3.5.3 Energy and Ecosystems

Question 1

The ultimate source of energy for an ecosystem

Answer 1

Sunlight - conserved as chemical energy by plants

Question 2

What do plants use sunlight for?

Answer 2

• To make organic compounds (including sugars - most of which are used by plants as respiratory substrates)
• Remainder are used to make other groups of biological molecules which form the biomass of plants

Question 3

Biomass

Answer 3

• The means by which energy is passed between other organisms
• Measured in terms of mass of carbon or dry mass of tissue per given area.

Question 4

How can the chemical energy stored in biomass be measured?

Answer 4

Calorimetry

Question 5

Producers

Answer 5

Photosynthetic organisms that synthesise organic molecules using light energy, water, carbon dioxide and mineral ions

Question 6

Consumers

Answer 6

Any organisms that obtain energy by ‘eating’ another organism

Question 7

Primary consumers

Answer 7

Directly eat producers

Question 8

Secondary consumers

Answer 8

Animals that eat primary consumers

Question 9

Tertiary consumers

Answer 9

Animals that eat secondary consumers

Question 10

Groups of organisms according to how they obtain energy and nutrients

Answer 10

• Producers
• Consumers
• Saprobiants

Question 11

Saprobiants (decomposers)

Answer 11

• A group of organisms that break down the complex materials in dead organisms into simple ones
• In doing so, they release valuable minerals and elements in a form that can be absorbed by plants and so contribute to recycling

Question 12

Food chain

Answer 12

Describes a feeding relationship in which the producers are eaten by primary consumers, which are eaten by secondary consumers, etc.

Question 13

Trophic lebel

Answer 13

Stages in a food chain

Question 14

What does the arrow in a food chain diagram represent?

Answer 14

The direction of energy flow

Question 15

Food webs

Answer 15

A more realistic representation of what actually occurs
* Mant food chains linked together

Question 16

Biomass definition

Answer 16

The total mass of living material in a specific area at a given time

Measured in: gm-2 for area samples, gm-3 for volume samples

Question 17

Why isn’t fresh mass used to assess?

Answer 17

The presence of varying amounts of water makes it unreliable

Question 18

Problem with measuring dry mass

Answer 18

Organisms must be killed, so normally only a small sample is taken. This sample may not be representative

Question 19

How can calorimetry be used to measure the chemical energy in dry mass?

Answer 19

Bomb calorimetry
1. A sample of dry material is weighed and then burnt in pure oxygen within a sealed chamber (called a bomb)
2. The bomb is surrounded by a water bath and the heat of combustion causes a small temperature rise in this water
3. As we know the specific heat capacity of water, we can calculate the energy released