1.6 - Waste Materials - Plants & Animals

Many trees shed their leaves each year and most animals produce droppings at least once a day. All plants and animals eventually die. Microorganisms play an important part in decomposing this material so that it can be used again by plants. The same material is recycled over and over again and can lead to stable communities.

Candidates should use their skills, knowledge and understanding to:

■ evaluate the necessity and effectiveness of schemes for recycling organic kitchen or garden waste.

B1.6.1 Decay processes

a) Living things remove materials from the environment for growth and other processes. These materials arereturned to the environment either in waste materials or when living things die and decay.

b) Materials decay because they are broken down (digested) by microorganisms. Microorganisms are more active and digest materials faster in warm, moist, aerobic conditions.

c) The decay process releases substances that plants need to grow.

d) In a stable community, the processes that remove materials are balanced by processes that return materials. The materials are constantly cycled.

B1.6.2 The carbon cycle

a) The constant cycling of carbon is called the carbon cycle.

In the carbon cycle:

• carbon dioxide is removed from the environment by green plants and algae for photosynthesis
• the carbon from the carbon dioxide is used tomake carbohydrates, fats and proteins, which make up the body of plants and algae
• when green plants and algae respire, some of this carbon becomes carbon dioxide and is released into the atmosphere
• when green plants and algae are eaten by animals and these animals are eaten by other animals, some of the carbon becomes part of the fats and proteins that make up their bodies
• when animals respire, some of this carbon becomes carbon dioxide and is released into the atmosphere
• when plants, algae and animals die, some animals and microorganisms feed on their bodies
• carbon is released into the atmosphere as carbon dioxide when these organisms respire
• by the time the microorganisms and detritus feeders have broken down the waste products and dead bodies of organisms in ecosystems and cycled the materials as plant nutrients, all the energy originally absorbed by green plants and algae has been transferred
• combustion of wood and fossil fuels releases carbon dioxide into the atmosphere.

Suggested ideas for practical work to develop skills and understanding include the following:

• design and carry out an investigation to measure the rate of decay of bread by, for example, exposing cubes of bread to air before placing them in sealed Petri dishes at different temperatures and/or different moisture levels
• investigate the rates of decay using containers (eg thermos flasks) full of grass clippings, one with disinfectant, one with dry grass, one with wet grass and one with a composting agent. If the container is sealed, a thermometer or temperature probe can be placed through a cotton wool plug to monitor the temperature
• potato decay competition, using fresh potatoes. Candidates decide on the environmental conditions and the rate of decay is measured over a two week period
• role play exercise – A4 sheets labelled with different stages of the carbon cycle. Candidates arrange themselves in the correct order to pass a ball along labelled as carbon
• using a sensor and data logger to investigate carbon dioxide levels during the decay process.