Investigating Populations And Speciation

Question 1

Describe the process of succession

Answer 1

• 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 2

Describe random sampling
[estimation of population density]

Answer 2

• 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 3

Describe systematic sampling

Answer 3

• 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 4

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

Answer 4

• 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 5

Describe what is meant by speciation (allopatric)

Answer 5

• 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 6

Describe what is meant by speciation (sympatric)

Answer 6

• 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 7

Describe how bacteria can become resistant to antibiotics

Answer 7

• 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 8

Describe the process of succession

Answer 8

• 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;
• /increase in diversity/biodiversity;
• Stability increases [population/richness/abiotic factors];
• Climax community;

Question 9

Describe the mark, release, recapture technique

Answer 9

• 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 sample2;

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;

Question 11

scientists used percentage cover rather than frequency to record abundance of algae present. explain why 1

Answer 11

Difficult/too many to count / individual organisms not identifiable / too small to identify/count / grows in clumps;

Ignore: easier/quicker/representative/ more accurate, unless qualified.

Question 12

describe how you would investigate the effect of an invasion by a non native species of plant (a biotic environmental factor) over many years on the abundance of a native species on a community 3

Answer 12

1. Set up grid system with coordinates;
2. Place large number of quadrats (at coordinates) selected at random;
3. Count number of / estimate percentage cover of native plant in quadrats;
4. Repeat at same time each year (for many years);

Question 13

explain the advantage of showing data using standard deviations rather than ranges 2

Answer 13

SD is spread of data around the mean;

Accept: variation around the mean.

Accept: range is difference between highest and lowest values/extremes or range includes anomalies/outliers.

2. (SD) reduces effect of anomalies/ outliers;

Reject: (SD) removes anomalies/outliers.

3. (SD) can be used to determine if (difference in results is) significant/not significant/due to chance /not due to chance;

Ignore: reliability/accuracy/validity.