Energy Flow in an Ecosystem - MS. SHEN'S CLASS WEBSITE

5.4

Energy Flow in an Ecosystem

Key Question: How does energy loss affect ecosystems?

Food chains and food webs show how energy flows in an ecosystem. They do not show how much energy each organism uses.

Organisms use energy in different ways. Some activities require more energy than other activities.

ENERGY USE IN AN ORGANISM

When an organism makes or eats food, it gets energy. The organism uses this energy in different ways.

Table 1 shows how organisms use energy (function) and where the energy goes (outcome).

Table 1 How Animals Use Energy

Functions of energy

fuels life processes helps organism grow and stay healthy not useable

Outcome

released as heat stored in the organism

released as waste

Percent of total energy from food

30 % 10 %

60 %

Organisms can use only some of the energy they obtain from food. Most of the energy that animals get from food is released as heat and waste. This energy is lost from the food chain.

Only the energy stored in an organism (about 10 % of energy intake) can pass to the next organism in the food chain.

96 Chapter 5 Worksheet 5.4-1

Copyright ? 2010 by Nelson Education Ltd.

intake 100 %

Figure 1 shows how a chicken uses energy.

life functions 30 %

gas and waste 60 % body growth and repair 10 %

Hint Remember that food chains always begin with a producer and end with a consumer.

pyramid of numbers a model that shows the number of individuals at each level in a food chain or food web

Figure 1 Chickens get energy from grain. Only about 10 % of this energy passes to organisms that eat chickens.

Food chains and food webs lose energy at each level. For example, only about 10 % of the energy in a chicken passes to the organism that eats the chicken. The top consumers get only a tiny amount of the energy that was in the producers.

Food chains and food webs usually have no more than four levels. If there are too many levels, the top consumers do not get enough energy.

PYRAMID OF NUMBERS

An ecological pyramid shows how energy loss affects a food chain or food web. Each level in the pyramid represents a level in the food chain. A pyramid of numbers is one type of ecological pyramid.

A pyramid of numbers shows the number of organisms at each level of a food chain or food web. As you move up the pyramid, each level has fewer organisms and less energy available. As a result, the higher levels often have only a few organisms.

Copyright ? 2010 by Nelson Education Ltd.

Chapter 5 Worksheet 5.4-1 97 TURN

Name: _________________________________________ Date: ________________________ Look at Figure 2. In this grassland ecosystem, the snake population needs hundreds of mice to survive and grow. These snakes provide enough energy for only one wolf.

1 tertiary consumer

100 secondary consumers

10 000 primary consumers

1 000 000 producers

Figure 2 This is a pyramid of numbers for a grassland food web.

Healthy ecosystems have enough producers to support their consumers. These ecosystems may have very large numbers of small producers, such as a field of wildflowers. They could also have a smaller number of large producers, such as a forest of mature trees.

CHECK YOUR UNDERSTANDING

1. How do organisms use the energy they get from food?

2. Why do food chains usually have no more than four levels?

98 Chapter 5 Worksheet 5.4-1

Copyright ? 2010 by Nelson Education Ltd.

Name: _________________________________________ Date: ________________________ 3. What is a pyramid of numbers?

4. Where are producers located in a pyramid of numbers? Why?

5. Think back to the Key Question. How does energy loss affect the number of levels in a food chain?

Copyright ? 2010 by Nelson Education Ltd.

Chapter 5 Worksheet 5.4-1 99 END

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