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

Cameroon GCE O-Level Biology practice questions

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Question 1Biological inquiry and interpretation of evidence

A researcher predicts that tomato plants given a nitrogen-enriched fertilizer will produce more fruit than plants given a standard fertilizer. In this study, the amount of fruit produced is best described as which of the following?

  1. The hypothesis
  2. A controlled variable
  3. The dependent variable Correct answer.
  4. The independent variable

Explanation

The dependent variable is the measured outcome that responds to the manipulation, which here is fruit yield. The fertilizer type is the factor the researcher deliberately changes, so it is the independent variable rather than the measured result.

Question 2Biological inquiry and interpretation of evidence

A student measures the mass of the same sample five times and obtains nearly identical values, but the balance was never zeroed and reads 2.0 g too high. How should these measurements be described?

  1. Both accurate and precise
  2. Precise but not accurate Correct answer.
  3. Accurate but not precise
  4. Neither accurate nor precise

Explanation

Precision refers to how closely repeated measurements agree with one another, while accuracy refers to how close they are to the true value. Because the readings cluster tightly but are systematically offset by the unzeroed balance, they are precise but inaccurate.

Question 3Biological inquiry and interpretation of evidence

Which of the following best distinguishes a scientific hypothesis from a scientific theory?

  1. A hypothesis is a testable proposed explanation, while a theory is a well-supported explanatory framework built from extensive evidence Correct answer.
  2. A hypothesis is always correct once tested, while a theory remains an untested guess
  3. A hypothesis is a broad framework, while a theory is a single testable prediction
  4. A hypothesis applies only to biology, while a theory applies only to physics

Explanation

In science, a hypothesis is a testable proposed explanation for a specific observation, whereas a theory is a broad, well-substantiated explanation supported by many lines of evidence. The common usage of theory as a mere guess is incorrect in scientific contexts.

Question 4Biological inquiry and interpretation of evidence

A scientist repeats an experiment several times and obtains consistent results. Which conclusion is most justified?

  1. The findings are reliable and reproducible under the tested conditions Correct answer.
  2. The results now apply to all organisms everywhere
  3. The hypothesis has been proven true beyond any doubt
  4. The experiment has no remaining sources of error

Explanation

Reproducible results indicate reliability, meaning the procedure yields consistent outcomes under the tested conditions. Science does not establish absolute proof, and replication does not eliminate error or guarantee universal applicability.

Question 5Biological inquiry and interpretation of evidence

A graph plots plant height on the y-axis against days of growth on the x-axis. Which statement correctly identifies the placement of these variables?

  1. Days of growth is the independent variable on the x-axis, and height is the dependent variable on the y-axis Correct answer.
  2. Both variables are dependent and should share the x-axis
  3. Days of growth is the dependent variable because it is measured over time
  4. Height is the independent variable on the y-axis, and days of growth is the dependent variable on the x-axis

Explanation

By convention, the independent variable is placed on the x-axis and the dependent variable on the y-axis. Height responds to elapsed time, so time is independent and height is dependent.

Question 6Biological inquiry and interpretation of evidence

A student notices that mold grows on bread left in a warm, humid place but not on bread stored in a dry, cool place. Which of the following is the most appropriate next step in the scientific process?

  1. Formulate a testable hypothesis and design a controlled experiment to test it Correct answer.
  2. Conclude immediately that warmth and moisture cause mold growth
  3. Publish the observation as a confirmed scientific law
  4. Discard the observation because it was not made in a laboratory

Explanation

An observation generates questions that should be framed as a testable hypothesis and examined through a controlled experiment. Reaching a firm causal conclusion from a single uncontrolled observation is premature.

Question 7Biochemistry

Which property of water is most directly responsible for its ability to moderate temperature in living organisms and large bodies of water?

  1. Its low specific heat
  2. Its inability to form hydrogen bonds
  3. Its nonpolar covalent bonds
  4. Its high specific heat Correct answer.

Explanation

Water has a high specific heat because hydrogen bonds must absorb or release substantial energy before water molecules change temperature. This allows water and water-rich organisms to resist large temperature swings, helping maintain homeostasis.

Question 8Cell structure, membranes and division

Which structure is found in a typical plant cell but NOT in a typical animal cell?

  1. Mitochondrion
  2. Nucleus
  3. Ribosome
  4. Cell wall made of cellulose Correct answer.

Explanation

Plant cells have a rigid cell wall composed primarily of cellulose that surrounds the plasma membrane, providing structural support. Animal cells lack a cell wall, relying on the cytoskeleton and extracellular matrix instead.

Question 9Genetics, inheritance and molecular information

Meiosis differs from mitosis in that meiosis produces

  1. Two genetically identical diploid cells
  2. One diploid cell with double the chromosomes
  3. Two haploid cells identical to the parent
  4. Four genetically varied haploid cells Correct answer.

Explanation

Meiosis consists of two divisions that produce four haploid gametes, each with half the chromosome number of the parent. Crossing over and independent assortment generate genetic variation, distinguishing meiosis from the identical-diploid products of mitosis.

Question 10Metabolism

An enzyme lowers the activation energy of a reaction. Which statement best describes how this affects the reaction?

  1. It increases the reaction rate without being consumed in the reaction Correct answer.
  2. It changes the overall free-energy difference between reactants and products
  3. It supplies the energy needed to make an endergonic reaction exergonic
  4. It permanently binds to the product to stop the reaction

Explanation

Enzymes are biological catalysts that lower activation energy, speeding up reactions without being consumed. They do not change the net free-energy difference (delta G) between reactants and products; they only make the reaction reach equilibrium faster.

Question 11Physiology

Which feature allows a steroid hormone to pass directly through the plasma membrane?

  1. Its lipid (hydrophobic) nature lets it dissolve through the phospholipid bilayer Correct answer.
  2. Its large size lets it push proteins aside
  3. Its negative charge attracts it to the membrane interior
  4. Its attachment to a carbohydrate tag opens a channel

Explanation

Steroid hormones are lipid-soluble (hydrophobic), so they can dissolve through the hydrophobic interior of the phospholipid bilayer without a transport protein. Once inside, they typically bind intracellular receptors that act on the DNA to regulate gene expression.

Question 12Evolution

Which of the following is a necessary condition for natural selection to occur in a population?

  1. All individuals are genetically identical
  2. Heritable variation exists and affects survival or reproduction Correct answer.
  3. The environment never changes
  4. Every individual produces the same number of offspring

Explanation

Natural selection requires heritable variation among individuals and differences in reproductive success linked to that variation. Individuals with advantageous heritable traits leave more offspring, shifting the population's traits over generations.

Question 13Plant Physiology

In a transverse section of a dicotyledonous root, which tissue is responsible for transporting water and dissolved mineral ions upward?

  1. Phloem
  2. Xylem Correct answer.
  3. Parenchyma
  4. Epidermis

Explanation

Xylem consists of dead, lignified vessels that conduct water and dissolved mineral ions from the root upward through the plant. Phloem transports organic solutes, and parenchyma is general packing tissue.

Question 14Neurobiology

What ionic mechanism is directly responsible for the rapid depolarizing phase of a neuronal action potential once the threshold potential (~ -55 mV) is reached?

  1. Opening of voltage-gated Na+ channels, causing rapid inward influx of Na+ down its electrochemical gradient Correct answer.
  2. Opening of voltage-gated K+ channels, causing rapid outward efflux of K+
  3. Active extrusion of 3 Na+ ions in exchange for 2 K+ ions by the Na+/K+ pump
  4. Opening of ligand-gated Cl- channels, causing hyperpolarizing influx of Cl-

Explanation

When depolarization reaches the threshold potential (~ -55 mV), voltage-gated sodium channels rapidly open. Sodium ions (Na+) rush into the axon down their steep electrical and chemical gradients, depolarizing the membrane potential to approximately +35 to +40 mV.

Question 15Ecology

In an energy pyramid, only about 10 percent of the energy at one trophic level is transferred to the next. Most of the remaining energy is

  1. Converted directly into new biomass at the next level
  2. Lost as heat, largely through cellular respiration and metabolic processes Correct answer.
  3. Stored permanently in the soil
  4. Recycled back to producers as light energy

Explanation

At each trophic level, organisms use most of the energy they consume for metabolism and lose much of it as heat through cellular respiration. Only about 10 percent is stored as biomass available to the next level, which limits food chain length.

Question 16Physiology

Which of the following biological processes correctly distinguishes excretion from egestion in living organisms?

  1. Excretion is the elimination of undigested dietary fiber through the anus, whereas egestion removes toxic cellular products.
  2. Excretion involves only the loss of water vapour through the skin, while egestion is the removal of mineral salts through the kidneys.
  3. Excretion is the removal of toxic metabolic waste products formed inside body cells, whereas egestion is the expulsion of undigested food materials from the alimentary canal. Correct answer.
  4. Excretion occurs exclusively in plants through stomata, whereas egestion occurs exclusively in animals through specialized excretory organs.

Explanation

Excretion is formally defined as the removal of toxic waste substances produced by cellular metabolism, such as urea, carbon dioxide, and excess mineral salts. In contrast, egestion is the expulsion of undigested, unabsorbed food residue (faeces) from the digestive tract through the anus, which has never crossed a cell membrane to participate in cellular metabolism.

Question 17Physiology

Mature mammalian erythrocytes (red blood cells) lack a nucleus, mitochondria, and endoplasmic reticulum. What is the primary functional advantage of this structural adaptation?

  1. It allows the cells to divide continuously by mitosis while circulating in the blood.
  2. It maximizes the internal cytoplasmic space available to pack haemoglobin molecules for oxygen transport. Correct answer.
  3. It enables the cells to synthesize large quantities of antibodies to fight bacterial infections.
  4. It allows the cells to carry out rapid aerobic respiration to generate heat in the bloodstream.

Explanation

During erythropoiesis in the bone marrow, mammalian red blood cells extrude their nucleus and organelles. This creates a biconcave disc shape that maximizes internal volume for packing approximately 270 million haemoglobin molecules per cell while increasing the surface area-to-volume ratio for rapid oxygen diffusion.

Question 18Physiology

What is the primary physiological function of ciliated epithelial cells lining the human trachea and bronchi?

  1. To beat in a coordinated wave-like motion, propelling mucus laden with trapped dust and bacteria upwards toward the pharynx. Correct answer.
  2. To secrete digestive enzymes directly into the incoming air stream to destroy airborne toxins.
  3. To absorb atmospheric oxygen directly into the tracheal wall via active transport.
  4. To contract rhythmically to force air in and out of the lungs during inspiration.

Explanation

Ciliated epithelial cells in the respiratory tract possess hair-like projections (cilia) on their apical surface. Working in conjunction with goblet cells that secrete sticky mucus, the cilia beat rhythmically and synchronously upward, moving the mucus blanket containing trapped airborne particles and microbes up to the throat to be swallowed or expectorated.

Question 19Physiology

Why is dietary fibre (roughage), composed mainly of indigestible cellulose from plant cell walls, an indispensable component of a healthy human balanced diet?

  1. It adds bulk to the faeces and stimulates rhythmic peristaltic contractions of the intestinal muscular wall, preventing constipation and bowel disorders. Correct answer.
  2. It is broken down in the stomach by hydrochloric acid to yield essential glucose molecules.
  3. It directly synthesizes haemoglobin molecules in the red bone marrow.
  4. It is absorbed into the bloodstream to act as a lipid carrier protein.

Explanation

Humans lack the enzyme cellulase required to hydrolyze beta-1,4-glycosidic bonds in cellulose. Dietary fibre passes through the alimentary canal undigested, absorbing water and adding non-digestible bulk to the contents of the colon. This mechanical bulk stimulates smooth muscle walls to contract rhythmically (peristalsis), facilitating smooth transit of faeces and preventing constipation and diverticulosis.

Question 20Physiology

What is the primary biological distinction between mechanical (physical) digestion and chemical digestion in the human alimentary canal?

  1. Mechanical digestion physically breaks large food pieces into smaller particles to increase surface area without altering chemical bonds, whereas chemical digestion uses enzymes to hydrolyze large insoluble polymers into small soluble molecules. Correct answer.
  2. Mechanical digestion occurs only in the stomach, while chemical digestion occurs only in the mouth.
  3. Mechanical digestion breaks peptide bonds, while chemical digestion crushes food using teeth.
  4. Mechanical digestion requires digestive juices at alkaline pH, while chemical digestion requires boiling temperatures.

Explanation

Mechanical digestion (mastication by teeth, churning in the stomach, emulsification by bile) physically breaks large food chunks into smaller pieces without breaking covalent bonds, greatly increasing the surface area available for enzymatic contact. Chemical digestion uses hydrolytic enzymes (amylases, proteases, lipases) to cleave complex macromolecules into absorbable monomers.

Question 21Physiology

What are the primary physiological roles of hydrochloric acid ($HCl$) secreted by the parietal (oxyntic) cells of the gastric glands in the human stomach?

  1. It hydrolyzes dietary triglycerides directly into fatty acids and glycerol.
  2. It neutralizes bile salts and converts maltose into glucose.
  3. It provides an optimal acidic medium (pH 1.5–2.0) for pepsin activity, activates inactive pepsinogen into active pepsin, and kills most ingested bacteria. Correct answer.
  4. It emulsifies large lipid globules into micro-droplets in the gastric lumen.

Explanation

Gastric hydrochloric acid serves three vital functions: (1) it lowers the gastric juice pH to approximately 1.5–2.0, providing the optimum acidic environment for gastric enzymes; (2) it cleaves inactive pepsinogen into active pepsin to initiate protein digestion; and (3) its strong acidity denatures dietary proteins and destroys pathogenic microorganisms ingested with food.

Question 22Physiology

Where is bile produced, where is it stored, and what is its primary biological function during digestion in the duodenum?

  1. Produced in the liver, stored in the gallbladder; it contains bile salts that emulsify large fat globules into tiny droplets (increasing surface area for lipase) and neutralizes acidic chyme. Correct answer.
  2. Produced in the gallbladder, stored in the pancreas; it chemically breaks down proteins into polypeptides.
  3. Produced in the stomach, stored in the liver; it converts excess glucose into glycogen.
  4. Produced in the duodenum, stored in the spleen; it secretes active amylase to digest carbohydrates.

Explanation

Bile is synthesized by hepatocytes in the liver and stored and concentrated in the gallbladder between meals. When fatty chyme enters the duodenum, bile is secreted via the common bile duct. Bile contains no enzymes; its bile salts (sodium glycocholate and taurocholate) act as biological detergents, mechanically emulsifying large fat droplets into tiny micelles and neutralizing acidic gastric chyme.

Question 23Physiology

How is the internal epithelial lining of the human ileum structurally adapted to maximize the absorption of digested food nutrients?

  1. It has a completely smooth, thick keratinized wall to prevent digestive enzymes from entering the bloodstream.
  2. It contains numerous large ciliated pits that pump water backward into the stomach.
  3. It is lined with a thick layer of cartilage rings that keep the lumen permanently dilated.
  4. It is folded into millions of finger-like villi with microvilli on epithelial cells, a single-layer epithelium, a dense capillary network, and central lacteals. Correct answer.

Explanation

The ileum maximizes absorption efficiency through multiple structural adaptations: circular folds (plicae circulares), millions of villi, and microvilli on enterocytes, which collectively provide a vast surface area (approx. 250 m²). The epithelium is only one cell thick for a short diffusion distance, and each villus contains a capillary network (absorbing glucose, amino acids) and a central lacteal (absorbing fatty acids and glycerol).

Question 24Physiology

Which major blood vessel directly transports deoxygenated, nutrient-rich blood containing absorbed glucose and amino acids from the capillary networks of the small intestine to the liver?

  1. Hepatic artery
  2. Hepatic portal vein Correct answer.
  3. Renal vein
  4. Inferior vena cava

Explanation

The hepatic portal vein is a unique vessel that connects two capillary beds: it receives blood enriched with absorbed simple sugars, amino acids, vitamins, and minerals from the capillary networks of the stomach and intestines and carries it directly to the liver sinusoids for assimilation, processing, and detoxification before entering the general circulation.

Question 25Physiology

What happens to excess dietary amino acids that cannot be stored by the human body?

  1. They are excreted completely unchanged by the kidneys directly into urine.
  2. They are converted directly into digestive enzymes in the spleen.
  3. They undergo deamination in the liver, where their amino groups ($-NH_2$) are converted into highly toxic ammonia and rapidly synthesized into urea for renal excretion, while the keto acid residue is respired or converted to glycogen. Correct answer.
  4. They are stored in subcutaneous adipose tissue as structural proteins.

Explanation

The human body cannot store excess amino acids. In the liver, hepatocytes remove the nitrogen-containing amino group ($-NH_2$) in a process called deamination. The amino group is converted into toxic ammonia ($NH_3$) and then safely combined with carbon dioxide in the ornithine cycle to form urea, which is excreted by the kidneys. The remaining keto acid is oxidized for energy or converted to glycogen/fat.

Question 26Physiology

Which structure prevents swallowed food boluses from accidentally entering the larynx and trachea, and what supports the tracheal wall to keep the airway permanently open?

  1. The epiglottis prevents food entry, and C-shaped rings of flexible hyaline cartilage keep the trachea patent. Correct answer.
  2. The uvula prevents food entry, and smooth muscle sphincters keep the trachea closed.
  3. The thyroid gland prevents food entry, and dense bone rings support the trachea.
  4. The vocal cords prevent food entry, and fluid hydrostatic pressure keeps the trachea open.

Explanation

During swallowing (deglutition), the larynx elevates and a flexible cartilaginous flap called the epiglottis folds downward to cover the glottis (the opening to the larynx), directing food into the esophagus. The trachea is reinforced with C-shaped rings of hyaline cartilage that prevent airway collapse during negative pressure inhalation while allowing the adjacent esophagus to expand during swallowing.

Question 27Physiology

Which sequence of muscular actions and pressure changes occurs in the human thorax during normal inhalation (inspiration)?

  1. External intercostals relax, diaphragm relaxes and curves up, thoracic volume decreases, alveolar pressure rises above atmospheric.
  2. External intercostals contract (lifting ribs up and out), diaphragm contracts and flattens downward, thoracic volume increases, internal pressure drops below atmospheric, and air rushes into the lungs. Correct answer.
  3. Internal intercostals contract vigorously, abdominal muscles push the diaphragm up, thoracic volume increases, and air is forced out.
  4. Diaphragm contracts into a dome shape, ribs move downwards and inwards, thoracic pressure drops, and air is pushed into the stomach.

Explanation

During inhalation, the diaphragm contracts and flattens downward while external intercostal muscles contract, pulling the rib cage upward and outward. This dual action increases the volume of the thoracic cavity in all dimensions. According to Boyle's law, the increased thoracic volume causes intrapulmonary pressure to drop below atmospheric pressure, drawing air into the lungs.

Question 28Physiology

Which of the following sets of structural characteristics explains why human alveoli function as exceptionally efficient respiratory exchange surfaces?

  1. Thick muscular walls, dry inner surface, small total surface area, and sparse capillary supply.
  2. Ciliated columnar epithelium, cartilaginous rings, and impermeable keratinized lining.
  3. Dense fibrous tissue, acidic mucosal layer, and high positive internal hydrostatic pressure.
  4. Extremely thin walls (single layer of flattened squamous epithelial cells), a moist inner lining, a vast aggregate surface area, and an extensive network of surrounding blood capillaries. Correct answer.

Explanation

Human lungs contain roughly 300–500 million alveoli offering a massive surface area of 70–100 m². Their walls consist of a single layer of squamous epithelial cells (~0.1 μm thick) tightly apposed to capillary endothelium, minimizing diffusion distance. The moist inner surfactant lining dissolves gases, and constant blood flow and ventilation maintain steep partial pressure gradients for $O_2$ and $CO_2$.

Question 29Physiology

Which chemical equation correctly summarizes the complete aerobic breakdown of one mole of glucose in human body cells?

  1. $\text{C}_6\text{H}_{12}\text{O}_6 \to 2\text{C}_2\text{H}_5\text{OH} + 2\text{CO}_2 + 2\text{ ATP}$
  2. $\text{C}_6\text{H}_{12}\text{O}_6 \to 2\text{C}_3\text{H}_6\text{O}_3 + 2\text{ ATP}$
  3. $\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \to 6\text{CO}_2 + 6\text{H}_2\text{O} + 36\text{ to } 38\text{ ATP}$ Correct answer.
  4. $6\text{CO}_2 + 6\text{H}_2\text{O} \to \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2$

Explanation

Aerobic respiration involves the complete oxidation of glucose in the presence of molecular oxygen within the cytoplasm (glycolysis) and mitochondria (Krebs cycle and oxidative phosphorylation): $\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \to 6\text{CO}_2 + 6\text{H}_2\text{O} + \text{approx. } 36\text{–}38\text{ ATP}$.

Question 30Physiology

During a 100-meter sprint in a school athletics competition in Bamenda, an athlete's leg muscles respire anaerobically due to insufficient oxygen delivery. What toxic end product accumulates in the muscle fibers, and how much ATP is generated per glucose molecule?

  1. Lactic acid (lactate), generating only 2 ATP molecules per glucose molecule Correct answer.
  2. Ethanol and carbon dioxide, generating 38 ATP molecules per glucose molecule
  3. Urea and water, generating 4 ATP molecules per glucose molecule
  4. Carbonic acid, generating 36 ATP molecules per glucose molecule

Explanation

When energy demand outstrips cardiovascular oxygen delivery during intense anaerobic exertion, pyruvate produced in glycolysis is reduced by NADH to lactic acid ($C_3H_6O_3$) by lactate dehydrogenase. Because glucose is only partially broken down without the Krebs cycle and oxidative phosphorylation, it yields only 2 ATP per glucose, and accumulating lactic acid causes muscle fatigue and cramping.

Question 31Physiology

What is the biological definition of the 'oxygen debt' incurred during strenuous physical exercise, and how is it repaid during the recovery period?

  1. The volume of oxygen lost from red blood cells that must be replaced by drinking pure water.
  2. The extra volume of oxygen that must be inhaled after exercise to transport accumulated lactic acid to the liver and aerobically oxidize it back into pyruvate and glucose, while replenishing ATP and creatine phosphate stores. Correct answer.
  3. The amount of carbon dioxide trapped inside alveoli that must be exhaled through rapid breathing.
  4. The deficiency of atmospheric oxygen in high-altitude environments like Mount Cameroon.

Explanation

Oxygen debt (excess post-exercise oxygen consumption, EPOC) represents the extra volume of oxygen required after strenuous anaerobic exertion. This oxygen is consumed to: (1) oxidize roughly 20% of accumulated lactate in the liver to $CO_2$ and $H_2O$ to generate ATP used to convert the remaining 80% back into glucose/glycogen (gluconeogenesis); (2) re-oxygenate myoglobin; and (3) resynthesize phosphocreatine and ATP.

Question 32Physiology

Which of the following equations represents anaerobic respiration in baker's yeast (*Saccharomyces cerevisiae*), and which industrial processes exploit this pathway?

  1. $\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \to 6\text{CO}_2 + 6\text{H}_2\text{O}$; used in vinegar manufacture.
  2. $\text{C}_6\text{H}_{12}\text{O}_6 \to 2\text{C}_3\text{H}_6\text{O}_3$; used in cheese and yoghurt production.
  3. $\text{C}_6\text{H}_{12}\text{O}_6 \to 6\text{CH}_4 + 3\text{O}_2$; used in biogas generation.
  4. $\text{C}_6\text{H}_{12}\text{O}_6 \to 2\text{C}_2\text{H}_5\text{OH} + 2\text{CO}_2 + \text{energy (2 ATP)}$; exploited commercially in alcoholic brewing (beer/wine) and bread baking. Correct answer.

Explanation

Under anaerobic conditions, yeast converts glucose into ethanol and carbon dioxide gas via alcoholic fermentation: $\text{C}_6\text{H}_{12}\text{O}_6 \to 2\text{C}_2\text{H}_5\text{OH} + 2\text{CO}_2 + 2\text{ ATP}$. In baking, trapped $CO_2$ gas bubbles cause dough to rise; in brewing, the produced ethanol is utilized to make alcoholic beverages like beer and palm wine.

Question 33Physiology

In the human heart, why is the muscular wall (myocardium) of the left ventricle significantly thicker than that of the right ventricle?

  1. The left ventricle stores blood for several minutes before releasing it into the pulmonary artery.
  2. The left ventricle receives deoxygenated blood under extremely high venous pressure from the vena cava.
  3. The left ventricle must generate a much higher hydrostatic pressure to pump oxygenated blood throughout the entire systemic circulation, whereas the right ventricle only pumps blood a short distance to the lungs under low pressure. Correct answer.
  4. The left ventricle contains the sinoatrial node, which requires a thicker muscular base.

Explanation

The left ventricle pumps blood into the systemic circuit via the aorta to supply all organs and tissues of the body against high peripheral vascular resistance. Its thick muscular myocardium generates high systolic pressures (~120 mmHg). In contrast, the right ventricle pumps blood only a short distance through the low-resistance pulmonary circuit to the delicate capillary beds of the lungs (~25 mmHg).

Question 34Physiology

What is the primary physiological function of the atrioventricular valves (tricuspid and bicuspid/mitral) and semilunar valves during the mammalian cardiac cycle?

  1. To ensure unidirectional blood flow through the heart chambers by preventing the backflow of blood during ventricular contraction (systole) and relaxation (diastole). Correct answer.
  2. To oxygenate deoxygenated blood mechanically as it passes through the valve cusps.
  3. To generate electrical impulses that synchronize atrial and ventricular contractions.
  4. To filter out aged red blood cells from the bloodstream before they enter the aorta.

Explanation

Heart valves act as one-way mechanical check valves. The atrioventricular valves (tricuspid on the right, bicuspid on the left) close during ventricular systole to prevent backflow into the atria, while the aortic and pulmonary semilunar valves close during ventricular diastole to prevent blood from flowing back from the great arteries into the relaxing ventricles.

Question 35Physiology

Which of the following structural comparisons between arteries, veins, and capillaries is accurate?

  1. Arteries have thin walls and wide lumens with valves; veins have thick muscular elastic walls without valves.
  2. Arteries have thick muscular and elastic walls with narrow lumens and carry blood under high pressure; veins have thinner walls, wide lumens, and pocket valves to carry blood under low pressure; capillaries have walls one cell thick. Correct answer.
  3. Capillaries have thick muscular walls to pump blood rapidly into body tissues.
  4. Veins carry blood under the highest pressure directly from the left ventricle.

Explanation

Arteries withstand and maintain high pulsatile pressure from the heart via thick tunica media with smooth muscle and elastic fibers and narrow lumens. Veins carry low-pressure blood back to the heart, featuring wider lumens, thinner walls, and semi-lunar pocket valves to prevent retrograde flow. Capillaries consist solely of a single endothelial cell layer to enable rapid solute exchange.

Question 36Physiology

Which major white blood cell type (leukocyte) is correctly matched with its specific mechanism of defense against infectious pathogens?

  1. Erythrocytes : engulf bacteria by phagocytosis
  2. Platelets (thrombocytes) : secrete histamine and specific agglutinins
  3. Renal podocytes : produce monoclonal antibodies against viral antigens
  4. Phagocytes (e.g. neutrophils/macrophages) : engulf and digest pathogens by phagocytosis; Lymphocytes : produce specific chemical antibodies and antitoxins. Correct answer.

Explanation

The human immune system utilizes two primary classes of leukocytes: phagocytes (such as neutrophils and monocytes/macrophages) that ingest, engulf, and destroy pathogens intracellularly via phagocytosis and lysosomal enzymes; and lymphocytes (B-cells and T-cells) that recognize specific foreign antigens, synthesize neutralizing antibodies, and eliminate infected cells.

Question 37Physiology

When a blood vessel is damaged, which sequence of biochemical events leads to the formation of a stable blood clot (thrombus)?

  1. Platelets adhere to exposed collagen and release thromboplastin $\to$ converts inactive plasma prothrombin into active thrombin in the presence of $\text{Ca}^{2+}$ $\to$ thrombin converts soluble fibrinogen into an insoluble mesh of fibrin fibers that traps blood cells. Correct answer.
  2. Soluble fibrin fibers dissolve $\to$ red blood cells lyse and release hemoglobin $\to$ forming a hard calcium crust.
  3. Heparin is released by liver cells $\to$ converts albumin into globulin $\to$ forming an impermeable plug.
  4. White blood cells phagocytose blood plasma $\to$ releasing sodium chloride crystals that seal the vessel.

Explanation

Blood clotting (hemostasis) is an enzymatic cascade: damaged tissue and activated platelets release thromboplastin (thrombokinase). In the presence of calcium ions ($\text{Ca}^{2+}$) and vitamin K, thromboplastin converts inactive prothrombin into active thrombin. Thrombin then enzymatically cleaves soluble fibrinogen into insoluble fibrin monomers, which polymerize into a mesh that traps erythrocytes and platelets.

Question 38Physiology

Why is the circulatory system of mammals described as a 'closed, double circulation'?

  1. Blood flows freely through open body cavities (hemocoels) twice every 24 hours.
  2. Blood is contained entirely within vessels and passes through the heart only once during a complete circuit of the body.
  3. Blood is enclosed within blood vessels at all times and passes through the heart twice for every complete circuit of the body (pulmonary circuit to the lungs and systemic circuit to the body tissues). Correct answer.
  4. There are two separate hearts: one pumping arterial blood and one pumping venous blood.

Explanation

Mammals possess a closed circulatory system because blood remains strictly confined within a continuous network of blood vessels. It is a double circulation because for every complete circuit around the body, blood passes through the heart twice: first through the right side to the lungs for gas exchange (pulmonary circuit), and then returning to the left side to be pumped to all body organs (systemic circuit).

Question 39Physiology

Which of the following correctly pairs a human excretory organ with its primary metabolic waste product?

  1. Kidneys : urea, excess water, and mineral salts in urine; Lungs : carbon dioxide and water vapour in expired air. Correct answer.
  2. Lungs : urea and bile pigments; Liver : carbon dioxide gas.
  3. Skin : solid feces and undigested dietary cellulose.
  4. Kidneys : digestive enzymes and glycogen granules.

Explanation

Human excretory organs remove specific metabolic wastes: kidneys filter and excrete nitrogenous waste (urea), excess mineral salts, and water as urine; lungs excrete carbon dioxide and water vapour produced by cellular respiration; skin excretes sweat containing small amounts of urea, water, and salts; and liver excretes bile pigments (bilirubin) from haemoglobin breakdown.

Question 40Physiology

During ultrafiltration in the renal corpuscle of a human nephron, which structural feature creates the high hydrostatic pressure required to force fluid from the glomerulus into the Bowman's capsule?

  1. The afferent arteriole entering the glomerulus has a wider lumen diameter than the narrower efferent arteriole leaving it. Correct answer.
  2. The active pumping of cilia lining the Bowman's capsule wall.
  3. The high osmotic pressure of glucose in the proximal convoluted tubule.
  4. The rapid contraction of striated skeletal muscle surrounding the renal pelvis.

Explanation

Ultrafiltration is driven by high hydrostatic blood pressure within the glomerular capillaries. This high pressure is generated because the incoming afferent arteriole has a significantly wider diameter than the outgoing efferent arteriole, creating a bottleneck that forces water, glucose, amino acids, urea, and salts through the fenestrated endothelium and podocyte basement membrane into the Bowman's capsule.

Question 41Physiology

A student spends a hot afternoon playing football in Garoua without drinking water. How does the endocrine and renal system respond to restore normal blood water potential (osmoregulation)?

  1. The pituitary gland stops secreting ADH, making collecting ducts impermeable so that large volumes of dilute urine are voided.
  2. The thyroid gland secretes thyroxine to increase water excretion through the skin.
  3. The pancreas secretes glucagon to break down water molecules in the liver.
  4. Osmoreceptors in the hypothalamus detect decreased blood water potential and stimulate the posterior pituitary to secrete Antidiuretic Hormone (ADH), which increases the water permeability of the collecting ducts, producing a small volume of concentrated urine. Correct answer.

Explanation

When blood water potential drops (dehydration/sweating), hypothalamic osmoreceptors stimulate the posterior pituitary to release Antidiuretic Hormone (ADH). ADH binds to receptors on the collecting ducts of nephrons, inserting aquaporin water channels that dramatically increase water reabsorption by osmosis into the hypertonic renal medulla, conserving body water and producing concentrated urine.

Question 42Physiology

What is the biological definition of homeostasis in mammals, and what is the fundamental control mechanism that maintains it?

  1. The maintenance of a relatively constant internal physiological environment (e.g. core temperature, blood glucose, water potential) around a dynamic set point through negative feedback mechanisms. Correct answer.
  2. The permanent inhibition of all metabolic reactions during periods of starvation.
  3. The continuous variation of body temperature to match the fluctuating external ambient temperature.
  4. The irreversible change in blood pH during intense exercise to enhance cellular respiration.

Explanation

Homeostasis is the maintenance of a stable, constant internal environment within narrow physiological limits despite external environmental fluctuations. It operates primarily via negative feedback loops: sensors detect any deviation from an optimal set point and trigger corrective effector responses that reverse the change back toward the baseline.

Question 43Physiology

When human core body temperature rises above 37 °C during vigorous exercise in a warm climate, which physiological responses in the mammalian skin help lower body temperature back to normal?

  1. Arterioles supplying superficial skin capillaries constrict (vasoconstriction), and sweat glands stop secreting.
  2. Arterioles supplying skin surface capillary loops dilate (vasodilation) to increase radiant heat loss, and eccrine sweat glands secrete sweat which cools the body as water evaporates (latent heat of vaporization). Correct answer.
  3. Hair erector muscles contract to raise hair shafts, trapping an insulating blanket of air.
  4. Skeletal muscles shiver involuntarily to radiate excess heat away from the skin.

Explanation

In response to hyperthermia, the hypothalamic thermoregulatory center triggers two primary skin mechanisms: (1) vasodilation of cutaneous arterioles, which directs more warm blood through superficial capillary beds near the skin surface, increasing heat loss via radiation and convection; and (2) active secretion of sweat by eccrine glands, which absorbs heat energy from the skin as it evaporates.

Question 44Physiology

Which set of physiological responses is triggered by the hypothalamus when a person is exposed to extreme cold in the Mount Cameroon highlands?

  1. Vasodilation of skin arterioles, copious sweating, and relaxation of hair erector muscles.
  2. Increased breathing rate, cessation of shivering, and dilation of skin capillaries.
  3. Vasoconstriction of superficial skin arterioles (diverting blood to deep core organs), involuntary shivering of skeletal muscles to generate metabolic heat, and contraction of hair erector muscles (piloerection). Correct answer.
  4. Inhibition of thyroxine release and decreased cellular metabolic rate.

Explanation

When exposed to cold, the thermoregulatory center in the hypothalamus initiates heat-conserving and heat-generating responses: precapillary sphincters and cutaneous arterioles constrict (vasoconstriction) to minimize heat loss; hair erector muscles contract (goosebumps/piloerection); and shivering thermogenesis is activated in skeletal muscles to generate heat.

Question 45Physiology

Following a carbohydrate-rich meal of fufu and soup, a person's blood glucose level rises above the normal set point (approx. 90 mg/100 cm³). How does the endocrine system respond to restore normoglycemia?

  1. Alpha cells of the islets of Langerhans secrete glucagon to convert glycogen into glucose in muscle cells.
  2. Beta cells of the islets of Langerhans in the pancreas secrete insulin, which stimulates liver and muscle cells to increase glucose uptake and convert excess glucose into insoluble stored glycogen (glycogenesis). Correct answer.
  3. Adrenal glands secrete adrenaline to stimulate glucose excretion in sweat.
  4. Thyroid gland secretes thyroxine to stop cellular respiration.

Explanation

Elevated blood glucose levels stimulate beta cells in the pancreatic islets of Langerhans to secrete insulin into the bloodstream. Insulin promotes cellular uptake of glucose via GLUT transporters, stimulates liver and skeletal muscle cells to synthesize glycogen from glucose (glycogenesis), and enhances fat synthesis in adipose tissue, reducing blood glucose back to baseline.

Question 46Physiology

During a sudden life-threatening emergency, such as encountering a venomous viper in the forest, the adrenal medulla secretes adrenaline (epinephrine) into the bloodstream. Which set of physiological changes is induced by adrenaline to prepare the body for 'fight or flight'?

  1. Increased heart rate and cardiac output, dilation of bronchioles, elevation of blood glucose via glycogenolysis, and diversion of blood flow from digestive viscera to skeletal muscles. Correct answer.
  2. Decreased heart rate, constriction of bronchioles, increased digestive peristalsis, and pupil constriction.
  3. Decreased blood pressure, inhibition of breathing, and rapid conversion of glucose into glycogen.
  4. Immediate induction of sleep and suppression of sensory awareness.

Explanation

Adrenaline prepares the organism for rapid emergency action ('fight or flight'): it increases heart rate and stroke volume, elevates blood pressure, dilates bronchioles to maximize alveolar oxygen delivery, stimulates hepatic glycogenolysis to elevate blood glucose, and selectively constricts arterioles to digestive organs while dilating arterioles to skeletal muscles and brain.

Question 47Evolution

According to the binomial system of nomenclature developed by Carl Linnaeus, which of the following is the correct scientific format for writing the name of the common housefly?

  1. Musca domestica (with the genus capitalized and specific epithet in lowercase, italicized or underlined) Correct answer.
  2. musca Domestica (with the genus in lowercase and specific epithet capitalized)
  3. Musca Domestica (with both genus and specific epithet capitalized)
  4. musca domestica (with both genus and specific epithet in lowercase and unitalicized)

Explanation

In binomial nomenclature, each organism is assigned a two-part Latinized name. The first part is the genus name, which always starts with a capital letter, and the second part is the specific epithet (species name), which starts with a lowercase letter. The entire scientific name must be printed in italics or underlined when handwritten.

Question 48Evolution

Which combination of characteristics distinguishes organisms in Kingdom Fungi from organisms in Kingdom Plantae?

  1. Fungi possess chloroplasts and autotrophic nutrition, whereas plants have chitinous cell walls.
  2. Fungi possess cellulose cell walls and store starch, whereas plants store glycogen.
  3. Fungi are exclusively unicellular prokaryotes, whereas plants are multicellular eukaryotes.
  4. Fungi have cell walls made of chitin, lack chlorophyll, and exhibit heterotrophic saprophytic nutrition, whereas plants have cellulose walls and are autotrophic. Correct answer.

Explanation

Fungi are non-photosynthetic eukaryotic heterotrophs that obtain nutrients by absorbing organic compounds from dead matter (saprophytism) or living hosts (parasitism). Their cell walls are composed of chitin, and they store carbohydrates as glycogen. Plants, by contrast, are photosynthetic autotrophs with cellulose cell walls that store carbohydrates as starch.

Question 49Evolution

A student uses a dichotomous key to identify an arthropod collected during an ecological survey. The organism has two body regions (cephalothorax and abdomen), four pairs of walking legs, and lacks antennae and wings. Which class of arthropods does this organism belong to?

  1. Class Insecta
  2. Class Arachnida Correct answer.
  3. Class Crustacea
  4. Class Myriapoda

Explanation

Class Arachnida (which includes spiders, scorpions, ticks, and mites) is characterized by having two main body divisions (a fused head and thorax called the cephalothorax, and an abdomen), exactly four pairs of jointed walking legs (8 legs), chelicerae, and no antennae or wings.

Question 50Cell structure, membranes and division

A microscopic unicellular organism is isolated from stagnant water in Buea. Electron microscopy reveals that it contains circular DNA free in the cytoplasm, a peptidoglycan cell wall, and 70S ribosomes, but completely lacks a nuclear membrane and membrane-bound organelles. To which kingdom does this organism belong?

  1. Kingdom Protista
  2. Kingdom Monera (Prokaryotae) Correct answer.
  3. Kingdom Fungi
  4. Kingdom Plantae

Explanation

Organisms in Kingdom Monera (Prokaryotae), such as bacteria and cyanobacteria, are characterized by a prokaryotic cell organization. They lack a true membrane-bound nucleus and membrane-bound organelles like mitochondria and endoplasmic reticulum, possessing circular DNA (nucleoid), 70S ribosomes, and a peptidoglycan (murein) cell wall.