Natural selection and speciationEdexcel A-Level Biology B: Flashcards
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What is natural selection?
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- What is natural selection?
- Individuals with advantageous alleles are more likely to survive and reproduce, so those alleles increase in frequency in the next generation.
- What is a selection pressure? Give two examples.
- An environmental factor that affects survival and reproduction, e.g. predation, disease, competition for food.
- Define evolution.
- A change in the allele frequencies of a population over many generations.
- What is the original source of new alleles?
- Random mutation.
- What is an anatomical adaptation? Give an example.
- A structural feature that aids survival, e.g. thick fur or long hind legs.
- What is a physiological adaptation? Give an example.
- A process in the body that aids survival, e.g. producing concentrated urine to save water.
- What is a behavioural adaptation? Give an example.
- The way an organism acts to increase survival, e.g. nocturnal feeding or hibernation.
- Define niche.
- The role of a species in its ecosystem, including where it lives, what it eats and when it is active, determined by its adaptations.
- What is allopatric speciation?
- Speciation in which populations are separated by a geographical barrier, so gene flow stops and they diverge into new species.
- What is sympatric speciation?
- Speciation in the same area with no physical barrier, caused by reproductive isolation such as different breeding times or polyploidy.
- What is reproductive isolation?
- Populations can no longer breed together to produce fertile offspring, so gene flow between them stops.
- Why does antibiotic resistance spread quickly in bacteria?
- Short generation times, large populations, strong selection from antibiotics, and horizontal transfer of resistance alleles on plasmids.
- What is the 'evolutionary race' between pathogens and medicines?
- Pathogens evolve resistance to a medicine, so new medicines are needed, which then select for further resistance.
Exam questions on Natural selection and speciation
- Rock pocket mice live in the Arizona desert. On pale sandy ground most of the mice have pale fur, but on areas of dark volcanic rock most have dark fur. Owls hunt the mice by sight at night. Fur colour is controlled by a single gene with a dark allele and a pale allele, and mice of both fur colours are born in both types of area.Explain how natural selection has led to a higher proportion of dark-furred mice on the dark rock.2 marks
- The kangaroo rat lives in North American deserts. It has long, powerful hind legs and a long tail, spends the hot day in a cool burrow, forages for seeds at night, and produces very small volumes of highly concentrated urine.Explain how the kangaroo rat's behaviour of spending the day in a burrow increases its chance of survival in the desert.2 marks
- About 10 000 years ago a river changed course and became a wide, fast-flowing barrier that ground squirrels cannot cross, splitting one population into two. The environment differs on the two sides: one side is dry scrubland and the other is woodland. The two populations now differ in body size and breeding season, and in captivity their members do not produce fertile offspring.Explain how the change in the course of the river could have led to the formation of two species of ground squirrel.3 marks
Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).