variation and selection

differences between individuals of the same species

discontinuous variation and continuous variation

limited number of phenotypes

a range of phenotypes between two extremes

genetic changes

through mutation

• ionising radiation such as gamma rays, X-rays and high energy ultraviolet electromagnetic waves. • some chemicals.

a change in the sequence of bases in DNA

• Mutations • Meiosis • Random mating • Random fertilization

an inherited feature that helps an organism to survive and reproduce in its environment

plants that only grow on water

plants that need very little water

• large, thin leaves with most stomata on the upper surface rather than lower surface • little or no waxy cuticle on their leaves because water loss is not a problem • long leaf stalks with large air spaces to help them float • a reduced root system because they do not need to be anchored in the ground • aerial flowers to attract flying pollinators • poorly developed xylem tissue that allows the transport of water but provides little support

• a thick waxy cuticle covering the upper epidermis of the leaves to reduce water loss • few stomata, or stomata that are sunken into pits surrounded by hair to reduce water loss by transpiration ( • curled, rolled or folded leaves, which reduce the surface area available for transpiration • a thick succulent stem • widely spread roots that are close to the surface, so the plant can absorb as much water as possible even when there is limited rainfall, or • very deep roots to reach underground water sources

• There is variation in the inherited characteristics shown by individuals in a population. • Populations tend to produce many offspring, more than can be supported in the habitat where they live. • There is competition between individuals for limited resources such as food, mates or space • There is a struggle for survival in which some individuals are more likely to survive than others • Individuals that are better adapted to their environment are more likely to survive and reproduce • The offspring of the better adapted individuals are more likely to inherit alleles that make them better adapted to the environment. They are more likely to survive to reproduce successfully than other individuals in the population.

the method used by humans to produce varieties of animals and plants with desirable characteristics

• humans select those individuals with most desirable features • those individuals are bred • offspring that display the desirable features are selected for further breeding