Edexcel IGCSE Biology

52 - Feeding Relationships

Specification Point 4.6 - Understand the names given to different trophic levels, including
producers, primary, secondary and tertiary consumers and decomposers.

Specification Point 4.7 - Understand the concepts of food chains, food webs, pyramids of
number, pyramids of biomass and pyramids of energy transfer.

Specification Point 4.8 - Understand the transfer of substances and energy along a food
chain.

Specification Point 4.9 - Understand why only about 10% of energy is transferred from one
trophic level to the next.

There are different trophic levels within the food chain. These include: producers, primary,
secondary and tertiary consumers and decomposers.

Important considerations here are food webs, pyramids of number, pyramids of biomass
and pyramids of energy transfer following the movement of energy along the food chain.

1
 Part A - Short Answer Questions

1. Define a trophic level.

The position of an
organism
within a
feeding relationship .

2. What is a predator?

Organisms that eat other ,

3. What is meant by the term prey?

eaten by predator
4. What is a secondary consumer?

feed primary consumers,

5. How much energy is lost between trophic levels?

10 %

6. What do pyramids of biomass show?

dry organic.

2
 Part B - Fill in the Blanks

feeding relationships. Organisms that eat other

Organisms in ecosystems will exhibit ______________

predators
organisms are called ________________. Organisms that are eaten by other organisms are called

prey
________.

trophic level.
The position of an organism within a feeding relationship is called its ______________

This is often used to demonstrate the role an organism plays within a food chain.

habitat Food chains show the flow

A food chain shows what eats what in a particular ______________.

producer Sunlight
of ____________ from one trophic level to the next, starting with a ______________. ________________
energy ,

continually adds energy to the start of the food chain.

web is a network of connected food chains. They are more realistic depictions of
A food ______

feeding relationships. An organism rarely relies on one food source. Food webs show

interdependence
____________________________
, - this is how a change in the population of one species can have

effects on the populations of other species.

Sunlight is the original source of energy for a food chain. Producers convert sunlight
_________________
,

chemical energy during photosynthesis.

into ________________

Other organisms then consume this chemical energy by ____________.

eating .

10.
trophic levels. Only around ______%
Energy is lost between ____________ of the total available energy is

passed onto the next trophic level.

3
 Part C - Exam Style Questions

Question 1

Below is a diagram of a food chain.

(a) Which is the primary consumer in this food chain? (1)

Bee
(b) How does the producer get energy? (3)
Sun .

(c) Give reasons why some of the energy is not transferred to the next trophic level. (2)

Not all the lights pass into

the chloroplast .

(Total for question 1 = 6 marks)

4
Question 2

Grassland → Mice → Owl

(a) Which is the secondary consumer in this food chain? (1)

Om
(b) Draw a pyramid of numbers for the food chain above. Label the pyramid. (3)

ow

↳
-

Mice
-
Grassland
(c) How would a pyramid of biomass compare to the pyramid you have drawn? (2)

larger base of Grassland.

same
type .

(Total for question 2 = 6 marks)

Question 3

The diagram below shows a food chain in a lake.

Plants → Small fish → Big fish → Birds

5
(a) Which trophic level is the big fish? (1)

Secondary consumer
.

(b) Draw a pyramid of energy for the food chain above. Label the pyramid. (3)

Aside
(c) Why does energy change on each trophic level?
enrich
(3)

decrease
as going up the fod chain.

(Total for question 3 = 7 marks)

6
 Answers

Part A
1. The position of an organism within a feeding relationship.
2. Organisms that eat other organisms.
3. Organisms that are eaten by other organisms.
4. Organisms that feed on primary consumers are carnivores.
5. 10%
6. The dry organic matter at each trophic level.

Part B
Organisms in ecosystems will exhibit feeding relationships. Organisms that eat other
organisms are called predators. Organisms that are eaten by other organisms are called
prey.

The position of an organism within a feeding relationship is called its trophic level. This is
often used to demonstrate the role an organism plays within a food chain.

A food chain shows what eats what in a particular habitat. Food chains show the flow of
energy from one trophic level to the next, starting with a producer. Sunlight continually
adds energy to the start of the food chain.

A food web is a network of connected food chains. They are more realistic depictions of
feeding relationships. An organism rarely relies on one food source. Food webs show
interdependence - this is how a change in the population of one species can have effects
on the populations of other species.

Sunlight is the original source of energy for a food chain. Producers convert sunlight into
chemical energy during photosynthesis.

Other organisms then consume this chemical energy by eating.

Energy is lost between trophic levels. Only around 10% of the total available energy is
passed onto the next trophic level.

Part C
Question 1

Question Number Answer Additional Guidance Mark

(a) Bee 1

(b) Energy from the sun 3

7
 provides stimulus for
photosynthesis which
creates carbohydrates

(c) Not all sunlight hits 2

chloroplasts
Some light is incorrect
wavelength
Some is converted to
heat

Question 2

Question Number Answer Additional Guidance Mark

(a) Owl 1

(b) Organisms named 3

In correct order
Correct shape

(c) Larger base for the 2

grassland
Pyramid the same
shape

Question 3

Question Number Answer Additional Guidance Mark

(a) Secondary consumer 1

(b) Organisms named 3

In correct order
Correct shape

(c) Energy must decrease 3

as we go up the food
chain
Some is waste when a
organism is eaten
For heat
Or respiration