ESAT Biology: Cells, membranes and transport, set 1

• Answer all questions. No calculator.
• Each question has exactly one correct answer.

1. 11 mark

   Both animal and plant cells contain a number of sub-cellular components with different functions. Which of the following structures is the site of the reactions of aerobic respiration, releasing energy for the cell to use?

   1. A Mitochondrion
   2. B Nucleus
   3. C Cell membrane
   4. D Cytoplasm
2. 21 mark

   A student compares a plant cell and an animal cell under a microscope. Which structure is found in the plant cell but not in the animal cell, and is the site where photosynthesis takes place?

   1. A Mitochondrion
   2. B Chloroplast
   3. C Nucleus
   4. D Cell membrane
3. 31 mark

   A student examines a bacterial cell. Which statement correctly describes a feature of this prokaryotic cell?

   1. A Its DNA is enclosed within a nucleus, as in a plant or animal cell.
   2. B It has no cell wall, only a cell membrane.
   3. C It has chromosomal DNA free in the cytoplasm, and no true nucleus.
   4. D It contains mitochondria to carry out aerobic respiration.
4. 41 mark

   Which sequence correctly gives the levels of organisation within a multicellular organism, from the simplest level to the most complex?

   1. A Cells, organs, tissues, organ systems
   2. B Tissues, cells, organs, organ systems
   3. C Cells, tissues, organ systems, organs
   4. D Cells, tissues, organs, organ systems
5. 51 mark

   Oxygen moves from the air in the lungs into the blood by diffusion, across the exchange surface of the alveoli. Which change would increase the rate of this diffusion?

   1. A Decreasing the concentration gradient of oxygen between the alveoli and the blood
   2. B Increasing the surface area of the alveoli available for exchange
   3. C Increasing the thickness of the exchange surface
   4. D Decreasing the temperature of the surrounding tissue
6. 61 mark

   A red blood cell is placed in a beaker of pure water, which has a higher water potential than the cytoplasm of the cell. The cell membrane is partially permeable. What is the most likely outcome, and by which process does it happen?

   1. A Water moves into the cell by osmosis, and the cell may burst as a result.
   2. B Water moves out of the cell by active transport, causing the cell to shrink.
   3. C Water moves into the cell by diffusion through channel proteins, a process that requires energy.
   4. D Solute particles move out of the cell by osmosis, causing the water concentration inside to fall.
7. 71 mark

   The mitotic cell cycle includes an interphase followed by mitosis. In which phase does DNA replication take place, and what does mitosis itself produce?

   1. A DNA replication occurs during mitosis itself; mitosis produces four genetically different daughter cells.
   2. B DNA replication occurs during interphase; mitosis produces two genetically different daughter cells.
   3. C DNA replication occurs during interphase; mitosis produces two genetically identical daughter cells.
   4. D DNA replication occurs during mitosis; mitosis produces two genetically identical daughter cells.
8. 81 mark

   Which of the following is NOT a role of mitosis in a multicellular organism?

   1. A Repairing tissue that has been damaged or worn out
   2. B Increasing the number of cells as the organism grows
   3. C Allowing some organisms to reproduce asexually without a mate
   4. D Producing genetically varied gametes for sexual reproduction
9. 91 mark

   Which statement best describes the biological basis of cancer, as understood at this level?

   1. A Cancer results from mutations in cells that lead to uncontrolled cell division.
   2. B Cancer is caused by a virus that directly infects healthy cells and kills them outright.
   3. C Cancer is a failure of osmosis to regulate the water balance of cells within body tissues.
   4. D Cancer occurs when cells stop dividing altogether, so that tissue gradually shrinks and wastes away.
10. 101 mark

    A human body cell contains 46 chromosomes. A cell in the testes undergoes meiosis to produce sperm cells. How many chromosomes will each sperm cell contain, and how many sperm cells are produced from one parent cell?

    1. A 46 chromosomes; 2 cells
    2. B 23 chromosomes; 4 cells
    3. C 23 chromosomes; 2 cells
    4. D 46 chromosomes; 4 cells
11. 111 mark

    Both the mitotic and meiotic cell cycles begin with an interphase in which the cell grows and its DNA is replicated. What is the key difference between mitosis and meiosis that follows this shared interphase?

    1. A Mitosis involves two divisions producing four genetically different cells; meiosis involves one division producing two genetically identical cells.
    2. B Mitosis and meiosis both involve two divisions, but only meiosis produces genetically identical cells.
    3. C Mitosis involves one division producing two genetically identical cells; meiosis involves two divisions producing four genetically different cells.
    4. D Mitosis involves one division producing four genetically identical cells; meiosis involves two divisions producing two genetically different cells.
12. 121 mark

    Gametes produced by meiosis are haploid, each containing a single copy of each chromosome. Why is this important at fertilisation?

    1. A So that the zygote formed is haploid, matching the gametes that produced it.
    2. B So that the zygote is genetically identical to both parents.
    3. C So that the zygote contains twice the diploid number of chromosomes, doubling the parents' genetic material.
    4. D So that the zygote formed has the full diploid chromosome number, from both parents.
13. 131 mark

    A gardener takes a cutting from a plant and grows it into a new, separate plant. Assuming no mutations occur, which statement about this new plant is correct?

    1. A It is genetically identical to the parent plant, because it was produced asexually from one parent.
    2. B It is genetically different from the parent plant, because two parents contributed genetic material.
    3. C It shows increased variation compared with the parent plant, because meiosis has taken place.
    4. D It cannot be genetically identical to the parent, because all reproduction involves some variation.
14. 141 mark

    In humans, all egg cells carry an X chromosome, and sperm cells carry either an X chromosome or a Y chromosome, in roughly equal numbers. Based on this, what proportion of children born to a couple are expected to be male (XY)?

    1. A 1/4
    2. B 1/2
    3. C 1/3
    4. D 3/4
15. 151 mark

    A genetic diagram is used to predict the sex of offspring. A father's sperm cells are shown as carrying either an X chromosome or a Y chromosome, and a mother's egg cells are all shown carrying an X chromosome. Which combination in the diagram represents a female offspring?

    1. A Father's Y combines with mother's X
    2. B Father's Y combines with mother's Y
    3. C Father's X combines with mother's X
    4. D Father's X combines with father's X

Worked solutions

Every question below carries the reasoning, not just the answer. The official material for this test publishes a correct option letter and nothing else.

1. Question 1Answer: A

   1. The question asks for the named sub-cellular structure responsible for aerobic respiration.
   2. The nucleus controls the cell's activities and holds its genetic material, but it does not release energy from respiration.
   3. The cell membrane and cytoplasm are involved in movement of substances and general cell chemistry, but neither is the specific site of aerobic respiration.
   4. The mitochondrion is the sub-cellular component whose function is to carry out the reactions of aerobic respiration, releasing energy the cell can use.
   5. Therefore the answer is A.
   • Why not B: This treats the nucleus as a general control centre that carries out every important job in the cell, when its specific role is storing and controlling access to the genetic material, not releasing energy.
   • Why not C: This confuses the cell membrane's role of controlling which substances enter and leave the cell with the separate job of releasing energy through respiration.
   • Why not D: This is a partial truth: some early respiration reactions do occur in the cytoplasm, but the specification names the mitochondrion as the organelle responsible for aerobic respiration, and this option fails to give the more specific, correct structure.

2. Question 2Answer: B

   1. The question needs a structure that is both plant-only and the site of photosynthesis.
   2. Mitochondria and nuclei appear in both plant and animal cells, so neither can be the plant-only answer.
   3. The cell membrane is common to essentially all cell types and is not where photosynthesis happens.
   4. The chloroplast is described in the specification as plant-only, and it is the structure where photosynthesis takes place.
   5. Therefore the answer is B.
   • Why not A: The mitochondrion is present in both plant and animal cells and is the site of respiration, not photosynthesis, so it is neither plant-only nor the correct process.
   • Why not C: The nucleus is present in both plant and animal cells; this wrongly treats a structure common to both as if it were unique to plants.
   • Why not D: The cell membrane is present in every cell, plant, animal and bacterial alike, so it cannot be the plant-only, photosynthesising structure the question asks for.

3. Question 3Answer: C

   1. The specification lists the sub-cellular components of a prokaryotic cell as: cell membrane, cytoplasm, cell wall, chromosomal DNA with no true nucleus, and plasmid DNA.
   2. A bacterial cell does have a cell wall, so option B is wrong to remove it.
   3. A bacterial cell has no nucleus and no mitochondria, so options A and D each wrongly add a eukaryotic feature.
   4. The chromosomal DNA of a bacterial cell lies free in the cytoplasm rather than being enclosed in a nucleus.
   5. Therefore the answer is C.
   • Why not A: This wrongly gives the bacterial cell a eukaryotic feature; a defining feature of prokaryotic cells is that they have no true, membrane-bound nucleus.
   • Why not B: This confuses a bacterial cell with an animal cell; bacteria do have a cell wall, in addition to a cell membrane.
   • Why not D: This wrongly assigns mitochondria, a eukaryotic organelle, to a prokaryotic cell, which has no mitochondria.

4. Question 4Answer: D

   1. The specification gives the levels of organisation as cells, tissues, organs and organ systems, in that order.
   2. Cells are the simplest level, and a group of similar cells forms a tissue.
   3. Different tissues combine to form an organ, and different organs work together as an organ system.
   4. Only one option keeps this order intact without swapping any two levels.
   5. Therefore the answer is D.
   • Why not A: This swaps organs and tissues, treating an organ as a simpler level than a tissue, when a tissue is a simpler group of similar cells that combine to form an organ.
   • Why not B: This starts the sequence at tissues rather than cells, missing that a tissue is itself built up from cells.
   • Why not C: This places organ systems before organs, when an organ system is a group of organs working together, so it must come after organs, not before them.

5. Question 5Answer: B

   1. Diffusion is faster across a larger concentration gradient, a larger surface area, a shorter distance, and at a higher temperature.
   2. Decreasing the concentration gradient would slow diffusion, not speed it up, so option A is the wrong direction.
   3. Increasing the thickness of the exchange surface increases the distance particles must travel, which slows diffusion, so option C is the wrong direction.
   4. Decreasing the temperature reduces particle movement, which slows diffusion, so option D is the wrong direction.
   5. Increasing the surface area gives more room for oxygen molecules to cross at once, which increases the rate of diffusion.
   6. Therefore the answer is B.
   • Why not A: This reverses the relationship between gradient and rate; diffusion is faster with a larger concentration gradient, not a smaller one.
   • Why not C: This reverses the relationship between distance and rate; a thicker exchange surface means particles travel further, which slows diffusion rather than speeding it up.
   • Why not D: This reverses the effect of temperature; a lower temperature gives particles less kinetic energy, which slows diffusion rather than speeding it up.

6. Question 6Answer: A

   1. Water potential describes the tendency of water to move, and water moves from a region of higher water potential to a region of lower water potential across a partially permeable membrane.
   2. Here the water outside the cell has a higher water potential than the cytoplasm, so water moves into the cell.
   3. This movement of water across the partially permeable membrane, down the water potential gradient, is osmosis, and osmosis needs no energy input.
   4. A red blood cell has no cell wall to resist the resulting pressure, so too much water entering can cause it to burst.
   5. Therefore the answer is A.
   • Why not B: This reverses the direction water actually moves, which is into the cell from the higher water potential outside, and it wrongly names the process as active transport, which needs energy and moves substances against a gradient rather than water moving passively down one.
   • Why not C: This correctly has water moving into the cell but wrongly claims the process needs energy; osmosis is a passive process that needs no energy input from the cell.
   • Why not D: This confuses osmosis, which specifically describes the movement of water across a partially permeable membrane, with the movement of solute particles, which osmosis does not describe.

7. Question 7Answer: C

   1. Interphase is the stage of the cell cycle in which the cell grows and its DNA is replicated, ready for division.
   2. Mitosis is the single division that follows, splitting the replicated DNA between two new cells.
   3. Because each new cell receives an identical copy of the original DNA, the two daughter cells produced by mitosis are genetically identical to each other and to the parent cell.
   4. Only one option places DNA replication correctly in interphase and correctly describes two genetically identical daughter cells.
   5. Therefore the answer is C.
   • Why not A: This misplaces DNA replication into mitosis itself, and it also wrongly gives mitosis the outcome of meiosis, four cells that are genetically different, rather than mitosis's own outcome.
   • Why not B: This correctly times DNA replication in interphase but wrongly claims the two daughter cells are genetically different; mitosis produces daughter cells genetically identical to the parent cell.
   • Why not D: This correctly gives two genetically identical daughter cells but wrongly places DNA replication during mitosis itself, rather than the interphase that precedes it.

8. Question 8Answer: D

   1. The specification lists mitosis's roles as increasing the number of cells in growth, repairing tissues, replacing cells, and allowing asexual reproduction.
   2. Options A, B and C each restate one of those listed roles, so none of them is the exception the question asks for.
   3. Producing genetically varied gametes is instead the role of meiosis, which produces daughter cells that differ genetically, unlike mitosis's identical daughter cells.
   4. Therefore the answer is D.
   • Why not A: Repairing damaged tissue by replacing cells is one of the genuine roles of mitosis listed in the specification, so a candidate unsure of this wrongly treats it as the exception.
   • Why not B: Increasing the number of cells during growth is one of the genuine roles of mitosis, so a candidate unsure of this wrongly treats it as the exception.
   • Why not C: Many organisms reproduce asexually using mitotic division alone, so this is a genuine role of mitosis, and a candidate unsure of this wrongly treats it as the exception.

9. Question 9Answer: A

   1. The specification describes cancer as the result of changes in cells, including mutations, that lead to uncontrolled cell division.
   2. This is a description of a fault in the control of division, not an infection, a transport failure, or a stopping of division.
   3. Only one option matches this: mutations leading to uncontrolled cell division.
   4. Therefore the answer is A.
   • Why not B: This describes an infectious mechanism rather than the genetic one the specification names; cancer is defined here in terms of mutation and division, not viral infection killing cells.
   • Why not C: This substitutes an unrelated transport process, osmosis, for the actual cause of cancer, which is changes in cells including mutations.
   • Why not D: This reverses the real mechanism; cancer involves excessive, uncontrolled cell division, not a halt in division.

10. Question 10Answer: B

    1. Meiosis involves two cell divisions, producing four daughter cells from one parent cell, each with a single copy of each chromosome.
    2. A single copy of each chromosome is half the parent cell's chromosome number.
    3. Half of 46 is 23, so each sperm cell contains 23 chromosomes.
    4. The parent cell produces four such cells in total.
    5. Therefore the answer is B.
    • Why not A: This gives both the chromosome number and the cell count of mitosis rather than meiosis; meiosis halves the chromosome number and produces four cells, not two.
    • Why not C: This correctly halves the chromosome number but keeps the cell count of mitosis, two cells, rather than the four cells meiosis produces.
    • Why not D: This correctly gives the meiosis cell count of four but forgets that the chromosome number must also halve, from 46 to 23.

11. Question 11Answer: C

    1. Mitosis is a single division that produces two daughter cells, genetically identical to the parent cell.
    2. Meiosis is two successive divisions that produce four daughter cells, each genetically different from the others.
    3. Checking each option against this pairing rules out any that swap the division count, the cell count, or the identical and different outcomes.
    4. Only one option keeps mitosis at one division and two identical cells, and meiosis at two divisions and four different cells.
    5. Therefore the answer is C.
    • Why not A: This swaps which process has one division and which has two, and it also swaps the genetically identical and genetically different outcomes between the processes; mitosis is the one with a single division producing identical cells, and meiosis the one with two divisions producing different cells.
    • Why not B: This wrongly gives mitosis two divisions, when mitosis has only one, and it also swaps the identical and different outcomes between the two processes.
    • Why not D: This correctly keeps one division for mitosis and two for meiosis, and correctly pairs identical cells with mitosis and different cells with meiosis, but it pairs each process with the wrong resulting cell count, giving mitosis four cells and meiosis two.

12. Question 12Answer: D

    1. Each gamete is haploid, carrying a single copy of each chromosome, which is half the normal diploid number.
    2. At fertilisation, one gamete from each parent fuses to form the zygote.
    3. Combining the two single copies restores the full, diploid number of chromosomes in the zygote, with one set of chromosomes coming from each parent.
    4. This is why the gametes must be haploid: fusing two diploid gametes would double the chromosome number in every generation, which does not happen.
    5. Therefore the answer is D.
    • Why not A: This misses that fusing two haploid gametes restores the full diploid chromosome number; the zygote is diploid, not haploid like the gametes that formed it.
    • Why not B: This wrongly gives the zygote the identical-copy outcome that is characteristic of mitosis; the zygote instead combines chromosomes from two parents, giving genetic variation.
    • Why not C: This overshoots the correct chromosome number; fusing two haploid sets restores the normal diploid number, it does not double it.

13. Question 13Answer: A

    1. A cutting is a form of asexual reproduction, involving only one parent and no fusion of gametes.
    2. With no mutation, mitosis produces cells, and ultimately a whole new plant, genetically identical to the parent.
    3. Meiosis and the mixing of genetic material from two parents belong to sexual reproduction, which is not what is happening here.
    4. Therefore the new plant is genetically identical to the parent plant, and the answer is A.
    • Why not B: This wrongly applies the two-parent, variation-producing feature of sexual reproduction to a cutting, which involves only one parent plant and no fusion of gametes.
    • Why not C: This wrongly invokes meiosis, which is part of producing gametes for sexual reproduction; taking a cutting does not involve meiosis or gamete formation at all.
    • Why not D: This wrongly assumes all reproduction produces variation; asexual reproduction with no mutation gives offspring that are genetically identical to the parent.

14. Question 14Answer: B

    1. Every egg cell carries an X chromosome, so the mother's contribution is fixed.
    2. A sperm cell carries either an X chromosome or a Y chromosome, with each type equally likely.
    3. A child is male (XY) only if a Y-carrying sperm fertilises the egg, which happens with probability 1/2.
    4. Therefore the answer is B.
    • Why not A: This wrongly multiplies two separate 1/2 probabilities together, as in a cross tracking two different genes, when only one step of chance, which type of sperm fertilises the egg, applies here.
    • Why not C: This treats the outcome as one of three equally likely possibilities, when there are only two possible types of sperm, X-carrying or Y-carrying, each equally likely.
    • Why not D: This imports the 3:1 ratio typical of a heterozygous single-gene cross into a situation where there are only two, equally likely outcomes, X-sperm or Y-sperm.

15. Question 15Answer: C

    1. A female offspring has two X chromosomes, one from each parent.
    2. The mother's egg cell always contributes an X chromosome.
    3. For the offspring to be female, the father's sperm cell must also contribute an X chromosome, giving XX.
    4. Any combination involving a Y chromosome, or combining two chromosomes from the same parent, cannot represent this outcome.
    5. Therefore the answer is C.
    • Why not A: This combination gives an XY zygote, which the diagram represents as a male offspring, not a female one.
    • Why not B: Mother's egg cells never carry a Y chromosome in this system, so this combination cannot appear in the diagram at all.
    • Why not D: This wrongly takes both chromosomes from the father's sperm; a genetic diagram must combine one chromosome contributed by each parent, not two from the same parent.