variation and selection

Question 1

variation

Answer 1

differences between individuals of the same species

Question 2

two types of phenotypic variation:

Answer 2

discontinuous variation and continuous variation

Question 3

Discontinuous variation

Answer 3

limited number of phenotypes

Question 4

Continuous variation

Answer 4

a range of phenotypes between two extremes

Question 5

What are mutations?

Answer 5

genetic changes

Question 6

how are new alleles formed?

Answer 6

through mutation

Question 7

Factors that increase the rate of mutations:

Answer 7

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

Question 8

gene mutation

Answer 8

a change in the sequence of bases in DNA

Question 9

sources of genetic variation in population:

Answer 9

• Mutations
• Meiosis
• Random mating
• Random fertilization

Question 10

adaptive feature

Answer 10

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

Question 11

hydrophytes

Answer 11

plants that only grow on water

Question 12

xerophytes

Answer 12

plants that need very little water

Question 13

hydrophyte adaptations

Answer 13

• 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

Question 14

xerophyte adaptations

Answer 14

• 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

Question 15

steps of natural selection (6)

Answer 15

1. There is variation in the inherited characteristics shown by individuals in a population.
2. Populations tend to produce many offspring, more than can be supported in the habitat where they live.
3. There is competition between individuals for limited resources such as food, mates or space
4. There is a struggle for survival in which some individuals are more likely to survive than others
5. Individuals that are better adapted to their environment are more likely to survive and reproduce
6. 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.

Question 16

selective breeding

Answer 16

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

Question 17

selective breeding steps

Answer 17

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