AQA GCSE Combined Science (8464), Higher tier · Biology › Inheritance, variation and evolution › The development of understanding of genetics and evolution
Practise Extinction. 11 exam-style questions plus unlimited generated ones on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
A species is extinct when no individuals of that species remain alive. You need the factors that can cause extinction and to apply them to examples in 'suggest why' and data questions.
Grade by grade
What you need to be able to do, from the first marks up to the top grade.
3
Define extinctionA species is extinct when there are no remaining individuals of that species still alive.
4
List the causes of extinctionEnvironmental change, new predators, new diseases, new competitors and catastrophic events.
5
Give examples of catastrophic eventsMassive volcanic eruptions or collisions with asteroids.
6
Explain how a factor leads to extinctionLink the factor to fewer individuals surviving and reproducing until none are left.
7
Explain why variation reduces extinction riskSome individuals are more likely to have characteristics that let them survive the change.
7
Suggest causes from information givenUse clues in a description or data to name the factor and explain its effect.
Notes
What extinction is
A species is extinct when there are no remaining individuals of that species still alive.
Extinction is permanent: the species and its alleles are lost for ever.
Fossils show that very many species that once lived are now extinct.
Causes of extinction
Changes to the environment over geological time, such as changes in climate. If a species cannot survive in the new conditions, it dies out.
New predators, e.g. animals brought to an island by humans that eat native animals or their eggs.
New diseases: if no individuals are resistant, the whole population can be killed.
New, more successful competitors that take the food, space or other resources the species needs.
A single catastrophic event, such as a massive volcanic eruption or a collision with an asteroid. An asteroid collision is thought to have contributed to the extinction of the dinosaurs.
Which species are most at risk
Species with little genetic variation: there may be no individuals with characteristics that help them survive a change.
Species facing a rapid change: natural selection takes many generations, so there may not be time for the population to change.
Species with small populations, or that live in only one place such as a single island.
Cheatsheet
Extinct = no individuals of the species remain alive
Causes: changes to the environment over geological time; new predators; new diseases; new, more successful competitors; a catastrophic event
Catastrophic events: massive volcanic eruptions, collisions with asteroids
Little variation or rapid change → greater risk of extinction
How to answer each type of question
Give factors that can cause extinction
1 to 3 marks4
Choose from: environmental change, new predators, new diseases, new competitors, catastrophic events.
Give clearly different factors, not two versions of the same one.
Example. Give three factors that can cause a species to become extinct. [3 marks]
Show the model answer
Any three: changes to the environment, e.g. climate (1); new predators (1); new diseases (1); new, more successful competitors (1); a catastrophic event such as an asteroid collision or a massive volcanic eruption (1).
Suggest why a species became extinct
2 to 3 marks6
Find the clue in the information (a new animal arrived, the climate changed, a disease spread).
Name the factor.
Explain the effect: fewer survive and reproduce, until the population falls to zero.
Example. A species of flightless bird lived only on one island. Sailors brought rats to the island. The rats ate the birds' eggs. Within 100 years the bird species was extinct. Explain why the bird became extinct. [3 marks]
Show the model answer
The rats were a new predator on the island (1). The birds had no defence against them, so many eggs were eaten (1). Fewer young birds survived to reproduce, so the population fell until none were left (1).
Explain why variation reduces the risk of extinction
2 to 3 marks7
More variation means some individuals are likely to have characteristics suited to the change.
They survive, reproduce and pass on their alleles.
So the species does not die out.
Example. Explain why a species with a lot of genetic variation is less likely to become extinct when a new disease appears. [3 marks]
Show the model answer
With more variation, some individuals are more likely to be resistant to the disease (1). These individuals survive and reproduce (1), passing on the alleles for resistance, so the species does not die out (1).
Shortcuts and memory tricks
Causes of extinction: 'Every Panda Dreads Catastrophic Competition' (Environment change, Predators, Diseases, Catastrophes, Competitors).
'New' is the key word: new predators, new diseases, new competitors.
Where marks are lost
Writing 'the environment changed' without explaining how that stopped the species surviving and reproducing.
Confusing extinct with endangered. An endangered species still has living individuals.
Giving 'humans' as a cause without saying what humans did (e.g. brought in a new predator, destroyed a habitat).
Exam technique
Use the clues in the question: examiners expect you to name the factor that is described.
Link each factor to its effect on survival and reproduction.
When asked for several factors, make each one clearly different.
Quick recall
Cover the answers and test yourself. The app has these as flashcards that come back just before you'd forget them.
Many species that once lived on Earth are now extinct. What does extinct mean?
There are no living individuals of the species left
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy4 marks
Many species that once lived on Earth are now extinct.
(a) What does extinct mean?[1]
(b) Which two of the following could cause a species to become extinct? Tick (✓) two boxes.[2]
A new disease
A new predator
An increase in the food supply
A decrease in the number of competitors
An increase in the area of habitat
(c) Give one other factor that could cause a species to become extinct.[1]
Show the answer and mark scheme
(a)Answer: There are no living individuals of the species left
there are no living individuals of the species left (anywhere)
(b)Answer: A new disease; A new predator
(c)
new / more successful competitors
changes to the environment / climate over geological time
a single catastrophic event, e.g. an asteroid collision / massive volcanic eruption
habitat destruction (by humans)
hunting / overfishing by humans
Question 2Medium6 marks
A species of flightless bird lived only on one small island. The birds nested on the ground. In 1880, ships brought rats to the island for the first time. Rats eat eggs and chicks. {table} shows the number of breeding pairs of the bird on the island.
[object Object]
(a) Calculate the percentage decrease in the number of breeding pairs between 1870 and 1910.[2]
(b) Suggest why the arrival of rats caused this species of bird to become extinct.[3]
(c) Suggest one other factor that may have contributed to the extinction of this bird.[1]
Show the answer and mark scheme
(a)Answer: 74.2%
(1200 − 310) ÷ 1200 × 100
74.2 (%)
(b)
rats were a new predator (on the island)
the birds had no adaptations / defences against rats (e.g. they nested on the ground)
rats ate eggs / chicks, so fewer young survived to breed
(so) deaths were greater than births / the population kept falling
the birds could not fly away / lived only on this island, so they could not escape
(c)
rats may have competed with the birds for food
rats / people may have brought a new disease
habitat destruction by people who arrived on the ships
hunting by people
Question 3Hard8 marks
About 66 million years ago, a large asteroid hit the Earth. Scientists think that about three-quarters of all species on Earth became extinct soon afterwards, including most dinosaurs. The impact threw huge amounts of dust into the atmosphere, which blocked much of the sunlight for several years.
(a) Explain how blocking sunlight could cause large animals, such as plant-eating dinosaurs and the carnivores that ate them, to become extinct.[4]
(b) Many small animals that ate seeds, insects or dead material survived. Suggest why.[2]
(c) Explain how fossils could show that many species became extinct at about the same time.[2]
Show the answer and mark scheme
(a)
less light so less photosynthesis
(so) many plants / producers died / less plant biomass was produced
herbivores had less food so starved / died
carnivores had less prey / food so died
large animals need large amounts of food
temperatures fell, so many plants and animals could not survive
(b)
seeds can survive for a long time without light / seeds were still available after plants died
there was plenty of dead material (after many organisms died)
small animals need less food
small animals can shelter / burrow to avoid the cold
small animals reproduce quickly, so populations could recover
(c)
fossils of many species are found in rock layers older than 66 million years
but are not found in younger rock layers (above the 66-million-year layer)