Pyramids of Biomass
Biomass is the mass of living material in plants and animals, it is often measured as the dry mass of biological materials in grams. Ultimately all biomass is built up using energy from the sun.
A pyramid of biomass represents the mass of the organisms at each stage in a food chain. It may be more accurate than a pyramid of numbers, e.g. one busy may have many insects feeding on it but the mass of the bush is far greater than the mass of the insects.
The biomass found at each stage of a food chain is less than it was at the previous. This is because:
- not all organisms at one stage are eaten by the stage above
- some material taken in is passed out as waste
- when a herbivore eats plants, it turns some of the plant material into a new herbivore, but much of the biomass from the plant is used by the herbivore in respiration to release energy for living. It doesn't get passed on to the carnivore when the herbivore is eaten.
In a food chain, there are usually more producers than primary consumers, and more primary consumers than secondary consumers. This can be shown using a pyramid of numbers, however it does not accurately reflect what is happening.
Not all of the food eaten can be digested, so energy is lost in faeces.
Some of the energy is used for respiration, which releases energy for living processes. This includes movement, so the more something moves the more energy it uses and the less is available for growth.
In animals that need to keep a constant temperature, energy from the previous stage of the food chain is used simply to keep the animal at the correct temperature (e.g. 37°C in human).
Sankey Diagrams: Carnivores
Sankey Diagrams: Herbivores
Energy in Food Production
Biomass and energy are lost at each stage of a food chain. The efficiency of food production can be improved by reducing the number of stages in our food chains. It would be more efficient if we all just ate plants.
We can artificially produce meat more efficiently by:
- Preventing the animal from moving so it doesn't waste energy on movement then they lose a lot less energy in moving their muscles and so will have more biomass available from their food for growth. This is seen as cruelty by many people and is controversial.
- Keeping the animal at a warmer temperature so it doesn't use as much energy from food to keep itself at a constant temperature.
All of the materials from the waste and dead organisms are recycled.
Detritus feeders (such as worms) may start the process of decay by eating dead animals or plants and producing waste materials. Decay organisms then break down the waste and dead plants and animals. They use come of the nutrients to grow and reproduce and also produce waste products, e.g. CO2, water, minerals.
Decay organisms are microorganisms (bacteria and fungi). Decay is faster if it is warm and wet. Moisture makes it easier to dissolve their food and also prevents them from drying out.
In sewage plant microorganisms are used to break down the bodily waste produced, which makes it safe to be released into rivers and sea.
Many gardeners have a compost heap where grass cuttings, vegetable peelings and weeds are left to let decomposing microorganisms break down all the plant material then forms a fine, rich powdery substance known as compost which can take up to a year.
Photosynthesis removes CO2 from the atmosphere.
Green plants as well as animals respire. This returns CO2 to the atmosphere.
Animals eat green plants and build the carbon into their bodies. When plants or animals die (or produce waste) microorganisms release the CO2 back into the atmosphere through respiration.
Fossil fuels contain carbon, which was locked away by photosynthesising plants millions of years ago. When we burn fossil fuels, we release some of that carbon into our atmosphere.
Photosynthesis: Carbon Dioxide + Water (+ light energy) --> Glucose + Oxygen
Respiration: Glucose + Oxygen --> Carbon Dioxide + Water (+ energy)
Combustion: Fossil fuel or wood + Oxygen --> Carbon Dioxide + Water (+ energy)