Life Science: Biology — Final exam worked answers

Question 1 · 1 point

Three independent rates are 4, 6, and 8 units/min. Find the mean.

Worked answer

6 units/min

18 ÷ 3 = 6.

1 point for the correct objective answer; no written-method marks for this item.

Question 2 · 1 point

Water's ability to dissolve salts depends on its

1. nonpolar tails
2. polarity and partial charges
3. high density
4. lack of hydrogen bonds

Worked answer

polarity and partial charges

Partial charges surround and separate ions, keeping them in solution.

1 point for the correct objective answer; no written-method marks for this item.

Question 3 · 1 point

Which pairing of macromolecule and monomer is correct?

1. Protein — nucleotide
2. Nucleic acid — amino acid
3. Carbohydrate — monosaccharide
4. Lipid — glucose

Worked answer

Carbohydrate — monosaccharide

Carbohydrates are polymers of monosaccharides.

1 point for the correct objective answer; no written-method marks for this item.

Question 4 · 1 point

An enzyme speeds a reaction by

1. raising the temperature
2. lowering the activation energy
3. making a reaction spontaneous
4. being consumed

Worked answer

lowering the activation energy

It lowers the barrier without changing the overall energy balance.

1 point for the correct objective answer; no written-method marks for this item.

Question 5 · 1 point

Breaking a chemical bond, considered alone,

1. always releases energy
2. always requires energy
3. never involves energy
4. creates mass

Worked answer

always requires energy

Energy is released overall only when the bonds formed are more stable than those broken.

1 point for the correct objective answer; no written-method marks for this item.

Question 6 · 3 points

An enzyme study varies temperature but also changes enzyme quantity between groups. Explain the confound and redesign using independent replicates.

Worked answer

The original design cannot isolate temperature; repeated controlled groups improve inference.

Two factors change, so either can influence measured rate.

Hold enzyme quantity and other conditions comparable, vary temperature and use independently prepared samples.

Marking criteria

• 1 point: identify the confound.
• 1 point: controlled redesign with measured rate.
• 1 point: independent replicates and a valid limitation.

Question 7 · 3 points

Explain how ATP hydrolysis can support cell work without claiming that breaking a bond alone releases energy.

Worked answer

Energy transfer depends on all chemical changes and coupling, not on bond breaking by itself.

Breaking bonds requires energy.

The full reaction and coupling mechanism can yield an overall favorable change and drive another process.

Marking criteria

• 1 point: correct bond-breaking statement.
• 1 point: overall reaction/products reasoning.
• 1 point: coupling to a named cell process such as transport or synthesis.

Question 8 · 1 point

Which statement is NOT one of the three tenets of cell theory?

1. All living things are made of one or more cells
2. The cell is the basic unit of structure and function
3. All cells arise from pre-existing cells
4. All cells contain a nucleus

Worked answer

All cells contain a nucleus

Prokaryotic cells (like bacteria) have no nucleus, so 'all cells contain a nucleus' is false and is not part of cell theory.

1 point for the correct objective answer; no written-method marks for this item.

Question 9 · 1 point

Which statement is part of the cell theory?

1. All cells have a nucleus
2. Cells come only from pre-existing cells
3. All cells are the same size
4. Cells form spontaneously

Worked answer

Cells come only from pre-existing cells

Sealed-flask experiments established this third statement.

1 point for the correct objective answer; no written-method marks for this item.

Question 10 · 1 point

Which crosses the phospholipid bilayer most readily without a transport protein?

1. A sodium ion
2. Glucose
3. Oxygen
4. A protein

Worked answer

Oxygen

Small nonpolar molecules dissolve in the nonpolar interior.

1 point for the correct objective answer; no written-method marks for this item.

Question 11 · 1 point

An animal cell placed in distilled water will

1. shrivel
2. swell and may burst
3. stay the same
4. become turgid safely

Worked answer

swell and may burst

Water enters by osmosis and the cell has no wall to resist it.

1 point for the correct objective answer; no written-method marks for this item.

Question 12 · 1 point

As a cell grows larger, its surface-area-to-volume ratio

1. increases
2. decreases
3. stays constant
4. doubles

Worked answer

decreases

Volume grows with the cube of length while area grows with the square.

1 point for the correct objective answer; no written-method marks for this item.

Question 13 · 3 points

For cube-shaped model cells with sides 1 and 3 units, compare surface-area/volume ratios and explain an exchange consequence.

Worked answer

The larger cube has one third the area per unit volume; real shapes and transport mechanisms modify the model.

Area/volume=6/L: ratios are 6 and 2 per length unit.

Volume grows faster than area, reducing area available per unit contents.

Marking criteria

• 1 point: correct ratio formula.
• 1 point: both ratio values.
• 1 point: exchange consequence plus geometry limitation.

Question 14 · 3 points

A cell enters an equal-pressure solution with higher impermeant solute concentration. Predict initial water flow and distinguish passive from active transport.

Worked answer

Water initially leaves the cell; movement depends on permeability and stated pressure conditions.

In the simple osmosis model, water moves toward higher effective solute concentration.

Active transport uses energy to move against a relevant gradient; diffusion does not directly use that energy input.

Marking criteria

• 1 point: outward water prediction.
• 1 point: permeability/osmosis explanation.
• 1 point: passive/active transport distinction.

Question 15 · 1 point

Which process happens in lung exchange surfaces?

1. Gas moves between air and blood
2. Food is chewed
3. All ATP is made
4. DNA is replicated for every tissue

Worked answer

Gas moves between air and blood

Thin barriers permit gas exchange.

1 point for the correct objective answer; no written-method marks for this item.

Question 16 · 1 point

In a negative feedback loop the effector's response

1. amplifies the change
2. opposes the change
3. removes the receptor
4. has no effect

Worked answer

opposes the change

Opposing the deviation returns the variable toward its set point.

1 point for the correct objective answer; no written-method marks for this item.

Question 17 · 1 point

Oxygen reaches a muscle cell through the combined action of the

1. digestive and excretory systems
2. respiratory and circulatory systems
3. nervous system alone
4. skeletal system

Worked answer

respiratory and circulatory systems

Gas exchange at the lungs then transport in the blood.

1 point for the correct objective answer; no written-method marks for this item.

Question 18 · 1 point

A hormone reaches every tissue but only some respond because responding cells have

1. more blood supply
2. the matching receptor
3. thicker membranes
4. no nucleus

Worked answer

the matching receptor

Specificity lies in the receiving cell's receptors.

1 point for the correct objective answer; no written-method marks for this item.

Question 19 · 1 point

A second exposure to the same antigen produces a faster, larger response because of

1. barriers
2. memory lymphocytes
3. fever alone
4. inflammation alone

Worked answer

memory lymphocytes

Memory cells specific to that antigen are already numerous.

1 point for the correct objective answer; no written-method marks for this item.

Question 20 · 3 points

Trace oxygen from air to a muscle cell and explain how exercise illustrates system cooperation.

Worked answer

Respiratory exchange and circulatory delivery cooperate; the muscle then uses oxygen in aerobic metabolism.

Gas diffuses across lung exchange surfaces into blood.

Circulation carries it to tissues, where exchange supplies cells; ventilation and circulation adjust to demand.

Marking criteria

• 1 point: lung exchange.
• 1 point: blood transport and tissue exchange.
• 1 point: cell use and coordinated exercise demand.

Question 21 · 3 points

Body temperature rises, triggering sweating. Name the feedback type and explain why a hormone cannot directly trigger its usual response in a cell lacking its receptor.

Worked answer

Negative feedback regulates temperature; missing receptor blocks the usual direct response through that pathway.

Sweating can oppose warming through evaporation, a negative feedback.

Signal reception requires an appropriate receptor for the specified pathway.

Marking criteria

• 1 point: correctly trace negative feedback.
• 1 point: evaporation mechanism.
• 1 point: receptor-specific signal reasoning.

Question 22 · 1 point

ATP is best described as

1. the organelle where respiration happens
2. the cell's main energy currency
3. the molecule that stores genetic information
4. a green pigment that absorbs light

Worked answer

the cell's main energy currency

ATP is the small, spendable energy-carrying molecule cells use to power almost every activity — its nickname is the cell's energy currency.

1 point for the correct objective answer; no written-method marks for this item.

Question 23 · 1 point

In an ecosystem, energy

1. cycles like matter
2. flows through and is lost as heat
3. is created by producers
4. is destroyed by consumers

Worked answer

flows through and is lost as heat

Matter cycles; energy passes through once and degrades.

1 point for the correct objective answer; no written-method marks for this item.

Question 24 · 1 point

The oxygen released by photosynthesis comes from

1. carbon dioxide
2. water
3. glucose
4. chlorophyll

Worked answer

water

Water is split in the light-dependent reactions.

1 point for the correct objective answer; no written-method marks for this item.

Question 25 · 1 point

Oxygen's role in aerobic respiration is to

1. break glucose apart
2. accept electrons at the end of the transport chain
3. produce carbon dioxide directly
4. supply carbon

Worked answer

accept electrons at the end of the transport chain

As final electron acceptor it keeps the chain running.

1 point for the correct objective answer; no written-method marks for this item.

Question 26 · 1 point

A plant kept in continuous darkness loses mass because it

1. stops respiring
2. respires without photosynthesising
3. loses chloroplasts
4. absorbs no water

Worked answer

respires without photosynthesising

Stored organic matter is consumed and not replaced.

1 point for the correct objective answer; no written-method marks for this item.

Question 27 · 3 points

A plant gains organic carbon while producing oxygen in light. Identify the sources of that carbon and released oxygen, then explain why the plant still respires.

Worked answer

CO₂ supplies incorporated carbon; water supplies released O₂; respiration and photosynthesis can operate in the same plant.

Carbon enters from CO₂, while released oxygen in oxygenic photosynthesis derives from water.

Cellular work still requires ATP regeneration, so respiration can continue.

Marking criteria

• 1 point: carbon source.
• 1 point: oxygen source.
• 1 point: respiration/ATP reasoning.

Question 28 · 3 points

A plant's measured net oxygen output is 8 units/hour and respiration consumes 3 units/hour in the supplied model. Find gross oxygen production and state a condition limiting the calculation.

Worked answer

11 units/hour in the stated accounting; changing light or temperature could change either rate.

Net output=gross production−consumption.

Gross=8+3=11 units/hour, assuming measured rates apply over the same conditions and interval.

Marking criteria

• 1 point: net/gross relationship.
• 1 point: correct calculation and units.
• 1 point: valid matching-conditions limitation.

Question 29 · 1 point

In the standard model without new copying errors, what is the main result of mitosis followed by cytokinesis?

1. Two genetically identical daughter cells
2. Four sex cells with half the DNA
3. A cell with double the normal chromosome number
4. A finished protein

Worked answer

Two genetically identical daughter cells

Mitosis produces two daughter cells genetically identical to the parent, used for growth and repair.

1 point for the correct objective answer; no written-method marks for this item.

Question 30 · 1 point

DNA is replicated during

1. prophase
2. the S phase of interphase
3. anaphase
4. cytokinesis

Worked answer

the S phase of interphase

Replication precedes mitosis so each chromosome enters already duplicated.

1 point for the correct objective answer; no written-method marks for this item.

Question 31 · 1 point

Meiosis I differs from mitosis because in meiosis I

1. chromosomes do not replicate
2. homologous pairs separate
3. no cytokinesis occurs
4. chromosome number doubles

Worked answer

homologous pairs separate

Separating homologues is what halves the chromosome number.

1 point for the correct objective answer; no written-method marks for this item.

Question 32 · 1 point

A muscle cell and a nerve cell in one person differ mainly in

1. which genes they carry
2. which genes they express
3. their number of chromosomes
4. their DNA sequence

Worked answer

which genes they express

Both carry the same genome; expression differs.

1 point for the correct objective answer; no written-method marks for this item.

Question 33 · 1 point

During cleavage, cell number rises while total embryo size changes little because

1. cells shrink as cytoplasm is divided
2. new material is added
3. cells fuse
4. mass is lost

Worked answer

cells shrink as cytoplasm is divided

The existing cytoplasm is partitioned among more cells.

1 point for the correct objective answer; no written-method marks for this item.

Question 34 · 3 points

A species has diploid number 20. Give normal chromosome counts after mitosis, in gametes and after fertilization, and distinguish homologs from sister chromatids.

Worked answer

20 per normal somatic daughter, 10 per gamete and 20 in the zygote under the model.

Mitosis preserves 20; meiosis produces gametes with 10; two gametes restore 20.

Homologs carry corresponding loci from different parental sets; sister chromatids are replicated copies of one chromosome.

Marking criteria

• 1 point: mitosis count.
• 1 point: gamete and zygote counts.
• 1 point: homolog/sister distinction.

Question 35 · 3 points

Explain why a neuron and muscle cell can function differently with largely the same genome; distinguish differentiation from division.

Worked answer

Shared DNA can support specialized functions through regulated expression without deleting every unused gene.

Different gene-expression patterns produce different proteins and structures.

Division increases cell number while differentiation changes cell identity and function.

Marking criteria

• 1 point: shared genome.
• 1 point: differential expression linked to proteins/function.
• 1 point: differentiation/division distinction.

Question 36 · 1 point

In DNA, the base adenine (A) always pairs with

1. thymine (T)
2. cytosine (C)
3. guanine (G)
4. another adenine (A)

Worked answer

thymine (T)

A-T and C-G are the complementary base pairs; adenine always bonds with thymine.

1 point for the correct objective answer; no written-method marks for this item.

Question 37 · 1 point

A DNA sample is 22 percent cytosine. The percentage of adenine is

1. 22
2. 28
3. 44
4. 56

Worked answer

28

G = C = 22, leaving 56 for A and T equally, so 28 percent each.

1 point for the correct objective answer; no written-method marks for this item.

Question 38 · 1 point

Deleting a single base from a coding sequence is usually more damaging than substituting one because it

1. removes the gene
2. shifts the reading frame downstream
3. stops replication
4. changes the chromosome number

Worked answer

shifts the reading frame downstream

Every subsequent codon is regrouped and misread.

1 point for the correct objective answer; no written-method marks for this item.

Question 39 · 1 point

Two parents showing a dominant phenotype have a child with the recessive phenotype. The parents are

1. both homozygous dominant
2. both heterozygous
3. both homozygous recessive
4. one of each homozygote

Worked answer

both heterozygous

Each must have contributed a recessive allele while showing the dominant trait.

1 point for the correct objective answer; no written-method marks for this item.

Question 40 · 1 point

A mother is blood type O and a father type AB. A possible child blood type is

1. O
2. AB
3. A
4. none of these

Worked answer

A

Children are AO or BO, so type A or B; neither O nor AB is possible.

1 point for the correct objective answer; no written-method marks for this item.

Question 41 · 3 points

In a hypothetical complete-dominance model, cross Aa with aa. Give genotype and phenotype probabilities and explain why four offspring need not match the ratio.

Worked answer

50% Aa and 50% aa; 50% dominant phenotype and 50% recessive under the stated model, without a guaranteed family count.

The first parent supplies A or a; the second supplies only a.

Half the combinations are Aa and half aa; each offspring is a new event.

Marking criteria

• 1 point: allele contributions/genotype calculation.
• 1 point: phenotype probabilities under the specified dominance.
• 1 point: probability versus guaranteed count.

Question 42 · 3 points

A hormone changes transcription without changing DNA sequence. Explain whether this is a mutation and why a skin-cell mutation is not automatically inherited by offspring.

Worked answer

The described hormone response is expression regulation; a somatic skin mutation is not automatically passed through gametes.

Transcription change can be regulation rather than mutation.

A stable DNA sequence change is a mutation; ordinary offspring inheritance requires the reproductive lineage.

Marking criteria

• 1 point: expression versus sequence change.
• 1 point: correct mutation distinction.
• 1 point: somatic versus reproductive-lineage inheritance.

Question 43 · 1 point

What is the ultimate source of the new heritable variation that natural selection acts upon?

1. An organism's conscious effort to change
2. The environment directly rewriting an organism's genes as needed
3. Mutation (with reshuffling of genes in sexual reproduction)
4. Traits organisms build up through exercise and practice

Worked answer

Mutation (with reshuffling of genes in sexual reproduction)

New alleles arise from random mutation; sexual reproduction then reshuffles this variation. Natural selection can only act on variation that already exists.

1 point for the correct objective answer; no written-method marks for this item.

Question 44 · 1 point

Natural selection acts on

1. variation produced in response to need
2. heritable variation already present
3. acquired characteristics
4. individual effort

Worked answer

heritable variation already present

Selection sorts existing variation; mutation supplies it blindly.

1 point for the correct objective answer; no written-method marks for this item.

Question 45 · 1 point

A bird's wing and an insect's wing are similar in function but differ in structure and ancestry. They are

1. homologous
2. analogous
3. vestigial
4. identical

Worked answer

analogous

Analogous similarity arises independently and is not evidence of relatedness.

1 point for the correct objective answer; no written-method marks for this item.

Question 46 · 1 point

Genetic drift has its largest effect in populations that are

1. very large
2. small
3. growing
4. migrating

Worked answer

small

Chance variation in reproduction matters proportionally more when numbers are small.

1 point for the correct objective answer; no written-method marks for this item.

Question 47 · 1 point

On a cladogram, two groups are most closely related if they

1. are drawn closest together
2. share the most recent common ancestor
3. are furthest right
4. have the most derived characters

Worked answer

share the most recent common ancestor

Relatedness is read from node position, not from spacing on the page.

1 point for the correct objective answer; no written-method marks for this item.

Question 48 · 3 points

A random flood leaves ten survivors regardless of their alleles. Frequencies differ from the original population. Identify a mechanism and compare with selection.

Worked answer

A bottleneck with genetic drift fits the stated random survival; it is not evidence of an adaptive allele advantage.

Random survivor sampling can change frequencies, especially in small populations.

Selection requires heritable differences associated with reproductive success in the environment.

Marking criteria

• 1 point: bottleneck/drift identification.
• 1 point: chance sampling mechanism.
• 1 point: distinguish from selection.

Question 49 · 3 points

A tree groups A and B at a recent node and joins C at an older node. Identify the closest pair and explain why rotating branches does not change the result.

Worked answer

A and B are closest in this tree; spacing and left-to-right tip order are not the relationship criterion.

Relatedness follows the most recent common ancestor.

Rotation changes drawing order but preserves connections.

Marking criteria

• 1 point: correct pair.
• 1 point: shared-ancestor reasoning.
• 1 point: rotation/tip-order explanation.

Question 50 · 1 point

All the members of a single species living and interbreeding in the same area make up a

1. community
2. biome
3. trophic level
4. population

Worked answer

population

A population is one species in one area; a community is all the different populations together.

1 point for the correct objective answer; no written-method marks for this item.

Question 51 · 1 point

Competition for food within a population is a

1. density-independent factor
2. density-dependent factor
3. abiotic factor only
4. non-limiting factor

Worked answer

density-dependent factor

Its intensity increases as the population becomes denser.

1 point for the correct objective answer; no written-method marks for this item.

Question 52 · 1 point

Food chains are usually short because at each transfer

1. species run out
2. about ninety percent of the energy is not passed on
3. matter is destroyed
4. predators disappear

Worked answer

about ninety percent of the energy is not passed on

Only roughly a tenth is available to the next level.

1 point for the correct objective answer; no written-method marks for this item.

Question 53 · 1 point

Decomposers are essential because they

1. add energy to the ecosystem
2. return elements to inorganic forms producers can reuse
3. occupy the first trophic level
4. prevent energy loss

Worked answer

return elements to inorganic forms producers can reuse

They close the matter cycle; they add no energy.

1 point for the correct objective answer; no written-method marks for this item.

Question 54 · 1 point

Resistance and resilience differ because resilience describes

1. how little a community changes
2. how fully and quickly it recovers
3. its species richness
4. its total biomass

Worked answer

how fully and quickly it recovers

Resistance is the size of the initial change; resilience is the recovery.

1 point for the correct objective answer; no written-method marks for this item.

Question 55 · 3 points

A population starts at 500, has 60 births, 40 deaths, 15 immigrants and 25 emigrants. Calculate final size; explain why carrying capacity can change.

Worked answer

510 individuals; carrying capacity is context dependent rather than a universal fixed species value.

Net=60−40+15−25=10.

Final=510; resource and environmental conditions affect capacity.

Marking criteria

• 1 point: include all four flows with signs.
• 1 point: correct final size.
• 1 point: capacity linked to resources/environment.

Question 56 · 3 points

A conservation survey finds 20 species at site A in 5 h and 12 at B in 1 h. Explain the comparison's limitation, propose a fairer survey and identify an outcome to monitor after an intervention.

Worked answer

Counts alone cannot rank true diversity confidently; monitor measures such as occupancy, recruitment or habitat connectivity with a baseline.

Unequal sampling effort affects detection and observed counts.

Use comparable replicated effort, account for detectability and monitor an outcome linked to the actual threat.

Marking criteria

• 1 point: detection/effort limitation.
• 1 point: repeatable comparable survey.
• 1 point: threat-linked measurable outcome and baseline.