This free quiz has 19 multiple choice questions on ecosystems and populations, all taken from OCR A Level Biology A exam papers. It marks itself, so you get your score as soon as you finish.
What the quiz covers (OCR A spec 6.3.1 and 6.3.2)
What an ecosystem is, and how biotic and abiotic factors affect organisms
Transfer of biomass between trophic levels and why food chains are short
Units of productivity and the efficiency of different uses of land for food
Nitrogen cycle reactions and the bacteria that carry them out
Pioneer communities and the order of plants during primary succession
Stages of a population growth curve, and competition between species
Interpreting graphs of predator and prey numbers and of plant density across a habitat
What sustainable management of an ecosystem means
How to use it
Several questions are built around a graph, diagram or table, so read the axes, labels and units before you look at the options. Watch for questions that ask which statement is not true or not correct.
Where students lose marks (from OCR examiners' reports and mark schemes)
Each point below is followed by wording that gained marks.
Energy transfer calculations: Many students multiplied by 8 when told a value was 800% greater, forgot to convert J to kJ, or lost the mark for an efficiency by not giving the significant figures asked for.
✔ Gains credit: Recognising that a value 800% greater is nine times the original, dividing by 1000 to convert J to kJ, and calculating efficiency as energy in the receiving level divided by energy in the source level, multiplied by 100, to the significant figures requested.
Preservation is not conservation: Many students called any form of protection 'conservation', giving an unrelated example or a ban on visitors, and when asked where preservation is needed they simply named a place without saying why.
✔ Gains credit: Recognising that banning visitors or restricting all human interference is preservation, while active management such as repairing boardwalks and fences, raising water levels or blocking ditches is conservation; preservation is needed where a habitat is sensitive to damage, for example because a rare or endangered species lives there.
Nitrogen cycle names and products: Many students located Rhizobium vaguely in 'roots' or 'soil', mixed up oxidation and reduction, recalled the wrong bacterial genus, or said plants convert absorbed nitrates into ammonia or nitrogen.
✔ Gains credit: Rhizobium in the root nodules of legumes, genus names spelled correctly or phonetically, the term 'nitrogen-fixing' (not 'nitrogen-fixating'), and plants using absorbed nitrates to make amino acids, proteins or nucleic acids.
Succession changes the soil: Many students missed that a change other than in the species meant the soil, offering evolution or speciation instead; some said soil was present before the first community, and some gave 'pioneer species' or 'climax population' when asked for the end point.
✔ Gains credit: Changes to the soil or substrate, such as increasing humus, a starting point of bare rock, sand, mud, water or lava rather than soil, and 'climax community' as the collective name for the final stage.
Linking explanations to the graph: Many students gave a reason such as 'plenty of food' without saying which part of the population graph it explained, explained only the rise, or wrote generally about competition and predator and prey relationships without naming which species would change.
✔ Gains credit: Explanations tied to each part of the curve, such as numbers rising while resources are available and competition is low, then levelling off or falling as competition increases, including from a species with an overlapping niche, and stating which named species would increase or decrease and why.
Ignoring facts in the stem: Many students suggested explanations the question had already ruled out, such as a top predator being eaten by a larger predator, wolves competing with herbivorous deer for food, or dropped litter attracting rats to islands that have no rats.
✔ Gains credit: Explanations consistent with the information given, such as a fall in the prey population leaving less food for the predator, deliberate killing, pesticides, pollution or disease reducing a top predator, and mammalian predators arriving on boats.
Precise sustainable harvesting methods: Many students wrote 'net size' instead of mesh size, or 'allow trees to grow' without saying they must fully regrow before the next felling, and some discussed fish farms when the question was about commercial fishing.
✔ Gains credit: Quotas, nets with a larger mesh, fishing banned at certain times or in certain areas, and strict enforcement; for timber, replanting, limiting the area felled, rotational coppicing or selective felling, and leaving time for trees to fully regrow before harvesting again.
Keep practising
Go on to the Biodiversity quiz, the Photosynthesis quiz or the Classification and Evolution quiz, or browse all our OCR A Level Biology quizzes. Our OCR A masterclasses (Year 12 on Wednesdays at 5.15pm, Year 13 on Tuesdays at 6.30pm) work through real exam questions on one topic each week.