Energy Transfer

Standard Level

Energy Source Energy Flow Energy Loss Food Chains Food Webs Energy Pyramids

SL Content Statements

C4.2.1

Ecosystems as open systems in which both energy and matter can enter and exit
Students should know that in closed systems only energy is able to pass in and out.
C4.2.2

Sunlight as the principal source of energy that sustains most ecosystems
Include exceptions such as ecosystems in caves and below the levels of light penetration in oceans.
NOS: Laws in science are generalized principles, or rules of thumb, formulated to describe patterns observed in nature. Unlike theories, they do not offer explanations, but describe phenomena. Like theories, they can be used to make predictions. Students should be able to outline the features of useful generalizations.
C4.2.3

Flow of chemical energy through food chains
Students should appreciate that chemical energy passes to a consumer as it feeds on an organism that is the previous stage in a food chain.
C4.2.4

Construction of food chains and food webs to represent feeding relationships in a community
Represent relationships in a local community if possible. Arrows indicate the direction of transfer of energy and biomass.
C4.2.5

Supply of energy to decomposers as carbon compounds in organic matter coming from dead organisms
Include faeces, dead parts of organisms and dead whole organisms.
C4.2.6

Autotrophs as organisms that use external energy sources to synthesize carbon compounds from simple inorganic substances
Students should understand that energy is required for carbon fixation and for the anabolic reactions that build macromolecules.
C4.2.7

Use of light as the external energy source in photoautotrophs and oxidation reactions as the energy source in chemoautotrophs
Students should understand that oxidation reactions release energy, so they are useful in living organisms. Include iron-oxidizing bacteria as an example of a chemoautotroph.
C4.2.8

Heterotrophs as organisms that use carbon compounds obtained from other organisms to synthesize the carbon compounds that they require
Students should appreciate that complex carbon compounds such as proteins and nucleic acids are digested either externally or internally and are then assimilated by constructing the carbon compounds that are required.
C4.2.9

Release of energy in both autotrophs and heterotrophs by oxidation of carbon compounds in cell respiration
Students are not required to be familiar with photoheterotrophs.
C4.2.10

Classification of organisms into trophic levels
Use the terms “producer”, “primary consumer”, “secondary consumer” and “tertiary consumer”. Students should appreciate that many organisms have a varied diet and occupy different trophic levels in different food chains.
C4.2.11

Construction of energy pyramids
AOS: Students should use research data from specific ecosystems to represent energy transfer and energy losses between trophic levels in food chains.
C4.2.12

Restrictions on the number of trophic levels in ecosystems due to energy losses
Decomposers and detritus feeders are not usually considered to be part of food chains. However, students should understand the role of these organisms in energy transformations in food chains. Consider the causes of energy loss.
C4.2.13

Heat loss to the environment in both autotrophs and heterotrophs due to conversion of chemical energy to heat in cell respiration
Include the idea that energy transfers are not 100% efficient so heat is produced both when ATP is produced in cell respiration and when it is used in cells.
C4.2.14

Restrictions on the number of trophic levels in ecosystems due to energy losses
At each successive stage in food chains there are fewer organisms or smaller organisms. There is therefore less biomass, but the energy content per unit mass is not reduced.

Energy Transfer

Standard Level

SL Content Statements

C4.2.1

Ecosystems as open systems in which both energy and matter can enter and exit

Students should know that in closed systems only energy is able to pass in and out.

C4.2.2

Sunlight as the principal source of energy that sustains most ecosystems

C4.2.3

Flow of chemical energy through food chains

Students should appreciate that chemical energy passes to a consumer as it feeds on an organism that is the previous stage in a food chain.

C4.2.4

Construction of food chains and food webs to represent feeding relationships in a community

Represent relationships in a local community if possible. Arrows indicate the direction of transfer of energy and biomass.

C4.2.5

Supply of energy to decomposers as carbon compounds in organic matter coming from dead organisms

Include faeces, dead parts of organisms and dead whole organisms.

C4.2.6

Autotrophs as organisms that use external energy sources to synthesize carbon compounds from simple inorganic substances

Students should understand that energy is required for carbon fixation and for the anabolic reactions that build macromolecules.

C4.2.7

Use of light as the external energy source in photoautotrophs and oxidation reactions as the energy source in chemoautotrophs

Students should understand that oxidation reactions release energy, so they are useful in living organisms. Include iron-oxidizing bacteria as an example of a chemoautotroph.

C4.2.8

Heterotrophs as organisms that use carbon compounds obtained from other organisms to synthesize the carbon compounds that they require

Students should appreciate that complex carbon compounds such as proteins and nucleic acids are digested either externally or internally and are then assimilated by constructing the carbon compounds that are required.

C4.2.9

Release of energy in both autotrophs and heterotrophs by oxidation of carbon compounds in cell respiration

Students are not required to be familiar with photoheterotrophs.

C4.2.10

Classification of organisms into trophic levels

Use the terms “producer”, “primary consumer”, “secondary consumer” and “tertiary consumer”. Students should appreciate that many organisms have a varied diet and occupy different trophic levels in different food chains.

C4.2.11

Construction of energy pyramids

AOS: Students should use research data from specific ecosystems to represent energy transfer and energy losses between trophic levels in food chains.

C4.2.12

Restrictions on the number of trophic levels in ecosystems due to energy losses

Decomposers and detritus feeders are not usually considered to be part of food chains. However, students should understand the role of these organisms in energy transformations in food chains. Consider the causes of energy loss.

C4.2.13

Heat loss to the environment in both autotrophs and heterotrophs due to conversion of chemical energy to heat in cell respiration

Include the idea that energy transfers are not 100% efficient so heat is produced both when ATP is produced in cell respiration and when it is used in cells.

C4.2.14

Restrictions on the number of trophic levels in ecosystems due to energy losses

At each successive stage in food chains there are fewer organisms or smaller organisms. There is therefore less biomass, but the energy content per unit mass is not reduced.