Materials cycle through ecosystems
Definition
Nutrient cycle
The repeated movement of a nutrient, such as carbon or nitrogen, between the living organisms and the non-living environment of an ecosystem.
- A biotic component is a living part of an ecosystem, including organisms and the dead material that came from them.
- An abiotic component is a non-living part of an ecosystem, such as the atmosphere, water or soil.
- Atoms of carbon, nitrogen, water and mineral ions move repeatedly between these components because matter is conserved.
Example
- A carbon atom may enter a leaf as carbon dioxide during photosynthesis, pass to a caterpillar by feeding and return to the atmosphere during respiration.
- If the caterpillar dies first, decomposers feed on it and release carbon dioxide as they respire.
Materials enter living organisms
- Producers absorb carbon dioxide from the air and take up water and mineral ions from their surroundings.
- Plants use these materials to make biomass, including carbohydrates, lipids, proteins and nucleic acids.
- Feeding transfers the atoms in this biomass along food chains from producers to consumers.
- Animals obtain water and nitrogen-containing compounds by eating and drinking because they cannot make matter from energy.
Materials return to the environment
Definition
Decomposer
An organism that gets its energy from dead or waste organic material.
- Respiration returns carbon dioxide and water to the abiotic environment.
- Excretion returns water and nitrogen-containing waste to the surroundings.
- Death and the production of faeces create organic material that bacteria, fungi and detritivores can break down.
- Decomposition releases mineral ions into the soil, while decomposer respiration releases carbon dioxide into the atmosphere.
Exam technique
- When you describe a cycle, name the substance, the process and the two places between which it moves.
- Write linked steps such as carbon dioxide in the atmosphere to plant biomass by photosynthesis, rather than saying that carbon goes into plants.
Recycling keeps materials available
- The supply of each chemical element on Earth is finite, so ecosystems depend on atoms being reused.
- Without decomposition, atoms would remain locked in dead biomass and the supply available to producers would fall.
- Energy is not a material and is not recycled because energy transferred through food chains is eventually dissipated to the surroundings as heat.
- A continuous input of light from the Sun supports new photosynthesis while materials continue to cycle.
Self review
- What is the difference between a biotic component and an abiotic component?
- How does carbon move from the atmosphere into a consumer?
- Name three processes that return materials to the abiotic environment.
- Why would nutrient cycles slow if decomposers were absent?
