investigating population and succession

Question 1

Describe how bacteria can become resistant to antibiotics

Answer 1

• 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 2

Describe the process of succession.

Answer 2

• (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 3

Explain how succession results in a wide variety of fish living on coral reefs.

Answer 3

• Increase in variety/diversity of species/plants/animals OR increase in number of species/populations OR increase in species richness/biodiversity;
• Provides more/different habitats/niches OR provides greater variety/types of food OR becomes less hostile;

Question 4

Describe random sampling
[estimation of population density]

Answer 4

• 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 5

Describe systematic sampling

Answer 5

• 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 6

Describe how you would determine the mean percentage cover for beach grass on a sand dune.
Describe a method that could be used to determine the mean percentage cover of algae on a coral reef.

Answer 6

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

Question 7

Describe the mark, release, recapture technique

Answer 7

• Capture sample, ethically mark and release;
• Appropriate method of marking suggested / method of marking does not harm fish / marking does not affect survival, feeding, predation;
• Allow time for redistribution into original population;
• Take second sample and count marked organisms;
• No in Population =
  No in sample1 × No in sample2
  ———————————————–
  Number marked in sample2;

Question 8

The mark-release-recapture method can bee used to estimate the size of a fish population.
Explain how.

Answer 8

• Capture/collect sample, mark and release;
• Ensure marking is not harmful (to fish) OR ensure marking does not affect survival (of fish);
• Allow (time for) fish to (randomly) distribute before collecting a second sample;
• (Population =) number in first sample x number in second sample divided by number of marked fish in second sample;

Question 9

Suggest why the mark-release-recapture method can produce unreliable results in very large lakes.

Answer 9

• Less chance of recapturing fish OR unlikely fish distribute randomly / evenly:
• Fish may remain in one area OR fish may congregate;

Question 10

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

Answer 10

• 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;