Method questions

Question 1

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

Answer 1

1. Method of randomly determining position (of quadrats) e.g. random numbers table/generator;
   Ignore line/belt transect
2. Large number/sample of quadrats;
   Accept many/multiple
   Ignore point quadrat
   If a specified number is given, it must be 20 or more
3. Divide total percentage by number of quadrats/samples/readings;

Question 2

The scientists concluded that the results shown in Figure 1 were due to succession taking place.
Use Figure 1 to explain why the scientists reached this conclusion.

Answer 2

1. Beach grass is the pioneer (species);
2. Pioneers/named species change the (abiotic) environment/habitat/conditions/factors;
   Must convey idea of change being caused by a species
   Accept example of change e.g. more humus
3. (So) less hostile for named species
   OR
   (So) more suitable for named species;
4. Conifer/hardwood trees represent climax community;

Question 3

Anolis sagrei is a species of lizard that is found on some of the smallest Caribbean islands. Describe how you could use the mark-release-recapture method to estimate the number of Anolis sagrei on one of these islands.

Answer 3

1. Capture / collect sample, mark and release;
2. Method of marking does not harm lizard / make it more visible to predators;
3. Leave sufficient time for lizards to (randomly) distribute (on island) before collecting a second sample;
4. (Population =) number in first sample × number in second sample divided by number of marked lizards in second sample / number recaptured.

Question 4

Large areas of tropical forest are still found on some Caribbean islands. The concentration of carbon dioxide in the air of these forests changes over a period of 24 hours and at different heights above ground.
Use your knowledge of photosynthesis and respiration to describe and explain how the concentration of carbon dioxide in the air changes:
• over a period of 24 hours
• at different heights above ground.

Answer 4

1. High concentration of / increase in carbon dioxide linked with respiration at night / in darkness;
2. No photosynthesis in dark / night / photosynthesis only in light / day;
   Neutral: less photosynthesis
3. In light net uptake of carbon dioxide / use more carbon dioxide than produced / (rate of) photosynthesis greater than rate of respiration;
4. Decrease in carbon dioxide concentration with height;

Question 5

The rate of water movement through a shoot in a potometer may not be the same as the rate of water movement through the shoot of a whole plant.
Suggest one reason why.

Answer 5

Plant has roots
OR
xylem cells very narrow;

Question 6

The student wanted to determine the rate of water loss per mm2 of surface area of the leaves of the shoot in Figure 1.
Outline a method she could have used to find this rate. You should assume that all water loss from the shoot is from the leaves.

Answer 6

1. Method for measuring area;
   e. g. draw round (each) leaf on graph paper and count squares;
2. Of both sides of (each) leaf;
3. Divide rate (of water loss / uptake from potometer) by (total) surface area (of leaves);

Question 7

Describe how the mark-release-recapture method could be used to determine the population of A. aegypti at the start of the investigation.

Answer 7

1. Capture / collect / sample, mark and release;
2. Leave time for mosquitoes / Aedes to disperse before second sampling / collection;
3. (Population =) number in first sample × number in second sample divided by number of marked in second sample / number recaptured;

Question 8

The scientists set up their cultures in sterile glass bottles.
Suggest one suitable method for sterilising the bottles and explain why it was necessary to sterilise them.

Answer 8

1. Suitable method;
   eg in boiling water / steam / autoclave / wash in disinfectant / wash in alcohol

Accept radiation
2. (Reason) to remove / kill other bacteria / organisms that might break down ammonia;