Cooperative behavior helps the others in the group.
2. B. ✓ No

Why: Washing its own fur cleans the cat itself.
Washing helps no other cat.
So the washing is not cooperative behavior.

Animals in a group behave in many ways toward one another.

What is cooperative behavior?

1. A. Behavior that one animal produces and another animal detects
   Something one animal produces and another detects is a signal.
   Cooperative behavior is judged by its cost to the individual and its help to the group.
2. B. Behavior that warms or cools the individual’s own body
   A behavior that changes the individual’s own body temperature helps only the individual.
   Cooperative behavior helps the others in its group.
3. C. ✓ Behavior that costs the individual now and helps the others in its group

Why: Cooperative behavior is behavior that costs the individual now and helps the others in its group.

A meerkat stands guard on the mound for an hour while the rest of its group digs for beetles. Then another meerkat takes its place on the mound.

What does the first meerkat get back for its hour on the mound?

1. A. ✓ An hour of digging and eating while another meerkat stands guard
2. B. The beetles the others dug up while it watched
   The others eat the beetles they dig up themselves.
   What the first meerkat gets is its own turn to dig, under another meerkat’s guard.
3. C. The first place in the burrow when the hawk comes
   Every meerkat dives for whatever cover is nearest when the hawk comes.
   What the first meerkat gets is its own turn to dig, under another meerkat’s guard.

Why: After its hour on the mound, the first meerkat climbs down and digs.
Another meerkat stands guard over it.
So the first meerkat gets an hour of eating under guard.

In a flock of small birds, one bird stops feeding to watch for hawks while the others feed. The birds take turns at watching. A student says: “The watcher only loses. Watching costs it feeding time and gets it nothing.”

Is the student correct?

1. A. Yes
   Later another bird watches while the watcher feeds.
   So the watcher gets feeding time under another bird’s guard.
2. B. ✓ No

Why: Watching costs the bird its feeding time now.
Later another bird watches while the watcher feeds.
So the watcher gets feeding time under guard.
The watcher does not only lose: it is helped in its turn.

A wolf that hunted carries meat back to the den for a pack member that stayed with the pups. Suppose on a later hunt this wolf is the one that stays at the den.

Which of the following does the wolf get back?

1. A. A larger share of every future kill
   Nothing in the pack’s sharing gives one wolf a larger share for good.
   The wolf gets back meat carried to it on the day it stays at the den.
2. B. Its own territory away from the pack
   A wolf that leaves the pack is fed by no one.
   What the wolf gets back is meat carried to it on the day it stays at the den.
3. C. ✓ Meat carried back to the den by the wolves that hunted

Why: The wolf gave up meat on the day it carried meat to the den.
On the day it stays at the den, the wolves that hunted carry meat back to it.
So the wolf is fed in its turn.

Thirty zebras graze together in one herd. Another thirty zebras graze alone, scattered across the same plain. Lions hunt on the plain all year.

Which group loses more zebras to the lions in a year?

1. A. The herd
   The herd has thirty pairs of eyes, and some are always up.
   A lion is seen far off, and the whole herd bolts.
2. B. ✓ The scattered zebras
3. C. The two groups lose the same number
   A zebra alone has one pair of eyes, down in the grass most of the time.
   A zebra in the herd is warned by the eyes that are up.

Why: A zebra grazing alone has one pair of eyes, down in the grass most of the time.
Between its looks a lion creeps close unseen.
In the herd some of thirty pairs of eyes are always up, so a lion is seen far off.
So the scattered zebras lose more.

Suppose one flock of forty starlings shares each patch of food a bird finds: when one bird starts to eat, the others see it and join it. A second group of forty starlings feeds with each bird searching alone.

Which group has more birds fed by nightfall?

1. A. ✓ The flock that shares each patch
2. B. The birds that search alone
   A bird searching alone eats only from the patches it finds itself.
   In the flock, one bird’s find feeds many.
3. C. The two groups feed the same number
   In the flock, one find feeds many birds.
   Alone, one find feeds one bird.

Why: In the flock, one bird’s find is seen by the others, and they join it.
So one patch of food feeds many birds.
Alone, each bird eats only from the patches it finds itself.
So the flock that shares has more birds fed.

In Unit 5, a gene for flower color came in two versions, one giving purple flowers and one giving white flowers.

What is each version of the gene called?

1. A. A chromosome
   A chromosome is one long DNA molecule carrying many genes.
   Each version of one gene is an allele.
2. B. A gamete
   A gamete is a sex cell, a sperm or an egg.
   Each version of one gene is an allele.
3. C. ✓ An allele

Why: When a gene comes in more than one version, each version is called an allele.
The purple version and the white version are two alleles of the flower-color gene.

In Unit 7, two guppies were compared for their evolutionary fitness.

What does evolutionary fitness count?

1. A. ✓ Offspring that survive to reproduce
2. B. Years the individual lives
   A long life with no offspring that reproduce is an evolutionary fitness of zero.
   Evolutionary fitness counts offspring that survive to reproduce.
3. C. How large and strong the individual grows
   Size and strength are not counted.
   Evolutionary fitness counts offspring that survive to reproduce.

Why: Evolutionary fitness is the number of offspring an individual leaves that themselves survive to reproduce.

A honeybee hive holds one queen and thousands of workers.

Do the workers breed?

1. A. Yes
   The workers are sterile.
   The queen lays every egg in the hive.
2. B. ✓ No

Why: The workers are sterile: they cannot breed.
The queen lays all the eggs.

Worker bees raise the queen’s offspring rather than offspring of their own.

Why can raising the queen’s offspring spread copies of a worker’s alleles?

1. A. Feeding the young passes the worker’s alleles into them
   Food carries no alleles.
   The young share the worker’s alleles because they and the worker came from the same queen.
2. B. Raising the young changes the alleles the worker itself carries
   An individual’s alleles do not change during its life.
   The young share the worker’s alleles because they and the worker came from the same queen.
3. C. ✓ The queen’s offspring share many alleles with the worker, and some of them breed

Why: The worker and the queen’s new offspring came from the same queen, so they share many alleles.
Some of those offspring are new queens, and a new queen breeds.
So copies of the worker’s alleles pass on through her.

A student says: “Worker bees raise the queen’s young for the good of the species. Kin selection is selection for what helps the species.”

Is the student correct?

1. A. Yes
   The worker’s help spreads alleles the worker itself carries, through relatives that share them.
   Kin selection works through shared alleles, not for the species as a whole.
2. B. ✓ No

Why: The queen’s young share many alleles with the worker.
When those young breed, copies of the worker’s alleles pass on.
Workers whose alleles made them help left more copies, so the helping stayed common.
Kin selection works through shared alleles, not for the good of the species.

A bird feeds the chicks of an unrelated pair nesting in the next tree.

Can kin selection explain this helping?

1. A. Yes
   The chicks are not the helper’s relatives, so they share no more of its alleles than any other bird does.
   Kin selection works only through relatives.
2. B. ✓ No

Why: The chicks are not the helper’s relatives.
So they share no more of the helper’s alleles than any other bird does.
Their breeding spreads no extra copies of the helper’s alleles.
So kin selection cannot explain the helping.

A young bird stays at its parents’ nest for a year and feeds the new chicks there, its own brothers and sisters.

Can kin selection explain this helping?

1. A. ✓ Yes
2. B. No
   The chicks are the helper’s brothers and sisters, so they share many of its alleles.
   Kin selection favors helping relatives that share the helper’s alleles.

Why: The chicks are the helper’s brothers and sisters.
So they share many of the helper’s alleles.
When they grow up and breed, copies of the helper’s alleles pass on.
So kin selection can explain the helping.

In an ant colony, sterile workers feed the queen’s larvae, their own sisters.

Can kin selection explain this helping?

1. A. ✓ Yes
2. B. No
   The larvae are the workers’ sisters, so they share many of the workers’ alleles.
   Some larvae become new queens and breed.

Why: The larvae are the workers’ sisters.
So they share many of the workers’ alleles.
Some larvae become new queens and breed, passing those alleles on.
So kin selection can explain the helping.

Some animals help their relatives to breed.

What is kin selection?

1. A. Selection that favors helping any member of the group, related or not
   An unrelated member of the group shares no more of the helper’s alleles than a stranger.
   Kin selection works through alleles shared with close relatives.
2. B. Selection that favors the strongest individual in a group
   Strength is not what kin selection favors.
   Kin selection favors helping relatives that share the helper’s alleles.
3. C. ✓ Selection that favors helping relatives that share the helper’s alleles

Why: Kin selection is selection that favors helping close relatives to breed, because the relatives share many of the helper’s alleles and pass copies of them on.

A shoal of two hundred herring swims as one school, and a seal hunts it. A student says: “A herring is safer in the school, because when the school turns as one the seal loses sight of any single fish.”

Is the student correct?

1. A. No: a herring in the school is as easy for the seal to pick out as a herring alone
   When the school turns as one, the seal loses sight of any single fish.
   So it catches fewer herring from the school than from herring swimming alone.
2. B. ✓ Yes: when the school turns as one, the seal loses sight of any single fish, so it catches fewer

Why: The seal catches a herring by picking one out.
When the school turns as one, the seal loses sight of any single fish.
So the seal catches fewer herring from the school.
So a herring in the school is safer than one swimming alone.

A badger digs a burrow and sleeps in it alone.

Is the digging cooperative behavior?

1. A. Yes
   The burrow shelters the badger itself and no other badger.
   Cooperative behavior helps the others in the group.
2. B. ✓ No

Why: The burrow shelters the badger itself.
The digging helps no other badger.
So the digging is not cooperative behavior.

Suppose a group of monkeys in which one monkey watches for eagles from a treetop while the others feed on the ground beneath it.

Which of the following would let kin selection favor the watching?

1. A. ✓ The monkeys feeding beneath the treetop are the watcher’s close relatives
2. B. The monkeys feeding beneath the treetop are the largest in the forest
   Size is not what kin selection favors.
   Kin selection favors helping relatives that share the helper’s alleles.
3. C. The monkeys feeding beneath the treetop are unrelated to the watcher
   Unrelated monkeys share no more of the watcher’s alleles than any other monkey does.
   Kin selection works through relatives.

Why: Kin selection favors helping close relatives, because they share many of the helper’s alleles.
If the monkeys the watcher guards are its close relatives, they share many of its alleles.
When they breed, copies of the watcher’s alleles pass on.
So kin selection would favor the watching.

A student says: “A worker bee leaves zero offspring, so it leaves zero copies of its alleles in the next generation.”

Is the student correct?

1. A. Yes
   The queen’s young share many of the worker’s alleles, and the new queens among them breed.
   So copies of the worker’s alleles do reach the next generation.
2. B. ✓ No

Why: The worker and the queen’s young came from the same queen, so they share many alleles.
The new queens among those young breed.
So copies of the worker’s alleles reach the next generation without the worker breeding.

Three animals behave in the ways listed.

Which of the following is cooperative behavior?

1. A. ✓ A hyena carries meat back to cubs at the den that did not hunt
2. B. A tortoise pulls its head into its shell when a shadow passes
   Pulling its head in protects the tortoise itself and helps no other tortoise.
3. C. A frog calls at night to attract a mate to itself
   The call brings a mate to the caller itself and helps no other frog.