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

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

Answer 2

1.      Males have one allele; Accept males only need one allele.

2.      Females need two recessive alleles

Question 3

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

Answer 3

1.      Crossing over;

2.      Independent segregation/assortment (of homologous chromosomes);

3.      Random fertilisation;

Question 4

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 4

1.      Small sample size;

2.      Fusion/fertilisation 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 type of gene interaction when one gene affected the expression of another (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 categoric results? (1)

Answer 8

Chi squared test

Question 9

Define gene pool. (1)

Answer 9

All the alleles in a population;

Question 10

Define species (1)

Answer 10

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

Question 11

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

Answer 11

1. 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 12

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

Answer 12

1. p + q = 1
2. p^2 + q^2 = 2pq = 1

Question 13

Describe allopatric speciation (5)

Answer 13

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.

3.      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 14

Why does speciation take a long time? (3)

Answer 14

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 15

Describe sympatric speciation (4)

Answer 15

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

5.      Cannot breed/mate to produce fertile offspring;

Question 16

Define community (1)

Answer 16

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

Question 17

Mark, Release, Recapture – Assumptions (5)

Answer 17

1. 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 18

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

Answer 18

 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 19

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

Answer 19

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 20

Why repeat/ large sample size

Answer 20

To be representative.

Question 21

Why random?

Answer 21

To avoid bias

Question 22

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

Answer 22

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

Question 23

Describe use of systematic sample to count plants (4)

Answer 23

1. 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 24

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

Answer 24

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. Increase in more different niche/habitat;

Question 25

Define niche (3)

Answer 25

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 26

Predator-Prey Relationship (4)

Answer 26

1. 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 27

Succession (5)

Answer 27

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 28

Succession – Competition (3)

Answer 28

1. 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 29

Give two features of a climax community.(3)

Answer 29

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 30

Suggest one reason for conserving woodlands. (1)

Answer 30

 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.