Where does the variation that natural selection acts on come from?

From mutations, which produce new variants of genes.

Describe the steps by which natural selection leads to evolution.

Mutation produces variation, the best suited individuals survive and breed, they pass their variants to their offspring, and over many generations those variants become common in the population.

What happens to an individual whose phenotype is poorly suited to its environment?

It is less likely to survive long enough to reproduce, so its variants are passed on less often.

Does an individual organism evolve during its own lifetime?

No, individuals do not evolve; it is the population that changes across generations.

OCR GCSE Combined Science Biology J250

Cell Level Systems

Topic overview Microscopy, and sub-cellular structures DNA structure: polymer, double helix and nucleotides Enzyme action, and investigating enzymes Cellular respiration as an exothermic process Aerobic and anaerobic respiration compared Synthesis and breakdown of carbohydrates, proteins and lipids Photosynthesis: producers and the process Photosynthesis as endothermic, and investigating it Limiting factors in photosynthesis

Community Level Systems

Topic overview Cycling materials, and the role of microorganisms The carbon and water cycles, and decomposition Levels of organisation, and abiotic and biotic factors Interdependence, competition, mutualism and parasitism

Genes, Inheritance and Selection

Topic overview Genetic terms, and the genome Genome, environment and mutations Haploid, diploid and meiosis Single gene inheritance and Punnett squares Sex determination and characteristics controlled by many genes Variation within a population, and classification Natural selection and evolution Evidence for evolution from fossils and antibiotic resistance

Global Challenges

Topic overview Field investigations, and human impact on ecosystems Maintaining biodiversity, monitoring conservation and ecotourism Selective breeding and genetic engineering Health, disease, and types of disease Interactions between diseases, and how they spread Reducing the spread of disease, and named examples White blood cells, antibodies and platelets Non-specific defences and the immune system Vaccines, medicines and aseptic technique Developing new medicines, and non-communicable disease Treating cardiovascular disease, and lifestyle factors Cancer, and the use of stem cells in medicine Gene technology in medicine, and the human genome

Organism Level Systems

Topic overview The nervous system and coordinated responses The reflex arc Hormonal coordination, thyroxine and adrenaline Hormones in reproduction and the menstrual cycle Contraception and treating infertility Homeostasis and control systems in the body Insulin and glucagon in blood sugar control Type 1 and type 2 diabetes

Scaling Up

Topic overview Diffusion, osmosis and active transport Mitosis, the cell cycle and cell differentiation Stem cells in animals and meristems in plants Surface area to volume ratio and exchange surfaces The circulatory system, the heart and blood vessels Red blood cells and plasma Root hair cells, transpiration and translocation Xylem and phloem Factors affecting water uptake, and the potometer

Genes, Inheritance and Selection

Natural selection and evolution

3 things to know
Paper 8 (Biology)

Overview

What natural selection is, where variation comes from, the steps from mutation to a changed population, why individuals do not evolve, what evolution and a species are, and how new species form.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

A population is split in two by a mountain range. Explain how this can lead to two new species.

Key term

What is natural selection?

Key term

Explain why natural selection cannot work without variation.

Questions from this subtopic

Each one with the model answer underneath.

1
What is natural selection?
Model answer
The process by which individuals whose phenotypes are best suited to their environment are the most likely to survive and reproduce.
2
Where does the variation that natural selection acts on come from?
Model answer
From mutations, which produce new variants of genes.
3
Describe the steps by which natural selection leads to evolution.
Model answer
Mutation produces variation, the best suited individuals survive and breed, they pass their variants to their offspring, and over many generations those variants become common in the population.
4
Explain why natural selection cannot work without variation.
Model answer
If every individual were identical none would be better suited than another, so there would be nothing for selection to act on.
5
What happens to an individual whose phenotype is poorly suited to its environment?
Model answer
It is less likely to survive long enough to reproduce, so its variants are passed on less often.
6
Does an individual organism evolve during its own lifetime?
Model answer
No, individuals do not evolve; it is the population that changes across generations.

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Cell Level Systems

Community Level Systems

Genes, Inheritance and Selection

Global Challenges

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AA diet high in sugar and fat leads to obesity.

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