18. Variation

Question 1

Variation

Answer 1

Differences between individuals of the same species.

Question 2

Genotypic variation

Answer 2

Differences in genotype between individuals

–> occurs because of different combination of alleles

Question 3

Phenotypic variation

Answer 3

Differences between the phenotypes of organisms

–> occurs due to different genotypes + different environmental factors

Question 4

Two types of phenotypic variation

Answer 4

Continuous variation
–> Range of phenotypes between two extremes. (eg. height)

Discontinuous variation
–> A particular characteristic can be divided into distinct categories. (eg. blood groups)

Question 5

Mutation

Answer 5

Genetic change.

Happens when the sequence of bases is altered.

If a mutation occurs in a gamete –> they can be inherited

(How new alleles are formed)

Question 6

How do mutations occur?

Answer 6

Naturally through DNA replication errors

–> rate of mutation can increase due to…

• Ionising radiation
• Certain chemicals

Question 7

Causes of variation

Answer 7

• Mutations
• Meiosis
• Random mating
• Random fertilisation

Question 8

Adaptive features

Answer 8

An inherited feature that increases the fitness of an organism, and helps it to survive and reproduce in its environment.

Question 9

Birds - Adaptive features (hawk vs hummingbird)

Answer 9

Beak shaped for diet

Hawk - Hooked + sharp for flesh

Hummingbird - Thin + long for nectar

Question 10

Hares - Adaptive features (arctic vs american desert)

Answer 10

Both…

• Widely spaced eyes (to see predators because of the wide field of vision)
• Long + mobile ears (hearing is adapted to low sounds + many angles)
• Long strong hind legs + large feet (rapid movement)

Arctic hare - Smaller ears to reduce heat loss + brown fur during summer but white during winter.

American desert hare - larger ears to increase heat loss + brown fur all year round

Question 11

Hydrophytes

Answer 11

Plants that only grow in or on water (water-lily)

Question 12

Xerophytes

Answer 12

Plants that need very little water (cactus)

Question 13

Hydrophytes - Adaptations

Answer 13

• Large, thin leaves + stomata on the upper surface instead of the lower surface (which would be below water)
• Little/no waxy cuticle since water loss isn’t a problem
• Long leaf stalks (with air spaces to help them float)
• Barely any roots since they’re not anchored to the ground
• Aerial flower → flying pollinators
• Xylem allows for water transport (but has no structural support as the stem doesn’t need to hold the flower upright/instead the flower floats on water).

Question 14

Xerophytes - Adaptations

Answer 14

• Thick waxy cuticle limiting water loss
• Few stomata/ stomata in sunken pits surrounded by hair → reducing water loss
• Leaves are curled or rolled → Reduces surface area available for transpiration (through stomata)
• Thick stem (for water storage)
• Widespread root system close to soil surface (for better water absorption)
• Long tap roots (to absorb water from underground aquifers)
• Leaves = sharp spines / needles (deter herbivores + limit water loss)

Question 15

Natural selection - Stages

Answer 15

1) Overproduction of species
2) Genetic variation
3) Selective pressure (only some survive)
4) Survival of the fittest (adaptive feature)
5) Increase in alleles in population

Question 16

Natural selection of bacteria - Stages

Answer 16

1) Bacteria asexually reproduce thorugh binary fission

2) Some bacteria mutate to become antibiotic-resistant

3) Antibiotics are used

4) Only antibiotic resistant bacteria survive.

5) The resistant bacteria are able to multiply and increase.