Chapter 3: How Ecosystems Work Section 3.2: The Cycling of Materials

In ecosystems resources are used over and over again: otherwise, they would soon be gone, and life could no longer exist.

There are three cycles that allows materials to be reused: The Water Cycle The Carbon Cycle The Nitrogen Cycle

Water Cycle Water is essential to life. Although water is destroyed in photosynthesis and created during cellular respiration, the overall amount on Earth stays the same. The sun provides the energy that drives the water cycle. As water vapor cools in the atmosphere, it condenses to form tiny droplets in clouds.

Water Cycle cont. When the clouds meet cold air, the water returns to the Earth again in the form of precipitation. The precipitation that falls onto land may just evaporate again. Some collects into streams and rivers – flows into the ocean Some absorbs into the ground.

Water Cycle cont. Water that soaks into the soil may be used immediately by plants, or it may seep down into the soil and rocks until it can’t travel further.

This layer of underground water is called groundwater.

Carbon is essential component of the proteins, fats and carbohydrates necessary for life.

Carbon Cycle Carbon enters an ecosystem when producers take in carbon dioxide from the atmosphere during photosynthesis. When consumers eat the producers, they obtain carbon. As the consumer breaks down food particles during cellular respiration, the carbon is released back into the atmosphere, as carbon dioxide.

Humans effect on carbon cycle Fossil fuels are essentially stored carbon left over from the remains of organisms. When we burn fossil fuels, we release this carbon into the atmosphere as CO 2.

All organisms need nitrogen to build proteins.

Nitrogen is around us in large quantities; nitrogen composes 78% of the atmosphere

Nitrogen cycle The only organisms that can use nitrogen directly from the atmosphere are a few bacteria known as nitrogen-fixing bacteria. All other organisms are dependent on these bacteria for nitrogen. Nitrogen fixing bacteria live within the roots of legumes such as peas, beans, and clover.

Nitrogen cycle The bacteria use sugars produced by the plants and, in exchange, produce nitrogen containing compounds. The excess nitrogen is released into the soil. Some nitrogen-fixing bacteria live freely in the soil. Plants that do not have this type of bacteria get nitrogen from the soil.

Nitrogen Cycle Animals get nitrogen by eating plants or other animals. The nitrogen is returned back into the atmosphere by decomposers breaking down wastes such as urine, dung, dead organisms.