Module 7

Question 1

On islands in the Caribbean, there are almost 150 species of lizards belonging to the genus Anolis. Scientists believe that these species evolved from two species found on mainland USA. Explain how the Caribbean species could have evolved.

Answer 1

• Geographic(al) isolation;
• Separate gene pools / no interbreeding / gene flow (between populations);
• Variation due to mutation;
• Different selection pressures / different abiotic / biotic conditions / environments
  / habitats;
• Different(ial) reproductive success / selected organisms (survive and)
  reproduce;
• Leads to change / increase in allele frequency

Question 2

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

Answer 2

• divide the area into a grid
• use a random number generator to generate coordinates
• use a large sample size of quadrats
• place quadrats at coordinates and work out percentage cover
• divide total percentage by number of quadrats (work out mean)

Question 3

An environmental scientist investigated a possible relationship between air pollution and the size of seeds produced by one species of tree. He was provided with a very large number of seeds collected from a population of trees in the centre of a city and also a very large number of seeds collected from a population of trees in the countryside.

Describe how he should collect and process data from these seeds to investigate whether there is a difference in seed size between these two populations of trees. (5)

Answer 3

• use a random sample of seeds
• large sample so it is representative of the whole population
• measure mass
• calculate a mean and standard deviation for each population
• student t test
• see whether or not there is a significant difference between the means of the two populations

Question 4

A weed is a plant growing where it is not wanted. Fat hen is a weed which grows in some crop fields.

Describe how you could estimate the number of fat hen plants in a field. (5)

Answer 4

• split field up into a grid
• random number generator to generate coordinates
• count the number of plants in each quadrat
• large sample and calculate mean number for each quadrat
• divide area of field by area of quadrat x mean number of plants per quadrat

Question 5

In potato plant fields, fat hen plants can grow up to a height of 2 m and absorb large quantities of nutrients from the soil.
Fat hen has a negative effect on the growth of potato plants.

Use the information provided to explain why.
In your answer, name the type of competition occurring between fat hen plants and potato plants. (3)

Answer 5

• interspecific competition
• less light for potato plant so less photosynthesis
• less nitrates to produce amino acids/ DNA