Topic 7 learn and churns

Question 1

on the islands in the Caribbean, there are almost 150 species of lizards that belong to the genus Anolis. Scientists believe that these species evolved from 2 species found on mainland USA. Explain how the Caribbean species could have evolved (6 marks)

Answer 1

1. geographical isolation
2. separate gene pools/no interbreeding/no gene flow
3. variation due to mutation
   4.different selectional pressures/environments/habitats
4. different reproductive success/ selected organisms survive and reproduce
   6.leads to change/increase in allele frequency

Question 2

It has been suggested that a new species of grass may evolve on the soil that has been polluted with copper. Explain how a new species might evolve (5 marks)

Answer 2

1. variation
2. mutation
3. some plants have the allele to survive and grow in high concentration of copper
4. adapted organisms reproduce
   5.increase in frequency of allele
5. no interbreeding/seperate gene pool

Question 3

succession occurs in natural ecosystems. Describe and explain how succession occurs (4 marks)

Answer 3

1. colonisation by pioneer species
2. pioneer species change the environment/conditions/factors
   3.environment becomes less hostile for other species
   4.changes/increase in biodiversity
   5.to climax community

Question 4

changes in ecosystem can lead to speciation. In Southern California 10000 years ago, a number of interconnecting lakes contained a single species of pupfish. increasing temperatures caused evaporation and the formation of separate lakes and streams. this led to the formation of different species of pupfish. explain how these different species evolved (5 marks)

Answer 4

1. geographical isolation
2. variation due to mutation
3. different environmental conditions/selectional pressures
4. selection for different characteristics/alleles/selected organisms survive and reproduce
5. leads to change in allele frequency

Question 5

between 1982 and 1992 the number of fish in a lake decreased. Explain how changes in phosphate concentration may have resulted in this decrease in fish population (6 marks)

Answer 5

1. increase phosphate causes increased algal bloom
2. plants block out light so plants under the surface die
3. increase in aerobic bacteria/decomposers
   4.reduced oxygen concentration in water
4. used in respiration
5. plants unable to photosynthesis so less oxygen produced

Question 6

lemmings are prey for stoats. Describe and explain the changes which occur in the lemming and stoat populations (6 marks)

Answer 6

1. state the duration of cycles
2. predator/stoat increases after prey
   3.lemmings increase due to low number of stoats
3. more food for stoats so numbers increase
   5.increased predation reduces the number of lemmings
4. number of stoats decrease due to lack of food/starvation

Question 7

explain how 2 species of lemming evolved from the original species
(4 marks)

Answer 7

1. geographical isolation of populations
   2.variation present in populations
2. different environmental conditions/different selectional pressures
3. changes in allele frequency/gene pool of populations

Question 8

describe how you would investigate the distribution of marram grass from one side of the dune to another (3 marks)

Answer 8

1. transect from one side of the dune to the other
2. place quadrants at regular intervals along line
3. count plants/percentage cover

Question 9

the final stage of succession is a climax community. During this stage the number of species in the habitat and size of each population remains fairly constant. Explain what limits the size of populations in a climax community (5 marks)

Answer 9

1. named nutrient availability
2. number of producers providing energy/light intensity affecting the rate of photosynthesis
   3.disease/predation killing weaker members of species
3. space for nest building/niches
   5.competition for named resource/ intra/interspecific competition

Question 10

what does the Hardy-Weinberg principle predict? (3 marks)

Answer 10

1. the frequency of alleles of a particular gene
   2.will stay constant from one generation to the next
   3.providing no mutation/selection/mating at random/no migration

Question 11

describe how you could estimate the size of a population of sundews (small flowers) in a small marsh (5 marks)

Answer 11

1. use a grid
   2.method of obtaining random coordinates e.g. random number generator
   3.count number/frequency in a quadrat
2. large sample and calculate the mean
3. valid method of calculating the total number of sundews

Question 12

describe how you would determine the mean % cover for beach grass on a sand dune (3 marks)

Answer 12

1. method of randomly determining the position of quadrants e.g. random number generator
2. large number of quadrants
3. divide total percentage by number of quadrants