Ecology-Enviroment

A2 Biology – Revision Notes

Unit 5 – Environment

Energy Flows Through Ecosystems

1. An autotroph is an organism that can produce energy from inorganic sources:

a. Phototrophs – produce energy from photosynthesis/sunlight (plants).

b. Chemotrophs – produce energy from simple inorganic processes (usually oxidative processes involving

nitrogen or sulphur compounds).

2. Other organisms require an organic source of energy and are heterotrophs. The feeding relationships in an ecosystem are as

follows:

a. Producers – photoautotrophs (plants).

b. Consumers – herbivores, carnivores and omnivores.

c. Decomposers (also consumers) – detritivores and saprophytes.

3. Humus is the rotting organic matter in the soil, giving it texture and allowing it to hold more water. It is a sticky mass of dead

plants, animals and faeces, which are being broken down by saprophytes (extracellular digestion) and detritivores (intracellular

digestion) to release the nutrients.

4. Of the energy reaching the Earth from the Sun, about 99% is reflected or absorbed and re-radiated by the atmosphere, so only

1% actually reaches the surface. Only about 0.1% of this energy strike spart of a plant, and of this, between 0.5% and 1% can

Be used for photosynthesis (mainly red and blue light is used).

5. Photosynthetic reactions are very inefficient (there is a lot of wasted heat). The energy that can be absorbed and converted into

chemical energy is the gross primary production (GPP). This is measured in kJ per m2 per year.

6. The net primary production (NPP) is the energy that is actually made available to other organisms (primary consumers). The

rest of the energy is lost in respiration.

This satisfies the relationship NPP = GPP – R. The NPP varies according to:...