Food Chains

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  • Created on: 08-05-10 11:53
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Food chains and webs
All food chains start with a producer. This is a living thing which makes its own food. Green plants
are producers because they use sunlight energy to produce food by photosynthesis.
The rest of the organisms in a food chain are consumers. A consumer is a living thing which uses
other living things for food. All animals are consumers.
A food chain is a diagram which shows simple feeding relationships. An example of a food chain is:
floating algae water fleas minnows
The arrows in a food chain show the direction of energy flow.
Most animals have more than one source of food and so they are a link in several food chains.
When all the food chains are put together we get a food web. Here is an example of part of a food
web in a Scottish loch.
If one species is lost from a food web all the others are affected. In the web above, if the mosquito
larvae were removed the ducks will have less food and the floating algae will be eaten less. So the
duck population is likely to decrease and the floating algae population may increase.
Other populations will also be affected. For instance, the water flea population might be expected to
increase as there will be more floating algae to eat. The snails do not appear to have any
connection to the mosquito larvae, and yet their population may decrease if the hungry ducks eat
more of them.
Pyramids of numbers and biomass

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Energy is lost from a food web when it is used for movement or converted to heat. This means
that an organism converts only a small percentage of the food it eats into new cells. For this reason
there are usually fewer organisms at each stage of a food chain.
This situation can be represented by a pyramid of numbers. A pyramid of numbers is a diagram
showing the numbers of organisms present in each level of a food chain.…read more

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Sample questions and answers
Here are some typical Standard Grade questions. Use the information in the revision bite to
help answer them if you are unsure. Look at the answer after you have tried each one.
Question 1
the graph below shows how a population of microorganisms changes over a period of 50
hours.…read more

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The population was 400 at 10 hours. Double that is 400 x 2 = 800.
The curve reaches 800 at 40 hours. So it takes 30 hours to double.
Examiner's Note
Well done! Being able to see trends in graphs is an important mark getting skill. You
remembered to look for the steepest part of the curve as this shows where the population
increase is greatest.…read more

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Happening Hints
For your biology exam you should be able to:
follow a food chain through a food web
suggest what would happen in a food web if one species was removed
say what is meant by a pyramid of numbers and a pyramid of biomass
explain how the size of populations are limited
identify examples of competition
describe the sequence of the nitrogen cycle
Wise-up words
producer a green plant that makes its own food by photosynthesis
consumer an organism that can not make…read more

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Top of Form
How it Works
The diagram shows part of a food web on a oak tree.
Use the web above to answer questions 1 to 6 by entering the corresponding number in the boxes
1. wasp 4. spider
2. caterpillar 5. greenfly 7. hoverfly
3. blue tit 6. oak
1. Name the producer in this food web.
2. Use five organisms from the food web to construct a food chain. (NB do not leave any spaces
between each organism eg 1+2+3+4+5).
3.…read more

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The diagram below represents a simple food chain.
The diagram shows a:
a. Pyramid of numbers
b. Pyramid of biomass
Use the nitrogen cycle diagram below to answer questions 7 to 10.…read more

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Match the letters on the diagram with the statements below. Type your answers in the boxes
7. The decay of dead plant and animal material by bacteria and fungi:
8. The addition of extra nutrients by farmers as fertilisers:
9. Nodules on the roots of clover that fixes nitrogen from the air:
10.…read more


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