Unit 7

Question 1

Define Phenotype (2)

Answer 1

1. Expression of genetic constitution of an organism
2. And its interaction with the enviroment

Question 2

Define Genotype (1)

Answer 2

1. The genetic constitution of an organism

Question 3

If a gene is sex-linked on the X chromosome, why is the phenotype more common in XY organisms? (2)

Answer 3

1. Males have one allele
2. Females need two recessive alleles

Question 4

Mutation is one cause of genetic variation in
organisms.
Give two other causes of genetic variation.(2

Answer 4

1. Crossing over
2. Independent segregation
3. Causes random fertilisation

Question 5

In genetic crosses, the observed phenotypic ratios obtained in the offspring are often not the same as the expected ratios.
Suggest two reasons why. (2)

Answer 5

1. Small sample size
2. Fusion of gametes is random
3. Linked Genes
4. Epistasis
5. Lethal Genotypes

Question 5

Name the relationship between two alleles when both alleles appear in the phenotype (1)

Answer 5

Co-Dominance

Question 6

Name the relationship between the two alleles when both alleles appear in the phenotype (1)

Answer 6

Epistasis

Question 7

Explain what it means when two genes are linked (1)

Answer 7

On the Same chromosome

Question 8

Which statistical test could the scientist use to
determine whether his observed results were
significantly different from the expected results?
Give the reason for your choice of statistical test.
(2)

Answer 8

1. Chi Squared Test
2. Categorical Test

Question 9

Define Gene Pool (1)

Answer 9

All alleles in a population

Question 10

Define species (1)

Answer 10

Organisms that can breed together and produce fertile offspring

Question 11

The conditions under which the
Hardy-Weinberg Principle
applies (5)

Answer 11

1. No mutations
2. Random mating
3. Large Population
4. Isolated Population
5. No selection pressure

Question 12

What are the two equations used in the Hardy-Weinberg equation? (2)

Answer 12

1. P + Q = 2
2. P2 + Q2 = 2PQ = 1

Question 13

Describe Allopatric Speciation (5)

Answer 13

1. Geographical Isolation
2. Reproductive separation
3. Different selection pressures
4. Variation due to mutations
5. Different alleles passed on
6. Eventually different species cannot interbreed to produce fertile offspring

Question 14

Why does speciation take a long time? (3)

Answer 14

1. Initially few animals with favourable allele
2. Individuals with allele will have more offspring
3. Takes many generations for favourable mutation to become the most common allele

Question 15

Natural Selection in Resistant Strains (5)

Answer 15

1. Some individuals in population are naturally resistant
2. Due to mutation
3. These survive when non-resistant are killed
4. To reproduce and pass on the allele for resistance
5. Increase in frequency of allele for resistance

Question 16

Describe sympatric speciation (4)

Answer 16

1. Not Geographically isolated
2. Mutation causes reproductive isolation
3. Gene pools kept separate
4. Different alleles are passed on
5. Cannot breed to produce fertile offspring

Question 17

Define Community (1)

Answer 17

All groups of populations living and interacting with each other in an area

Question 18

Assumptions with Mark, Release and Recapture (5)

Answer 18

1. No Immigration
2. No losses to predation
3. Marking does not affect survival
4. Birth rate and Death rate equal
5. All belongs to one population

Question 19

Outline method of Mark, Release and Recapture (4)

Answer 19

1. Capture sample, mark then release
2. Ensure marking isn’t harmful to survival
3. Allow time for organism to randomly distribute before collecting a second sample
4.  (Population =) number in first sample × number in second sample divided by number of marked fish in second sample/number recaptured

Question 20

Describe how you could estimate the size of a population using random sampling (4)

Answer 20

1. Use a grid
2. Method of obtaining random numbers, example random number generator
3. Count number in a quadrat
4. Large sample and calculate the mean
5. Valid method of calculating total number of plants, example mean number of plants per quadrat

Question 21

Why repeat/large sample size? (1)

Answer 21

So representative

Question 22

Why random? (1)

Answer 22

Avoid bias

Question 23

The scientist used percentage cover rather
than frequency to record the abundance of
algae present. Suggest why. (1)

Answer 23

Too many to accurately count

Question 24

Describe use of systematic sample to count plants (5)

Answer 24

1. Systemic sampling at regular intervals along transect line
2. Transect the line from measurement told
3. Count number in a quadrat
4. Large sample and calculate mean

Question 25

Effect of increased plant/animal diversity on ecosystem (3)

Answer 25

1. Increase in plant diversity leads to more different types of food for animals
2. Increase in variety of animals leads to increase in predator species
3. Increases in more different niche

Question 26

Define Niche (3)

Answer 26

1. Niche is the role that a species plays in within a community
2. Includes food resources
3. No two species can occupy identical niche

Question 27

Predator-Prey Relationship (4)

Answer 27

1. As pest numbers increase, more predators, so they increase
2. Increased predation of pests reduces numbers
3. Low number of pests results in less food for predators so their numbers decrease
4. Low predator numbers allow pest population to rise

Question 28

Describe Succession (5)

Answer 28

1. Colonisation by pioneer species
2. Pioneers change the environment
3. Changes make the environment less hostile for new species
4. Increase in Diversity
5. To climax community

Question 29

Describe Competition in Succession (3)

Answer 29

1. Pioneer species increases then decreases
2. Principle of a species makes the conditions
3. New species are better competitor so pioneer species outcompeted

Question 30

Give two features of a climax community (3)

Answer 30

1. Same species present over long time
2. Abiotic Factors are constant over time
3. Populations are stable

Question 31

Suggest one reason for conserving woodlands (1)

Answer 31

1. Conserving habitats
2. Protecting endangered species
3. Reduces global warming
4. Source of medicines
5. Reduces Erosion

Question 32

Succession occurs in natural ecosystems. Describe and explain how succession occurs (4)

Answer 32

1. Colonisation by pioneer species
2. Pioneer species change the environment
3. Makes the environment less hostile for new species
4. Increase in diversity/biodiversity