4. Energy Flow

Question 1

What do all the organisms in a community need?

Answer 1

a supply of energy

Question 2

Where do plants, algae and some bacteria get their energy from? What are these organisms called? Why?

Answer 2

• light energy and convert it by photosynthesis into chemical energy in carbon compounds
• producers
• because they produce their own food

Question 3

Where do consumers, detritivores and saprotrophs obtain energy from?

Answer 3

• chemical energy in the carbon compounds in their food

HOWEVER

• carbon compounds and the energy contained in them move from organism to organism along food chains, but all food chains start with a producer that originally made the carbon compounds by photosynthesis.
• light is therefore the initial source of energy for the whole community

Question 4

Draw the diagram explaining energy sources. p56

Answer 4

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Question 5

What does food contain? How is it passed along?

Answer 5

• energy

- by food chains

Question 6

How does a food chain occur?

Answer 6

when the primary consumer feeds on the producer, and the secondary consumer feeds on the primary consumer, etc.

Question 7

What happens the further up the food chain you go? Why?

Answer 7

• less food is available and therefore less chemical energy

- due to loss of food and energy between the stages in a food chain

Question 8

What are the three ways by which food and energy can be passed to detritivores or saprotrophs rather than to the next stage in the food chain?

Answer 8

• some organisms die before they are eaten by the next organism in the chain e.g. foxes do not eat every rabbit; some rabbits die from disease
• some parts of organisms are not eaten e.g. bones, hair, gall bladders
• some parts of organism are indigestible e.g. cellulose in food eaten by humans so is egested in feces

Question 9

Name another cause of energy loss, that isn’t: death; parts not eaten; parts indigestible.

Answer 9

cell respiration - use energy for essential process such as muscle contraction and active transport

Question 10

What is the energy conversion in cellular respiration?

Answer 10

chemical to heat

- heat is then lost from the organism

Question 11

Can any organisms convert heat energy back into chemical energy? What happens to it?

Answer 11

• no

- heat is eventually lost from the ecosystem

Question 12

Organisms cannot convert heat energy back into chemical energy and heat is lost from the ecosystem. What is the significance of this?

Answer 12

ecosystems need an energy source, usually light, to replace energy lost

Question 13

Summarise energy transfer in an ecosystem with a chart. p56

Answer 13

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