4.2 Energy flow

Question 1

Supply of Energy of most ecosystems

Answer 1

Most ecosystems rely on a supply of energy from the sun.

For most biological communities - initial source of energy is sunlight
Living organisms can harvest this energy through photosynthesis

Heterotrophs (consumers, saprotrophs, detritivores) do not use sunlight but indirectly depend on it
All of them use carbon compounds in their food as a source of energy
In most ecosystems, all/almost all the energy in carbon compounds will originally have been harvested by photosynthesis in producers

Question 2

Groups of autotrophs that can carry out photosynthesis

Answer 2

Plants
Eukaryotic algae (e.g. seaweeds that grow of rocky shores)
Cyanobacteria

Also referred to as producers

Question 3

Percentage of energy harvested by producers and available to other organisms

Answer 3

The amount of energy supplied to ecosystems in sunlight varies around the world
The percentage of energy harvested by producers and therefore, available to other organisms also varies

e. g. Sahara desert - intensity of sunlight is very high but only a little of the energy becomes available to organisms as there are only a few producers
e. g. Redwood forests of California - intensity of light is less than Sahara but much more energy becomes available to organisms because producers are abundant