Transfers of energy and matter

Question 1

What is the difference between an open and closed system, and which is an ecosystems?

Answer 1

Open systems: both energy and matter can enter and exit (ecosystem)

Closed systems: only energy is able to pass in and out.

Question 2

What is the principal source of energy that sustains most ecosystems? Are there exceptions?

Answer 2

Sunlight

Yes, e.g ecosystems in caves, deep ocean water
Exist in total darkness.

Question 3

What is the flow of chemical energy through food chains

Answer 3

The process of passing energy from one organism to another through feeding

Question 4

What is a food chain?
What is a food web?
What do they both represent?

Answer 4

A sequence showing the feeding relationships and energy flow between species.

Multiple food chains and how they are connected

Feeding relationships in a community

Question 5

What are the two types of decomposers?

How do they acquire energy? Include examples

Answer 5

Saprotrops and detritivores.

Decomposers break down non-living food sources e.g faeces, dead parts of organisms, dead whole organisms
Saprotrophs secrete enzymes onto dead matter and absorb the nutrients
Detritivores ingest dead matter and digest it inside their bodies

Question 6

What are autotrophs/producers?

Answer 6

Organisms that use external energy sources to synthesize carbon compounds from simple inorganic substances

Question 7

What are the two different types of autotrophs and how do they differ? Include examples.

Answer 7

Photoautotrophs take light energy from the sun, combine it with inorganic substances, and obtain chemical energy in the form of a carbon compound. E.g cynobacteria, pine trees

Chemoautotrophs use oxidation reactions as an energy source to convert carbon dioxide into complex food molecules. E.g iron-oxidising bacteria

Question 8

What are heterotrophs?

Answer 8

Organisms that use carbon compounds obtained from other organisms (autotrophs or other heterotrophs) to synthesize the carbon compounds that they require

Question 9

How do autotrophs and heterotrophs release energy?

Answer 9

Oxidation of carbon compounds (e.g glucose) in cell
respiration

Question 10

What are trophic levels used for and how are organisms classified into them?

Answer 10

To indicate how many organisms the energy in the system has flowed through

1st trophic level: producers
2nd trophic level: primary consumers
3rd trophic level: secondary consumers
4th trophic level tertiary consumers

Question 11

What are energy pyramids used for?

Answer 11

To show how much and how fast energy flows from one trophic level to the next in a community

Question 12

Reductions in energy availability at each successive stage in food chains due to large energy
losses between trophic levels

Answer 12

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.

Question 13

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

Answer 13

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.

Question 14

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

Answer 14

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.

Question 15

Primary production as accumulation of carbon compounds in biomass by autotrophs

Answer 15

The units should be mass (of carbon) per unit area per unit time and are usually g m−2 yr−1. Students should
understand that biomes vary in their capacity to accumulate biomass. Biomass accumulates when
autotrophs and heterotrophs grow or reproduce.

Question 16

Secondary production as accumulation of carbon compounds in biomass by heterotrophs

Answer 16

Students should understand that, due to loss of biomass when carbon compounds are converted to
carbon dioxide and water in cell respiration, secondary production is lower than primary production in an
ecosystem.

Question 17

Constructing carbon cycle diagrams

Answer 17

Students should illustrate with a diagram how carbon is recycled in ecosystems by photosynthesis,
feeding and respiration.

Question 18

Ecosystems as carbon sinks and carbon sources

Answer 18

If photosynthesis exceeds respiration there is a net uptake of carbon dioxide and if respiration exceeds
photosynthesis there is a net release of carbon dioxide.

Question 19

Release of carbon dioxide into the atmosphere during combustion of biomass, peat, coal, oil and
natural gas

Answer 19

Students should appreciate that these carbon sinks vary in date of formation and that combustion
following lightning strikes sometimes happens naturally but that human activities have greatly increased
combustion rates.

Question 20

Analysis of the Keeling Curve in terms of photosynthesis, respiration and combustion

Answer 20

Include analysis of both the annual fluctuations and the long-term trend.

Question 21

Dependence of aerobic respiration on atmospheric oxygen produced by photosynthesis, and of
photosynthesis on atmospheric carbon dioxide produced by respiration

Answer 21

The fluxes involved per year are huge, so this is a major interaction between autotrophs and heterotrophs.

Question 22

Recycling of all chemical elements required by living organisms in ecosystems

Answer 22

Students should appreciate that all elements used by living organisms, not just carbon, are recycled and
that decomposers play a key role. Students are not required to know details of the nitrogen cycle and
other nutrient cycles.