Energy and biomass in ecosystems

First law of thermodynamics - energy can be transformed from one to another but cannot be lost or created.

Second law - as energy is transformed, some is transformed into a less useful form ( as heat)

Energy transformations in an ecosystem are inefficient.

• Sunlight from the sun is transformed into many other types of energy.

• But as it does so energy is ‘wasted’ in the form of heat.

• The biggest losses in ecosystems comes from cellular respiration.

• The more stages, the more transformation, and therefore more heat loss.

• Hence energy transfers are not 100% efficient.

Photosynthesis

• The conversion of light energy to chemical energy (glucose)

• Carried out by plants, algae and photosynthetic bacteria.

• These organisms are autotrophs - they make their own food.

• They form the first trophic level in food chains - producers

• Some of the chemical energy is stored as biomass - the mass living or recently living organisms.

• Carbon dioxide + water → glucose + oxygen

• Carbon dioxide and water have relatively low chemical energy.

• Plants use sunlight to convert these into glucose (which has a lot more chemical potential energy).

Respiration

• Respiration transforms both energy and matter

• The process by which living organisms convert oxygen and glucose into a useful energy form, releasing carbon dioxide and water in the process.

• Glucose + oxygen → carbon dioxide + water

• The chemical potential energy of the glucose is released during this reaction.

• It is converted from one form to another.

• The energy is ‘stored’ within the chemical bonds of the glucose, and as the glucose is broken the energy released is used to create another chemical, ATP, which our cells can already use.

Trophic levels