Investigating Populations

Question 1

Describe what is meant by speciation (allopatric) (8)

Answer 1

1. Geographical isolation;
2. Separate gene pools / no interbreeding (between populations);
3. Variation due to mutation;
4. Different environmental/abiotic/biotic conditions / selection pressures;
5. Selection for different/advantageous, features/characteristics/mutation/ /allele;
6. Differential reproductive success / (selected) organisms survive and reproduce;
7. Leads to change in allelic frequencies;
8. Cannot breed/mate to produce fertile offspring.

Question 2

Describe what is meant by speciation (sympatric) (7)

Answer 2

• NOT Geographical isolation;
• Leads to reproductive isolation
• Separate gene pools / no interbreeding (between populations);
• Selection for different/advantageous, features/characteristics/mutation/ /allele;
• Differential reproductive success / (selected) organisms survive and reproduce;
• Leads to change in allelic frequencies;
• Cannot breed/mate to produce fertile offspring.

Question 3

Describe how bacteria can become resistant to antibiotics (6)

Answer 3

1. Variation/variety (due to mutation)
2. Mutation;
3. Some plants have allele to survive/grow/live in high concentration of copper/polluted soils;
4. (Differential) reproductive success / adapted organisms reproduce;
5. Increase in frequency of allele;
6. No interbreeding (with other populations) / separate gene pool / gene pool differs (from other populations);

Question 4

Describe the process of succession (7)

Answer 4

1. Colonisation by pioneer species;
2. Pioneers cause change in environmental abiotic / biotic factors(give an example);
3. Pioneers make the environment less hostile for new species;
4. New species change/make conditions less suitable for previous species;
5. Change/increase in diversity/biodiversity;
6. Stability increases [population/richness/abiotic factors];
7. Climax community;

Question 5

Describe random sampling
[estimation of population density] (6)

Answer 5

• Use a grid
• Method of obtaining random coordinates = random number generator;
• Count number of plants in a quadrat;
• Large sample (20+ quadrats)
• Calculate mean/average number (per quadrat/section);
• Valid method of calculating total number of = mean number of plants per quadrat * number of quadrats

Question 6

Describe systematic sampling (3)

Answer 6

• Transect
• Place quadrats at regular intervals along the line;
• Count plants in quadrats
  OR
• Count plants and record where they touch transect;

Question 7

Describe how you would determine the mean percentage cover for beach grass on a sand dune (4)

Answer 7

• Method of randomly determining position (of quadrats) e.g. random numbers table/generator;
• Large number/sample of quadrats; (min 20)
• Divide total percentage by number of quadrats/samples/readings;

Question 8

Describe the mark, release, recapture technique (5)

Answer 8

1. Capture sample, mark and release;
2. method of marking does not harm fish;
3. Take second sample and count marked organisms;
4. No in No in Population =
5. No in sample1 × No in sample2 / Number marked in sample2;

Question 9

Describe how you would determine how many quadrats to use when investigating a habitat (5)

Answer 9

• Calculate running mean/description of running mean;
• When enough quadrats, this shows little change/levels out (if plotted as a graph);
• Enough to carry out a statistical test;
• A large number to make sure results are reliable;
• Need to make sure work can be carried out in the time available