Chapter 2 Lesson 2 Cycles in Nature

The Water Cycle The movement among the oceans, atmosphere, land and living things is known as the water cycle Precipitation: water moving from the atmosphere to the land and oceans in the form of rain, snow, sleet and hail.

Evaporation: sun’s heat causes water to change from liquid to vapor. When the water vapor cools during the process of condensation it forms a liquid that can fall back to the Earth as precipitation.

Ground Water: Some precipitation seeps into the ground and may stay underground for hundreds or thousands of years. Transpiration: All organisms are made of ~70% water. One function is to regulate body temperature through perspiration and evaporation which returns water to the environment in a process known as transpiration

The Carbon Cycle The element carbon is essential to living things because it is part of all biological molecules (organic compounds) The movement of carbon from the environment, into living things, and back to the environment is called the Carbon Cycle.

Photosynthesis: the process by which carbon cycles from the environment into living things. Plants use CO2 from the air to make sugars. Most animals get the carbon they need from eating plants Respiration: sugar molecules (C6H12O6) are broken down to release energy. CO2 & H20 are released.

Decomposition: the breakdown of dead materials into CO2 & H20 Decomposition: the breakdown of dead materials into CO2 & H20. This returns carbon to the environment Combustion: the carbon in coal, oil, & natural gas returns to the atmosphere when these fuels are burned.

The Nitrogen Cycle Nitrogen cycle is the movement of nitrogen from the environment to living things and back again. ~ 78% of the Earth’s atmosphere is nitrogen gas, but most organisms can’t use the gaseous form Nitrogen-fixing bacteria in the soil are able to change the gas into a form used by plants

Most animals get the nitrogen they need by eating plants The final step in the cycle is also performed by bacteria in the soil. Bacterial decomposers return the nitrogen to the atmosphere as nitrogen gas.