Microbial decomposition in material cycling

Materials move between the living and non-living parts of an ecosystem. The living parts are its biotic components, such as plants and microorganisms. The non-living parts are its abiotic components, such as soil and air. Recycling makes materials available again as resources and building blocks for future organisms.

Microorganisms, including bacteria and fungi, decompose dead organisms and waste by breaking down their material. This releases mineral ions into the soil. As the microorganisms respire, they also return carbon to the atmosphere as carbon dioxide, $$\ce{CO2}$$.

Plants absorb mineral ions from the soil and use them for growth. Materials in plants can then pass to other organisms when they feed. When organisms die or produce waste, microorganisms can break down this material, returning materials to the non-living environment.

Chemical cycling in ecosystems

The substances that organisms need do not remain in one place. They move between organisms and the non-living environment, which includes the air, water and soil. As they move, the matter in these substances is reused.

Organisms take substances in from their surroundings. For example, plants take up water and mineral substances from the soil. Chemicals can then pass from one organism to another when one feeds on the other.

Organisms also release waste, and eventually they die. Decomposers break down waste and dead material, returning substances to the non-living environment. These substances become available for organisms to take up again.

This repeated movement between living organisms and their surroundings is chemical cycling. The substances may change form as they move, but their matter is reused rather than being used only once.

Carbon cycle

The carbon cycle transfers carbon between organisms and the non-living environment. Carbon moves from the atmosphere into living things and is then returned to the atmosphere, where plants can take it in again.

Carbon entering organisms

During photosynthesis, plants take in carbon dioxide from the atmosphere. They use its carbon to make organic substances that become part of the plant. When other organisms feed on plants, carbon passes to them in the food. Carbon can then pass between organisms as they feed, providing material for growth.

Carbon returning to the atmosphere

Organisms release carbon dioxide into the atmosphere through respiration. This includes plants, animals and microorganisms.

When organisms die or produce waste, decomposer microorganisms break down the material. As the decomposers respire, they release carbon dioxide into the atmosphere. Plants can take up this carbon dioxide during photosynthesis, allowing the carbon to pass through the cycle again.

Water cycle

The water cycle is the continuous movement of water between the environment and organisms. Water changes location and can change state, but it is continually reused.

Water evaporates from surfaces, including seas, becoming water vapour in the air. Plants also release water vapour into the air through transpiration.

As water vapour cools, it condenses into tiny liquid water droplets that form clouds. Water then falls to the ground as precipitation, such as rain or snow.

Precipitation supplies fresh water on land. Plants and animals take in this water and return water to the environment. Water also moves over and through the ground into rivers, which eventually drain into seas. From there, it can evaporate again, continuing the cycle.