I85PREP
⌘ K
GCE O/L Science study materials
GCE O/L Science study resources

GCE O/L Science practice questions

One question at a time. Build your GCE O/L Science understanding.

First 50 of 200 questions. Each one lists the choices, the correct answer, and an explanation. The checker at the top of this page saves progress in this browser when it is available.

Continue in the practice tool above to load more questions, 50 at a time.

Question 1Biology: cells, transport and biological molecules

Which structure controls the movement of substances into and out of a typical plant cell?

  1. The chloroplast envelope
  2. The large permanent vacuole
  3. The cellulose cell wall
  4. The cell surface membrane Correct answer.

Explanation

The cell surface membrane is a partially permeable phospholipid bilayer that determines which substances enter or leave the cell. The cell wall is fully permeable and provides support rather than selective control, and the vacuole and chloroplast membranes only regulate their own compartments.

Question 2Biology: cells, transport and biological molecules

A student views onion epidermal cells using a light microscope with a x10 eyepiece and a x40 objective lens. What is the total magnification?

  1. x50
  2. x4000
  3. x400 Correct answer.
  4. x30

Explanation

Total magnification is calculated by multiplying the eyepiece magnification by the objective magnification, so 10 x 40 gives x400. Adding the values would be incorrect because magnification is multiplicative, not additive.

Question 3Biology: cells, transport and biological molecules

Which row correctly describes the test and positive result for reducing sugars?

  1. Benedict's solution, heated in a water bath; brick-red precipitate Correct answer.
  2. Biuret reagent at room temperature; purple colour
  3. Ethanol emulsion test; cloudy white emulsion
  4. Iodine solution at room temperature; blue-black colour

Explanation

Reducing sugars such as glucose reduce blue copper(II) sulfate in Benedict's solution to a brick-red precipitate of copper(I) oxide, and heating is needed for the reaction to occur at a useful rate. Iodine tests for starch, Biuret for protein and the emulsion test for lipid, so those pairings are mismatched here.

Question 4Biology: cells, transport and biological molecules

Which feature is present in a bacterial cell but absent from a human liver cell?

  1. A murein cell wall Correct answer.
  2. A cell surface membrane
  3. Cytoplasm
  4. Ribosomes

Explanation

Bacteria possess a cell wall made of murein (peptidoglycan), a structure that animal cells never have. Ribosomes, a surface membrane and cytoplasm are found in both bacterial and human cells, so they cannot distinguish the two.

Question 5Biology: cells, transport and biological molecules

Which statement best explains why oxygen moves from an alveolus into a blood capillary?

  1. Oxygen diffuses down a concentration gradient from the alveolus to the blood Correct answer.
  2. Oxygen is actively transported against its concentration gradient
  3. Oxygen moves by diffusion from the blood into the alveolus
  4. Oxygen is carried by osmosis across the alveolar wall

Explanation

The oxygen concentration in alveolar air is higher than in the deoxygenated blood arriving at the lungs, so oxygen diffuses passively down this gradient across the thin alveolar and capillary walls. Diffusion requires no energy input and moves particles from high to low concentration.

Question 6Biology: cells, transport and biological molecules

A plant cell is placed in a solution with a lower water potential than its own cell contents. Which change is expected?

  1. The cell wall dissolves and the cell bursts
  2. Water enters and leaves at equal rates, so nothing changes
  3. The cell becomes turgid as water enters the vacuole
  4. The cell loses water and the protoplast shrinks away from the wall Correct answer.

Explanation

Water moves by osmosis from higher to lower water potential, so a cell in a more concentrated external solution loses water. In plants this causes plasmolysis, where the shrinking protoplast pulls away from the cell wall.

Question 7Biology: cells, transport and biological molecules

Which combination of molecules correctly matches the elements they contain?

  1. Lipid: carbon, hydrogen, oxygen, nitrogen, sulfur
  2. Carbohydrate: carbon, hydrogen, oxygen, nitrogen
  3. Protein: carbon, hydrogen, oxygen, nitrogen Correct answer.
  4. Protein: carbon, hydrogen, oxygen only

Explanation

Proteins are polymers of amino acids, which always contain carbon, hydrogen, oxygen and nitrogen, and often sulfur. Carbohydrates and most lipids contain only carbon, hydrogen and oxygen, so options listing nitrogen in these molecules are incorrect.

Question 8Biology: cells, transport and biological molecules

Which property of water makes it an effective coolant in living organisms?

  1. It is a good solvent for salts
  2. It has a low density when frozen
  3. It has a high specific heat capacity Correct answer.
  4. It is transparent to visible light

Explanation

A high specific heat capacity means water absorbs a large amount of heat energy for only a small rise in temperature, so it stabilises body temperature and buffers against overheating. The other properties listed are real but do not explain cooling.

Question 9Biology: cells, transport and biological molecules

A red blood cell placed in pure water will burst. Which explanation is correct?

  1. Water enters by active transport until the membrane ruptures
  2. Water enters by osmosis because the cell contents have a lower water potential than pure water Correct answer.
  3. Solutes leave the cell by diffusion, causing it to swell
  4. The cell wall cannot withstand the pressure and splits

Explanation

Pure water has the highest possible water potential, so water moves by osmosis into the cell, whose cytoplasm has a lower water potential. Animal cells lack a rigid wall, so the membrane cannot resist the increasing pressure and bursts.

Question 10Biology: cells, transport and biological molecules

Which statement about enzymes is correct?

  1. Enzymes work equally well at all temperatures and pH values
  2. Enzymes increase the activation energy of a reaction
  3. Enzymes lower the activation energy needed for a reaction Correct answer.
  4. Enzymes are consumed during the reactions they catalyse

Explanation

Enzymes are biological catalysts that provide an alternative reaction pathway with a lower activation energy, speeding up the reaction. They are not used up and are sensitive to temperature and pH because these affect the shape of the active site.

Question 11Biology: cells, transport and biological molecules

Which observation would best support the conclusion that a sample of food contains a protein but no starch?

  1. Biuret gives purple and iodine gives blue-black
  2. Biuret gives purple and iodine remains yellow-brown Correct answer.
  3. Benedict's gives brick-red and iodine gives blue-black
  4. Ethanol gives a cloudy emulsion and Biuret gives purple

Explanation

A purple Biuret result confirms protein, and iodine staying yellow-brown shows starch is absent. Both tests must be interpreted together to support the combined conclusion.

Question 12Biology: cells, transport and biological molecules

Which adaptation of a root hair cell increases the rate of absorption of mineral ions from the soil?

  1. A long, thin extension that increases the surface area of the membrane Correct answer.
  2. A thick, rigid cell wall that resists water entry
  3. A small vacuole that reduces the cell's water content
  4. A large number of chloroplasts in the hair

Explanation

The elongated hair greatly increases the surface area over which ions can be absorbed, and mineral ions are taken up by active transport using energy from respiration. A large surface area relative to volume speeds absorption.

Question 13Biology: cells, transport and biological molecules

A plant is watered with a solution containing a respiratory poison that stops ATP production. Which process in the root is most directly affected?

  1. Diffusion of oxygen into the root hair
  2. Uptake of water by osmosis
  3. Movement of water through the cell wall
  4. Uptake of nitrate ions by active transport Correct answer.

Explanation

Active transport requires ATP produced by respiration, so poisoning respiration directly blocks the uptake of mineral ions such as nitrate. Osmosis and diffusion are passive processes that continue without a supply of ATP.

Question 14Biology: cells, transport and biological molecules

In an experiment, potato cylinders were placed in sucrose solutions of different concentrations. Which result would indicate that the potato tissue has the same water potential as the solution?

  1. The mass of the cylinder stays the same Correct answer.
  2. The mass of the cylinder decreases noticeably
  3. The mass of the cylinder increases noticeably
  4. The cylinder becomes soft and flaccid

Explanation

When the external solution has the same water potential as the cell contents, there is no net movement of water by osmosis, so the mass does not change. This point is used to estimate the water potential of the tissue.

Question 15Biology: cells, transport and biological molecules

Which statement best explains why a plant wilts on a hot, dry day?

  1. Photosynthesis stops completely, so the leaves collapse
  2. Water loss by transpiration exceeds water uptake, so cells lose turgor Correct answer.
  3. The roots actively pump water out of the plant
  4. The cell walls dissolve, removing support from the stem

Explanation

On a hot, dry day transpiration removes water from leaves faster than roots can absorb it, so cells lose water and turgor pressure falls. Without turgid cells the non-woody parts of the plant can no longer stay upright.

Question 16Biology: cells, transport and biological molecules

Which statement describes the structure of a phospholipid molecule?

  1. A chain of amino acids linked by peptide bonds
  2. A glycerol backbone joined to two fatty acids and a phosphate group Correct answer.
  3. A glycerol backbone joined to three fatty acids
  4. A polymer of glucose units joined by glycosidic bonds

Explanation

A phospholipid consists of glycerol bonded to two fatty acid chains and one phosphate group, giving a hydrophilic head and hydrophobic tails. This arrangement allows phospholipids to form the bilayer of cell membranes.

Question 17Biology: nutrition, respiration and gas exchange

Which food test gives a brick-red precipitate when a solution of reducing sugar is heated with it?

  1. Biuret test
  2. Benedict's test Correct answer.
  3. Emulsion test
  4. Iodine test

Explanation

Benedict's solution contains blue copper(II) ions that are reduced to red copper(I) oxide by a reducing sugar such as glucose during heating, giving a brick-red precipitate. The colour change from blue through green and yellow to brick-red indicates increasing sugar concentration.

Question 18Biology: nutrition, respiration and gas exchange

A student chews a piece of bread for several minutes and notices it begins to taste sweet. Which enzyme and product explain this change?

  1. Amylase converting starch into maltose Correct answer.
  2. Catalase converting hydrogen peroxide into water
  3. Lipase converting fat into glycerol
  4. Protease converting protein into amino acids

Explanation

Saliva contains amylase, which hydrolyses starch in bread into maltose, a sugar that tastes sweet. Chewing mixes the food with saliva and increases the surface area for enzyme action, so sweetness develops over time.

Question 19Biology: nutrition, respiration and gas exchange

Which structure in the human breathing system is the site where oxygen passes into the blood?

  1. Larynx
  2. Alveolus Correct answer.
  3. Bronchus
  4. Trachea

Explanation

Alveoli are tiny air sacs with thin, moist walls surrounded by a dense network of capillaries, so gases diffuse across a short distance. Oxygen diffuses from alveolar air into the blood while carbon dioxide diffuses out.

Question 20Biology: nutrition, respiration and gas exchange

Which statement correctly describes aerobic respiration in cells?

  1. Glucose is converted into lactic acid with the release of oxygen
  2. Glucose is broken down using oxygen to release carbon dioxide, water and energy Correct answer.
  3. Glucose is converted into alcohol and carbon dioxide without using oxygen
  4. Glucose is stored as glycogen without any chemical change

Explanation

Aerobic respiration is the controlled release of energy from glucose using oxygen, producing carbon dioxide and water as waste products. Most of the energy is transferred to ATP for cell activities, with some released as heat.

Question 21Biology: nutrition, respiration and gas exchange

During vigorous exercise a runner's breathing rate and depth both increase. Which change in the blood most directly stimulates this response?

  1. A rise in oxygen concentration
  2. A rise in carbon dioxide concentration Correct answer.
  3. A fall in glucose concentration
  4. A fall in water content

Explanation

Increased muscular respiration raises the carbon dioxide concentration in the blood, which is detected by chemoreceptors and stimulates the breathing centre to increase rate and depth. This removes the extra carbon dioxide and supplies more oxygen.

Question 22Biology: nutrition, respiration and gas exchange

A leaf is tested with iodine solution after being boiled in ethanol and rinsed in warm water. A blue-black colour appears only in the areas that were exposed to light. Which conclusion is best supported?

  1. Starch is made only in parts of the leaf that receive light Correct answer.
  2. Starch is made only in parts of the leaf kept in darkness
  3. Starch is removed from the leaf by boiling in ethanol
  4. Starch is produced equally in all parts of the leaf

Explanation

Iodine turns blue-black where starch is present, so colour appearing only in illuminated regions shows that starch formation depends on light. Boiling in ethanol removes chlorophyll to decolourise the leaf so the iodine colour can be seen clearly.

Question 23Biology: nutrition, respiration and gas exchange

Which combination of features increases the rate of absorption of digested food in the small intestine?

  1. A short tube with smooth walls and few blood vessels
  2. A wide tube lined with thick muscle and mucus
  3. A long tube with a folded lining and many villi Correct answer.
  4. A coiled tube with a hard lining and little surface area

Explanation

The small intestine is long and its lining is folded into villi, greatly increasing the surface area for absorption. Each villus contains a rich blood supply and a lacteal to carry absorbed nutrients away quickly, maintaining a steep diffusion gradient.

Question 24Biology: nutrition, respiration and gas exchange

Which equation summarises anaerobic respiration in a human muscle cell?

  1. Glucose → lactic acid + energy Correct answer.
  2. Glucose + oxygen → carbon dioxide + water + energy
  3. Glucose + carbon dioxide → oxygen + water + energy
  4. Glucose → alcohol + carbon dioxide + energy

Explanation

In human muscle cells deprived of sufficient oxygen, glucose is broken down to lactic acid with the release of a small amount of energy. The lactic acid later accumulates and causes muscle fatigue until it is removed.

Question 25Biology: nutrition, respiration and gas exchange

A potted plant is kept in darkness for two days while a control plant is kept in light. Both are then tested for starch. What is the expected result and reason?

  1. The darkened plant shows starch in all leaves because carbon dioxide was available
  2. Both plants show equal starch because temperature was the same
  3. The darkened plant shows more starch because respiration stops in darkness
  4. The darkened plant shows no starch because light is needed for photosynthesis Correct answer.

Explanation

In darkness, photosynthesis cannot occur because light energy is required to split water and drive the light-dependent reactions. The plant continues to respire and uses up stored starch, so iodine gives no blue-black colour.

Question 26Biology: nutrition, respiration and gas exchange

A person's diet is very low in iron. Which symptom is most likely to develop and why?

  1. Constipation, because fibre cannot be digested
  2. Scurvy, because collagen cannot be formed
  3. Rickets, because calcium cannot be absorbed
  4. Anaemia, because less haemoglobin is made to carry oxygen Correct answer.

Explanation

Iron is needed to form haemoglobin in red blood cells, which transports oxygen around the body. A prolonged shortage reduces haemoglobin production, causing anaemia with tiredness and breathlessness.

Question 27Biology: nutrition, respiration and gas exchange

Bile is produced by the liver and stored in the gall bladder. Which function does bile perform in digestion?

  1. It digests proteins into amino acids in the stomach
  2. It emulsifies fats into small droplets and neutralises acidic chyme Correct answer.
  3. It breaks down starch into maltose in the mouth
  4. It absorbs glucose directly into the blood

Explanation

Bile salts emulsify fats, breaking large droplets into smaller ones so lipase has a greater surface area to act on. Bile is also alkaline, so it neutralises the acidic chyme entering the duodenum and provides a suitable pH for pancreatic enzymes.

Question 28Biology: nutrition, respiration and gas exchange

Which feature of a fish gill makes it efficient for absorbing oxygen from water?

  1. A thick gill plate that stores oxygen for later use
  2. A flow of water and blood in the same direction at equal speed
  3. A counter-current flow of water and blood across thin lamellae Correct answer.
  4. A single large gill arch with a smooth surface

Explanation

Water flows over the gill lamellae in the opposite direction to the blood, maintaining a concentration gradient along the whole length so oxygen continues to diffuse into the blood. The lamellae are thin and richly supplied with blood, giving a large surface area.

Question 29Biology: nutrition, respiration and gas exchange

Which statement best explains why the walls of the alveoli are kept moist?

  1. Moisture stops carbon dioxide leaving the blood
  2. Gases must dissolve in moisture before they can diffuse across the alveolar wall Correct answer.
  3. Moisture prevents oxygen from diffusing into the blood
  4. Moisture increases the thickness of the alveolar wall

Explanation

Oxygen and carbon dioxide must dissolve in the thin film of moisture lining the alveoli before they can diffuse across the wall. This dissolved state allows rapid exchange, and the moisture also protects the delicate alveolar surfaces.

Question 30Biology: nutrition, respiration and gas exchange

A patient's small intestine has a reduced number of villi. Which effect on the body is most likely?

  1. Faster digestion of proteins in the stomach
  2. Less absorption of digested nutrients, leading to weight loss Correct answer.
  3. Greater production of bile by the liver
  4. Increased absorption of water, leading to constipation

Explanation

Villi provide the large surface area needed for absorbing digested nutrients such as glucose and amino acids. Fewer villi mean a smaller absorptive surface, so less nutrient uptake occurs and the person may lose weight.

Question 31Biology: nutrition, respiration and gas exchange

A plant is supplied with water containing a radioactive isotope of oxygen. After several hours, radioactivity is detected in the oxygen gas released by the plant. Which conclusion is supported?

  1. The oxygen released in photosynthesis comes from water Correct answer.
  2. The oxygen released comes from carbon dioxide
  3. The oxygen released comes from glucose
  4. The oxygen released comes from soil minerals

Explanation

The oxygen released during photosynthesis is produced when water is split in the light-dependent reactions. Labelled oxygen appearing in the released gas therefore shows that water, not carbon dioxide, is the source of that oxygen.

Question 32Biology: nutrition, respiration and gas exchange

In an experiment, a leaf is partly covered with opaque foil and the plant is destarched beforehand. After exposure to light, the leaf is decolourised and tested with iodine. Which result and explanation are correct?

  1. Only the uncovered area turns blue-black because light is needed for starch formation Correct answer.
  2. Neither area turns blue-black because the leaf was destarched
  3. Both areas turn blue-black because carbon dioxide reaches the whole leaf
  4. Only the covered area turns blue-black because darkness speeds up photosynthesis

Explanation

Destarching removes existing starch so any starch detected must have formed during the experiment. Only the illuminated region can carry out photosynthesis and make starch, so only that area gives the blue-black iodine colour.

Question 33Biology: transport systems, excretion and homeostasis

Which blood vessel carries oxygenated blood away from the heart to the body tissues?

  1. Pulmonary artery
  2. Vena cava
  3. Pulmonary vein
  4. Aorta Correct answer.

Explanation

The aorta is the large artery that leaves the left ventricle carrying oxygen-rich blood to the systemic circulation. Arteries carry blood away from the heart, and the aorta is the main systemic artery.

Question 34Biology: transport systems, excretion and homeostasis

Which component of blood is mainly responsible for transporting oxygen from the lungs to respiring tissues?

  1. Red blood cells Correct answer.
  2. White blood cells
  3. Platelets
  4. Plasma proteins

Explanation

Red blood cells contain haemoglobin, which binds oxygen in the lungs and releases it in respiring tissues. This reversible binding is the main oxygen transport mechanism in blood.

Question 35Biology: transport systems, excretion and homeostasis

A student's urine contains glucose after a meal rich in carbohydrate. Which statement best explains this observation in a healthy person?

  1. The glucose concentration in the filtrate exceeds the reabsorption capacity of the kidney tubules. Correct answer.
  2. The ureter absorbs glucose before urine is stored.
  3. The kidney tubules actively secrete glucose into the urine.
  4. The glomerulus has stopped filtering water and salts.

Explanation

Glucose is normally reabsorbed completely by the proximal tubule, but reabsorption uses a limited number of carrier proteins. If filtered glucose exceeds this capacity, the excess passes into the urine.

Question 36Biology: transport systems, excretion and homeostasis

Sweating helps to cool the body because:

  1. sweat insulates the skin and traps warmth
  2. sweat carries excess oxygen away from the skin
  3. sweat glands produce heat that replaces body heat
  4. evaporation of sweat removes latent heat from the skin Correct answer.

Explanation

As sweat evaporates from the skin surface it absorbs latent heat from the body, lowering body temperature. This is an example of evaporative cooling used in thermoregulation.

Question 37Biology: transport systems, excretion and homeostasis

Which feature of the alveoli increases the rate of gas exchange in the lungs?

  1. A large surface area with a thin wall Correct answer.
  2. A thick, moist wall
  3. A small blood supply
  4. A rich supply of cartilage rings

Explanation

Alveoli are numerous and give the lungs a very large surface area, and their walls are only one cell thick so gases diffuse over a short distance. Both features increase the rate of diffusion of oxygen and carbon dioxide.

Question 38Biology: transport systems, excretion and homeostasis

Which sequence correctly describes the pathway of blood through the heart and lungs?

  1. Right atrium → left atrium → lungs → right ventricle → left ventricle
  2. Left atrium → left ventricle → lungs → right atrium → right ventricle
  3. Right atrium → right ventricle → lungs → left atrium → left ventricle Correct answer.
  4. Right ventricle → right atrium → lungs → left ventricle → left atrium

Explanation

Deoxygenated blood enters the right atrium, passes to the right ventricle, and is pumped to the lungs via the pulmonary artery. Oxygenated blood then returns to the left atrium and enters the left ventricle before being pumped to the body.

Question 39Biology: transport systems, excretion and homeostasis

During exercise, heart rate and breathing rate both increase. Which combination best explains why?

  1. Body temperature falls, so breathing must increase.
  2. The blood becomes more dilute, so the heart pumps faster.
  3. More carbon dioxide is produced, and muscles need more oxygen for respiration. Correct answer.
  4. Less oxygen is needed, and carbon dioxide levels fall.

Explanation

Muscles respire faster during exercise, using more oxygen and producing more carbon dioxide. Rising carbon dioxide and falling oxygen are detected and stimulate faster breathing and a faster heart rate to deliver oxygen and remove carbon dioxide.

Question 40Biology: transport systems, excretion and homeostasis

Which structure in the kidney is the site where blood is filtered under pressure to form filtrate?

  1. Ureter
  2. Collecting duct
  3. Glomerulus Correct answer.
  4. Loop of Henle

Explanation

The glomerulus is a knot of capillaries inside the Bowman's capsule where high blood pressure forces water, salts, glucose and urea into the capsule to form filtrate. Larger molecules and blood cells are retained in the blood.

Question 41Biology: transport systems, excretion and homeostasis

A person drinks a large volume of water. Which change is expected in the urine produced?

  1. A larger volume of more concentrated urine
  2. A smaller volume of more dilute urine
  3. A smaller volume of more concentrated urine
  4. A larger volume of more dilute urine Correct answer.

Explanation

Drinking a lot of water raises the water content of the blood, so less ADH is released from the pituitary gland. The collecting ducts reabsorb less water, producing a larger volume of dilute urine.

Question 42Biology: transport systems, excretion and homeostasis

Why is the wall of the left ventricle thicker than the wall of the right ventricle?

  1. It must pump blood at high pressure to the whole body. Correct answer.
  2. It stores more blood before each contraction.
  3. It contains more valves to prevent backflow.
  4. It pumps blood only a short distance to the lungs.

Explanation

The left ventricle pumps oxygenated blood into the aorta and around the systemic circulation, which requires a high pressure. Its thick muscular wall generates this pressure, whereas the right ventricle pumps blood only to the nearby lungs.

Question 43Biology: transport systems, excretion and homeostasis

Which statement correctly describes the role of the liver in excretion?

  1. It converts excess amino acids into urea, which the kidneys then excrete. Correct answer.
  2. It breaks down urea into glucose for storage.
  3. It removes urea from the blood and excretes it in bile.
  4. It filters urea directly from the blood into the bladder.

Explanation

The liver deaminates excess amino acids, forming ammonia which is converted into less toxic urea. The urea is released into the blood and removed by the kidneys, so the liver prepares the waste but does not excrete it.

Question 44Biology: transport systems, excretion and homeostasis

A patient with damaged kidneys has urine containing a large amount of protein. Which part of the kidney is most likely damaged?

  1. The collecting duct
  2. The bladder wall
  3. The renal artery
  4. The glomerular capillaries Correct answer.

Explanation

Protein molecules are too large to pass through healthy glomerular capillary walls, so they normally remain in the blood. If the glomeruli are damaged, proteins leak into the filtrate and appear in the urine.

Question 45Biology: transport systems, excretion and homeostasis

Which statement best explains why the body needs a transport system in multicellular organisms?

  1. Their cells are too small to absorb substances directly.
  2. Their surface area to volume ratio is too small for diffusion alone to supply all cells. Correct answer.
  3. Diffusion is too fast and would damage the cells.
  4. Their cells do not carry out respiration.

Explanation

As an organism increases in size, its surface area to volume ratio decreases, so diffusion over the body surface cannot supply the inner cells fast enough. A transport system moves substances quickly between the exchange surfaces and all cells.

Question 46Biology: transport systems, excretion and homeostasis

Which of the following is a correct description of the role of ADH in the body?

  1. It increases the volume of water reabsorbed by the collecting ducts. Correct answer.
  2. It increases the amount of glucose reabsorbed by the tubules.
  3. It causes more water to be lost in the urine.
  4. It speeds up the filtration of blood in the glomerulus.

Explanation

Antidiuretic hormone, released from the pituitary gland, makes the walls of the collecting ducts more permeable to water. More water is reabsorbed into the blood, so a smaller volume of more concentrated urine is produced.

Question 47Biology: transport systems, excretion and homeostasis

Which statement correctly compares arteries and veins?

  1. Arteries carry blood away from the heart, while veins carry blood towards the heart. Correct answer.
  2. Veins carry oxygenated blood, while arteries always carry deoxygenated blood.
  3. Arteries have valves, while veins do not.
  4. Veins have thick muscular walls, while arteries have thin walls.

Explanation

By definition, arteries carry blood away from the heart and veins carry blood back towards it. Wall thickness and oxygen content vary, so only the direction of flow is a reliable general difference.

Question 48Biology: transport systems, excretion and homeostasis

A person working in a hot environment produces a large volume of sweat but drinks no water. Which changes are most likely to occur?

  1. Urine volume increases and urine becomes more dilute.
  2. ADH release decreases and urine volume increases.
  3. Blood water content rises and ADH release falls.
  4. ADH release increases and urine becomes more concentrated. Correct answer.

Explanation

Sweating without replacement of water lowers the water content of the blood, which is detected as an increase in the concentration of body fluids. More ADH is released, increasing water reabsorption in the collecting ducts and producing a small volume of concentrated urine.

Question 49Biology: reproduction, inheritance and variation

In flowering plants, which structure produces the male gamete that fuses with the egg cell during fertilisation?

  1. Tube nucleus of the pollen grain
  2. Nucleus of the synergid cell
  3. Pollen tube nucleus
  4. Generative nucleus of the pollen grain Correct answer.

Explanation

When a pollen grain lands on the stigma it germinates and forms a pollen tube. The generative nucleus divides by mitosis to form two male gametes, one of which fuses with the egg cell. The tube nucleus only controls growth of the pollen tube and does not take part in fertilisation.

Question 50Biology: reproduction, inheritance and variation

A human cell contains 46 chromosomes. How many chromosomes are present in a single sperm cell produced by meiosis?

  1. 92
  2. 23 Correct answer.
  3. 12
  4. 46

Explanation

Meiosis halves the chromosome number so that gametes are haploid. A human body cell is diploid with 46 chromosomes, so each sperm receives one chromosome from each of the 23 pairs. Fusion at fertilisation restores the diploid number of 46 in the zygote.