Cameroon GCE O-Level Human Biology common mistakes
Cameroon GCE O-Level Human Biology · Understand the traps and how to avoid them.
When asked to explain why an enzyme stops working at high temperature, the candidate writes that the enzyme is 'killed' or 'dies', or simply says the reaction 'stops', without stating that the enzyme is a protein whose active site changes shape (denaturation) so the substrate no longer fits.
Everyday language treats anything that stops working as 'dead', and candidates memorise 'enzymes are destroyed by heat' as a slogan without linking it to the lock-and-key active-site model. Many also confuse the enzyme with the living cell that made it, so they apply the idea of cell death to a molecule.
What to do instead
Practise a fixed three-part answer for every 'effect of high temperature' question: (1) the enzyme is a protein; (2) high temperature denatures it, meaning the shape of the active site changes; (3) the substrate can no longer bind to form enzyme-substrate complexes, so the rate falls to zero. Contrast this explicitly with low temperature, where the enzyme is inactive but not denatured and works again on warming. Draw the active site before and after heating side by side.
The candidate describes the heart as pumping 'oxygenated blood around the body' without naming the chamber, valve or vessel involved, and cannot trace a drop of blood from the vena cava to the aorta, mixing up which side carries oxygenated blood.
Candidates learn a simplified slogan ('the heart pumps blood') and never build a spatial map of the double circulation. The left/right confusion arises because diagrams are drawn as if facing the patient, so the labelled 'right' appears on the reader's left.
What to do instead
Draw the heart from memory daily for a week, labelling chambers, valves, vena cava, pulmonary artery, pulmonary vein and aorta, and trace the path in numbered steps: vena cava, right atrium, right ventricle, pulmonary artery, lungs, pulmonary vein, left atrium, left ventricle, aorta. State the rule aloud: the left side of the heart carries oxygenated blood because it has just returned from the lungs; the right side carries deoxygenated blood.
In genetics questions the candidate writes phenotype ratios without a Punnett square, or writes 'the child will be a carrier' as a certainty rather than a probability, and confuses genotype with phenotype in the final sentence.
Under time pressure candidates skip the working and jump to a memorised 3:1 answer, even when the cross is a test cross or involves sex-linked inheritance. The word 'carrier' is learned as a label rather than as a heterozygous genotype with a specific probability.
What to do instead
Always show the cross: parental genotypes, gametes, Punnett square, then offspring genotypes with ratios, then phenotypes with ratios. Use the phrase 'there is a 50% chance that...' rather than 'the child will be...'. For each answer, underline the genotype and circle the phenotype so the two are visibly distinguished. Practise one test cross (heterozygote x homozygous recessive) and one sex-linked cross until the 1:1 and 1:1 male/female patterns are automatic.
For kidney questions the candidate says the kidney 'filters waste out of the blood' and calls the product 'urine' at every stage, without distinguishing filtration at the glomerulus (water, glucose, salts, urea pass into the capsule; proteins and blood cells do not) from selective reabsorption in the tubule (all glucose, some water and salts returned).
The two processes are taught in one lesson and collapse into a single word, 'filtering'. Candidates also assume that because glucose is in the blood it must appear in urine, missing the point that reabsorption normally removes it all.
What to do instead
Learn the kidney as two distinct stages with two distinct fluids: filtrate in the capsule (contains glucose) and urine in the collecting duct (contains no glucose). Write a two-column table listing each substance and whether it is filtered, reabsorbed, or neither. Then answer the classic diabetes question explicitly: if blood glucose is very high, not all glucose can be reabsorbed, so glucose appears in the urine.
When asked to explain a reflex action, the candidate writes 'the brain decides to move the hand away' or draws the pathway with the relay neurone in the wrong place, and omits the synapse or the motor neurone from the description.
Candidates reason from their own conscious experience, in which they feel the pain and then move, so they place the brain at the start of the pathway. The spinal cord route is abstract and the sequence of three neurones is easily scrambled.
What to do instead
Memorise the pathway as a fixed chain with arrows: receptor, sensory neurone, relay neurone in the spinal cord, motor neurone, effector (muscle). State the key advantage in one sentence: the relay neurone in the spinal cord allows the response before the impulse reaches the brain, so it is faster and protective. Practise labelling a blank spinal reflex arc diagram and explain why the brain is informed but not consulted.
In ecology questions the candidate uses 'food chain', 'food web' and 'energy pyramid' interchangeably, places decomposers at the top of a food chain, or states that energy is 'used up' or 'lost as heat' without saying where it goes and why only about 10% passes to the next level.
Textbook diagrams place arrows between organisms without explaining that arrows show energy flow, not 'who eats whom' alone. Decomposers are drawn separately, so candidates assume they belong at the end of the chain. Energy loss is memorised as a number without a mechanism.
What to do instead
State the arrow rule explicitly: the arrow points from the organism being eaten to the eater, and shows the direction of energy transfer. Keep decomposers out of the grazing chain and describe them as recycling nutrients from dead matter back to producers. For the 10% figure, list the reasons in order: respiration releases energy as heat, movement, excretion of undigested material, and parts not eaten. Draw a pyramid of numbers and a pyramid of energy for the same chain and explain why they can differ in shape.
The candidate answers a 'compare' or 'explain why' question with a single word or a list of nouns, for example writing 'diffusion' when asked how oxygen reaches a muscle cell, or writing 'because of osmosis' with no reference to a partially permeable membrane or a concentration gradient.
Many candidates treat the command word as decoration and answer only the topic word. They have learned definitions but not the habit of applying them to the situation described in the question stem, and they run out of time writing long answers elsewhere.
What to do instead
Before writing, underline the command word and the number of marks, then write one sentence per mark. For transport processes, use a three-part template every time: what moves, from where to where (down a concentration gradient or through a partially permeable membrane), and by which process. Check that each sentence names a mechanism, not just a substance.
When describing temperature regulation the candidate says sweating 'cools the body' but cannot say that sweat must evaporate and that evaporation takes latent heat from the skin, and gives the same response for both hot and cold conditions, or claims that hairs 'trap heat' by standing up in the heat.
The everyday phrase 'sweat cools you down' is repeated without the physics, and the hair-erector response is learned as a single fact ('hairs stand up when cold') that is then applied in the wrong direction. Candidates also forget that vasodilation and vasoconstriction act on arterioles near the skin surface.
What to do instead
Write the hot and cold responses as two opposed lists and pair each with its mechanism: sweating plus evaporation taking latent heat; vasodilation bringing more warm blood to the skin surface so more heat is lost by radiation; hairs lying flat; versus shivering releasing heat by respiration in muscles, vasoconstriction reducing blood flow near the surface, and hairs standing up to trap an insulating layer of air. State the evaporation step explicitly in every sweating answer.
In health and immunity questions the candidate says 'vaccination gives you antibodies' or 'white blood cells eat germs' without distinguishing antibody production by lymphocytes from phagocytosis by phagocytes, and confuses immunity gained by vaccination with immunity gained after an illness.
Both responses are performed by white blood cells, so candidates merge them into one vague phrase. The words 'active' and 'passive' are memorised as labels without the underlying distinction of who made the antibodies and whether memory cells are formed.
What to do instead
Build a two-column table: phagocytes engulf and digest pathogens non-specifically; lymphocytes produce specific antibodies that lock onto antigens, and memory cells give a faster second response. Then place vaccination in the table: it introduces a harmless form of the antigen so the body makes its own antibodies and memory cells, which is active immunity, just like recovery from the disease. Explain the booster dose as raising antibody levels and memory cells again.
On the skeleton the candidate names a joint as 'hinge' or 'ball and socket' but cannot give an example with the bones involved, or describes antagonistic muscles by saying 'the biceps pulls and the triceps pushes' rather than that both muscles can only pull and they work in opposing pairs.
Joint types are learned as a list of words, and the idea that a muscle can push is intuitively plausible because we feel our arms push against objects. Without a labelled example, the classification stays abstract.
What to do instead
Attach each joint type to one memorised example with named bones: hinge at the elbow (humerus, radius and ulna) allowing movement in one plane; ball and socket at the shoulder (humerus and scapula) allowing movement in all planes; pivot between the atlas and axis allowing head rotation. For muscles, state the rule in one line: muscles can only contract and pull, so they must work in antagonistic pairs; when the biceps contracts to bend the elbow, the triceps relaxes, and the reverse straightens it.