Variation and Selection.

Question 1

What is variation?

Answer 1

Variation is the differences between individuals of the same species.

Question 2

What are the two types of variation?

Answer 2

The two types of variation within a species are continuous and discontinuos.

Question 3

What is continuous variation or phenotypic variation?

Answer 3

Differences between the features of different individuals are called phenotypic variation and are caused by both genes and the environment.

Question 4

What are the 2 environmental influences of continuous variation on plants?

Answer 4

• Affected by the availability of or competition of soil nutrients, light intensity, or water.
• Their exposure to disease.

Question 5

What are the 2 environmental influences of continuous variation on animals?

Answer 5

• Availability of food or balanced diet.
• Exposure to disease.

Question 6

Give 3 examples of continuous variation.

Answer 6

Examples of continuous variation include height, body mass, and intelligence.

Question 7

What type of graph is produced by continuous variation?

Answer 7

A histogram with a smooth normal distribution curve.

Question 8

What is discontinuous variation?

Answer 8

Usually caused by genes only and results in a limited number of phenotypes with no intermediates.

Question 9

Give 5 examples of discontinuous variation.

Answer 9

Blood groups in humans, ability to tongue roll, distinct or indistinct earlobes, gender, seed shape in peas, and seed color in peas.

An organism either has the characteristic or doesn’t have it.

Question 10

What type of graph is produced by discontinuous variation?

Answer 10

When the frequencies are plotted on a bar graph, the bars cannot be linked with a smooth curve.

Question 11

What are the four sources of genetic variation in the population?

Answer 11

• Meiosis.
• Random mating.
• Random fertilization.
• Genetic mutation.
• Ionising radiation.

Question 12

What is a genetic mutation?

Answer 12

Genetic mutation is a genetic change and is the way in which new alleles are formed.

Question 13

Give four examples of ionizing radiation.

Answer 13

UV rays, X rays and gamma rays, and some chemicals.

Question 14

What is an adaptive feature?

Answer 14

An inherited feature that helps an organism to survive and reproduce in its environment e.g. giraffe.

Question 15

What is a xerophyte and give an example?

Answer 15

Xerophytes are plants that are able to exist in conditions where water is scarce and are well adapted to hot, dry environments e.g. cacti.

Question 16

Name three features of xerophyte.

Answer 16

• The leaves are reduced to spines to reduce the surface area for water loss and to deter grazing animals.
• A thick, waxy cuticle covers the plants’ surfaces and reduces transpiration.
• They have shiny surfaces which reflect heat and light
• The stomata are sunk in grooves to avoid drying winds.
• The green stem carries out photosynthesis. The stomata only open at night to take in carbon dioxide which is stored for use in photosynthesis during the day.
• The swollen stem stores water.
• Shallow roots absorb water from the lightest rainfall.
• Deep roots penetrate to a very low water table.

Question 17

What are hydrophytes?

Answer 17

Hydrophytes are plants that grow submerged or partly submerged in water.

Question 18

Name three features of a hydrophyte.

Answer 18

• The leaves and stem have very little lignin in the xylem since the leaf is supported by water.
• The leaf has a very thin cuticle since water conservation is not a problem.
• Stomata on the upper surface to allow COz uptake from the atmosphere.
• Roots, if present, are only for anchorage and they have no root hairs.
• Hydrophytes have a lot of air spaces in their stems and leaves through which gases diffuse quickly. These air spaces also provide buoyancy to keep the plant close to the light and are a reservoir for oxygen and carbon dioxide.

Question 19

What is adaption?

Answer 19

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

Question 20

What is natural selection?

Answer 20

Natural selection is the process by which organisms that are well-adapted to their environment have a greater chance to breed and pass on their genes to the next generation than those that are less well-adapted.

Question 21

Describe the process of natural selection.

Answer 21

• Variation within populations.
• Production of many offspring.
• Competition for resources.
• Reproduction by individuals that are better adapted to the environment than others.

Question 22

What are three differences between natural selection and artificial selection?

Answer 22

NATURAL SELECTION:
- Environment is the selective agent.
- No interbreeding.
- Have easy-care characteristics.

ARTIFICIAL SELECTION:
- Humans are the selective agents.
- Can lead to interbreeding.
- Individuals would no longer survive in the wild.

Question 23

What is selective breeding?

Answer 23

Over thousands of years, domestic plants and animals have changed considerably due ti artificial selection and this has resulted in improved features of economic importance to maximize the farmer’s profits.

Question 24

Give an example of natural selection.

Answer 24

Development of strains of antibiotics resistant bacteria is an example of evolution of natural selection.

Question 25

What causes antibiotic-resistant bacteria?

Answer 25

A mutation may enable a bacterium to be resistant to an antibiotic, by producing an enzyme that breaks down the antibiotic.

Question 26

What are the steps to selective breeding or artificial breeding?

Answer 26

- Humans select an individual with desirable features e.g. fast growth, high yield, disease resistance, drought resistance. - The individuals are crossed and bred to produce the next generation. - The offspring are checked to find those that show an improvement in the desired feature.