Unit 18 - Variation and selection

Question 1

Variation

Answer 1

The differences between individuals of the same species

Question 2

Genotypic variation

Answer 2

A difference between the genotypes (alleles) of individuals of the same species

Question 3

Phenotypic variation

Answer 3

A difference between the phenotypes (physical features) of individuals of the same species

Question 4

Factors of phenotypic variation

Answer 4

• Genetic
• Environmental

Question 5

Two types of phenotypic variation

Answer 5

• Discontinuous variation
• Continuous variation

Question 6

Discontinuous variation

Answer 6

When there is a limited number of phenotypes with no intermediates e.g. blood groups

Question 7

Continuous variation

Answer 7

When there is a range of phenotypes between two extremes e.g. height

Question 8

Mutations

Answer 8

genetic changes that happen when there is a change in the DNA sequence of a cell

Question 9

Factors that can increase the rate of mutation

Answer 9

• Ionizing radiation e.g gamma rays, x-rays and high energy ultraviolet waves
• Some chemicals

Question 10

Gene mutation

Answer 10

When there is a change in the sequences of bases in DNA

Question 11

Inherited mutation

Answer 11

Occurs in a gamete

Question 12

Adaptive feature

Answer 12

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

Question 13

Hydrophytes

Answer 13

Plants that only grow in or on water

Question 14

Xerophytes

Answer 14

Plants that need very little water

Question 15

Adaptations of hydrophytes

Answer 15

• Large thin leaves with most stomata on the upper surface
• Little or no waxy cuticle on the leaves
• Long leaf stalks with large air spaces to help float
• Reduced root system due to a lack of needing to be anchored
• Aerial flowers to attract flying pollinators
• Poorly developed xylem

Question 16

Adaptations of xerophytes

Answer 16

• Thick waxy cuticle covering upper epidermis to reduce water loss
• Few stomata or stomata are sunken into pits surrounded by hair
• Curled, rolled or folded leaves to reduce surface area for transpiration
• Thick succulent stem
• Widely spread roots close to the surface
• Very deep roots

Question 17

Steps of natural selection

Answer 17

1. Variation in the inherited characteristics shown by individuals in the population
2. Population produces offspring in excess to the habitat
3. There is competition for limited resources
4. Struggle for survival where some are more likely to survive
5. Better adapted individuals survive and reproduce
6. Offspring of better adapted individuals inherit alleles to make them better adapted

Question 18

Example of natural selection

Answer 18

• Antibiotic resistant bacteria
• Pathogenic bacteria reproduces and one has a DNA mutation
• Antibiotics are used but only the drug-resistant bacterium survives
• Drug resistant bacterium thrives and reproduces

Question 19

Selective breeding

Answer 19

When humans produce varieties of animals and plants with desirable characteristics

Question 20

How selective breeding works

Answer 20

Only the individuals with the desired characteristics are allowed to breed

Question 21

Differences between natural and artificial selection

Answer 21

• Natural is done naturally whereas artificial is done by humans
• Natural is more resistant to diseases and better suited for the environment whereas artificial reduces variation and becomes susceptible to environmental change