5 high-yield, syllabus-aligned questions on Ecology, covering 14 individually creditable mark points. Each one shows the answer that scores full marks under our guide, which phrase earns which mark, and a common incomplete answer — so you can see the difference rather than guess at it.
Free to read. No account needed for anything on this page.
Every question and solution is reviewed by examiners versed in WAEC and JAMB, each with more than thirty years of experience.
Mark allocations are TopMarks’ own, written against the published syllabus and Chief Examiners’ reports. They are a guide to how these answers are usually credited, not an official marking scheme.
Define2 marks
Define ecology.
TopMarks model answer
Ecology is the scientific study of the relationship between living organisms and their environment, and of the relationships among the organisms themselves.
Suggested marking guide
1Names it as the study of living organisms in relation to their environment
2Includes the relationships between the organisms themselves
Why it scores
“Define” asks for a precise statement, and this one is worth two marks because there are two ideas in it, not one. The first mark is for organisms IN RELATION TO their environment. The second is the mark most candidates never see: ecology also studies how organisms relate to EACH OTHER — predation, competition, symbiosis. A definition that stops at “organisms and their environment” has answered only half the question.
A common incomplete answer
“Ecology is the study of the environment.”
What it costs: Scores nothing. The organisms are the subject of ecology — leaving them out turns the definition into geography. There is also no mention of relationships, so the second mark is gone too.
Key ideas to include: study, organisms, environment, relationship / interaction.
State4 marks
State four ABIOTIC (non-living) factors that affect the distribution of organisms in a fresh-water habitat.
TopMarks model answer
Light intensity. Water temperature. Concentration of dissolved oxygen. pH of the water.
Suggested marking guide
1Light
2Temperature
3Dissolved oxygen
4pH / acidity of the water
Why it scores
Four marks means four separate factors, and “State” means you write them and stop — no explanation is required and none is credited. Naming three factors in beautiful sentences scores 3, not 4. Count the marks, then count your points before you move on.
A common incomplete answer
“Light, temperature and food.”
What it costs: Two marks under this guide. Light and temperature are credited. Food availability genuinely does affect distribution — but it is a BIOTIC factor, and this question asks for abiotic ones, so it falls outside what was asked. Only three items were offered for four marks in any case.
Explain why the amount of available energy decreases at successive trophic levels in a food chain.
TopMarks model answer
Energy is lost at each trophic level as heat during respiration, and in undigested material and excretion. Typically only about ten per cent of the energy at one level is transferred to the next, although the proportion varies between ecosystems. Less energy is therefore available at each successive level, so fewer organisms can usually be supported.
Suggested marking guide
1Energy is lost at each level
2Names how it is lost — heat, respiration, excretion, undigested matter
3So less energy is available at the next level
Why it scores
“Explain” means give reasons, so each sentence must answer a “why”. The three marks map onto three linked ideas: energy is lost → here is HOW it is lost → therefore fewer organisms are supported. Notice that the chain of reasoning is what earns the marks, not the fact that energy is lost on its own.
A common incomplete answer
“Energy is lost as you go up the food chain.”
What it costs: One mark of three under this guide. It states the fact but never says HOW the energy is lost, and never completes the argument by linking that loss to the energy available at the next level — which is what the question asked about.
Key ideas to include: trophic level, energy loss, respiration, heat, ten per cent.
Describe2 marks
Describe how a food web differs from a food chain.
TopMarks model answer
A food chain shows a single, linear pathway of energy transfer from a producer through successive consumers. A food web is made up of several interconnected food chains, showing that one organism can feed on, and be fed on by, more than one other organism.
Suggested marking guide
1Food chain is a single linear pathway
2Food web is several interconnected chains
Why it scores
A difference question needs BOTH sides stated. Describing only the web leaves the examiner to supply the contrast, and examiners do not supply it. Each mark here belongs to one side of the comparison.
A common incomplete answer
“A food web is bigger than a food chain.”
What it costs: Nothing is credited. “Bigger” is not a biological difference — the difference is between a single linear pathway and several interconnected ones.
Key ideas to include: linear, pathway, interconnected, producer, consumer.
State3 marks
State three ways in which nitrogen is returned to the soil.
TopMarks model answer
By the decay of dead plants and animals through the action of decomposers. By the excretion of nitrogenous waste such as urea and urine by animals. By nitrogen fixation carried out by nitrogen-fixing bacteria in root nodules, and by lightning.
Suggested marking guide
1Decay / decomposition of dead organisms
2Excretion of nitrogenous waste
3Nitrogen fixation by bacteria or lightning
Why it scores
Three marks, three distinct routes. The commonest way to lose a mark here is to give two versions of the same route — “dead plants rot” and “dead animals rot” are one point, not two. Make sure each item you write is a genuinely different process.
A common incomplete answer
“By dead animals rotting in the soil.”
What it costs: One mark of three. Decay is correct, but excretion and nitrogen fixation are untouched, so two marks are simply left on the table.
Reading a full-mark answer is the first half. Writing one under time is the other. A free account opens exam-standard practice in Biology with the full solution on every question.