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Cameroon GCE O-Level Human Biology study materials
Cameroon GCE O-Level Human Biology study resources

Cameroon GCE O-Level Human Biology practice questions

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Question 1Cell biology, cell division and organisation of the human body

Which cell structure controls the entry and exit of substances in a human cheek cell?

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

Explanation

The cell membrane is a thin partially permeable layer surrounding the cytoplasm. It allows small molecules such as oxygen and water to pass while restricting or regulating larger substances, so it acts as the gatekeeper of the cell.

Question 2Cell biology, cell division and organisation of the human body

A student examines a stained slide of human tissue and sees many cells with no nucleus and a biconcave shape. Which tissue is most likely on the slide?

  1. Smooth muscle
  2. Red blood cells Correct answer.
  3. Epithelial tissue of the cheek
  4. Nervous tissue

Explanation

Mature human red blood cells lose their nucleus and are biconcave discs, which increases surface area for carrying oxygen. The absence of a nucleus and the biconcave shape are the identifying features described.

Question 3Cell biology, cell division and organisation of the human body

During which stage of mitosis do the chromosomes line up along the equator of the cell?

  1. Anaphase
  2. Metaphase Correct answer.
  3. Telophase
  4. Prophase

Explanation

In metaphase the chromosomes become attached to spindle fibres and arrange themselves along the middle plane of the cell. This alignment ensures that each daughter cell receives one chromatid from every chromosome when they separate.

Question 4Cell biology, cell division and organisation of the human body

Which of the following is the main function of the mitochondrion in a human liver cell?

  1. Synthesis of lipids for the membrane
  2. Release of energy by aerobic respiration Correct answer.
  3. Storage of genetic information
  4. Secretion of digestive enzymes

Explanation

Mitochondria are the site of the later stages of aerobic respiration, where glucose is broken down with oxygen to release energy as ATP. Liver cells are very active and therefore contain large numbers of mitochondria.

Question 5Cell biology, cell division and organisation of the human body

Which level of organisation comes immediately after 'cell' in the sequence used to describe the human body?

  1. Organism
  2. Tissue Correct answer.
  3. Organ system
  4. Organ

Explanation

The accepted order of organisation is cell, tissue, organ, organ system and organism. A tissue is a group of similar cells working together to perform a particular function, so it follows directly after the cell.

Question 6Cell biology, cell division and organisation of the human body

Which type of human tissue covers body surfaces and lines internal cavities?

  1. Connective tissue
  2. Epithelial tissue Correct answer.
  3. Nervous tissue
  4. Muscle tissue

Explanation

Epithelial tissue forms continuous sheets of cells that cover the skin and line cavities such as the mouth and intestine. Its close packing and ability to renew make it suited to protection, absorption and secretion.

Question 7Cell biology, cell division and organisation of the human body

A cell from the lining of the small intestine has many tiny folds on its free surface. What is the main advantage of these folds?

  1. They store excess glucose as glycogen
  2. They allow the cell to divide more rapidly
  3. They reduce the loss of water from the cell
  4. They increase the surface area for absorption of digested food Correct answer.

Explanation

The folds, called microvilli, greatly increase the surface area of the cell membrane across which digested nutrients are absorbed. This adaptation links cell structure to the function of efficient uptake of food molecules.

Question 8Cell biology, cell division and organisation of the human body

Which statement correctly describes what happens to the chromosome number when a human skin cell divides by mitosis?

  1. It becomes random in each daughter cell
  2. It is halved in each daughter cell
  3. It stays the same in each daughter cell Correct answer.
  4. It doubles permanently in each daughter cell

Explanation

Before mitosis the chromosomes replicate, and during division the chromatids separate equally, so each daughter cell receives the same diploid number of 46 chromosomes as the parent cell. Mitosis therefore maintains chromosome number in body cells.

Question 9Cell biology, cell division and organisation of the human body

Why does a red blood cell burst when placed in distilled water?

  1. The cell actively pumps water inwards
  2. Salts move out of the cell by diffusion faster than water enters
  3. Water moves into the cell by osmosis because the cell contents are more concentrated Correct answer.
  4. The cell membrane dissolves in pure water

Explanation

Distilled water has a higher water potential than the cytoplasm, so water enters the cell across the partially permeable membrane by osmosis. The cell swells and bursts because it has no rigid cell wall to resist the pressure.

Question 10Cell biology, cell division and organisation of the human body

Which pair of structures is found in a human cell but absent from a bacterial cell?

  1. Cell membrane and cytoplasm
  2. Cell wall and capsule
  3. Ribosomes and DNA
  4. Nucleus and mitochondria Correct answer.

Explanation

Human cells are eukaryotic and contain a true membrane-bound nucleus and mitochondria. Bacteria are prokaryotic, lacking these membrane-bound organelles, although both cell types share a membrane, cytoplasm, ribosomes and DNA.

Question 11Cell biology, cell division and organisation of the human body

A tissue sample shows cells that are long, cylindrical and have several nuclei per cell, with faint cross-striations. Which tissue is this?

  1. Smooth muscle
  2. Cardiac muscle
  3. Skeletal muscle Correct answer.
  4. Nervous tissue

Explanation

Skeletal muscle fibres are long, unbranched cylinders with many nuclei and clear cross-striations, reflecting their role in voluntary movement. These features distinguish them from the other muscle types.

Question 12Cell biology, cell division and organisation of the human body

Which organelle is most abundant in a cell that secretes large amounts of protein hormone?

  1. Lysosome
  2. Centriole
  3. Ribosome Correct answer.
  4. Vacuole

Explanation

Protein hormones are assembled on ribosomes, often those attached to the rough endoplasmic reticulum, before being processed and secreted. A cell specialising in protein secretion therefore contains many ribosomes.

Question 13Cell biology, cell division and organisation of the human body

During which phase of the cell cycle does DNA replication take place?

  1. Anaphase
  2. Cytokinesis
  3. Interphase Correct answer.
  4. Prophase

Explanation

DNA replication occurs during interphase, before the visible stages of mitosis begin, so that each chromosome consists of two identical chromatids. This ensures each daughter cell receives a complete set of genetic material.

Question 14Cell biology, cell division and organisation of the human body

A student argues that because nerve cells and muscle cells contain the same genes, they should look and behave identically. Why is this reasoning faulty?

  1. Only nerve cells contain a nucleus
  2. Muscle cells have no cell membrane
  3. Different cells contain completely different sets of genes
  4. Different genes are switched on in different cells, so different proteins are made Correct answer.

Explanation

All body cells derived from the zygote carry the same genes, but selective gene expression means each cell type manufactures only the proteins needed for its specialised function. This is why cells with identical genetic material can differ greatly in structure and behaviour.

Question 15Cell biology, cell division and organisation of the human body

Which of the following best describes the role of the Golgi apparatus in a human cell?

  1. Producing spindle fibres during mitosis
  2. Modifying and packaging proteins for secretion Correct answer.
  3. Containing enzymes that digest worn-out organelles
  4. Generating ATP by aerobic respiration

Explanation

The Golgi apparatus receives proteins from the endoplasmic reticulum, modifies them and packages them into vesicles for release from the cell. It is therefore central to the secretion of substances such as enzymes and hormones.

Question 16Cell biology, cell division and organisation of the human body

A cell is treated with a chemical that prevents the formation of spindle fibres. Which process will be most directly affected?

  1. Breakdown of glucose in the cytoplasm
  2. Formation of the cell membrane during interphase
  3. Movement of water across the cell membrane
  4. Movement of chromosomes to opposite poles during division Correct answer.

Explanation

Spindle fibres attach to chromosomes and pull the chromatids to opposite poles during anaphase. If they cannot form, chromosomes will not be separated correctly, so nuclear division is disrupted.

Question 17Cell biology, cell division and organisation of the human body

Which sequence correctly traces the path of a secreted protein from its site of synthesis to release from the cell?

  1. Golgi apparatus → ribosome → vacuole
  2. Nucleus → lysosome → cell membrane
  3. Ribosome → Golgi apparatus → vesicle → cell membrane Correct answer.
  4. Mitochondrion → ribosome → nucleus

Explanation

Proteins are synthesised on ribosomes, passed to the Golgi apparatus for modification and packaging, then carried in vesicles that fuse with the cell membrane to release their contents. This route reflects the coordinated work of organelles in secretion.

Question 18Cell biology, cell division and organisation of the human body

A human cell at the end of meiosis produces gametes. How does the chromosome number of each gamete compare with that of the parent cell?

  1. It is the same, 46 chromosomes
  2. It is double, 92 chromosomes
  3. It is one quarter, 12 chromosomes
  4. It is half, 23 chromosomes Correct answer.

Explanation

Meiosis involves two divisions with only one round of chromosome replication, so the chromosome number is halved. Each human gamete therefore receives 23 chromosomes, restoring the diploid number at fertilisation.

Question 19Cell biology, cell division and organisation of the human body

Two slides are compared: slide A shows cells with large numbers of mitochondria and many ribosomes, while slide B shows cells with few organelles and much stored fat. Which conclusion is best supported?

  1. Cells on slide B are dead
  2. Cells on slide A cannot divide
  3. Cells on slide B are nerve cells
  4. Cells on slide A have a higher rate of energy use and protein synthesis Correct answer.

Explanation

Abundant mitochondria indicate a high demand for energy, and numerous ribosomes indicate active protein synthesis. Fat-storing cells need fewer of these organelles because their main role is storage rather than rapid metabolism.

Question 20Cell biology, cell division and organisation of the human body

Why is it important that the cells lining the human gut are replaced continuously by mitosis?

  1. Mitosis produces genetically varied cells that resist disease
  2. Mitosis allows cells to change into any other cell type
  3. Mitosis replaces worn-out cells with genetically identical cells Correct answer.
  4. Mitosis halves the chromosome number to prevent cancer

Explanation

The gut lining is constantly worn away by friction and digestive action, so mitosis produces new cells that are genetically identical to the parent cells. This maintains a healthy, functioning lining without changing the tissue type.

Question 21Nutrition, digestion and enzymes

Which food class is the main immediate source of energy for the human body, especially during vigorous activity?

  1. Carbohydrates Correct answer.
  2. Vitamins
  3. Proteins
  4. Minerals

Explanation

Carbohydrates are broken down to glucose, which is oxidised during respiration to release energy quickly. This makes them the body's preferred fuel, particularly for active muscles. Proteins and vitamins are not used as the primary rapid energy source.

Question 22Nutrition, digestion and enzymes

A student eats a meal containing starch. Which enzyme begins the chemical digestion of this starch, and where does it act?

  1. Trypsin acting in the duodenum
  2. Pepsin acting in the stomach
  3. Lipase acting in the small intestine
  4. Salivary amylase acting in the mouth Correct answer.

Explanation

Salivary amylase (ptyalin) is secreted by the salivary glands and starts converting starch to maltose in the mouth. Chewing mixes the food with saliva so this digestion begins before swallowing. The other enzymes listed act on proteins or fats elsewhere in the gut.

Question 23Nutrition, digestion and enzymes

Which structure in the human alimentary canal is the main site of absorption of digested food into the blood?

  1. Oesophagus
  2. Small intestine Correct answer.
  3. Large intestine
  4. Stomach

Explanation

The small intestine has a very long length and a folded lining covered with villi, giving a large surface area for absorption. Its walls are thin and richly supplied with blood capillaries, so digested nutrients pass quickly into the blood. The other regions absorb little or none of the main nutrients.

Question 24Nutrition, digestion and enzymes

Which of the following is a function of water in the human diet?

  1. Acting as the main source of dietary fibre
  2. Supplying most of the energy for muscle contraction
  3. Acting as a solvent for body reactions and transport Correct answer.
  4. Building strong bones and teeth directly

Explanation

Water is the solvent in which digested nutrients, gases and wastes are dissolved and transported around the body. It also forms the medium in which most metabolic reactions occur. Energy supply, bone building and dietary fibre are provided by other food components.

Question 25Nutrition, digestion and enzymes

Which reagent is used to test a food sample for the presence of reducing sugar, and what colour change shows a positive result?

  1. Dilute hydrochloric acid turning milky white
  2. Biuret reagent turning purple
  3. Iodine solution turning blue-black
  4. Benedict's solution turning brick-red on heating Correct answer.

Explanation

Benedict's solution contains copper(II) ions that are reduced by reducing sugars such as glucose when heated, forming a brick-red precipitate. The colour change from blue through green and yellow to brick-red indicates the amount of reducing sugar. The other reagents test for different food substances.

Question 26Nutrition, digestion and enzymes

Which part of a tooth is the hardest outer layer that protects the crown from wear?

  1. Dentine
  2. Cement
  3. Enamel Correct answer.
  4. Pulp cavity

Explanation

Enamel is the hardest substance in the body and forms the outer protective covering of the crown. It is mainly mineral and resists the wear of chewing. Dentine, pulp and cement lie beneath or below the crown.

Question 27Nutrition, digestion and enzymes

Which condition is caused by a deficiency of vitamin C in the diet?

  1. Anaemia
  2. Rickets
  3. Scurvy Correct answer.
  4. Night blindness

Explanation

Vitamin C is needed for the formation of collagen, which strengthens skin, gums and blood vessel walls. A lack of it causes scurvy, with bleeding gums and poor wound healing. The other conditions are linked to different nutrient deficiencies.

Question 28Nutrition, digestion and enzymes

Which statement correctly describes the action of enzymes in digestion?

  1. They supply the energy needed to break chemical bonds in food molecules.
  2. They are biological catalysts that speed up the breakdown of large food molecules without being used up. Correct answer.
  3. They are broken down with the food they digest and must be replaced each meal.
  4. They raise the temperature of the gut so that food molecules break apart faster.

Explanation

Enzymes are proteins that act as biological catalysts, speeding up the hydrolysis of large molecules into smaller ones. They are not consumed in the reaction, so small amounts can act repeatedly. They do not supply energy or raise body temperature to break food apart.

Question 29Nutrition, digestion and enzymes

A food sample is tested with Biuret reagent and turns purple. Which food class is present?

  1. Starch
  2. Reducing sugar
  3. Protein Correct answer.
  4. Fat

Explanation

Biuret reagent changes from blue to purple or violet in the presence of peptide bonds, which occur in proteins. This makes it the standard test for protein. Starch, reducing sugar and fat are detected by different tests.

Question 30Nutrition, digestion and enzymes

Which region of the alimentary canal secretes hydrochloric acid, and what is one function of this acid?

  1. Ileum, where it helps absorb glucose
  2. Duodenum, where it neutralises bile
  3. Mouth, where it softens food before swallowing
  4. Stomach, where it kills bacteria and provides an acidic pH for pepsin Correct answer.

Explanation

Gastric glands in the stomach secrete hydrochloric acid, giving the stomach contents a low pH. This acidity kills many swallowed bacteria and provides the acidic conditions pepsin needs to digest proteins. The other regions do not secrete acid for this purpose.

Question 31Nutrition, digestion and enzymes

Bile helps in the digestion of fats. Which statement best explains how bile assists this process?

  1. It provides the enzyme lipase that breaks down fats.
  2. It converts fats into proteins that can be absorbed.
  3. It chemically digests fats into fatty acids and glycerol.
  4. It emulsifies fats into small droplets, increasing the surface area for lipase action. Correct answer.

Explanation

Bile salts break large fat globules into many small droplets, a process called emulsification. This greatly increases the surface area on which lipase can act, speeding up fat digestion. Bile itself contains no digestive enzymes and does not chemically change fats.

Question 32Nutrition, digestion and enzymes

A patient's gall bladder is removed, so bile flows directly and continuously into the small intestine. Which meal would be hardest for this patient to digest?

  1. A meal rich in fat such as fried fish Correct answer.
  2. A meal rich in protein such as lean meat
  3. A meal rich in starch such as boiled rice
  4. A meal rich in vitamin C such as oranges

Explanation

Without a gall bladder to store and release bile in a concentrated burst after a fatty meal, fat emulsification is less efficient. Fat digestion and absorption are therefore reduced when a fatty meal is eaten. Starch, protein and vitamin-rich foods are less dependent on bile.

Question 33Nutrition, digestion and enzymes

Which feature of the villi in the small intestine most directly increases the rate of absorption of digested food?

  1. A thick muscular wall surrounding each villus
  2. The presence of goblet cells that secrete mucus
  3. A single layer of thin epithelial cells over a dense network of blood capillaries Correct answer.
  4. The presence of many lymph nodes inside each villus

Explanation

Each villus has a very thin epithelium, only one cell thick, and a rich blood supply close to the surface. This short diffusion distance and continuous blood flow maintain a steep concentration gradient, so absorbed nutrients enter the blood rapidly. The other features do not directly speed up absorption.

Question 34Nutrition, digestion and enzymes

Which enzyme digests proteins in the small intestine and is secreted by the pancreas?

  1. Trypsin Correct answer.
  2. Amylase
  3. Maltase
  4. Lipase

Explanation

The pancreas secretes trypsin, a protease that breaks proteins into smaller peptides in the small intestine. It acts in the alkaline conditions created by bile and pancreatic bicarbonate. Amylase, lipase and maltase act on other substrates.

Question 35Nutrition, digestion and enzymes

A boy eats a meal containing bread, meat and butter. Which combination correctly matches each food to an enzyme that digests it?

  1. Bread-protein to pepsin; meat-fat to lipase; butter-starch to amylase
  2. Bread-fat to lipase; meat-starch to amylase; butter-protein to pepsin
  3. Bread-starch to lipase; meat-fat to amylase; butter-protein to pepsin
  4. Bread-starch to amylase; meat-protein to pepsin; butter-fat to lipase Correct answer.

Explanation

Bread is rich in starch, which is digested by amylase; meat is rich in protein, digested by pepsin in the stomach; butter is fat, digested by lipase. Each enzyme is specific to its substrate. Only the first option matches each food to the correct enzyme.

Question 36Nutrition, digestion and enzymes

Which of the following best describes the role of peristalsis in the alimentary canal?

  1. Chemical breakdown of food by enzymes in the gut wall
  2. Secretion of bile into the duodenum
  3. Absorption of glucose into the blood capillaries
  4. Waves of muscular contraction that move food along the gut Correct answer.

Explanation

Peristalsis is the rhythmic contraction of circular and longitudinal muscles in the gut wall behind and in front of a bolus. These waves push food forward along the oesophagus and intestines and also mix it with digestive juices. It is a mechanical process, not a chemical or absorptive one.

Question 37Nutrition, digestion and enzymes

Which statement about the effect of temperature on enzyme activity is correct?

  1. Activity increases to an optimum and then falls sharply as the enzyme is denatured. Correct answer.
  2. Activity is highest at very low temperatures because molecules are stable.
  3. Activity is unaffected by temperature as long as substrate is present.
  4. Activity increases steadily without limit as temperature rises.

Explanation

Raising temperature increases the kinetic energy of enzyme and substrate molecules, so reaction rate rises up to an optimum. Beyond the optimum, the enzyme's shape is altered and its active site is destroyed, so activity falls sharply. This change of shape is called denaturation.

Question 38Nutrition, digestion and enzymes

Starch is digested to maltose and then to glucose. Which enzyme completes the final step?

  1. Amylase
  2. Lipase
  3. Pepsin
  4. Maltase Correct answer.

Explanation

Maltase, an enzyme in the intestinal lining, hydrolyses maltose into two glucose molecules. Amylase only breaks starch down as far as maltose, while pepsin and lipase act on proteins and fats. The glucose produced is then absorbed into the blood.

Question 39Nutrition, digestion and enzymes

A student tests a food sample with iodine solution and then with Benedict's solution. The iodine test gives a blue-black colour, but the Benedict's test remains blue after heating. Which conclusion is best supported?

  1. The sample contains fat but no reducing sugar.
  2. The sample contains starch but no reducing sugar. Correct answer.
  3. The sample contains reducing sugar but no starch.
  4. The sample contains protein but no starch.

Explanation

A blue-black colour with iodine shows that starch is present. Benedict's solution staying blue after heating shows that no reducing sugar was detected. Together these results indicate starch without reducing sugar. The tests give no information about protein or fat.

Question 40Nutrition, digestion and enzymes

Which adaptation of the small intestine is most important for increasing the surface area available for absorption?

  1. The intestinal wall is thick and muscular.
  2. The intestine is short and straight.
  3. The intestine contains a large amount of mucus.
  4. The lining is folded and covered with millions of finger-like villi. Correct answer.

Explanation

Folds in the intestinal lining, together with villi and the microvilli on their cells, multiply the surface area many times. A large surface area allows rapid absorption of digested nutrients. Length, thickness and mucus do not increase surface area in the same way.

Question 41Nutrition, digestion and enzymes

An enzyme that normally works in the stomach is placed in a test tube at pH 7. Which prediction is most reasonable?

  1. Its activity will be higher because neutral pH suits all enzymes.
  2. Its activity will increase because pepsin works best in alkaline conditions.
  3. Its activity will be much lower than at its optimum acidic pH. Correct answer.
  4. Its activity will be unchanged because pH does not affect enzymes.

Explanation

Each enzyme has an optimum pH at which its active site shape is best suited to its substrate. Stomach enzymes such as pepsin have an acidic optimum, so moving them to pH 7 reduces activity. Extreme pH changes can alter the active site and reduce or destroy catalytic action.

Question 42Nutrition, digestion and enzymes

A person with a damaged pancreas produces very little pancreatic juice. Which effect on digestion is most likely?

  1. Increased absorption of glucose in the stomach
  2. Loss of bile production by the liver
  3. Reduced digestion of fats and proteins in the small intestine Correct answer.
  4. Complete failure of starch digestion in the mouth

Explanation

Pancreatic juice supplies lipase, trypsin and amylase to the small intestine, so reduced secretion impairs fat and protein digestion there. Starch digestion in the mouth is due to salivary amylase and is not directly affected. Bile production by the liver is separate from pancreatic secretion.

Question 43Nutrition, digestion and enzymes

Which sequence correctly traces the path of a swallowed piece of food through the alimentary canal?

  1. Mouth, stomach, small intestine, oesophagus, large intestine
  2. Mouth, oesophagus, small intestine, stomach, large intestine
  3. Mouth, oesophagus, stomach, small intestine, large intestine Correct answer.
  4. Mouth, stomach, oesophagus, large intestine, small intestine

Explanation

Food passes from the mouth into the oesophagus, which carries it to the stomach. From the stomach it enters the small intestine, where most digestion and absorption occur, and then the large intestine. The rectum and anus follow the large intestine.

Question 44Nutrition, digestion and enzymes

Which statement best explains why a diet high in refined sugar but low in dietary fibre may lead to constipation?

  1. Less fibre means less bulky, softer faeces to stimulate peristalsis in the large intestine. Correct answer.
  2. Sugar is not digested and blocks the small intestine.
  3. Sugar increases bile production, which hardens the faeces.
  4. Refined sugar absorbs all the water from the blood.

Explanation

Dietary fibre adds bulk to the contents of the large intestine and holds water, keeping faeces soft. This bulk stimulates peristalsis, so a low-fibre diet can produce hard, dry faeces and constipation. Refined sugar itself does not block the gut or remove water from the blood.

Question 45Transport: blood, blood vessels and the heart

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

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

Explanation

The pulmonary vein is the only vein that carries oxygenated blood, returning it from the lungs to the left atrium of the heart. Its name refers to its connection to the lungs, not to the oxygen level of the blood inside it.

Question 46Transport: blood, blood vessels and the heart

A student's blood smear shows cells that are biconcave discs without a nucleus. These cells are best identified as

  1. red blood cells Correct answer.
  2. lymphocytes
  3. phagocytes
  4. platelets

Explanation

Mature red blood cells in humans lose their nucleus and are shaped as biconcave discs, which increases surface area for oxygen uptake. The biconcave shape also allows them to bend through narrow capillaries.

Question 47Transport: blood, blood vessels and the heart

Which chamber of the human heart pumps oxygenated blood into the aorta?

  1. Right ventricle
  2. Left ventricle Correct answer.
  3. Left atrium
  4. Right atrium

Explanation

The left ventricle has the thickest muscular wall because it must generate enough pressure to push oxygenated blood through the aorta to the whole body. Blood reaches it from the left atrium.

Question 48Transport: blood, blood vessels and the heart

The liquid part of blood that transports dissolved glucose, hormones and urea is called

  1. serum
  2. lymph
  3. plasma Correct answer.
  4. tissue fluid

Explanation

Plasma is the pale yellow liquid component of blood in which cells are suspended, and it dissolves and transports many substances including glucose, hormones, carbon dioxide and urea. Serum is plasma from which clotting factors have been removed.

Question 49Transport: blood, blood vessels and the heart

Which feature of capillaries makes them suited for exchange of materials with tissues?

  1. Walls one cell thick and narrow lumen Correct answer.
  2. A wide lumen with elastic walls
  3. Thick muscular walls that maintain high pressure
  4. Valves along their length to prevent backflow

Explanation

Capillary walls are only one cell thick, giving a short diffusion distance, and the narrow lumen slows blood flow so more time is available for exchange. These features suit diffusion of oxygen, glucose and waste products.

Question 50Transport: blood, blood vessels and the heart

The pacemaker of the human heart, which initiates each heartbeat, is located in the

  1. medulla oblongata
  2. atrioventricular node
  3. septum
  4. sinoatrial node Correct answer.

Explanation

The sinoatrial node lies in the wall of the right atrium and generates the electrical impulse that starts each heartbeat. It sets the basic rhythm, so it is called the natural pacemaker.