Topic 18

Question 1

Variation

Answer 1

Differences between individuals of the same species -> caused by genes (inherited variation) or the environment

Question 2

Continous variation

Answer 2

. Range of phenotypes which vary between two extremes
. Caused by bothe genes and the environment
EG: body length and body mass

Question 3

Discontinous variation

Answer 3

. Limited number of phenotypes with no intermediates
. Caused by genes only
EG: ABO blood groups, seed shape in peas and seed colour in peas

Question 4

Investigating continous variation in organisms

Answer 4

1. Ask each person to remove their shoes
2. Use a measuring tape to measure from the top of a person’s head to the ground
3. Record the height of the person using a suitable table
4. Plot your height data aginst the number of people, and compare the shape of your plot to the graph on previous page

Question 5

Mutations

Answer 5

Gene mutation: random change the base sequence of DNA -> when mutations occur within a gene they result in a different version of the gene called and allele
-> Increasing the rate of mutation:
. Ionising radiation
. Chemicals called mutagens

Question 6

Sources of genetic variation

Answer 6

. Mutation
. Random mating
. Meiosis
. Random fertilisation

Question 7

Adaptive features

Answer 7

Characteristics that an organism inherits which help it to survive and reproduce in its environment

Question 8

Plants in extreme environments: Xerophytes

Answer 8

Xerophytes: plants adapted to live in dry climates
. Stomata: sunk in pits and surrounded by hairs -> these slow transpiration down because they both trap a layer of humid air close to the leaf’s surface
. Rolled leaves: trap humid air
. Thick, waxy layer on epidermis: reduces water loss by evaporation
-> Example: marram grass

Question 9

Plants in extreme environments: Hydrophytes

Answer 9

Hydrophytes: plants adapted to live in the water
. Air spaces: so the plants can float on the surface of water and be exposed to the most light
. Stomata: only present on the upper surface of floating leaves -> helps maximise gas exchange
. Stems are felxible: help prevent damage from currents
-> Example: water lillies

Question 10

Natural selection

Answer 10

Results in those organisms that are better adapted to their environment being more likely to survive

Question 11

How natural selection happens

Answer 11

. Genetic variation within populations
. Production of many offspring
. Struggle for survival (competition for resources)
. A greater chance of reproduction by individuals that are better adapted to the environment than others
. Better adapted individuals pass on their alleles to the next generation

Question 12

Adaptation

Answer 12

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

Question 13

Antibiotic resistance: Bacteria

Answer 13

Sometimes develop random mutations in their DNA -> these can create new alleles, which can change the bacteria’s characteristics

Question 14

Antibiotic resistance

Answer 14

Shows adaptation

Question 15

Selective breeding

Answer 15

humans artificially select the plants or animals that are going to breed so frequency of alleles for desired characteristics increases in a population

Question 16

Process involved in selective breeding

Answer 16

1. Selection by humands of individuals with desirable features
2. Crossing these individuals to produce the next generation
3. Selection of offspring showing desirable features

Question 17

Artificial VS natural selection: Artificial selection

Answer 17

. The individuals that reproduce have characteristics that humans think are desirable
. Faster process
. Only happens to organisms humans choose
. Involves breeding from closely related organisms, which causes inbreeding (variation in a population is reduced and individuals may be more likely to have genetic disorders)
. If a new disease appears or the environment changes, the chances that the population will survive are lower for offspring of artificially selected organisms as there’s not much variation in the population

Question 18

Artificial VS natural selection: natural selection

Answer 18

. The individuals that survive and reproduce have characteristics that suit their environment
. Long and slow process
. Happens to all wild organisms
. Individuals are ‘healthier’ as they’re less likely to be inbread
. Chances of survival are increased for the population of offspring as there’s more variation in the population