18 - Variation and Selection

Question 1

Define variation

Answer 1

Differences between individuals (3)
of the same species (2)

Question 2

Differentiate continuous and discontinuous variation

Answer 2

Continuous variation results in a range of phenotypes (between two extremes) (2)
Discontinuous variation results in a limited number of phenotypes with no intermediates (2)
Discontinuous variation is usually caused by genes only whereas continuous variation is caused by genes and the environment (1)

Question 3

Define mutation

Answer 3

Mutation is genetic change (1)
Mutation is the way in which new alleles are formed (2)
(Gene) mutation is a random change in the base sequence of DNA (2)

Question 4

State sources of genetic variation in populations

Answer 4

mutation, meiosis, random mating, and random fertilization (2 for each)

Question 5

Describe and explain the adaptive features of xerophytes

Answer 5

Xerophytes need to be able to survive in extreme dry conditions - they have
A thick, waxy cuticle to limit evaporation, shiny to reflect sunlight (1)
Sunken stomata to trap moist air, reducing evaporation (1)
Small leaves to reduce surface area for evaporation (1)
Extensive shallow roots to allow for maximal water evaporation at once (1)
Thickened leaves/stem to allow for more storage of water (1)

Question 6

Define an adaptive feature

Answer 6

An inherited feature (1)
that increases the fitness of an organism (1)
helping it survive and reproduce in its environment (3)

Question 7

Describe and explain the adaptive features of hydrophytes

Answer 7

Hydrophytes are adapted to live underwater - they have
Large air spaces in leaves to to keep them close to the surface of water (1)
Small roots to extract nutrients from surrounding water through their tissues (2)
Stomata usually open and found on upper epidermis to exchange gases easier (in the air) (2)