Natural Cycles

Ecology Unit

• Water and certain chemicals- such as carbon, oxygen, and nitrogen- are constantly being exchanged between air, water, soil, plants and animals.

The Water Cycle

Water Cycle

• EVAPORATION. The sun heats water in soil, rivers, lakes, and oceans causing it to evaporate and become water vapor, a gas.

• CONDENSATION. Water vapor rises, cools, and condenses to form tiny water droplets or ice crystals in clouds.

• PRECIPITATION. The water falls back to earth as rain, snow or other precipitation. Most water returns to the sea or sinks into underground water sources.

• Plants take up water from the soil through their roots. They transpire most of the water they take up.

• Water makes up almost 75% of living things. • When plants decompose, water is released.

The Carbon Cycle

Carbon and Oxygen Cycle

• Carbon and oxygen make up the gas carbon dioxide.

• Plants take in carbon dioxide during photosynthesis. Plants use the carbon to make food.

• This food provides matter and energy to form new plants

• During photosynthesis, plants also release oxygen into the air. Animals breathe in oxygen.

• Plants also take in oxygen during respiration.• Both animals and plants give off carbon

dioxide during respiration.

• Dead plants and animals produce carbon dioxide as they decay.

• Carbon from ancient dead plants is stored as fossil fuels, such as coal, oil and gas.

Nitrogen Cycle

• Nitrogen gas makes up about 78% of our air. But, plants and animals cannot use nitrogen directly from the air.

• Instead:

The Nitrogen Cycle

• 1. Certain bacteria in the soil and plant roots are able to take nitrogen gas from the air and change it into a form of nitrogen that is usable.

• This process is called nitrogen fixation.

• 2. Some tissue in dead plants and animals, and even in animal wastes, contains nitrogen. Several kinds of soil bacteria change this nitrogen into nitrate, which plants can absorb through their roots.

• The cycle is complete when other soil bacteria take in nitrates and release nitrogen gas back into the air.

The Phosphorus Cycle

The Phosphorus Cycle

• There are many environmental conditions which will affect the availability of phosphorus to plants.

• Phosphorus is most readily available to be absorbed by plants in an environment which is just slightly acidic.

• If conditions are too acidic or too basic, phosphorus will be converted into an insoluble or unusable form.