ESAT Biology practice questions

A student compares a typical bacterial cell with a palisade cell from a leaf.

Which of the following statements is/are correct?

1. Both cells have a cell wall, a cell membrane and cytoplasm.

2. Both cells contain mitochondria, where aerobic respiration takes place.

3. In the leaf, a layer of palisade cells forms a tissue, and the leaf itself is an organ.

An electron micrograph of a rod-shaped bacterium includes a scale bar labelled 0.5 µm. On the printed micrograph, the scale bar is 10 mm long and the bacterium is 48 mm long.

What is the magnification of the micrograph, and what is the actual length of the bacterium?

Cylinders of potato tissue were cut to the same size, weighed and placed in sucrose solutions of different concentrations. After 24 hours they were blotted dry and reweighed. The table shows the mean percentage change in mass at each concentration.

Which of the following statements is/are correct?

1. The contents of the potato cells have the same water potential as a sucrose solution with a concentration between 0.4 and 0.6 mol dm⁻³.

2. In the 0.8 mol dm⁻³ solution, water moved out of the potato cells by osmosis, from a region of higher water potential to a region of lower water potential.

3. A cylinder with a starting mass of 4.00 g placed in the 0.6 mol dm⁻³ solution would be expected to finish with a mass of about 3.64 g.

A length of tubing is filled with a solution containing starch and glucose, tied at both ends and placed in a beaker of pure water. The tubing is permeable to water and glucose but not to starch.

Which of the following statements is/are correct?

1. After some time, glucose will be present in the water in the beaker.

2. Starch molecules will diffuse out of the tubing until the starch concentration is the same on both sides.

3. Once the glucose concentration is the same inside and outside the tubing, glucose molecules stop crossing the wall of the tubing.

Two small aquatic organisms, neither of which has a specialised gas exchange system, are modelled as simple shapes. Organism P is a cube with sides of 2 mm. Organism Q is a flat cuboid measuring 8 mm × 4 mm × 0.25 mm. Oxygen enters each organism by diffusion across its whole surface.

Which of the following statements is/are correct?

1. P and Q have the same volume, but the surface area to volume ratio of Q is more than twice that of P.

2. If every length of P were doubled, its surface area to volume ratio would halve.

3. The point inside Q that is furthest from Q's surface is one-eighth as far from the surface as the corresponding point inside P.

The body cells of a species of mammal each contain 44 chromosomes. A body cell that has just been formed by cell division contains a mass $m$ of DNA in its nucleus.

Which option gives, in this order: the number of chromosomes in each daughter cell when a body cell divides by mitosis; the number of chromosomes in each gamete; and the mass of DNA in the nucleus of each gamete?

In humans, assume that a baby is equally likely to be a boy or a girl at each birth, independently of any earlier births.

Which of the following statements is/are correct?

1. The sex of a baby is determined by the egg cell, because each egg cell carries either an X or a Y chromosome.

2. If a couple's first three children are all girls, the probability that their fourth child will be a boy is greater than $\frac{1}{2}$.

3. Before a couple has any children, the probability that their first three children will all be girls is $\frac{1}{8}$.

In pea plants, the allele for purple flowers (P) is dominant to the allele for white flowers (p). Two plants that are both heterozygous for this gene are crossed, and 240 of the resulting seeds are grown into plants.

How many of the 240 offspring would be expected to have white flowers, and what fraction of the purple-flowered offspring would be expected to be heterozygous?

An inherited condition is controlled by a single gene on an autosome. Rosa and Tom do not have the condition, but their son Sam does. Their daughter Lily does not have the condition.

Lily's partner, Omar, does not have the condition, but his mother does. Assume that no new mutations occur.

What is the probability that a child of Lily and Omar will have the condition?

A sample of double-stranded DNA is analysed, and 18% of its bases are found to be adenine (A).

Which of the following statements is/are correct?

1. 32% of the bases in the sample are guanine (G).

2. Each of the two strands in the sample must contain exactly 32% cytosine (C).

3. If the sample contains 5000 base pairs in total, it contains 900 adenine bases.

The table shows the amino acids coded for by some triplets of DNA bases. One strand of a short section of a gene has the sequence below, read in triplets starting from the first base on the left.

Original: ATGAAGGGCTTTCACTGG

Three mutated versions of this section were found.

Mutation P: ATGAAAGGCTTTCACTGG

Mutation Q: ATGTAGGGCTTTCACTGG

Mutation R: ATGAAGGCTTTCACTGG (one base has been lost)

Which of the following statements is/are correct?

1. Mutation P does not change the sequence of amino acids in the polypeptide.

2. Mutation Q changes the second amino acid but leaves the rest of the polypeptide unchanged.

3. In mutation R, the third amino acid is different from the original, but the fourth amino acid is the same as the original.

A scientist wants to insert a human gene into a bacterial plasmid. Restriction enzyme X cuts DNA wherever one particular short base sequence occurs.

The plasmid is a closed loop of DNA that contains this sequence at exactly one place. A linear piece of human DNA contains the sequence at exactly two places, one on each side of the gene.

Which of the following statements is/are correct?

1. Cutting the plasmid with enzyme X produces two separate pieces of DNA.

2. Cutting the human DNA with enzyme X produces three pieces, one of which carries the whole gene.

3. After the gene and the cut plasmid are mixed, the enzyme ligase is needed to join them into a single closed loop.

Which of the following statements about stem cells is/are correct?

1. Each cell of an embryo at the two-cell stage can develop into a complete organism, which is one way that identical twins can form.

2. Embryonic stem cells taken from an embryo a few days old can usually differentiate into any type of body cell.

3. Stem cells in adult bone marrow are pluripotent, so they can differentiate into any type of body cell.

The table shows the percentage of bacteria of one species, in samples collected from a hospital, that were resistant to antibiotic Z. Use of antibiotic Z in the hospital increased greatly from 2016 onwards.

Which of the following statements is/are correct?

1. The rise in resistance happened because exposure to antibiotic Z caused mutations for resistance in the bacteria.

2. The rise is consistent with natural selection: resistant bacteria survived exposure to antibiotic Z and passed on the gene for resistance when they reproduced.

3. The data show that the number of resistant bacteria in the hospital in 2022 was 20 times the number in 2016.

A student mixed amylase with starch solution at different temperatures and recorded the time taken for all the starch to be broken down, testing samples with iodine solution every 30 seconds. The results are shown in the table.

Which of the following statements is/are correct?

1. The optimum temperature of this amylase must be exactly 40 °C.

2. The rate of reaction at 50 °C is double the rate at 40 °C.

3. The rate of reaction at 30 °C is four times the rate at 10 °C.

Which of the following statements about human digestion is/are correct?

1. Amylase, produced by the salivary glands and the pancreas, breaks down starch into sugars.

2. Bile is an enzyme, made in the liver, that breaks down fats into fatty acids and glycerol.

3. Glucose and amino acids are absorbed into the blood through the villi of the small intestine.

Which of the following statements is/are correct?

1. During vigorous exercise, muscle cells can respire anaerobically, converting glucose into lactic acid and carbon dioxide.

2. When a person breathes in, the diaphragm contracts and flattens, increasing the volume of the thorax and lowering the pressure inside it.

3. Alveoli have very thin walls and a rich supply of blood capillaries, which give a short diffusion distance and help to keep the concentration gradients steep.

A person touches a hot pan and pulls their hand away without thinking about it. This is a reflex action.

Which option gives the order in which the impulse passes through the neurones, where the relay neurone is found, and how the signal crosses a synapse?

An ECG is recorded from a person at rest. The trace shows one tall peak (the R wave) for every heartbeat, and the time from the first R wave to the seventh R wave is 4.8 s. Each beat pumps 80 cm³ of blood out of the left ventricle.

What volume of blood does the left ventricle pump out per minute?

A person drinks a large volume of water in a short time.

Compared with before the drink, which option correctly describes the release of ADH by the pituitary gland, the amount of water reabsorbed into the blood from the kidney tubules, and the urine produced, over the following hour?

Two people, R and S, each had a drink containing 75 g of glucose after fasting overnight. Their blood glucose concentrations were then measured every 30 minutes.

Which of the following statements is/are correct?

1. In person R, the fall in blood glucose concentration between 30 and 90 minutes is brought about by insulin, which causes cells to take up glucose and the liver to convert glucose into glycogen.

2. In person R, the secretion of glucagon increases between 0 and 30 minutes.

3. Person S's results are consistent with type 1 diabetes, which can be treated with injections of insulin.

Hormone J is released by the pituitary gland. A sharp surge in the concentration of J, about halfway through the menstrual cycle, triggers the release of an egg from an ovary.

Hormone K is released by the ovary. Its concentration is low before ovulation, rises after ovulation and keeps the lining of the uterus thick; it falls at the end of the cycle if the woman is not pregnant.

Which option correctly identifies J and K and gives an example of a non-hormonal method of contraception?

A person was given an injection of a vaccine on day 0 and a second (booster) injection of the same vaccine on day 30. The table shows the concentration of antibodies against the pathogen in their blood.

Which of the following statements is/are correct?

1. The antibodies made after the first injection stayed in the blood at a high concentration, and this explains the large response after the second injection.

2. If the person had instead been given a vaccine against a different, unrelated pathogen on day 30, a similarly fast and large antibody response would be expected.

3. The peak antibody concentration after the second injection is 50 times the peak after the first injection.

A field is a rectangle measuring 40 m by 60 m. A pond covers 400 m² of the field, and no dandelions grow in the pond. A student placed ten square quadrats, each 0.5 m × 0.5 m, at random positions on the grassed part of the field and counted the dandelion plants in each.

The numbers of dandelions in the ten quadrats were 3, 0, 5, 2, 4, 1, 0, 6, 2 and 7.

What is the best estimate of the number of dandelion plants in the field?

Which of the following statements is/are correct?

1. When fertiliser runs off farmland into a lake, fish die mainly because the nitrates in the fertiliser are directly poisonous to them.

2. Decomposers return carbon to the atmosphere as carbon dioxide when they respire.

3. A tapeworm living in a human gut is an example of mutualism, because both organisms obtain food.

The rate of photosynthesis of a pondweed was measured at different light intensities and at two carbon dioxide concentrations. The temperature was kept constant. The table shows the rates in arbitrary units.

Which of the following statements is/are correct?

1. At light intensity 2, light intensity is the factor limiting the rate at both carbon dioxide concentrations.

2. At light intensity 4, increasing the light intensity would increase the rate at 0.01% carbon dioxide.

3. At light intensity 6, increasing the light intensity would increase the rate at 0.04% carbon dioxide.

A leafy shoot is set up in a potometer. The capillary tube has an internal radius of 0.5 mm, and in 5 minutes the air bubble moves 40 mm along it.

Which option gives the rate of water uptake by the shoot, and a change in conditions that would make the bubble move faster?