Six causes — each with its own mechanism
Climate change moves or shrinks suitable habitat faster than a species can migrate or adapt. Habitat destruction removes the food, shelter and breeding sites needed. Hunting is deliberate killing by humans for meat, trophies or as pests. Overharvesting removes individuals faster than they can be replaced. Pollution poisons or injures organisms and degrades habitat. Introduced species out-compete, prey on, or bring disease to natives with no defence.
Four conservation methods — and only these four
Monitoring and protecting means recording population numbers and locations, then enforcing reserves and anti-poaching patrols. Education informs the public so demand for wildlife products falls and support and funding rise. Captive breeding raises animals in a controlled environment away from wild threats, aiming to reintroduce them. Seed banks store plant seeds long term at low temperature and low humidity, preserving genetic diversity for future germination.
Extinction is the end of a pathway, and it is irreversible
A population declines under one or more of the six factors, becomes endangered, then reaches extinction if nothing changes. Extinction is permanent: once a species is gone from the wild and from captivity its genetic information is lost for good, unless material such as seed was banked in advance. That is why conservation acts while a species is still endangered, before numbers reach zero.
Drawn from real examiner reports.
Endangered ≠ extinct
Endangered means the population has declined to a level that risks dying out, but living individuals still exist. Extinct means no living members remain anywhere on Earth. A species with a tiny surviving population — however small — is endangered, not extinct. Calling a severely declining species extinct loses the definition mark.
Hunting ≠ overharvesting
Hunting is the deliberate killing of individuals by humans for meat, trophies or as perceived pests. Overharvesting is removing individuals by ANY method — fishing, logging, collecting or hunting — faster than the population can reproduce and replace itself. Overharvesting is defined by the RATE of removal, not the method, so a merged "over-hunting" earns no credit.
Captive breeding ≠ seed bank
Captive breeding raises animals in a controlled environment for eventual reintroduction to the wild. A seed bank stores plant seeds — it breeds nothing. Naming captive breeding for a threatened plant, or a seed bank for a threatened animal, is a mismatch that costs the mark even though both sit on the syllabus list of four methods.
Habitat destruction is a cause, not a method
Habitat destruction is a CAUSE of a species becoming endangered — food, shelter and breeding sites are cleared. Monitoring and protecting species and habitats is the conservation METHOD that answers that cause by preventing further loss. Listing habitat protection as a cause, or destruction as a method, reverses the logic of the whole sub-topic.
Naming a factor is not explaining it
The causes statement carries the command word explain, so naming pollution or an introduced species and stopping there scores nothing. State the mechanism — HOW the factor kills, injures, out-competes or removes breeding sites — then how that lowers survival or reproduction, then the effect on population size.
Flagged digest cross-cutting note: command word not answered; points not matched to tariff
Climate change ≠ ozone depletion
Rising carbon dioxide traps heat and causes global warming, which shifts the temperature and rainfall a species depends on. Candidates routinely blame the ozone layer instead. Ozone depletion is a separate problem with a different cause, and invoking it in a climate-change answer removes the mechanism the mark scheme wants.
Flagged Jun 2023 P31 Q11bii
Answer a cause as a four-step chain
Name the syllabus factor, state the mechanism by which it reduces survival or breeding, state the effect on population size, then state the outcome — endangered, or extinct if numbers reach zero. Four linked steps carry a 3-4 mark explain question; a bare factor name none.
Match the method to the stated problem
Do not list all four methods. A small, fragmented animal population points to captive breeding; a threatened plant to a seed bank; poaching to monitoring and protecting; public demand for wildlife products to education. Name the one method that fits and say how it operates.
Describe still needs detail — then count the marks
The conservation statement uses describe, so a bare method name is not enough: add one sentence on what it involves in practice. Then check the tariff — a 4-mark question wants four creditable points, usually two methods with a detail each, not four bare names.
Endangered species — a species whose population has declined to a level that puts it at risk of extinction in the near future.
Extinct — a species that has no living members left anywhere on Earth.
Species — a group of organisms that can interbreed to produce fertile offspring.
Six causes of a species becoming endangered or extinct, and their mechanism:
| Cause | Mechanism |
|---|---|
| Climate change | Shifts temperature/rainfall patterns and moves or shrinks suitable habitat faster than the species can migrate or adapt |
| Habitat destruction | Removes or reduces food, shelter and breeding sites the species needs |
| Hunting | Deliberate killing of individuals by humans (meat, trophies, or as perceived pests) |
| Overharvesting | Removing individuals (by any method) faster than the population can reproduce and replace itself |
| Pollution | Harmful substances poison, injure or kill organisms directly, or reduce habitat quality |
| Introduced species | A non-native species out-competes, preys on, or brings new disease to a native species with no natural defence |
Four conservation methods for endangered species (limited to these):
| Method | What it involves |
|---|---|
| (a) Monitoring and protecting species and habitats | Recording population numbers/locations, and enforcing protected areas or legal restrictions (e.g. anti-poaching patrols) |
| (b) Education | Informing the public about causes/consequences of endangerment, to change behaviour and build support |
| (c) Captive breeding programmes | Breeding animals in a controlled environment away from wild threats, aiming to reintroduce individuals to the wild |
| (d) Seed banks | Storing plant seeds long-term to preserve genetic diversity and allow future germination |
Define "endangered species".
Define the terms endangered species and extinct, and explain how the two terms relate to each other. (3 marks)
