speciation, investigating populations & succession

Question 1

Describe what is meant by speciation (allopatric)

Answer 1

• Geographical isolation;
• Separate gene pools / no interbreeding (between populations);
• Variation due to mutation;
• Different environmental/abiotic/biotic conditions / selection pressures;
• 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 2

Describe what is meant by speciation (sympatric)

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

Answer 3

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

Question 4

Describe the process of succession

Answer 4

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

Question 5

Describe random sampling
[estimation of population density]

Answer 5

• Use a grid / split area into squares/sections;
• Method of obtaining random coordinates / numbers, e.g. calculator/computer/random numbers table/random number generator;
• Count number/frequency of plants in a quadrat;
• Large sample (20+ quadrats) AND Calculate mean/average number (per quadrat/section);
• Valid method of calculating total number of ……… e.g. mean number of plants per quadrat/section/m2 multiplied by number of quadrats/sections/m2 in wood;

Question 6

Describe systematic sampling

Answer 6

• Transect/lay line/tape measure (from one side of the dune to the other);
• Place quadrats at regular intervals along the line;
• Count plants/percentage cover/abundance scale (in quadrats) OR Count plants and record where they touch line/transect;

Question 7

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

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

Answer 8

• Capture sample, mark and release;
• Appropriate method of marking suggested / method of marking does not harm fish;
• Take second sample and count marked organisms;
• No in No in Population =
No in sample1 × No in sample2 / number marked in sample 2

Question 9

Describe how you would determine how many quadrats to use when investigating a habitat.

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;

Question 10

Explain how succession results in a wide variety of fish living on coral reefs (2)

Answer 10

1. Increase in number of species
2. More habitats and niches

Question 11

Describe a method that could be used to determine the mean percentage cover of algae on coral reef (3)

Answer 11

1. Use random number generator to generate random coordinates
2. Large number of quadrats (min 20)
3. Divide total percentage by number of quadrats

Question 12

The mark release recapture method can be used to estimate the size of a fish population.
Explain how. (4)

Answer 12

1. Capture sample, mark and release
2. Appropriate method of marking suggested / method of marking does not harm fish
3. Allow time for fish to randomly redistribute before collecting second sample
4. No in Population = No in sample1 × No in sample2 divide
   Number marked in sample2

Question 13

Suggest why the mark release recapture method can produce unreliable results in very large lakes (2)

Answer 13

1. Fish may congregate
2. Unlikely fish distribute randomly

Question 14

What is meant by the term genetic drift, otherwise known as bottleneck? (1)

Answer 14

1. Random increase or decrease in allelic frequency

Question 15

What is meant by the term gene flow, otherwise known as the founder effect? (1)

Answer 15

1. Change in allelic frequency is due to migration of fertile individuals