Cambridge O Level Biology · Syllabus 5090 · Relationships of Organisms with One Another and with the Environment
Biodiversity
What is Biodiversity?
The number of different species living in an area. Biodiversity counts species, not individuals, so an area containing an enormous number of organisms belonging to only two or three species has low biodiversity, while an area with the same total number of organisms spread across many species has high biodiversity. Because each species occupies a different position in the food web, falling biodiversity means fewer feeding routes and an ecosystem that is less able to absorb change.
This definition is part of the Relationships of Organisms with One Another and with the Environment chapter in Cambridge O Level Biology.
Common mistakes with Biodiversity
- “Biodiversity means the total number of organisms in an area.” Why it is wrong: a wheat field holds millions of organisms and has very low biodiversity. Exam-safe: biodiversity is the number of different species living in an area.
- “Replanting restores the forest, and sustainable means never using it.” Why it is wrong: a single-species plantation restores tree cover but not the original biodiversity; and a sustainable resource is one that is used, at a rate it can be replaced. Exam-safe: replanting restores tree cover and some habitat, but monitoring of biodiversity is needed to judge recovery. A sustainable resource is produced or replaced as rapidly as it is removed, so it does not run out.
Examiner tips on Biodiversity
- Four conclusions that lose marks. “Ban all fishing” — ignores that conservation manages use rather than ending it. “Education will solve it” — education changes understanding, not the removal rate, on its own. “Quotas always work” — they work only when set correctly and enforced. “Replanting restores the ecosystem” — it restores tree cover; biodiversity is a separate measurement. Each of these states an outcome without the mechanism or the evidence.
Questions students ask about Biodiversity
Is biodiversity the same as the number of organisms?
No. Biodiversity is the number of different species living in an area. A wheat field contains an enormous number of organisms and has very low biodiversity, because nearly all of them are one species.
Does replanting a forest undo deforestation?
Partly. Replanting restores tree cover, so soil is bound again, rain is intercepted, photosynthesis resumes and a future timber supply is secured. But a plantation of one fast-growing species provides far fewer habitats and food sources than a diverse natural forest, so much of the lost biodiversity does not return. Monitoring biodiversity, not just tree cover, is what settles whether the ecosystem has recovered.