Section 7 - Unit 19: Populations in Ecosystems

Question 1

What term is used to describe populations of different species living in the same habitat? (1 mark)

Answer 1

Community

Question 2

Explain the advantage of species occupying different niches (1 mark)

Answer 2

Less competition for food/resource

Question 3

Explain the advantage of showing data using standard deviations rather than ranges (2 marks)

Answer 3

• SD is the spread of data around the mean
• SD reduces the effect of anomalies
• SD can be used to determine whether data is significant or not

Question 4

Suggest one reason for conserving woodlands (1 mark)

Answer 4

• Conserves/protects habitats/niches
• Conserves endangered species
• Reduces global warming
• Source of medicines/chemicals/wood
• Reduces erosion

Question 5

Explain how a species could evolve (6 marks)

Answer 5

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

Question 6

Describe how you could use the mark-release-recapture method to estimate the number of a specific species (4 marks)

Answer 6

• Capture collect sample, mark and release
• Method of marking does not harm the species/make it more visible to predators
• Leave sufficient time for species to distribute before collecting a second sample
• Population = number in first sample × number in second sample / number of marked species in second sample

Question 7

Suggest two reasons why a species may become dominant in a habitat (2 marks)

Answer 7

• No/few consumers

- Species outcompetes other species/better competitor for resources

Question 8

What is a species? (1 mark)

Answer 8

Organisms that can interbreed to produce fertile offspring

Question 9

What is meant by uniformly distributed? (1 mark)

Answer 9

Same number of organisms in each region/organisms equally spread

Question 10

How do the assumptions made in proportional sampling differ from those made in mark-release-recapture? (2 marks)

Answer 10

• No assumption that organisms are uniformly distributed

- Size of total area/size of sampled region not required

Question 11

Give one assumption about the animals caught in the mark-release-recapture method (1 mark)

Answer 11

• Animals are all part of the same population

Question 12

Suggest why percentage cover is used rather than frequency to record the abundance of a species present (1 mark)

Answer 12

Difficult/too many individual organisms to count

Question 13

Explain what is meant by the ecological term community (1 mark)

Answer 13

All the groups of species/populations/all the organisms

Question 14

Describe how you could use quadrats and a transect to measure the number of seeds at different distances from a tree (2 marks)

Answer 14

• Place quadrats at intervals along transect

- Count number of seeds per quadrat to calculate seeds per m^2

Question 15

Suggest how the shape of mouth is an adaptation to its niche (2 marks)

Answer 15

• Specific mouth shape for specific food

- Competition between species/interspecific competition is reduced

Question 16

What is meant by an abiotic factor? (1 mark)

Answer 16

Non living factors

Question 17

Explain why a statistical test is necessary in analysing results (2 marks)

Answer 17

• A statistical test determines the probability of results being due to chance
• Enables null hypothesis/description of null hypothesis to be accepted/rejected
  OR
• Determines whether correlation/result is significant

Question 18

Describe how you would use quadrats to determine whether a particular plant species has a clustered or random distribution (3 marks)

Answer 18

• Use of random no.s to place quadrats
• No of individuals counted using a large of quadrats.
• Little variation- random, large variation- clustered

Question 19

Explain how succession takes place (3 marks)

Answer 19

• Species changes the abiotic conditions/temperature
• Less hostile conditions
• Decline in initial species and increase in the dominant species
• Dominant species are better competitors

Question 20

Explain why the diversity of animal species is higher towards the end of succession (2 marks)

Answer 20

• Greater variety of food/ more food sources

- Greater variety of habitats/niches

Question 21

Describe and explain how succession occurs (4 marks)

Answer 21

• Colonisation by pioneer species
• Pioneers/species/organisms change the
  environment/habitat/conditions/factors
• Environment becomes less hostile for
  other/new species
• Change/increase in diversity/biodiversity
• To climax community