ESAT Biology: Cells, membranes and transport, set 2

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

1. 11 mark

   Plant cells, but not animal cells, are surrounded by a rigid cell wall in addition to the cell membrane. Which of the following best describes the function of this cell wall?

   1. A It provides structural support and prevents the cell from bursting when it takes up too much water.
   2. B It controls which substances enter and leave the cell, in place of the cell membrane.
   3. C It is the site where photosynthesis takes place, using light energy from the sun.
   4. D It stores cell sap and helps to keep the cell rigid by pressing outward against the cytoplasm.
2. 21 mark

   A student is asked to list all of the sub-cellular components present in a typical bacterial cell. Which of the following lists is correct and complete, according to the specification?

   1. A Cell membrane, cytoplasm, cell wall, mitochondria, chromosomal DNA
   2. B Cell membrane, cytoplasm, nucleus, cell wall, plasmid DNA
   3. C Cell membrane, cytoplasm, cell wall, chromosomal DNA, plasmid DNA
   4. D Cell membrane, nucleus, cell wall, chromosomal DNA, plasmid DNA
3. 31 mark

   Which of the following is an example of a tissue, rather than a cell, an organ or an organ system?

   1. A The stomach
   2. B Muscular tissue in the wall of the stomach
   3. C The digestive system
   4. D A red blood cell
4. 41 mark

   A small amount of perfume is released from an open bottle in the corner of a still room. Over the next few minutes, the scent gradually becomes noticeable throughout the room, even though the air is not stirred or fanned. Which process is directly responsible for the perfume spreading through the room in this way?

   1. A Active transport, since the perfume molecules move without any outside energy source.
   2. B Osmosis, since the perfume moves from a region of high concentration to a region of low concentration.
   3. C Osmosis, since the perfume molecules move across a partially permeable membrane formed in the air.
   4. D Diffusion, the net movement of particles from a region of higher concentration to a region of lower concentration.
5. 51 mark

   In parts of the small intestine, glucose can sometimes be present at a lower concentration in the gut than in the blood surrounding it, yet glucose still moves out of the gut and into the blood. Which process explains this movement, and why does it require energy from respiration?

   1. A Active transport; because the glucose is moving against its concentration gradient, from a lower to a higher concentration.
   2. B Osmosis; because moving a water-soluble substance like glucose across a membrane always needs energy.
   3. C Diffusion; because moving down a concentration gradient always requires an input of energy.
   4. D Active transport; because all movement of substances across a cell membrane requires energy, regardless of the concentration gradient.
6. 61 mark

   A visking tubing bag, which acts as a partially permeable membrane, is filled with a concentrated sugar solution, sealed, and placed in a beaker of pure water. After 20 minutes, the bag is noticeably more swollen than before. Which statement correctly explains this observation?

   1. A The pure water outside the bag has a lower water potential than the sugar solution inside, so water moves out of the bag by osmosis.
   2. B The sugar solution inside the bag has a lower water potential than the pure water outside, so water moves into the bag by osmosis.
   3. C Sugar molecules move out of the bag into the pure water by diffusion, causing the bag to swell as space is freed up inside.
   4. D The visking tubing actively pumps water into the bag, using energy released from the breakdown of sugar inside.
7. 71 mark

   A patient receives a skin graft made from their own skin cells, grown in the laboratory through repeated cell division before being transplanted back onto the patient. The graft is not rejected by the patient's immune system. Which of the following best explains this, in terms of the type of cell division used to grow the new skin cells?

   1. A The cells were produced by meiosis, so they carry a unique combination of alleles that matches the patient's immune cells exactly.
   2. B The cells were produced by meiosis, so they are genetically different from each other, giving the immune system many chances to accept at least one.
   3. C The cells were produced by mitosis, so they contain half the normal number of chromosomes, matching the patient's blood type.
   4. D The cells were produced by mitosis, so they are genetically identical to the patient's own original cells and are recognised as 'self'.
8. 81 mark

   Both the mitotic and meiotic cell cycles begin with an interphase, before mitosis or meiosis itself takes place. Which statement correctly describes what happens during this shared interphase?

   1. A The cell divides once, and the resulting two cells then each grow before dividing again.
   2. B The cell is inactive and resting, undergoing no significant biological activity until division begins.
   3. C The cell grows, and its DNA is replicated (copied), preparing it for the division that follows.
   4. D The cell's chromosome number is halved, in preparation for the divisions of mitosis or meiosis.
9. 91 mark

   A student writes in their notes: 'Cancer happens when a cell's genetic material is so badly damaged by mutations that the cell can no longer divide, and it eventually dies.' Which statement correctly identifies what is wrong with this claim?

   1. A The claim is wrong because cancer has nothing to do with mutations or changes in a cell's genetic material.
   2. B The claim is wrong because mutations of this kind instead cause the cell to divide in an uncontrolled way, forming a tumour, rather than stopping division and dying.
   3. C The claim is wrong because it describes osmosis, not mutation, as the underlying process behind cancer.
   4. D The claim is correct as it stands and needs no correction.
10. 101 mark

    In sheep, a typical body cell contains 54 chromosomes. A ewe's egg cell and a ram's sperm cell, each produced by meiosis, fuse together at fertilisation to form a zygote. How many chromosomes does each gamete contain, and how many chromosomes does the resulting zygote contain?

    1. A Each gamete contains 27 chromosomes; the zygote contains 54 chromosomes.
    2. B Each gamete contains 54 chromosomes; the zygote contains 108 chromosomes.
    3. C Each gamete contains 27 chromosomes; the zygote contains 27 chromosomes.
    4. D Each gamete contains 108 chromosomes; the zygote contains 54 chromosomes.
11. 111 mark

    Suppose that, instead of using meiosis, an organism produced its gametes using mitosis, so that each gamete had the same chromosome number as a normal body cell. Which outcome would most directly result from this, generation after generation?

    1. A The offspring would show much greater genetic variation than normal, since mitosis produces many different cell types.
    2. B The offspring would be unaffected, since fertilisation always restores the normal chromosome number regardless of how the gametes were produced.
    3. C The chromosome number would double at every generation, since fertilisation would combine two full sets of chromosomes each time.
    4. D Fertilisation would no longer be possible at all, since mitotically produced cells cannot fuse together.
12. 121 mark

    A hydra can reproduce by budding, a form of asexual reproduction in which a new individual grows from a small outgrowth on the parent's body, with no fusion of gametes involved. Which statement correctly compares budding with sexual reproduction, in terms of the number of parents involved and the expected genetic relationship between offspring and parent?

    1. A Sexual reproduction also produces genetically identical offspring, since both parents contribute an equal amount of genetic material.
    2. B Budding involves two parents, since the new individual and the original hydra both count as parents of any future offspring; sexual reproduction involves only one parent.
    3. C Budding and sexual reproduction both involve two parents, but only budding produces genetically identical offspring.
    4. D Budding involves one parent and produces offspring genetically identical to it, assuming no mutation; sexual reproduction involves two parents and produces offspring genetically different from each other and from both parents.
13. 131 mark

    A Punnett square for human sex determination is drawn with the mother's two egg cells, both carrying an X chromosome, along the top, and the father's two possible sperm types, one X-carrying and one Y-carrying, down the side, giving four boxes in total. How many of these four boxes represent a genetically male (XY) offspring?

    1. A 1
    2. B 2
    3. C 3
    4. D 4
14. 141 mark

    Fertilisation in humans produces male and female offspring in an expected ratio of approximately 1:1, since sperm cells carrying an X or a Y chromosome are produced in roughly equal numbers. Based on this expected ratio, in a school year group of 600 pupils, approximately how many pupils would be expected to be female?

    1. A 300
    2. B 400
    3. C 600
    4. D 150
15. 151 mark

    A human body cell contains 23 pairs of chromosomes, 46 chromosomes in total. One of these 23 pairs is the pair of sex chromosomes (XX or XY), which determines the individual's sex. How many chromosomes in a human body cell are NOT involved in determining sex?

    1. A 22
    2. B 23
    3. C 44
    4. D 45

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. Plant cells have a rigid cell wall, made of cellulose, outside the cell membrane.
   2. Its function is to provide structural support to the cell and to resist the pressure created as the cell takes up water, preventing it from bursting.
   3. Controlling which substances enter and leave the cell is instead the job of the partially permeable cell membrane.
   4. Photosynthesis takes place in the chloroplast and cell sap is stored in the vacuole, two separate plant-only structures from the cell wall.
   5. Therefore the answer is A.
   • Why not B: This wrongly gives the cell wall the cell membrane's job of controlling entry and exit of substances; the wall's function is structural support, not selective transport.
   • Why not C: This assigns the cell wall the function of the chloroplast, which is the actual plant-only structure where photosynthesis takes place.
   • Why not D: This assigns the cell wall the function of the vacuole, which stores cell sap and produces turgor pressure; the wall and the vacuole are two different plant-only structures.

2. Question 2Answer: C

   1. The specification lists the sub-cellular components of a prokaryotic (bacterial) cell as: cell membrane, cytoplasm, cell wall, chromosomal DNA with no true nucleus, and plasmid DNA.
   2. Any list that adds a nucleus or mitochondria wrongly gives the bacterial cell a eukaryotic feature it does not have.
   3. Any list that leaves out the cytoplasm or plasmid DNA is missing a component the specification includes.
   4. Only one option matches the specification's list exactly.
   5. Therefore the answer is C.
   • Why not A: This wrongly adds mitochondria, a eukaryotic organelle absent from prokaryotic cells, in place of the correct plasmid DNA.
   • Why not B: This wrongly adds a nucleus, a eukaryotic feature; a bacterial cell has no true, membrane-bound nucleus.
   • Why not D: This wrongly adds a nucleus and wrongly omits the cytoplasm, both eukaryotic-style errors, while still correctly keeping chromosomal and plasmid DNA.

3. Question 3Answer: B

   1. The levels of organisation, from simplest to most complex, are cells, tissues, organs, and organ systems.
   2. A red blood cell is a single cell, below the level of a tissue.
   3. Muscular tissue is a group of similar cells (muscle cells) working together, which is the definition of a tissue.
   4. The stomach is an organ, built from several different tissues, including muscular tissue, working together, and the digestive system is an organ system built from organs including the stomach.
   5. Therefore the answer is B.
   • Why not A: The stomach is a single organ, built from several different tissues working together, not a tissue itself.
   • Why not C: The digestive system is an organ system: a group of organs, including the stomach, working together, which is a higher level of organisation than a tissue.
   • Why not D: A red blood cell is a single cell, one level below a tissue; a tissue is a group of similar cells working together, not one cell on its own.

4. Question 4Answer: D

   1. The perfume molecules move from where they are in high concentration, near the bottle, to where they are in low concentration elsewhere in the room, until they are more evenly spread out.
   2. This net movement of particles down a concentration gradient, with no membrane and no energy input, is diffusion.
   3. Osmosis is a special case that only describes the movement of water across a partially permeable membrane, which does not apply here, since there is no membrane in the open air of the room.
   4. Active transport requires energy and moves substances against a concentration gradient, which is not what is happening here either.
   5. Therefore the answer is D.
   • Why not A: This wrongly names active transport; that process moves substances against a concentration gradient using energy, whereas the perfume moves down its own concentration gradient with no energy input at all.
   • Why not B: This correctly identifies the direction of movement, from high to low concentration, but wrongly names it osmosis, which refers specifically to the movement of water across a partially permeable membrane, not to perfume particles moving through open air.
   • Why not C: This wrongly invents a partially permeable membrane in the open air and wrongly calls the process osmosis; there is no membrane involved here, and the particles moving are perfume molecules, not water.

5. Question 5Answer: A

   1. Diffusion and osmosis are both passive processes: diffusion moves particles down a concentration gradient, and osmosis moves water down a water potential gradient, neither needing energy.
   2. Here, glucose moves from a lower concentration in the gut to a higher concentration in the blood, against its own concentration gradient.
   3. Moving a substance against its concentration gradient needs energy, supplied by respiration in the cell; this process is called active transport.
   4. Therefore the answer is A.
   • Why not B: This wrongly calls the process osmosis, which refers specifically to the movement of water, not a dissolved substance such as glucose, across a partially permeable membrane.
   • Why not C: This wrongly calls the process diffusion, and also wrongly claims diffusion needs energy; diffusion is a passive process, and in any case the gradient here runs the wrong way for diffusion to explain the movement.
   • Why not D: This correctly names active transport but wrongly justifies it by claiming that all membrane transport needs energy; diffusion and osmosis are both passive processes needing no energy, so the real reason here is specifically that the movement is against the concentration gradient.

6. Question 6Answer: B

   1. Pure water has a higher water potential than a concentrated sugar solution.
   2. Water moves, by osmosis, across a partially permeable membrane from a region of higher water potential to a region of lower water potential.
   3. Here, water moves from the pure water outside, which has the higher water potential, into the sugar solution inside the bag, which has the lower water potential, through the partially permeable visking tubing.
   4. This net inward movement of water increases the volume of liquid inside the bag, causing it to swell, and the process needs no energy input.
   5. Therefore the answer is B.
   • Why not A: This reverses which side has the higher water potential; pure water has a higher water potential than a concentrated solution, so this option gets the direction of water movement backwards.
   • Why not C: This wrongly explains the swelling as sugar leaving the bag rather than water entering it; the bag swells because it gains volume, which requires something moving in, not the solute moving out.
   • Why not D: This wrongly invokes active transport, claiming the tubing 'actively pumps' water using energy; osmosis is a passive process driven by the water potential gradient, needing no energy input.

7. Question 7Answer: D

   1. Cells grown from the patient's own tissue for a graft are produced by mitosis, the type of division used for growth and repair.
   2. Mitosis produces daughter cells that are genetically identical to the parent cell, with the same chromosome number.
   3. Because the grafted cells carry exactly the same genetic material as the rest of the patient's body, the immune system recognises them as 'self' rather than as foreign material to attack.
   4. Meiosis, by contrast, produces genetically different, haploid cells, which is not what is used to grow replacement tissue.
   5. Therefore the answer is D.
   • Why not A: This wrongly invokes meiosis, which produces genetically varied gametes, not identical body cells; skin cells for a graft are produced by mitosis, not meiosis.
   • Why not B: This wrongly invokes meiosis and its production of genetically different cells; a graft succeeds precisely because the new cells are identical to the patient's own, not because there are several different versions to choose from.
   • Why not C: This correctly names mitosis but wrongly claims mitosis halves the chromosome number; mitosis produces daughter cells with the same chromosome number as the parent cell, not half of it.

8. Question 8Answer: C

   1. Interphase is the stage of the cell cycle that comes before mitosis, or before the first division of meiosis.
   2. During interphase, the cell grows, and its DNA is replicated, so that there is enough genetic material for the division or divisions that follow.
   3. No cell division and no halving of chromosome number happens during interphase itself; both belong to the division stage that follows.
   4. Therefore the answer is C.
   • Why not A: This wrongly places a cell division within interphase itself; interphase comes before any division, whether that division is mitosis or the first division of meiosis.
   • Why not B: This wrongly treats interphase as an inactive 'resting' stage; the specification instead describes interphase as involving active cell growth and DNA replication.
   • Why not D: This wrongly places the halving of chromosome number in interphase; that reduction happens later, during the divisions of meiosis itself, not before them.

9. Question 9Answer: B

   1. The specification describes cancer as resulting from changes in cells, including mutations, that lead to uncontrolled cell division, forming a tumour.
   2. The student's claim keeps the correct link to mutations, but wrongly says the affected cell stops dividing and dies, which is the opposite of what actually happens.
   3. Correcting the claim means keeping the reference to mutations, but replacing 'stops dividing and dies' with 'divides in an uncontrolled way'.
   4. Therefore the answer is B.
   • Why not A: This wrongly denies any link between mutations and cancer, when the specification specifically describes cancer as resulting from changes in cells, including mutations.
   • Why not C: This wrongly substitutes an unrelated transport process, osmosis, for the real issue with the claim, which is about the direction of the mutation's effect on cell division, not about a different biological process altogether.
   • Why not D: This wrongly accepts the original claim, which has the actual effect of the mutation backwards: the specification describes uncontrolled cell division, not a stopping of division.

10. Question 10Answer: A

    1. Meiosis produces gametes with a single copy of each chromosome, half the number found in a normal body cell.
    2. Half of the body cell's 54 chromosomes is 27, so each gamete (egg cell or sperm cell) contains 27 chromosomes.
    3. At fertilisation, one gamete from each parent fuses, combining their chromosomes to restore the full, diploid number.
    4. Adding the 27 chromosomes from the egg cell to the 27 chromosomes from the sperm cell gives 54 chromosomes in the zygote, the same number as a normal sheep body cell.
    5. Therefore the answer is A.
    • Why not B: This wrongly keeps the full body-cell chromosome number in the gametes, as if meiosis did not halve it, and then doubles that already-unhalved number again at fertilisation.
    • Why not C: This correctly halves the chromosome number for each gamete, but then wrongly keeps the zygote at the same haploid number, forgetting that fertilisation fuses two gametes together, restoring the full number.
    • Why not D: This wrongly doubles the body-cell chromosome number for the gametes, the opposite of what meiosis actually does to chromosome number.

11. Question 11Answer: C

    1. Meiosis normally halves the chromosome number, so that fusing two haploid gametes at fertilisation restores the normal, diploid chromosome number.
    2. If gametes instead had the full, diploid chromosome number, as mitosis would produce, fusing two of them at fertilisation would add their chromosomes together, doubling the normal number.
    3. This doubled number would then be passed on and doubled again at the next fertilisation, and so on, each generation.
    4. Therefore the answer is C.
    • Why not A: This wrongly claims mitosis increases genetic variation; mitosis in fact produces genetically identical daughter cells, so gametes made this way would not be a source of variation.
    • Why not B: This wrongly assumes fertilisation always restores the normal chromosome number; that only happens because gametes are normally haploid, so fusing two of them gives the diploid number, not fusing two already-diploid cells.
    • Why not D: This wrongly claims fusion would be physically impossible; the problem described is a change in the resulting chromosome number, not an inability of the cells to fuse at all.

12. Question 12Answer: D

    1. Budding is a form of asexual reproduction: it involves only one parent, and no fusion of gametes takes place.
    2. With no mutation, the new individual produced by budding is genetically identical to its single parent.
    3. Sexual reproduction involves two parents, whose gametes fuse at fertilisation, combining genetic material from both.
    4. This combination of genetic material from two different parents is what makes offspring produced by sexual reproduction genetically different from each other and from both parents, regardless of the amount each parent contributes.
    5. Therefore the answer is D.
    • Why not A: This wrongly assumes that contributing equal amounts of genetic material means the offspring must be identical; sexual reproduction combines genetic material from two different parents in new combinations, which is exactly what produces genetic difference, regardless of the equal amounts contributed.
    • Why not B: This wrongly counts two parents for budding; only one hydra is involved in producing the bud, with no gametes contributed by a second individual.
    • Why not C: This wrongly gives budding two parents; budding, like other asexual reproduction, involves only one parent.

13. Question 13Answer: B

    1. In this grid, the mother contributes an X chromosome from every egg cell, so her contribution is the same across both columns.
    2. The father's two gamete types, X and Y, each appear in two of the four boxes, since each is paired against both of the mother's two egg columns.
    3. A box gives a male (XY) offspring whenever the father's Y chromosome is involved, and this happens in two of the four boxes.
    4. The other two boxes combine the father's X with the mother's X, giving a female (XX) offspring.
    5. Therefore the answer is B.
    • Why not A: This undercounts the combinations; every box that combines the father's Y-carrying sperm with the mother's X egg gives an XY offspring, and there is more than one such box in the grid.
    • Why not C: This overcounts the male combinations; not every box in the 2 by 2 grid can be male, since half of the father's sperm entries are X-carrying, which combine with the mother's X to give XX (female), not XY.
    • Why not D: This wrongly assumes every box in the grid gives a male offspring; the boxes combining the father's X-carrying sperm with the mother's X egg instead give a female (XX) offspring, which fills half the grid.

14. Question 14Answer: A

    1. The expected sex ratio at birth is approximately 1:1, male to female.
    2. This means approximately half of a large group of pupils would be expected to be female.
    3. Half of 600 is 300.
    4. Therefore the answer is A.
    • Why not B: This applies a 2:1 split rather than the correct 1:1 ratio, giving female pupils two-thirds of the total instead of half.
    • Why not C: This wrongly assumes all 600 pupils would be expected to be female, ignoring the roughly equal split between the sexes.
    • Why not D: This applies a 1:4 split, as if only a quarter were expected to be female, rather than the correct 1:2 (half) split.

15. Question 15Answer: C

    1. A human body cell contains 46 chromosomes, arranged as 23 pairs.
    2. One of these pairs, 2 chromosomes, is the pair of sex chromosomes, which determines sex.
    3. Removing this one pair from the total leaves 22 pairs, or 44 individual chromosomes, that are not involved in determining sex.
    4. Therefore the answer is C.
    • Why not A: This gives the number of non-sex-determining PAIRS (22) rather than the number of individual chromosomes, missing that each pair contains two chromosomes.
    • Why not B: This mistakenly treats the total number of pairs (23) as the answer, without first removing the one pair that does determine sex.
    • Why not D: This subtracts only one chromosome, rather than one whole pair of two chromosomes, from the total of 46.