Everything from the 4 lessons of this topic on a few pages: the key idea of each lesson, the diagram to remember, the points to learn and the traps examiners set. Read it, cover it, test yourself.
Variation is the differences between individuals of the same species. Continuous variation gives a range of phenotypes between two extremes (body length, body mass) and is caused by both genes and the environment. Discontinuous variation gives a limited number of phenotypes with no intermediates (ABO blood groups, pea seed shape and colour) and is usually caused by genes only. Mutation is genetic change and is the way new alleles are formed.
Continuous variation is not caused by the environment alone. Set the diet slider to zero in the sim: the heights still vary, because the people have different genes.
A feature measured in numbers is not automatically continuous. Shoe size is recorded in whole sizes, but foot length is really continuous. Ask whether intermediate values exist in nature.
Mutagens do not aim at particular genes. They increase the rate of mutation, but which base changes is random.
An adaptive feature is an inherited feature that helps an organism to survive and reproduce in its environment. To describe one, name the feature and link it to a problem in the habitat: cold, drought, predators, too much water. Extended: xerophytes are plants adapted to dry places and reduce water loss; hydrophytes are plants adapted to living in water.
Always link the feature to the environment. "It has thick fur" earns nothing on its own; "thick fur traps air, which insulates the fox against the cold" is an explanation.
Sunken stomata and hairs do not stop water loss completely. They trap moist air, so the concentration gradient of water vapour is smaller and the rate of diffusion out of the leaf is lower.
Natural selection: there is genetic variation within a population; organisms produce many offspring; there is a struggle for survival, including competition for resources; individuals that are better adapted to the environment have a greater chance of surviving and reproducing; they pass on their alleles to the next generation. Extended: over many generations this makes populations more suited to their environment, a process called adaptation.
The moths do not turn dark because the bark is sooty, and they do not choose to change. The dark allele was already in the population; the environment only changes which moths survive to breed.
The antibiotic does not cause the resistance mutation. The mutation happens at random; the antibiotic only selects the bacteria that already carry it.
Individuals do not adapt during their lifetime in this sense. A single moth cannot change its wing colour; only the population changes, as alleles are passed on.
In selective breeding (artificial selection) humans select individuals with desirable features, cross them to produce the next generation, and select the offspring showing the desirable features. Repeating this over many generations improves crop plants and domesticated animals. Extended: in natural selection the environment decides which individuals reproduce; in artificial selection humans decide.
Selective breeding only works on inherited variation. A plant that is large only because it grew in richer soil will not pass that on, which is why the sim's yield climbs gradually rather than in one leap.
Artificial selection can make an organism less able to survive in the wild. Very high-yield crops may need fertiliser and pesticides, and some dog breeds have breathing problems.