Trophic levels and pyramids of biomass, why so little biomass is transferred between levels, threats to food security, and sustainable farming and fishing. Biology only content.
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1.What is a trophic level?
The position an organism occupies in a food chain, numbered from level 1 upwards.
2.What is at trophic level 1?
Producers, which are plants and algae that make their own food by photosynthesis.
3.What is at trophic level 2?
Herbivores, the primary consumers that eat plants or algae.
4.What is at trophic levels 3 and 4?
Carnivores that eat herbivores, and then carnivores that eat other carnivores.
5.What are decomposers and where do they fit?
Bacteria and fungi that break down dead plant and animal matter, secreting enzymes and absorbing the dissolved products.
6.What is a pyramid of biomass?
A diagram drawn to scale showing the relative mass of living material at each trophic level, with producers at the bottom.
7.Why is a pyramid of biomass always a pyramid shape?
Biomass is lost at each level, so each level has less than the one below it.
8.Roughly what percentage of biomass is transferred between trophic levels?
About 10 per cent.
9.Give three reasons biomass is lost between trophic levels.
Not all of the organism is eaten or digested, biomass is lost as waste in faeces and urine, and much is used in respiration and lost as heat.
10.Why is so much biomass lost in respiration?
Energy transferred by respiration is used for movement and for keeping warm, and is eventually transferred to the environment.
11.How do you calculate the efficiency of biomass transfer?
Divide the biomass of the higher level by the biomass of the level below it, then multiply by 100.
12.A level has 1000 g and the next has 80 g. Calculate the efficiency.
80 divided by 1000 = 0.08. 0.08 x 100 = 8 per cent.
13.Why are food chains rarely longer than five trophic levels?
So little biomass remains after several transfers that it cannot support another level of consumers.
14.What is food security?
Having enough food to feed a population.
15.Give four threats to food security.
The rising human population, changing diets in wealthier countries, new pests and pathogens, environmental change such as drought, and the cost of farming inputs.
16.Why do changing diets in wealthy countries threaten food security elsewhere?
Scarce food resources are transported around the world to meet that demand, rather than staying where they are most needed.
17.How does eating meat affect food security?
Feeding crops to animals and then eating the animals loses about ninety per cent of the biomass at each step, so far more people could be fed by eating the crops directly.
18.Give two ways the efficiency of food production can be increased.
Limiting the movement of animals, and keeping them in a warm environment so less energy is used in movement and keeping warm.
19.Why is intensive farming controversial?
It is efficient and keeps food cheap, but many people object to the welfare conditions the animals are kept in.
20.Why does limiting movement increase efficiency?
Less energy is used in muscle contraction, so more of the biomass eaten goes into growth instead.
21.What is meant by sustainable fisheries?
Managing fish stocks so that enough fish remain to breed and maintain the population for the future.
22.Give two ways fish stocks are managed sustainably.
Controlling net size so young fish escape and can breed, and setting fishing quotas that limit how much of a species can be caught.
23.Why does controlling net mesh size help?
Larger holes let immature fish escape, so they survive to breed and replace the stock.
24.What happens if fish stocks fall too low?
Certain species may disappear from some areas altogether, and the fishing industry that depends on them collapses.
25.How is biotechnology used to help food security?
A fungus called Fusarium is grown on glucose syrup in aerobic conditions to produce mycoprotein, a protein rich food suitable for vegetarians.
26.How has genetic modification been used in food production?
Bacteria have been modified to produce human insulin, and crops have been engineered to give higher yields or added nutrients such as golden rice.
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