EPE Practice

Careful Reading 2

Food Chains

Originally, the idea of a "food chain" was developed by a scientist named Charles Elton
in 1927. Elton described a general food chain in terms of where plants and animals get their
energy. He started with plants, which get energy from sunlight. Next, plant-eating animals
get their energy by eating plants. At the next level of the chain, meat-eating animals get their
energy from eating other animals. Elton's idea of a "chain" related to the concept that all
these animals are linked together by what they eat. Anything that affects one part of the
chain affects all of the other parts in the chain. The first part of the chain, plants, is called
the producer. All of the parts of the chain above the producer are called consumers.
Here is a simple example of a food chain. Grass uses sunlight to produce sugars and
proteins so that it can grow. Rabbits eat the grass and get energy from it. Foxes eat rabbits
and get energy from them. Foxes are at the "top" of this food chain because nothing eats
them. Now imagine that a farmer plows up the field of grass where the rabbits usually eat.
Some of the rabbits might die. Others will probably move to another location to find food.
In either case, there are fewer rabbits. This means less food for the foxes. Thus, the foxes
depend on the grass in a way, even though they don't eat the grass directly.

In the natural world, of course, there are no simple food chains like this. Rabbits eat lots
of plants besides grass. ■ A) Foxes eat lots of things besides rabbits. ■ B) Additionally,
there are lots of other things in nature that eat grass and rabbits! ■ C)

However, that does not mean the idea of a simple food chain is not important. Food
chains are still a useful concept to consider, even if they are an oversimplification of reality.
Take, for example, the case of DDT's effect on animals. In the 1960s, DDT, a common
pesticide at that time, was used a lot by farmers. Farmers only used a little at a time, so large
animals were not harmed. However, once DDT was used in a field, it did not go away.
Whenever it was used, DDT just stayed in the environment. Eventually, rain washed it into
rivers and lakes. Plankton, a tiny water organism, absorbed the DDT. Then, fish ate the
plankton. There was not much DDT in one bit of plankton, but small fish consumed many
little bits of plankton. Then, larger fish ate lots of the smaller fish. So, the concentration of
DDT in the larger fish became higher. Then, birds such as the osprey ate large quantities of
the larger fish.
In the end, compared to the concentration of DDT in plankton, the concentration of DDT
in osprey was 10 million times greater! The DDT did not kill the osprey, though. It just made
the female osprey lay eggs with very thin shells. The shells were so thin that when the mother
sat on the eggs, they broke. Thus, the osprey population became greatly reduced before
rebounding to today's levels.
EPE Practice
Careful Reading 2

QUESTIONS

1. According to the passage, which of the following is true about Elton's idea of food
chains?
(A) He only looked at plants and animals near his home.
(B) Other scientists at the time rejected Elton's idea.
(C) The chains started with plants.

2. Which of the sentences below best expresses the essential information in the
highlighted sentence in the passage?
(A) Elton was the first person to show a chain of events linking plant eaters to meat
eaters.
(B) The image of a chain was used to help show the connection between the parts of a food
chain.
(C) Animals and plants are linked by chains according to Elton's theory of natural foods.

3. In paragraph 3, what does the author imply?

(A) Animals that do not eat other animals

(B) How simple food chains are limited
(C) The relationship of rabbits and foxes

4. Look at the four squares [■] that indicate where the following sentence couid be
added to the passage:

Therefore, when trying to describe the real world, it is more appropriate to think of food
webs rather than food chains.

Where would the sentence best fit? Choose the square [■] where the sentence should
be added to the passage.
(A) Paragraph 3, line 2
(B) Paragraph 3, line 2
(C) Paragraph 3, line 3

5. Why does the author mention DDT in reference to food chains?

(A) To compare this chemical's effect on producers and consumers
(B) To illustrate the true complexity of nature
(C) To show how the simple concept of food chains could be useful

6. All of the following are mentioned in the passage EXCEPT

(B) a simple example of a food chain
(C) consumers and producers in the jungle
(D) who came up with the idea of food chains
EPE Practice
Careful Reading 2

7. Why did large fish in rivers and lakes have high concentrations of DDT in their
bodies?
(A) The large fish ate small fish with DDT in them.
(B) The large fish laid eggs in plankton with DDT in it.
(C) The large fish swam in water with DDT in it.

8. What can be inferred from the last paragraph about osprey?

(A) They became extinct.
(B) They began laying more eggs.
(C) They were helped before all of them died.
EPE Practice
Careful Reading 2

ANSWER KEY

1. C

2. B

3. B

4. C

5. C

6. B

7. A

8. C

Source: Edmunds, P., & McKinnon, N., 2006, “Developing Skills for the TOEFL IBT”, pp.

612-15