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MATSEC SEC Biology study materials
MATSEC SEC Biology study resources

MATSEC SEC Biology practice questions

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Question 1Biology (SEC)

Which organelle is the main site of aerobic respiration and ATP production in a eukaryotic cell?

  1. Lysosome
  2. Ribosome
  3. Golgi apparatus
  4. Mitochondrion Correct answer.

Explanation

The mitochondrion contains the enzymes and membranes needed for the Krebs cycle and oxidative phosphorylation, which generate most of the cell's ATP. Ribosomes build proteins, the Golgi modifies and packages them, and lysosomes digest material.

Question 2Biology (SEC)

A plant cell is placed in a solution with a higher water potential than its cell sap. What happens to the cell?

  1. It shows no change because the wall blocks water
  2. It loses water and becomes plasmolysed
  3. It shrinks because solutes leave the cell
  4. It takes up water and becomes turgid Correct answer.

Explanation

Water moves by osmosis from the region of higher water potential (the external solution) into the cell, which has a lower water potential. The rigid cellulose wall limits swelling, so the cell becomes turgid rather than bursting.

Question 3Biology (SEC)

Which molecule carries the genetic code from the nucleus to a ribosome during protein synthesis?

  1. Messenger RNA Correct answer.
  2. Transfer RNA
  3. Deoxyribose sugar
  4. Ribosomal RNA

Explanation

Messenger RNA is transcribed from DNA in the nucleus and carries the base sequence to the ribosome, where it is translated. Transfer RNA delivers amino acids and ribosomal RNA forms part of the ribosome itself.

Question 4Biology (SEC)

An enzyme-catalysed reaction slows sharply when the temperature is raised well above the optimum. Which explanation is correct?

  1. The pH of the mixture always falls at high temperature
  2. The active site changes shape as the enzyme is denatured Correct answer.
  3. The substrate molecules stop moving completely
  4. The enzyme is used up in the reaction

Explanation

Above the optimum temperature, hydrogen bonds and other interactions holding the enzyme's tertiary structure break, so the active site loses its complementary shape. Substrate can no longer bind and the rate falls.

Question 5Biology (SEC)

In a cross between two heterozygous tall pea plants (Tt x Tt), what proportion of the offspring is expected to be short?

  1. One quarter Correct answer.
  2. One half
  3. Three quarters
  4. None

Explanation

A Tt x Tt cross gives genotypes TT, Tt, Tt and tt in equal proportions, so one quarter of offspring are tt. Since tall (T) is dominant, only the tt genotype shows the short phenotype.

Question 6Biology (SEC)

Which feature distinguishes a prokaryotic cell from a eukaryotic cell?

  1. Presence of ribosomes
  2. Absence of a membrane-bound nucleus Correct answer.
  3. Presence of a cell surface membrane
  4. Presence of cytoplasm

Explanation

Prokaryotes keep their circular DNA free in the cytoplasm and lack a nuclear envelope, whereas eukaryotes have a true nucleus. Both cell types share a membrane, ribosomes and cytoplasm.

Question 7Biology (SEC)

Which blood vessel carries oxygenated blood from the lungs to the heart?

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

Explanation

The pulmonary vein returns oxygenated blood from the lungs to the left atrium. This is the exception to the general rule that veins carry deoxygenated blood.

Question 8Biology (SEC)

A student counts 240 stomata on the lower epidermis of a leaf and 60 on the upper epidermis. What is the ratio of lower to upper stomata?

  1. 3:1
  2. 2:1
  3. 4:1 Correct answer.
  4. 1:4

Explanation

The ratio compares lower to upper counts, so 240:60 simplifies by dividing both by 60 to give 4:1. Stating it the other way round (1:4) would reverse the comparison.

Question 9Biology (SEC)

Which process in the carbon cycle releases carbon dioxide into the atmosphere?

  1. Transpiration
  2. Nitrogen fixation
  3. Respiration Correct answer.
  4. Photosynthesis

Explanation

Respiration oxidises organic molecules such as glucose and releases carbon dioxide as a waste product. Photosynthesis removes carbon dioxide, while nitrogen fixation and transpiration do not involve carbon dioxide release.

Question 10Biology (SEC)

A food chain is grass, then grasshopper, then frog, then snake. Approximately how much energy passes from the grasshopper level to the frog level?

  1. About 90 percent
  2. About 100 percent
  3. About 50 percent
  4. About 10 percent Correct answer.

Explanation

Only a small fraction, commonly estimated at around ten percent, of the energy in one trophic level is transferred to the next. The rest is lost mainly as heat from respiration, plus material not eaten or not digested.

Question 11Biology (SEC)

Which part of the human eye contains the light-sensitive cells that detect colour?

  1. Sclera
  2. Cornea
  3. Retina Correct answer.
  4. Iris

Explanation

The retina lines the back of the eye and contains rods and cones; cones detect colour in bright light. The cornea refracts light, the iris controls pupil size, and the sclera is the tough outer coat.

Question 12Biology (SEC)

Which hormone lowers blood glucose concentration when it rises after a meal?

  1. Thyroxine
  2. Glucagon
  3. Adrenaline
  4. Insulin Correct answer.

Explanation

Insulin is secreted by the beta cells of the pancreas and stimulates cells to take up glucose and the liver to store it as glycogen. This negative feedback lowers blood glucose back towards normal.

Question 13Biology (SEC)

A section of one strand of DNA has the base sequence A T G C C A. What is the sequence of the complementary strand?

  1. U A C G G U
  2. T A C G G T Correct answer.
  3. T A C C G T
  4. A T G C C A

Explanation

Base pairing rules state that adenine pairs with thymine and guanine with cytosine. Reading the original strand, A pairs with T, T with A, G with C, C with G, C with G and A with T, giving T A C G G T.

Question 14Biology (SEC)

Which structure in a flower produces the male gametes?

  1. Stigma
  2. Anther Correct answer.
  3. Ovary
  4. Sepal

Explanation

The anther is part of the stamen and contains pollen grains, inside which the male gametes form. The ovary and stigma are female parts, and sepals protect the developing bud.

Question 15Biology (SEC)

Which adaptation of a fish gill increases the efficiency of oxygen uptake from water?

  1. A small surface area with little blood flow
  2. Many thin filaments with a rich blood supply Correct answer.
  3. A thick, waterproof surface
  4. A dry surface exposed to air

Explanation

Gill filaments and lamellae give a very large surface area, and the dense capillary network maintains a steep diffusion gradient. The counter-current flow of water and blood further maximises oxygen uptake.

Question 16Biology (SEC)

A mutation changes a single base in a gene but the amino acid sequence of the protein is unchanged. What is this called?

  1. A nonsense mutation
  2. A silent mutation Correct answer.
  3. A chromosomal deletion
  4. A frameshift mutation

Explanation

The genetic code is degenerate, so several codons can specify the same amino acid. A base substitution that produces a codon for the same amino acid therefore has no effect on the protein and is described as silent.

Question 17Biology (SEC)

Which statement correctly describes the role of decomposers in an ecosystem?

  1. They convert atmospheric nitrogen into nitrates
  2. They transfer energy directly to primary consumers
  3. They break down dead organic matter and release mineral ions Correct answer.
  4. They fix carbon dioxide into glucose

Explanation

Decomposers such as bacteria and fungi digest dead organisms and waste, releasing mineral ions such as nitrates and phosphates back into the soil. This recycling makes nutrients available to producers again.

Question 18Biology (SEC)

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

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

Explanation

Increased respiration during exercise raises blood carbon dioxide, which is detected by chemoreceptors and stimulates the breathing centre in the medulla. Ventilation increases to remove the excess carbon dioxide.

Question 19Biology (SEC)

Which of these is an example of a behavioural adaptation for temperature control in a desert mammal?

  1. Large ears with a rich blood supply
  2. A thick layer of fat under the skin
  3. Producing concentrated urine
  4. Being active mainly at night Correct answer.

Explanation

Nocturnal activity is a behaviour that avoids the hottest part of the day and reduces heat gain and water loss. The other options are structural or physiological adaptations rather than behaviours.

Question 20Biology (SEC)

A test-tube contains starch solution and amylase. After ten minutes, which test would confirm that starch digestion has occurred?

  1. Benedict's test giving a brick-red precipitate Correct answer.
  2. Biuret test turning purple
  3. Iodine solution turning blue-black
  4. A glowing splint reigniting

Explanation

Amylase hydrolyses starch to maltose, a reducing sugar. Benedict's reagent turns brick-red on heating with a reducing sugar, confirming that digestion has taken place.

Question 21Biology (SEC)

In a genetic diagram, a woman who is a carrier of a sex-linked recessive condition (X^H X^h) has children with an unaffected man (X^H Y). What proportion of their sons is expected to be affected?

  1. No sons
  2. All sons
  3. One half of the sons Correct answer.
  4. One quarter of the sons

Explanation

Sons inherit their Y chromosome from the father and one of the mother's X chromosomes. Half the sons receive X^h and are affected, while the other half receive X^H and are unaffected.

Question 22Biology (SEC)

Which feature of the villi in the small intestine increases the rate of absorption of glucose?

  1. A low concentration of glucose in the blood capillaries
  2. A single layer of thin epithelial cells with a rich blood supply Correct answer.
  3. A thick, muscular outer wall
  4. A covering of mucus-secreting cells only

Explanation

A thin epithelium shortens the diffusion distance, and a dense capillary network removes absorbed glucose to maintain a steep concentration gradient. These features together speed up absorption.

Question 23Biology (SEC)

Which statement about the nitrogen cycle is correct?

  1. Decomposers convert nitrates into proteins in plants
  2. Nitrogen gas is directly absorbed by plant roots
  3. Denitrifying bacteria convert nitrates in the soil into nitrogen gas Correct answer.
  4. Nitrifying bacteria convert nitrates into ammonia

Explanation

Denitrifying bacteria in waterlogged, anaerobic soil reduce nitrates to nitrogen gas, which returns to the atmosphere. Plants cannot use nitrogen gas directly and rely on nitrates or ammonium ions.

Question 24Biology (SEC)

Which of the following best explains why a person with a low platelet count bruises and bleeds easily?

  1. Platelets produce antibodies against pathogens
  2. Platelets digest old red blood cells
  3. Platelets are needed for blood clotting at damaged vessel walls Correct answer.
  4. Platelets transport oxygen to the tissues

Explanation

Platelets adhere to damaged vessel walls and release factors that trigger the clotting cascade, forming a plug. A shortage therefore allows small injuries to bleed more readily.

Question 25Biology (SEC)

A population of insects shows variation in body colour; green insects are better camouflaged on green leaves than brown ones. Over many generations the proportion of green insects increases. Which term describes this process?

  1. Genetic engineering
  2. Natural selection Correct answer.
  3. Selective breeding by humans
  4. Asexual reproduction

Explanation

Green insects survive and reproduce more successfully in the leafy environment, so their alleles are passed on more often. This differential survival and reproduction of inherited variation is natural selection.

Question 26Biology (SEC)

Which cell structure controls the movement of substances into and out of an animal cell?

  1. The nucleus
  2. The mitochondrion
  3. The cell surface membrane Correct answer.
  4. The cell wall

Explanation

The cell surface membrane is a partially permeable barrier made of a phospholipid bilayer with proteins, and it regulates which substances enter or leave the cell. The other listed structures have different roles and do not form the outer boundary in animal cells.

Question 27Biology (SEC)

A student observes a cell with a cellulose cell wall, a large permanent vacuole and chloroplasts. To which group does this cell most likely belong?

  1. A mammal
  2. A green plant Correct answer.
  3. A bacterium
  4. A fungus

Explanation

The combination of a cellulose wall, a large permanent vacuole and chloroplasts is characteristic of photosynthetic plant cells. Chloroplasts allow the cell to carry out photosynthesis, and the permanent vacuole maintains turgor.

Question 28Biology (SEC)

Which reagent is used to test a food sample for the presence of reducing sugar?

  1. Iodine solution
  2. Benedict's solution Correct answer.
  3. Biuret reagent
  4. Ethanol emulsion test

Explanation

Benedict's solution contains copper(II) ions that are reduced to a brick-red precipitate when heated with a reducing sugar such as glucose. Each food test uses a specific reagent matched to the molecule being detected.

Question 29Biology (SEC)

Which molecule is the main energy storage carbohydrate in animals?

  1. Chitin
  2. Glycogen Correct answer.
  3. Cellulose
  4. Starch

Explanation

Glycogen is a branched polymer of glucose stored in the liver and muscles of animals and released when energy is needed. It is compact and easily broken down into glucose.

Question 30Biology (SEC)

A student examines a slide under a microscope using a x10 eyepiece and a x40 objective lens. What is the total magnification?

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

Explanation

Total magnification is calculated by multiplying the magnification of the eyepiece lens by that of the objective lens, so 10 x 40 gives x400. This value tells you how many times larger the image appears than the specimen.

Question 31Biology (SEC)

Which structure in the human breathing system warms and moistens the air before it reaches the lungs?

  1. The nasal cavity Correct answer.
  2. The diaphragm
  3. The alveoli
  4. The trachea

Explanation

The nasal cavity has a moist lining and a rich blood supply, so it warms and humidifies inhaled air and traps dust and pathogens in mucus. This protects the delicate alveolar surfaces further down the tract.

Question 32Biology (SEC)

Which component of blood transports most of the oxygen from the lungs to respiring tissues?

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

Explanation

Red blood cells contain haemoglobin, which binds oxygen in the lungs and releases it in tissues where oxygen concentration is low. Their biconcave shape and lack of a nucleus increase the surface area available for gas transport.

Question 33Biology (SEC)

Which process describes the movement of water molecules from a dilute solution to a more concentrated solution through a partially permeable membrane?

  1. Active transport
  2. Osmosis Correct answer.
  3. Diffusion
  4. Translocation

Explanation

Osmosis is the net movement of water across a partially permeable membrane down a water potential gradient, from a region of higher water potential to one of lower water potential. It is passive and requires no energy from the cell.

Question 34Biology (SEC)

A plant is placed in a solution with a higher water potential than its root hair cells. What is the likely result?

  1. Water leaves the root hair cells by osmosis
  2. Water enters the root hair cells by osmosis Correct answer.
  3. The root hair cells become plasmolysed
  4. The plant wilts rapidly

Explanation

Water moves by osmosis from the region of higher water potential outside the root into the cells, whose contents have a lower water potential due to dissolved solutes. This uptake helps maintain turgor and supports the plant.

Question 35Biology (SEC)

Which enzyme breaks down fats into fatty acids and glycerol?

  1. Catalase
  2. Amylase
  3. Lipase Correct answer.
  4. Protease

Explanation

Lipase hydrolyses lipids into fatty acids and glycerol, and in the human digestive system it is produced by the pancreas and small intestine. Each digestive enzyme acts on a specific substrate.

Question 36Biology (SEC)

A student investigates the effect of temperature on enzyme activity and finds the rate is highest at 37 degrees Celsius, then falls sharply at 60 degrees Celsius. Which explanation best accounts for the fall?

  1. The pH of the solution has increased
  2. The enzyme has been denatured and its active site changed shape Correct answer.
  3. The substrate has been used up entirely
  4. The enzyme is working faster because particles have more energy

Explanation

High temperatures break the bonds holding the enzyme's tertiary structure, so the active site loses its complementary shape and substrate molecules can no longer bind. This denaturation is irreversible and explains the sharp drop in rate.

Question 37Biology (SEC)

Which feature of a red blood cell is an adaptation for efficient oxygen transport?

  1. The presence of a large nucleus
  2. The presence of many mitochondria
  3. A biconcave disc shape giving a large surface area to volume ratio Correct answer.
  4. The ability to divide rapidly

Explanation

The biconcave shape provides a large surface area relative to volume, allowing rapid diffusion of oxygen into and out of the cell. Mature red blood cells also lack a nucleus, leaving more room for haemoglobin.

Question 38Biology (SEC)

Which structure of the human heart prevents blood from flowing back from the ventricles into the atria?

  1. The septum
  2. The semilunar valves
  3. The coronary arteries
  4. The atrioventricular valves Correct answer.

Explanation

The atrioventricular valves lie between the atria and ventricles and close when ventricular pressure rises, preventing backflow into the atria during ventricular contraction. Valves ensure blood flows in one direction through the heart.

Question 39Biology (SEC)

A person's cardiac output is 5 litres per minute and their heart rate is 70 beats per minute. What is the stroke volume?

  1. About 71 millilitres Correct answer.
  2. About 350 millilitres
  3. About 14 millilitres
  4. About 5 millilitres

Explanation

Cardiac output equals heart rate multiplied by stroke volume, so stroke volume is cardiac output divided by heart rate. Dividing 5000 millilitres per minute by 70 beats per minute gives approximately 71 millilitres per beat.

Question 40Biology (SEC)

Which statement best explains why a person's heart rate increases during strenuous exercise?

  1. To increase the delivery of oxygen and glucose to respiring muscles Correct answer.
  2. To lower blood pressure throughout the body
  3. To decrease the oxygen supply to the muscles
  4. To reduce the removal of carbon dioxide from the body

Explanation

During exercise, muscles respire faster and need more oxygen and glucose while producing more carbon dioxide. An increased heart rate raises cardiac output, so blood delivers these substances more quickly and removes waste products faster.

Question 41Biology (SEC)

Which structure in the human kidney carries out ultrafiltration of the blood?

  1. The glomerulus Correct answer.
  2. The loop of Henle
  3. The collecting duct
  4. The ureter

Explanation

The glomerulus is a knot of capillaries inside the Bowman's capsule where high pressure forces water, glucose, urea and small ions into the capsule. Large molecules and blood cells remain in the blood.

Question 42Biology (SEC)

During a reflex action, what is the correct order of the pathway?

  1. Receptor, motor neurone, relay neurone, sensory neurone, effector
  2. Receptor, sensory neurone, relay neurone, motor neurone, effector Correct answer.
  3. Receptor, relay neurone, sensory neurone, effector, motor neurone
  4. Effector, sensory neurone, relay neurone, motor neurone, receptor

Explanation

A reflex arc begins with a receptor detecting a stimulus and sending impulses along a sensory neurone to the spinal cord. A relay neurone connects to a motor neurone, which carries the impulse to an effector such as a muscle.

Question 43Biology (SEC)

Which part of the human nervous system contains the centres that control breathing rate and heart rate?

  1. The cerebrum
  2. The hypothalamus
  3. The cerebellum
  4. The medulla oblongata Correct answer.

Explanation

The medulla oblongata in the brain stem contains the respiratory and cardiovascular centres that adjust breathing and heart rate in response to blood carbon dioxide levels. These automatic controls maintain homeostasis without conscious effort.

Question 44Biology (SEC)

A tall pea plant that is heterozygous (Tt) is crossed with a short pea plant (tt). What proportion of the offspring is expected to be short?

  1. None
  2. All
  3. One half Correct answer.
  4. One quarter

Explanation

The heterozygous parent produces T and t gametes in equal numbers, while the short parent produces only t gametes. Combining them gives Tt and tt offspring in a 1:1 ratio, so half are expected to be short.

Question 45Biology (SEC)

Which statement describes the difference between a gene and an allele?

  1. A gene is a whole chromosome, while an allele is a single base
  2. A gene is made of protein, while an allele is made of DNA
  3. A gene is a section of DNA coding for a characteristic, while an allele is a different version of that gene Correct answer.
  4. A gene is found only in gametes, while an allele is found only in body cells

Explanation

A gene is a length of DNA that codes for a particular protein or characteristic, and alleles are the alternative forms of that gene that differ slightly in base sequence. An organism inherits one allele of each gene from each parent.

Question 46Biology (SEC)

Sickle cell anaemia results from a change in a single base in the gene for haemoglobin. Which term describes this type of mutation?

  1. Chromosome mutation
  2. Non-disjunction
  3. Gene mutation Correct answer.
  4. Frameshift mutation caused by an insertion

Explanation

A change affecting one or a few bases within a gene is a gene mutation, and in sickle cell anaemia it alters one amino acid in the haemoglobin chain. The resulting haemoglobin is less soluble and distorts red blood cells.

Question 47Biology (SEC)

Two species of finch live on the same island and feed on seeds of different sizes, with one having a large stout beak and the other a small slender beak. Which explanation best fits this observation?

  1. Both species compete directly for the same seeds
  2. The two species interbreed to produce a single beak type
  3. Natural selection has reduced competition by adapting each species to a different food source Correct answer.
  4. Beak size is determined only by the age of the bird

Explanation

When species occupy slightly different niches, competition between them is reduced, and natural selection favours individuals whose beaks suit the food available to them. Over generations this can lead to distinct beak forms in each population.

Question 48Biology (SEC)

In a food web, a disease drastically reduces the population of a primary consumer. Which change is most likely to occur in the short term?

  1. The decomposer population will immediately disappear
  2. The producer population will be eliminated entirely
  3. The producer population will decrease sharply
  4. The secondary consumer population will decrease because of reduced food supply Correct answer.

Explanation

Secondary consumers depend on primary consumers for food, so a fall in the number of primary consumers reduces the energy available to them and their numbers decline. Producers may initially increase because fewer primary consumers are eating them.

Question 49Biology (SEC)

A plant is grown in a sealed transparent chamber containing carbon dioxide labelled with a radioactive isotope. After several hours in bright light, where is the radioactivity most likely to be detected in the plant?

  1. In the mineral ions absorbed by the roots
  2. In the water released during transpiration
  3. In the sugars produced during photosynthesis Correct answer.
  4. In the oxygen released into the chamber

Explanation

Labelled carbon dioxide is fixed during the light-independent reactions of photosynthesis and incorporated into glucose and other carbohydrates. The carbon therefore appears in the sugars made by the plant.

Question 50Biology (SEC)

A person living at high altitude has a higher red blood cell count than someone at sea level. Which explanation best accounts for this?

  1. The higher carbon dioxide concentration prevents oxygen binding
  2. The lower oxygen concentration stimulates increased red blood cell production Correct answer.
  3. The lower air pressure destroys white blood cells, so red cells multiply
  4. The colder temperature causes blood to thicken

Explanation

At high altitude the partial pressure of oxygen in the air is lower, so less oxygen is carried per unit volume of blood. The body responds by producing more red blood cells, increasing the oxygen-carrying capacity of the blood.