Introduction to Biological Macromolecules

Unit 1 · Topic 1.3 end-of-topic test

Suggested time: about 47 minutes. Answer everything, then press Submit the test to see the feedback and scoring guides.

Answer every question. For each multiple-choice question, pick one answer. When you have answered every question, press Submit the test; the feedback then gives the reasoning for each. For each free-response question, write one short sentence for each step of your reasoning, each on its own line, and make every link clear (so, because, therefore). That is what the exam’s ‘paragraph form’ means for you: linked sentences, not bullet points. Write the steps in the box, then open the scoring guide and mark your own work against it.

Question 1

A molecule taken from a plant is a single chain of about 1,200 identical glucose units, linked one after another.

Which description fits?

A. One glucose unit is a polymer; the whole chain is a monomer. B. One glucose unit is a monomer; the whole chain is a polymer. C. Both a single glucose unit and the whole chain are monomers. D. The chain is not a polymer, because all of its units are identical.

Question 2

A molecule found in a cell is hundreds of times larger than a glucose molecule, and it is built as one large structure rather than as a chain of repeating units.

Which pair of words applies to it?

A. A polymer but not a macromolecule B. Both a polymer and a macromolecule C. Neither a polymer nor a macromolecule D. A macromolecule but not a polymer

Question 3

Monomers P and Q are joined by dehydration synthesis. P loses a hydrogen ion.

What happened to Q?

A. Q lost a hydroxyl group, and the two pieces left as one water molecule. B. Q also lost a hydrogen ion, so two water molecules were released. C. Q lost nothing, because P supplied the whole water molecule by itself. D. Q gained a hydroxyl group from the water around the monomers.

Question 4

Two monomers have just been joined by dehydration synthesis.

What now holds the two monomers together?

A. A hydrogen bond between the two monomers B. The water molecule that was released C. A covalent bond between the two monomers D. The attraction between their partial charges

Question 5

Two glucose units are joined by dehydration synthesis.

What are the products?

A. One two-unit molecule only B. One two-unit molecule and two water molecules C. Two separate glucose units and one water molecule D. One two-unit molecule and one water molecule

Question 6

A water molecule joins the bond between monomers M and N, and the bond breaks. Afterward, N carries an extra hydroxyl group.

What does M carry, and why?

A. An extra hydroxyl group too; water gives an –OH to both monomers. B. An extra hydrogen atom, H; the water split into H and –OH, one to each monomer. C. Nothing extra, because N took in the whole water molecule. D. A whole water molecule of its own, attached to M in one piece.

Question 7

You eat a slice of bread. Most of its dry weight is long chains of glucose units. Hours later, free glucose from that bread is in your blood.

Which reaction freed the glucose, and what happened to water?

A. Hydrolysis; a water molecule was added at each bond that broke. B. Hydrolysis; a water molecule was released at each bond that broke. C. Dehydration synthesis; water was released as the units came apart. D. Polymerization; the glucose units were joined to one another.

Question 8

A chain of eight monomers is completely broken apart by hydrolysis until eight separate monomers are free.

How many water molecules were consumed?

A. One; a single water molecule breaks each bond in turn. B. Seven, one for each bond between the eight monomers. C. Eight, one for each of the eight monomers that ended up free. D. Sixteen, a hydrogen ion and a hydroxyl group for each monomer.

Question 9

A cell joins 12 glucose units, one after another, into a single chain.

How many water molecules are released?

A. 12 B. 11 C. 6 D. 13

Question 10

Two monomers are joined into one molecule. The product weighs less than the two monomers did together, by the mass of exactly one water molecule.

What explains the missing mass?

A. The equivalent of one water molecule left the two monomers as they joined. B. Some atoms were destroyed when the new covalent bond between them formed. C. A water molecule was added to the bond, which should have made it heavier. D. Each of the two monomers lost a whole water molecule of its own.

Question 11

A sample of a chain of glucose units has a mass of 1.00 g. It is completely broken into free glucose by hydrolysis, and all the glucose is collected and weighed.

What is the total mass of the glucose?

A. Less than 1.00 g, because water was released as the bonds broke. B. Exactly 1.00 g, because atoms are never created or destroyed. C. Less than 1.00 g, because breaking bonds uses up part of the chain. D. More than 1.00 g, by the mass of the water added at the broken bonds.

Question 12

Inside one cell, a chain of monomers is being lengthened at the same moment that an identical chain nearby is being taken apart.

What happens to water in each process?

A. Water released by both processes, because water leaves whenever a bond changes. B. Water consumed by both processes, because both need water to work. C. Water released where the chain is lengthened, and consumed where it is taken apart. D. Water consumed where the chain is lengthened, and released where it is taken apart.

Question 13

A bacterium builds a long chain from a unit that is not a sugar. As the cell adds each unit, one water molecule leaves.

Which reaction is building the chain?

A. Hydrolysis, because water takes part in the reaction. B. Dehydration synthesis, the same reaction that joins sugar units. C. A different reaction, because the unit is not a sugar. D. Neither reaction; units that are not sugars are held together by hydrogen bonds.

Question 14

A student is comparing polymerization, the joining of monomers by dehydration synthesis repeated at every join, with hydrolysis.

Which statement about the two is correct?

A. Hydrolysis undoes what polymerization builds, whatever the monomer. B. Hydrolysis and dehydration synthesis both release water. C. Each kind of monomer is joined and broken by its own pair of reactions. D. Dehydration synthesis breaks chains, and hydrolysis builds them.

Question 15

A chain of five units, a sixth unit joining at the right-hand end, and a water molecule leaving.

The model shows a six-unit chain being made from a five-unit chain and one more unit.

Which reaction does the model show, and how many water molecules in total have moved in building the whole six-unit chain from single units?

A. Hydrolysis; 5 water molecules consumed. B. Dehydration synthesis; 6 water molecules released in total. C. Hydrolysis; 6 water molecules consumed. D. Dehydration synthesis; 5 water molecules released in total.

Question 16

Two units before the reaction (left) and after it (right).

The model shows two units before and after a reaction. Before, unit 1 carries an –OH group and unit 2 carries an –H at the positions shown.

Which reaction is shown, and where does the water molecule come from?

A. Hydrolysis; the water is added to break the bond between the units. B. Dehydration synthesis; the water is taken in from the surroundings. C. Dehydration synthesis; the –OH of one unit and the –H of the other leave as water. D. Hydrolysis; the water shown is released as the units separate.

Question 17

Units 1 and 2 joined through an oxygen that belongs to unit 1. The marked bond, between the oxygen and unit 2, is the one that breaks.

In the model, units 1 and 2 are joined through a bridging oxygen that belongs to unit 1. A water molecule approaches, and the bond between the oxygen and unit 2 breaks.

Which product receives the –H from the water molecule, and which receives the whole –OH?

A. Unit 1 receives only the –H from the water; unit 2 receives the whole –OH B. Unit 1 receives the whole –OH from the water; unit 2 receives only the –H C. Both units receive an –OH from the water; the bridging oxygen stays put D. Both units receive an –H from the water; the bridging oxygen leaves with it

Question 18

A chain of 20 monomers is cut once by hydrolysis into two chains of 10.

How many water molecules were consumed?

A. 2 B. 1 C. 19 D. 10

How to tackle the free-response questions. Read the verb first: describe asks what you see or know; explain asks why or how, so name the mechanism; predict asks what will happen and why; justify asks for the evidence that supports a claim. Each point is earned by one idea, stated in a sentence that names the thing and the mechanism. Extra words earn nothing; a wrong extra can lose the point. If there is a figure or table, use what it shows. When you finish, check the box for each point your answer earns and compare your sentences with the full-credit answer.

Free response 1 · Analyze Model or Visual Representation · 4 points

The model shows two reactions using generic units drawn as numbered shapes. Panel 1 shows units 1 and 2 before and after a reaction; the groups they carry where they face each other are labeled. Panel 2 shows four units joined into one chain through bridging oxygen atoms, with a water molecule beside the bond marked X, which is the bond between the bridging oxygen and unit 3.

Panel 1: two units before and after a reaction. Panel 2: a four-unit chain with a water molecule beside bond X, between the bridging oxygen and unit 3.

(a) Describe what happens to the –OH group of unit 1 and the –H of unit 2 in panel 1, and what holds the two units together afterward. (1 point)

A full-credit answer: The –OH from unit 1 and the –H from unit 2 leave together as one water molecule, and the two units are then held together by a covalent bond: dehydration synthesis.

Check the box for each point your answer earns

the –OH from unit 1 and the –H from unit 2 leave together as one water molecule, and a covalent bond forms between the two units (dehydration synthesis).

Accept: 'a hydroxyl group and a hydrogen ion are removed and leave as H₂O; the units are joined by a covalent bond'. Naming the reaction is not required.

Common slip: Saying the units are held together by a hydrogen bond, or that the water is added. In this panel the water leaves and a covalent bond forms.

(b) Describe the two products formed when bond X breaks: name the group at the end of each product where the bond was, and state where the atoms of that group came from. (1 point)

A full-credit answer: Bond X breaks into two products: units 1 and 2, and units 3 and 4.
Units 1 and 2 keep the bridging oxygen and gain only the –H from the water.
So that piece ends in an –OH group: O from the chain, H from the water.
Units 3 and 4 gain the water’s whole –OH group.
So unit 3 ends in an –OH group whose O and H both came from the water.

The two products: 1–O–2–O–H, where the O was the bridging oxygen and the H came from the water; and HO–3–O–4, where the whole –OH came from the water.

Check the box for each point your answer earns

two products of two units each (units 1 and 2; units 3 and 4), each ending in an –OH group where bond X was; the piece made of units 1 and 2 keeps the bridging oxygen and gains only the –H from the water, and the piece made of units 3 and 4 gains the water’s whole –OH.

Accept: any notation (for example 1–O–2–OH and HO–3–O–4) that shows two two-unit pieces with the –H added to the oxygen-keeping side and the whole –OH added to unit 3.

Do not award: four free units, both pieces receiving a whole –OH, or two –OH groups with no statement of where their atoms came from.

Common slip: Giving both pieces a whole –OH, or breaking every bond. One water molecule breaks one bond; its –H goes to the side that kept the bridging oxygen, and its –OH goes to the other side.

(c) Explain how the reaction in panel 2 is the reverse of the reaction in panel 1. (1 point)

A full-credit answer: In panel 2 a water molecule is added to the bond and split: its hydrogen ion goes to one unit and its hydroxyl group to the other, and the covalent bond between the units breaks (hydrolysis).
Panel 1 releases water and makes a bond; panel 2 uses water and breaks a bond.

Check the box for each point your answer earns

in panel 2 a water molecule is added to the bond and split, its hydrogen ion going to one unit and its hydroxyl group to the other, and the covalent bond between the units breaks (hydrolysis); this is the opposite of water leaving and a bond forming in panel 1.

Accept: 'water is consumed instead of released, and a bond is broken instead of made', provided both the water direction and the bond change are stated.

Common slip: Saying only that both reactions ‘involve water’. The point needs the direction: water in and a bond broken, the opposite of water out and a bond made.

(d) Explain how the two reactions in the model relate to what happens when you eat bread and then build new molecules of your own. (1 point)

A full-credit answer: Digestion breaks the bread’s chains of sugar units into free units by hydrolysis, water added at each bond; your cells then join units into chains of their own by dehydration synthesis, water released at each bond.
The same pair of reactions builds and breaks every kind of chain.

Check the box for each point your answer earns

digestion breaks the bread's chains of sugar units into free units by hydrolysis (water added at each bond), and your cells then join units into chains of their own by dehydration synthesis (water released at each bond); the same pair of reactions builds and breaks every kind of chain.

Accept: 'digestion is hydrolysis; building is dehydration synthesis', provided the direction water moves is stated for at least one of the two.

Common slip: Naming the two reactions with no direction for the water. Say which way the water moves in at least one of them.

Free-response score: 0 of 4

Free response 2 · Conceptual Analysis · 4 points

A seed stores its food as long chains of sugar units. When the seed is planted and begins to grow, the stored chains are broken into free sugar units, and the seedling uses those units to build its new cells.

(a) Describe how the bond between two sugar units in a stored chain is broken. (1 point)

A full-credit answer: The bond is broken when a water molecule is added and splits: its hydrogen ion goes to one sugar unit and its hydroxyl group to the other, and the covalent bond between them breaks.
This is hydrolysis.

Check the box for each point your answer earns

a water molecule is added to the bond and splits; its hydrogen ion goes to one unit and its hydroxyl group to the other, and the covalent bond between them breaks (hydrolysis).

Accept: 'water is added across the bond, giving –H to one unit and –OH to the other'. Naming the reaction alone, without the water, does not earn the point.

Common slip: Naming hydrolysis and stopping. The point is for what the water does: it splits, and its two pieces go to the two units.

(b) The seedling’s growing cells join the free sugar units into new chains. Describe how the reaction that joins the units in the growing cells differs from the reaction that breaks the stored chains. (1 point)

A full-credit answer: Joining the units is dehydration synthesis: an –OH from one unit and an H from the next leave as one water molecule, and a covalent bond forms between the units.
Breaking the stored chains is hydrolysis: a water molecule is added to a bond and the bond breaks.
The two reactions are reverses of each other: water leaves in one and is taken in by the other.

Check the box for each point your answer earns

joining is dehydration synthesis and releases a water molecule at each bond; breaking is hydrolysis and takes a water molecule in at each bond; the two are reverses of each other.

Accept: 'water out when units join, water in when they separate', with both reactions named or described.

Do not award: both reactions releasing water, or the two reactions named with no statement of how water moves in each.

Common slip: Saying water is released in both reactions. Water leaves when units join and is taken in when the bond breaks; so the two reactions are reverses of each other.

(c) Make a claim about how the total mass of the free sugar units compares with the mass of the stored chains they came from. (1 point)

A full-credit answer: The free sugar units together weigh more than the stored chains did.

Check the box for each point your answer earns

the claim: the free units together weigh more than the chains did. The point is for the assertion; the reasoning is scored in (d).

Accept: 'more, by the mass of the water added'.

Do not award: 'the same, because atoms are conserved', or 'less'.

Common slip: Claiming ‘the same, because atoms are conserved’. Atoms are conserved, and the water’s atoms have been added to the units.

(d) A stored chain of 100 sugar units is broken completely into free units. Determine the number of water molecules involved, and use that number to support your claim in (c). (1 point)

A full-credit answer: A chain of 100 units has 99 bonds.
Each break takes in one water molecule, so 99 water molecules are involved.
Every atom of those 99 water molecules ends up in the free units: an –H on one unit and an –OH on its neighbor at each break.
So the free units together weigh more than the chain by the mass of 99 water molecules.

units = 100

water molecules = units − 1

water molecules = 100 − 1

water molecules = 99

Check the box for each point your answer earns

the decision AND what it rests on: 99 water molecules (one per bond, one fewer than the number of units) AND their atoms end up in the free units, so the units weigh more than the chain by the mass of that water.

Accept: 'n − 1 water molecules for n units' stated with n = 100, together with the water's mass ending up in the products.

Do not award the point for 100 water molecules, or for a number with no statement of where the water's mass goes.

Common slip: Saying one water molecule per unit (100) instead of one per bond (99), or saying the mass 'stays the same because atoms are conserved' while forgetting the water that joined in.

Free-response score: 0 of 4

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Multiple choice checked: 0 of 18 correct.

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