18) Variation and selection

Question 1

1.1. Describe variation

Answer 1

Differences between individuals of the same species

Question 2

1.2. What is continuous variation?

Answer 2

A range of phenotypes between two extremes
(e.g. body length and body mass)

Question 3

1.3. What is discontinuous variation?

Answer 3

A limited number of phenotypes with no intermediates
(e.g. ABO blood groups, seed shape and colour in peas)

Question 4

1.4. What causes discontinuous variation vs continuous variation?

Answer 4

Discontinuous caused only by genes

Continuous variation caused by genes + environment

Question 5

1.6. Describe mutation

Answer 5

Genetic change

Question 6

1.7. How are new alleles formed?

Answer 6

Mutation

Question 7

1.8. What increases the rate of mutation?

Answer 7

Ionising radiation and some chemicals

Question 8

1.9. Describe gene mutation

Answer 8

A random change in the base sequence of DNA

Question 9

1.10. What are sources of genetic variation in populations?

Answer 9

Mutation, meiosis, random mating and random fertilisation

Question 10

2.1. Describe an adaptive feature

Answer 10

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

Question 11

2.3.1. Explain the adaptive features of hydrophytes to their environments

Answer 11

Large air spaces in leaves: keep them close to water surface where there is more light for photosynthesis

Small roots as they can also extract nutrients from surrounding water through their tissues

Stomata always open and mainly found on upper epidermis where they can exchange gases more easily with the air

Question 12

2.3.2. Explain the adaptive features of xerophytes to their environments

Answer 12

Thick waxy cuticle: prevents evaporation, shiny surface reflects heat, lowering temperature

Stomata sunk in pits in the epidermis: moist air trapped lengthens the diffusion pathway and reduces evaporation rate

Leaf rolled with stomata inside and inner surface covered in hairs traps moist air, preventing air movement across stomata which reduces transpiration

Small, needle-shaped leaves which reduce the surface area, aka the evaporating surface

Extensive shallow roots for quick absorption of large quantities of water when it rains

Thick leaves/stems have cells that store water

Question 13

3.1. Describe natural selection

Answer 13

(a) There is genetic variation in populations

(b) More offspring is produced than the environment can support

(c) This causes a struggle for survival and competition for resources

(d) Individuals with characteristics most suited to the environment have a higher chance of survival and more chances to reproduce

(e) These individuals pass on their alleles to the next generation, and there will be a greater number of individuals with the better adapted variations in characteristics

Question 14

3.2. Describe selective breeding

Answer 14

(a) Humans select individuals with desirable features

(b) They cross these individuals to produce the next generation

(c) Only some offspring show the desirable features

(d) This process is repeated for many generations before a “new breed” reliably shows those characteristics in all offspring

Question 15

3.3.1. Outline how selective breeding by artificial selection is carried out over many generations to improve crop plants

Answer 15

Disease resistance in food crops

Increased crop yield

Hardiness to weather conditions (e.g. drought tolerance)

Better tasting fruits

Large or unusual flowers

Question 16

3.3.2. Outline how selective breeding by artificial selection is carried out over many generations to improve domesticated animals

Answer 16

Cows, goats and sheep that produce lots of milk or meat

Chickens that lay large eggs

Domestic dogs that have a gentle nature

Sheep with good quality wool

Horses with fine features and a very fast pace

Question 17

3.4. Describe adaptation

Answer 17

The process, resulting from natural selection, by which populations become more suited to their environment over many generations

Question 18

3.5. What is an example of natural selection?

Answer 18

The development of strains of antibiotic
resistant bacteria

Question 19

3.6. Outline the differences between natural and artificial selection

Answer 19

Natural VS Artificial

Populations develop features better adapted to their environment and survival VS features useful to humans, not necessarily to the survival of the individual

Usually takes a long time VS takes less time as only individuals with desired features allowed to reproduce