Bacteria and fungi are micro-organisms, and important decomposers, obtaining their food by saprophytic nutrition;
When plants and animals die, bacteria & fungi secrete enzymes to break down the dead matter into simple organic and inorganic substances, of which some is absorbed and most is released into the environment;
Many of these inorganic substances released into the soil/water are needed for the growth of the producers/plants;
As the decomposers feed on the dead matter, they take in organic nutrients where the carbon becomes part of the decomposers’ bodies;
When the decomposers respire, they release carbon dioxide (an inorganic end product of decomposition) into the air (abiotic environment), which makes it available for photosynthesis;
2. Explain the significance of photosynthesis and respiration in the carbon cycle.
Photosynthesis is where inorganic carbon in carbon dioxide is converted into organic carbon molecules (eg. glucose) and enters the biotic environment (living organisms);
Respiration is where organic carbon molecules are converted back into inorganic carbon dioxide and returns to the abiotic (non-living) environment;
3. (a)(i) Explain what is meant by the term food chain and give an example of a food chain involving four organisms, beginning with a tree as the producer.
(ii) Draw and label a pyramid of energy and a pyramid of numbers for this food chain. [3]
(b) Use the food chain you have shown to illustrate how energy enters, passes through and leaves the food chain. [4]
(c) What is biological amplification and what effect does it have on biological equilibrium? [3]
ANSWERS
(a) (i) Food chain: A series of organisms through which energy is transferred in material form/shows flow of energy and material;
Any correct food chain(4 organisms) beginning with the Tree, eg. Tree -> Caterpillar -> Sparrow -> Eagle
(a) (ii) Correct drawing and labelling of pyramid of energy (should have proper pyramid shape, producer forms bottom level)
Correct drawing and labelling of pyramid of numbers (Bottom level representing tree should have a small bar, with the primary consumer having a longer bar on top of it)
(b)
• Energy flow is unidirectional/non-cyclical.
• It is either utilised or lost to the surroundings.
• Producers (Tree) carry out photosynthesis to store the radiant energy of the sun as chemical energy in the organic compounds/carbohydrates, proteins they formed.
• Energy is lost in respiration i.e. active transport during ion uptake, synthesis of amino acids, lipids enzymes.
• Chemical energy in these organic compounds is passed on to the primary consumers (must be named) when primary consumers eat the plant.
• Chemical energy is passed on to the secondary consumers (must be named) when they eat the primary consumers, and then the energy is passed on to the tertiary consumers (must be named) when they eat the secondary consumers.
• Energy is progressively lost to the environment. At each trophic level mainly as heat from respiration (90%). Respiration/energy loss/heat loss between trophic levels; e.g. energy used by predators to catch prey;
• Only some(10%) of energy in the prey biomass converted to predator biomass (growth and formation of new tissues)/ Successive members of the food chain only incorporates 10% of available energy as only some of the energy in prey biomass passed on, e.g. not all parts edible;
• When the organisms die, they decompose the remaining energy is converted to biomass of the decomposers or released to the environment as heat.
(c)
• Biological amplification is accumulation of chemicals in organisms along the food chain.
• e.g. the use of chemicals such as DDT can lead to unwanted side effects by killing animals that are not pests.
• Insecticides sprayed on farm produce may have washed into the waters during rainfall and enter into the producers/primary consumers may eat plants sprayed with insecticides.
• DDT enters the food chain because it is non-biodegradable,
• it remains and accumulate in the body of the animal. e.g. otter which eat fish have higher amounts than plant eaters/ eagles that eat birds may have higher amounts compared to birds that have consumed the caterpillars.
• Animals higher up the food chain/otter eating fish have highest contamination.Any predator higher up the food chain will also be accumulate more DDT in their body.
• This may lead to the near extinction of the tertiary consumers/organisms highest up in the affected food chain.
4. A fish farm is managed ecosystem.
The diagram above represents a salmon farm on a Scottish loch and shows some of the other organisms living in the area.
(a) Use the diagram to suggest how the fish farm maximizes its production. [3]
(b) Suggest two methods for removing the sea lice which damage the salmon’s skin. [2]
(c) The salmon are fed five times per day in small quantities rather than one large amount. What effect would this have on the oxygen content of the water? Explain your answer. [3]
ANSWERS
(a) Any three of the following (Max: 3 marks)
The net reduces movement (1), reducing energy wasted in swimming and the number of fish lost to predators (1).
Food is provided to maximise growth (1) by controlling the diet of the fish.
Since the fish are fed, there is reduced competition for food between the fish (1).
(b) Introduce cleaner wrasse which will eat the sea lice (1); Remove infected fish as soon as they are infected (1).
(c) Less food is not eaten/left from each feeding (1), hence, reducing the growth of bacteria (1) and keeping oxygen content at a healthy level (1).
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