Unit 7

Question 1

Define phenotype. (2)

Answer 1

1. Expression of genetic constitution of an organism/genotype;
2. And its interaction with the environment;

Question 2

Define genotype. (1)

Answer 2

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;
   Accept males only need 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/assortment (of homologous chromosomes);
3. 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/fertilisation of gametes is random;
2. Linked Genes;
3. Epistasis;
4. Lethal genotypes;

Question 6

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

Answer 6

Co-dominance

Question 7

Name the type of gene interaction when one gene
affected the expression of another (1)

Answer 7

Epistasis

Question 8

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

Answer 8

on same chromosome.

Question 9

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 9

1. Chi squared test; 2. Categorical data.

Question 10

Define gene pool. (1)

Answer 10

All the alleles in a population;

Question 11

Define species (1)

Answer 11

Organisms that) can breed together /
interbreed and produce fertile offspring;

Question 12

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

Answer 12

No mutations (arise);
2. Random mating;
3. Large population;
4. Population is isolated / no flow of alleles
into or out of population;
5. No selection / all alleles equally likely to be
passed on to next generation;

Question 13

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

Answer 13

1. p + q = 1
2. p2 + q2 = 2pq = 1

Question 14

Describe allopatric speciation (5)

Answer 14

1. Geographical isolation; 2. Reproductive separation/isolation OR
   No gene flow
   OR
   Gene pools remain separate;
   Accept no interbreeding but must be a separate idea from mp5 which relates to definition of a species.
   Reject no inbreeding.
2. Different selection pressures; 4. Variation due to mutations; 5. Different allele/s passed on/selected OR
   Change in frequency of allele/s; 6. Eventually different species cannot (inter)breed to produce fertile offspring;

Question 15

Why does speciation take a long time? (3)

Answer 15

1. Initially one/few animals with favourable
   mutation/allele;
2. Individuals with (favourable) mutation/allele
   will have more offspring;
3. Takes many generations for (favourable)
   mutation/allele to become the most common
   allele (of this gene);

Question 16

Natural Selection in Resistant Strains (5)

Answer 16

1. Some individuals in population naturally resistant/not killed by pesticide/antibiotic;
2. Due to mutation;
3. These survive when pesticide/antibiotic
   applied/non-resistant ones are killed;
4. To reproduce and pass on allele/gene (for
   resistance);
5. Increase in frequency of allele for
   resistance;

Question 17

Describe sympatric speciation (4)

Answer 17

1. Not geographically isolated; 2. mutation causes reproductive isolation 3. Gene pools kept separate/no gene flow; 4. Different allele/s passed on / selected OR
   Change in frequency of allele/s
2. Cannot breed/mate to produce fertile offspring;

Question 18

Define community (1)

Answer 18

All / group of species / all / group of
populations / all the organisms;

Question 19

Mark, Release, Recapture – Assumptions (5)

Answer 19

No emigration/immigration;
2. No losses to predation;
3. Marking does not affect survival;
4. Birth rate and death rate equal;
5. (In this case) all belong to one population;

Question 20

Mark, Release, Recapture – Outline the method (4)

Answer 20

1. Capture/collect sample, mark and release;
2. Ensure marking is not harmful (to fish) OR
   Ensure marking does not affect survival (of fish);
3. Allow (time for) fish 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 21

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

Answer 21

1. Use a grid
   OR
   Divide area into squares/sections;
2. Method of obtaining random coordinates/numbers e.g. calculator/computer/random numbers table/generator;
3. Count number/frequency in a quadrat/section;
   .
4. Large sample and calculate mean/average number (per quadrat/section); 5. Valid method of calculating total number of plant, e.g. mean number of plants per quadrat/section/m2 multiplied by number of quadrats/sections/m2 in area;

Question 22

Why repeat/ large sample size

Answer 22

So /representative;

Question 23

Why random

Answer 23

Avoid bias;

Question 24

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

Answer 24

too many to accurately count / individual organisms not identifiable / too small to identify / overlap;

Question 25

Describe use of systematic sample to count plants (5)

Answer 25

Systemic sampling (placing quadrat) at regular intervals along transect line; 2. Transect line from/to ........; 3. Count number/frequency in a quadrat/section; 4. Large sample and calculate mean/average number (per quadrat/section);

Question 26

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

Answer 26

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. Increase in more different niche/habitat;

Question 27

Define niche (3)

Answer 27

. 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 28

Predator-Prey Relationship (4)

Answer 28

As pest numbers increase more food or 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 as fewer are eaten;

Question 29

Succession (5)

Answer 29

1. (Colonisation by) pioneer species; 2. Pioneers/species/organisms change the environment/habitat/conditions/factors; 3. (Environment becomes) less hostile for other/new species Accept previous species out-competed. 4. increase in diversity/biodiversity; 5. (To) climax community;

Question 30

Succession – Competition (3)

Answer 30

Pioneer species increases then decreases; 2. Principle of a species changing the conditions / a species makes the conditions; 3. New/named species better competitor /pioneer species outcompeted;

Question 31

Give two features of a climax community.

Answer 31

1. Same species present (over long time) / stable community (over long time); 2. Abiotic factors (more or less) constant (over time) 3. Populations stable (around carrying capacity)

Question 32

Suggest one reason for conserving woodlands. (1)

Answer 32

1. Conserving / protecting habitats / niches; 2. Conserving / protecting (endangered) species / maintains / increases (bio) diversity; 3. Reduces global warming / greenhouse effect / climate change / remove / take up carbon dioxide; 4. Source of medicines / chemicals / wood; 5. Reduces erosion / eutrophication.