Question 2
2
The diagram shows levels of DDT, a pesticide, in an aquatic food web in Lake Kariba, Africa. Numbers represent ppm (parts per million) of DDT in fat tissue.
structured0 marks
Question 2(a)
2(a)
Justify the observation that the crocodile has a higher mean DDT level than the cormorant or tigerfish.
Mediumstructured2 marks
Answer
a. the crocodile feeds on three different species of animals / OWTTE; b. the crocodile can be a tertiary consumer while cormorant/tigerfish is a secondary consumer OR the crocodile has a higher trophic level than both the cormorant and tigerfish / vice versa; c. DDT doesn't break down/biodegrade/metabolize OR (bio)accumulates/builds up (in the fat/adipose tissues/crocodile); d. accumulation/biomagnification of DDT in the higher/across trophic levels; c. Do not award this marking point for "accumulates in the food chain". d. Trophic levels required. 2 max
Question 2(d)
2(d)
Discuss the impact of overfishing in Lake Kariba and how sustainable harvesting of resources can be assessed.
HardEssay4 marks
Answer
Impact: [2 max] a. overfishing can disrupt food chains/webs/ecosystems; b. named example from the diagram; c. decrease biodiversity / OWTTE; Assessing: [2 max] d. monitoring/measuring that the rate of harvesting of species is lower than the rate of replacement of species/OWTTE; e. monitoring/enforcing application of regulations; f. monitoring population size (over time) OR monitoring biodiversity (over time); e. Accept monitoring of regulations, e.g., size/age of fish, number in a catch, mesh size of nets, quotas, etc., but not setting of regulations. 4 max
Question 2
2
Populations evolve by natural selection due to interactions with the environment and other species within the ecosystem.
structured0 marks
Question 2(c)
2(c)
Explain how the loss of a keystone species affects an ecosystem.
Mediumstructured2 marks
Answer
a. keystone species have a disproportionate/significant/high/large effect on the structure of an ecosystem / OWTTE; b. loss of biodiversity/diversity of species will occur; c. change of population size/numbers of other species may occur; d. change/disruption in food webs/chains would occur; e. example of loss and its effect; 2 max
Question 3
3
Laboratory-scale mesocosms were built to investigate the effect of very small contaminants (nanoparticles) on ramshorn snails (Planorbarius corneus).
0 marks
Question 3(a)
3(a)
State two variables measured by the probes. 1: 2:
Easystructured2 marks
Answer
a. temperature; b. pH ; c. minerals / salt concentration / conductivity; d. \(\mathrm{O}_{2}\) (concentration); e. \(\mathrm{CO}_{2}\) (concentration); 2 max
Question 3(b)
3(b)
Suggest one advantage of using a mesocosm in this type of research.
Mediumstructured1 marks
Answer
environmentally safe/cheaper/control of variables easier;
Question 3(c)
3(c)
Outline the requirements for sustainability within a sealed mesocosm.
Hardstructured2 marks
Answer
a. photosynthetic organisms/autotrophs/plants as producers; b. light (as energy source) for photosynthesis; c. nutrient/water recycling (by saprotrophs); d. decomposers/saprotrophs to breakdown (toxic) wastes; The question is "outline", so do not accept only a list of variables without a brief account. 2 max
Question 3
3
Mean annual chlorophyll concentration was measured in surface water of Narragansett Bay along the Atlantic coast of the USA, from 1971 to 2006. Field data of chlorophyll concentrations are shown below.
0 marks
Question 3(b)
3(b)
Mesocosm experiments using water from Narragansett Bay were completed in the laboratory during a six month period. Discuss advantages and limitations of carrying out mesocosm investigations. be marked.
Mediumessay3 marks
Answer
Advantages of mesocosm experiments: a. scientist can alter/manipulate/control environmental conditions b. allows carrying out experiments with many samples / replicates c. ease of collection of continuous data Limitations of mesocosm experiments: d. difficult to mimic natural environmental conditions exactly e. Natural environments change /are not static Needs to suggest advantage and limitation for full marks. 3 max
Question 17
17
What is exchanged between a sealed mesocosm and the surrounding external environment? A. Energy B. Water C. Air D. Nothing can pass
Easymcq1 marks
Answer
A
Question 4
4
Beavers (Castor fiber) have been reintroduced into many European countries. They cut down trees and use them as a source of food as well as for building their homes and dams.
structured0 marks
Question 4(a)
4(a)
Beavers are a keystone species. Outline the importance of keystone species.
Easystructured2 marks
Answer
a. disproportionate effect/large impact on ecosystems/community structure; b. regulate (size/density of) populations of other organisms; c. maintain ecosystem stability/balance/community structure / prevent ecosystem collapse; 2 max
Question 4(c)
4(c)
Outline two methods of restoration of natural processes in ecosystems by rewilding, other than reintroducing a keystone species. 1. 2.
Mediumstructured2 marks
Answer
a. reintroduction of top/apex predators/native species/original forms OR retrobreeding/ artificial breeding/selection to restore wildtype OR remove invasive species; b. restore habitats/rehabilitate degraded habitats/re-establishment of connectivity of habitats over large areas (where natural ecosystems have become fragmented)/land protection/ reforesting; c. minimize human impact / regulate/limit/reduce/eliminate human activity in the ecosystem / creation of national parks/game/natural reserve; d. allow natural processes of regeneration and recovery; b. Do not accept "afforestation" 2 max
Question 18
18
A simple sealed terrestrial mesocosm was set up to demonstrate that natural ecosystems can be sustainable over long periods of time. What indicates that the mesocosm is still sustainable after several months? Wastes are constantly recycled. The diversity of living organisms increases. Energy is conserved. The mass of carbon increases.
Mediummcq1 marks
Answer
A
Question 18
18
Which factor(s) would be expected to vary in a closed terrestrial mesocosm? I. Carbon content II. Temperature III. Biomass I only I and II only II and III only I, II and III
Mediummcq1 marks
Answer
C
Question 19
19
Which is not essential in a viable mesocosm? Light source Autotroph Saprotroph Herbivore
Mediummcq1 marks
Answer
D
Question 4
4
Satellite imagery has been used for many years in the Amazon rainforest to monitor deforestation. Annual deforestation can be calculated using data from several satellites that have varying levels of accuracy. The graph shows the area of the Amazon rainforest that was deforested each year from 2001 to 2019, calculated using satellite images.
structured0 marks
Question 4(a)
4(a)
Calculate the percentage decrease from the maximum deforestation area on the graph to the area in 2019. Other researchers have studied deforestation in relation to the size of new clearings (deforested areas) within forests. The graphs show the numbers of new clearings smaller than 1 hectare and larger than 1000 hectares, between 2001 and 2013. 1 hectare is \(0.01 \mathrm{~km}^{2}\).
Mediumstructured1 marks
Answer
(-) 64 (\%); Allow 62 - 66 (\%). \[ \text { (28 000 - } 10 \text { 000) / } 28000 \times 100 \] Working is not required.
Question 4(b)
4(b)
Suggest a reason that the number of small clearings increased while the number of large clearings decreased greatly since 2004.
Mediumstructured1 marks
Answer
satellite imagery has improved over time (allowing smaller areas to be discerned) OR small scale farming/agriculture/clandestine logging has become more common AND government control has increased / become more effective OR laws/global pressures have reduced largescale industry/logging; Accept other reasonable responses that address both factors for the marking point e.g. more regulation on large clearings and little/none on small clearings. Accept larger areas are being reforested/disused, and smaller ones are farmed/ used more. Accept focus on reforestation of larger areas and smaller ones ignored.