topic 4.2- energy flow

Question 1

why do most ecosystems rely on sunlight?

Answer 1

it is the initial source of energy for both autotrophs (directly) and heterotrophs (indirectly)

Question 2

give 3 groups of autotroph that carry out photosynthesis and are therefore referred to as producers

Answer 2

• plants
• eukaryotic algae
• cyanobacteria

Question 3

how is light energy converted into chemical energy in carbon compounds?

Answer 3

by photosynthesis

Question 4

how does chemical energy in carbon compounds flow through food chains? what then happens to it?

Answer 4

by means of feeding; energy released from carbon compounds by respiration is used in living organisms and converted to heat.

Question 5

what is the function of cell respiration?

Answer 5

it transfers chemical energy from carbon compounds to ATP, which can be used directly for many activities.

Question 6

what is the drawback of cell respiration?

Answer 6

not all of the energy in cell respiration is transferred to ATP. The remainder is converted to heat. Some heat is also produced when ATP is used in cell activities.

Question 7

why is heat lost from ecosystems?

Answer 7

because living organisms cannot convert heat to other forms of energy. Heat then passes from hotter to cooler bodies, so it will eventually all be lost to the abiotic environment.

Question 8

define biomass

Answer 8

the total mass of a group of organisms

Question 9

what is the effect of energy losses on an ecosystem?

Answer 9

energy losses between trophic levels restrict the length of food chains and the biomass of higher trophic levels

Question 10

give 3 reasons why the energy added to biomass by each successive trophic level is less

Answer 10

• most of the energy in food that is digested and absorbed by organisms in a trophic level is released in respiration and lost as heat- the only energy available to organisms in the next trophic level is chemical energy in carbohydrates and other compounds that have not been used in respiration.
• the organisms in a trophic level are not usually entirely consumed by organisms in the next trophic level- the remaining energy passes to saprotrophs/detritivores instead.
• not all parts of food ingested by the organisms in a trophic level are digested and absorbed. some material is indigestible and egested as faces.

Question 11

distinguish between energy flow in ecosystems and cycling of inorganic nutrients

Answer 11

• there is a continuous but variable supply of energy in the form of sunlight
• the supply of nutrients in an ecosystem is finite and limited

Question 12

why does biomass in terrestrial ecosystems diminish with energy along food chains?

Answer 12

due to loss of carbon dioxide, water and other waste products (eg urea)