7.2.2 - How Materials Are Cycled

Describe how materials cycle through the living and non-living components of an ecosystem.

• Organisms take in element from their surroundings e.g. soil, air.

• Elements converted to complex molecules which become biomass.

• Elements transferred along food chains.

• Elements returned to environment during excretion and decomposition of dead organisms.

Give three molecules which are cycled through ecosystems.

Oxygen, carbon dioxide, and water.

Describe the carbon cycle.

• Plants fix carbon dioxide into organic molecules during photosynthesis.

• The organic carbon-containing molecules are passed onto organisms that eat the plants.

• Carbon dioxide is released back into the atmosphere by respiration from animals and plants.

• Burning fossil fuels also releases carbon dioxide into the atmosphere.

Why is the carbon cycle important?

Carbon-containing molecules such as glucose are important for living organisms to grow and provide energy for vital functions within cells.

Describe the water cycle.

• Water from lakes and oceans evaporates.

• The evaporated water condenses into clouds and returns to Earth as precipitation.

• The water from precipitation is useful for life on land.

• The water then returns to rivers and oceans through surface runoff.

Why is the water cycle important?

Living organisms require water and the water cycle provides organisms on land with a continuous supply of water.

Why are microorganisms important for the cycling of materials through an ecosystem?

• Microorganisms (bacteria and fungi) return carbon to the environment by releasing carbon dioxide through respiration while they decompose dead matter.

• The decomposition of dead matter in soil returns mineral ions to the environment for other organisms to use e.g. plants use mineral ions for growth.