(B) Explain Why the Term Dry Weight Is Used

1. The graph below shows the variation in insect biomass (measured in g m–2 dry weight) over the period of a year, in a shrubland ecosystem, on the west coast of South America. Note that the months along the horizontal axis commence in July, which is winter in the southern hemisphere.

Months

[Source: Cody et al, (1977), Convergent Evolution in the Consumer Organisms in the Mediterranean, Chile and California, Dowden, Hutchinson and Ross.]

(a) Define the term biomass.

......

(1)

(b) Explain why the term dry weight is used.

......

(1)

......

(3)

(d) Describe and evaluate a method for the estimation of the changes in plant biomass in an ecosystem over a period of a year.

......

(4)

(Total 9 marks)

2. (a) Examine the diagram below. It is not intended to represent any particular ecosystem and the organisms are not shown to the same scale. Choose one of the organisms shown in the diagram.

Write its name here ......

[Source: Adapted from Adds, J et al. The Organism and the Environment, 2nd edition (1997), page 81]

For the organism you have chosen, describe and evaluate a method for estimating its abundance.

......

(5)

(b) Explain why it might be important to know the abundance of the species of organisms in an ecosystem in assessing that ecosystem’s diversity.

......

(2)

......

(2)

(d) (i) Name and briefly describe an ecosystem of which you have made a special study.

......

(1)

(ii) Describe one human activity that might influence your chosen ecosystem.

......

(1)

(iii) State one abiotic factor that might be changed by this human activity.

......

(1)

(iv) Explain how this human activity might change the abiotic factor.

......

(2)

(v) Outline how you would measure changes in this abiotic factor.

......

(2)

(e) (i) Explain, with an example, what is meant by the term environmental gradient.

......

(2)

(ii) Explain how you would measure the changes in the species diversity of an ecosystem along an environmental gradient.

......

(2)

(Total 20 marks)

3. Figure 1

(a) Construct a key in the space below to identify the six organisms in figure 1 above by their visible physical characteristics. In your key, refer to each organism by letter, you are not expected to name them.

(4)

(b) State one method, other than a key, by which you might identify an organism that you do not recognize.

......

(1)

(c) (i) Name an organism in an ecosystem that you have studied and state one abiotic factor that might affect this organism.

Organism: ......

Factor: ......

(1)

(ii) Outline how you would measure changes in the abiotic factor over time.

......

(2)

(iii) Explain the ways in which a human activity might affect the organism selected in (c)(i).

......

(3)

(Total 11 marks)

4. The data in the graph below show the variation in the numbers of mule deer (a herbivore) in an area of the southwestern United States between 1905 and 1940.

[D Lack, The Natural Regulation of Animal Numbers, (Oxford: Clarendon Press, 1954).
Reproduced by permission of Oxford University Press]

(a) Describe and explain the shape of the graph.

......

(4)

(b) Outline how data for this graph might have been collected.

......

(3)

......

(3)

(d) Outline how you would measure the net primary productivity of a named ecosystem.

......

(4)

(e) (i) For the ecosystem named in (d), identify an abiotic factor that might change over time, and suggest how this change might influence a named biotic component in the ecosystem.

......

(2)

(ii) Outline and evaluate a method, which you could use in the field, to gather evidence for your suggestion in (e) (i).

......

(4)

(Total 20 marks)

5. The table below gives the mean dry weight biomass for the primary producers in certain ecosystems.

Ecosystem / Biomass/kg m–2
Tropical rainforest / 45.0
Deciduous forest / 35.0
Boreal (coniferous) forest / 30.0
Grassland / 6.0
Tundra / 0.6
Desert / 0.2
Freshwater lake / 0.1

(a) (i) Define the term dry weight biomass.

......

(1)

(ii) For one of the ecosystems listed above, describe and evaluate a method for obtaining such dry weight biomass data.

Selected ecosystem ......

Method ......

......

(4)

(iii) Name one abiotic factor important in the ecosystem you have selected, and describe how you would study its variation over time.

......

(3)

The table below gives the number of individuals of four species of trees in two small patches of Australian forest.

Tree species / Area A / Area B
Allocasurina huegelina / 4 / 1
Banksia grandis / 5 / 8
Eucalyptus calophylla / 7 / 9
Acacia saligna / 4 / 2

(b) (i) Using the formula for Simpson’s diversity index

D =

calculate which of area A or area B has the higher diversity index. Show your working.

......

(3)

(ii) Name one environmental factor that might explain this difference.

......

(1)

The sketch below shows four types of termite found in Australia. (Termites are burrowing, colonial insects.)

[Source: ‘Some Termites from Western Australia’, (1989).
Reprinted with the permission of the Western Australian Gould League Inc.]

(c) (i) List three characteristics displayed by the organisms illustrated above that might be used to construct a key to assist in identifying termites from the same part of Australia.

......

(2)

(ii) Name two methods, other than the use of a key, that you might use to identify an insect you had not seen before.

......

(2)

(iii) Bearing in mind that termites live in colonies of many thousands of individuals, and that these colonies sometimes form large mounds, suggest how you might estimate the number of termites on five hectares of land. Evaluate your methods.

......

(4)

(Total 20 marks)

6. Groups of students studied the species diversity of the beetle fauna found on two upland sites in Europe. The same number of students searched for a similar length of time in each of the two sites. The two sites were of equal area.

Aphodius beetle (enlarged)

[http://commons.wikimedia.org/wiki/File:Aphodius_bimaculatus.png]

The number of individuals of the four species found at each site is given in the table below.

Species / Site A / Site B
Trichius fasciatus / 10 / 20
Aphodius lapponum / 5 / 10
Cincidela campestris / 15 / 8
Stenus geniculatus / 10 / 2

(a) Define the term biodiversity.

......

(1)

(b) Calculate the Simpson diversity index (D) for the beetle fauna of the two sites using the formula:

D =

where N = total number of individuals
and n = the number of individuals of each species.

Show your working.

(i) Site A:

......

(2)

(ii) Site B:

......

(2)

(iii) State which site has the greater beetle diversity and give a possible cause for this difference.

......

(1)

(c) (i) Describe how you might estimate the population of one of these beetle species in 0.1 hectare of upland vegetation.

......

(4)

(ii) State two factors that might influence the accuracy of the results you obtain using the method described in (c) (i).

......

(2)

(d) Suggest how you might identify a species of beetle that you had not seen before.

......

(1)

(e) (i) Name and briefly describe an ecosystem you have studied, and name an abiotic factor that influences the abundance of organisms within it.

......

(1)

(ii) For the ecosystem and the abiotic factor named in (e) (i), describe how you would measure an environmental gradient.

......

(4)

(iii) Explain how a named human activity might affect the abiotic factor in the ecosystem selected in (e) (i).

......

(2)

(Total 20 marks)

7. Figures 1 and 2 show population data for the mayfly (Ephemerellal subvaria) in two similar streams, A and B, in Minnesota, USA. Data were collected on population size (number of mayfly m–2) and mean mass of mayfly between September 1970 and June 1971.

Figure 1: Population dynamics of mayfly in streams A and B

Stream A / Stream B
Month / Number of mayfly m–2 / Mean biomass /
g m–2 / Mean mass of mayfly / mg / Number of mayfly m–2 / Mean biomass /
g m–2 / Mean mass of mayfly / mg
September / 6350 / 1.4 / 0.2 / 5251 / 1.2 / 0.2
October / 4432 / 4.6 / 1.0 / 2001 / 1.3 / 0.6
November / 4082 / 6.6 / 1.6 / 905 / 0.7 / 0.8
December / 4053 / 10.8 / 2.6 / 400 / 0.4 / 1.1
January / 3660 / 13.0 / 3.5 / 123 / 0.2 / 1.7
February / 2007 / 12.8 / 6.3 / 99 / 0.2 / 2.4
March / 1587 / 18.4 / 11.6 / 98 / 0.3 / 3.2
April / 230 / 4.9 / 21.5 / 80 / 0.9 / 11.4
May / 84 / 1.8 / 22.4 / 34 / 0.3 / 10.6
June / 44 / 1.0 / 23.6 / 24 / 0.4 / 20.0

Figure 2: Population size and mean mass plotted against time for mayfly in streams A and B
(Both graphs plotted using the data above)

[Adapted from Waters and Crawford, Limnology and Oceanography (1973), Volume 18, pages 286-296.
© 1973 by the American Society of Limnology and Oceanography.]

(a) (i) Using the data in Figures 1 and 2, describe the relationship between population size and mean mass for mayfly in stream A.

......

(2)

(ii) Outline two differences in the populations of stream A and stream B during the study period.

......

(2)

(iii) Calculate the percentage change in the population of mayfly in stream A from September to June.

......

(1)

(b) (i) Define the term biomass.

......

(1)

(ii) Sketch below the values for mean biomass against time for stream A and stream B. (The data are available in Figure 1.) Label your graph lines.

(2)

......

(2)

(ii) Mayfly occupy an important niche at the lower end of the food chain. Predict, giving reasons, the impact of mayfly population change between September and June in stream B on other organisms within the stream.

......

(2)

(d) (i) Scientists wish to assess the abundance of a brown trout (Salmo trutta) population within a chalk stream using the Lincoln index. Describe a possible method for this.

Brown trout

[Courtesy of Alberta Sustainable Resource Development.]

......

(3)

(ii) It is suspected that a number of abiotic factors may influence the biology of the chalk stream. Outline three abiotic factors that may be important in the stream.

......

(3)

(iii) Both mayfly and brown trout are r-strategists. Outline what this means.

......

(2)

(Total 20 marks)

8. An ecological study has been carried out in a small deciduous woodland. The aim of the study is to establish the baseline ecological conditions within the site as part of an environmental impact assessment.

As part of the ecological survey, floral diversity has been monitored on a species by species basis. The results for primroses (Primula vulgaris) are shown below. Ten 50 cm × 50 cm quadrats were positioned randomly within the woodland and the number of primroses in each quadrat were recorded. The results are shown in table 1.

Table 1. Primrose counts

Quadrat / Number of Primroses
1 / 10
2 / 23
3 / 23
4 / 34
5 / 12
6 / 56
7 / 12
8 / 8
9 / 5
10 / 23

(a) (i) Calculate the mean number of primroses per quadrat.

......

(1)

(ii) Using the mean number of primroses, calculate their density per metre square of woodland.

......

(2)

(iii) Outline an environmental gradient that might be present in a woodland.

......

(1)

(iv) Outline a possible method for measuring changes along this gradient.