C4.2 - Transfers of energy and matter

Question 1

What are open and closed systems?

Answer 1

open ecosystems - systems in which both energy and matter can enter and exit
closed ecosystems - systems in which only energy is able to pass in and out

Question 2

What are the principal source of energy that sustains most ecosystems?

Answer 2

sunlight

Question 3

What are 2 exceptions where sunlight isn’t needed?

Answer 3

ecosystems in caves and below the levels of light penetration in oceans

Question 4

What are laws in science?

Answer 4

laws are generalised principles, or rules of thumb, formulated to describe patterns observed in nature
- do not offer explanations, but describe phenomena
- can be used to make predictions

Question 5

What is a heterotroph and how can it link to energy flow in an ecosystem?

Answer 5

Heterotroph - organisms that use carbon compounds obtained from other organisms to synthesise carbon compounds they require
- chemical energy from ingested nutrients are used for digesting complex carbon compounds internally or externally, then assimilating to construct required carbon compounds

Question 6

What is an autotroph and why do they require energy?

Answer 6

Autotroph - organism that uses an external energy source to synthesise carbon compounds from simple inorganic substances
- energy is needed for carbon fixation and for anabolic reactions that build up macromolecules

Question 7

How do chemoautotrophs receive energy?

Answer 7

use oxidation reactions as the energy source in chemosynthesis

Question 8

What are photoautotrophs?

Answer 8

organisms that use light as the external energy source during photosynthesis

Question 9

Why is energy described as flowing in an ecosystem?

Answer 9

energy cannot be recycled - it enters a food chain and is lost from that food chain

Question 10

How does energy flow through an ecosystem?

Answer 10

1. Energy from the sun is captured by autotrophs
2. Light energy is converted to chemical energy using photosynthesis
3. Chemical energy passes to a consumer as it feeds on an organism that is in the previous stage of a food chain
4. This energy transfer via feeding is repeated multiple times along a food chain
5. Respiration releases chemical energy as ATP and heat is lost from the food chain. ATP is used to carry out life functions

Question 11

What do food chains and webs represent?

Answer 11

feeding relationships in a community

Question 12

What do the arrows of food chains and webs indicate?

Answer 12

direction of transfer of energy of biomass

Question 13

What are the pros and cons of food webs?

Answer 13

advantages: food webs summarize all possible food chains in the community, realistic representation
disadvantages:some communities are too complex to represent, only shows qualitative data, impact of saprotrophs or abiotic factors are not taken into account

Question 14

What are challenges when trying to label the trophic level of each organism in a food web?

Answer 14

many organisms have a varied diet and occupy different trophic levels in different food chains

Question 15

Why is the number of trophic levels restricted?

Answer 15

due to large losses of about 90% between trophic levels meaning there is a reduction in the energy availability at each successive stage in a food chain

Question 16

Why doesn’t all the energy flow along a food chain?

Answer 16

• both autotrophs and heterotrophs release energy by oxidation of carbon compounds in cell respiration
• energy transfers aren’t 100% efficient so heat is produced when ATP is produced during respiration and when used in cells

Question 17

Why are there smaller or fewer organisms at each successive stage of a food chain?

Answer 17

production of carbon dioxide by respiration results in a loss of chemical energy contained within molecules, reducing biomass in a food chain as less energy is available for building biological molecules

Question 18

How is energy supplied to decomposers?

Answer 18

• after death, energy remains trapped as undigested detritus
• decomposers gain energy using carbon compounds from organic matter of dead organisms, dead parts or whole organisms

Question 19

Which type of organisms are not usually considered to be a part of the food chain?

Answer 19

decomposers and detritivores
- holozoic detritus feeders

Question 20

What is the classification of organisms into trophic levels?

Answer 20

producer, primary consumer, secondary consumer, tertiary consumer

Question 21

What must you know in order to find the trophic level of an organism?

Answer 21

• what it feeds on
• the trophic level of what it eats

Question 22

What are energy pyramids?

Answer 22

represent energy transfer and energy losses between trophic levels in food chains
- width shows the amount of energy at each trophic level over a period of time
- classic pyramid shape with larger bar at the bottom and successively smaller bars as you go up the trophic levels

Question 23

What information do you need to create an energy pyramid?

Answer 23

• the food chain
• energy content in biomass at each trophic level
• period of time the sample was taken
• units are KJ m⁻² yr⁻¹

Question 24

What are the advantages and disadvantages of an energy pyramid?

Answer 24

advantages: can show loss/transfer of energy between trophic levels, allows quantitative comparisons between ecosystems, shows change over time
disadvantages: hard to produce accurately, requires destructive methods to obtain data, don’t show all feeding relationships in a community, cannot show organisms that feed at different trophic levels