1. Carbon Cycles through the Environment

2. Carbon Cycles Through the Environment §Carbon dioxide makes up only.03% of the air but it is an important gas. It is used by plants during photosynthesis. The carbon dioxide is taken in through the plant leaves. Green plants use carbon dioxide to manufacture their own food; they release oxygen as a by-product. Animals then use the plants for food. For animals, carbon dioxide is a waste product that is given off when they obtain energy from their food. The process by which carbon dioxide is taken from the air, and then returned is called the carbon cycle. The amount of carbon dioxide used by plants is approximately equal to the amount used by animals and other natural processes. This balance is changed by the burning of fossil fuels such as oil and coal. As a result, it appears that the amount of carbon dioxide in the atmosphere is increasing.

3. Carbon Cycles Through the Environment Sketch the carbon cycle and describe in words what each arrow means.

4. Nitrogen Cycles through the Environment

5. §Notrogen is the most plentiful of all gasses in the air, making up about 78% of the volume of the atmosphere. You (and other animals) do not use the nitrogen in the air; although you take it into your lungs with each breath, you exhale it out. §There are plants that need nitrogen to make proteins, but they cannot get it from the air. Some bacteria that live in the soil and the roots of some plants, such as clover, take nitrogen from the air and change it into forms that plants can use. §The action of lightning can also make useable nitrogen compounds in the air. The compounds are carried by rain into the soil and absorbed through the roots of the plants. §Animals eat the plants and get the nitrogen they need through the food web. Decomposers eat dead plants and animals and cause nitrogen to be released back into the atmosphere. §This process is called the nitrogen cycle. The cycle returns as much nitrogen to the air as is removed, so that atmospheric nitrogen levels stay approximately constant.

6. Nitrogen Fixing Rhizobium Bacteria live in roots of leguminous plants like soybeans, clover and alfalfa. The spherical growths on soybean roots are nodules containing Rhizobium japonicum bacteria, which use nitrogen from the atmosphere to make nitrogenous plant nutrients.

7. A mass of the bacteria are revealed through the microscope in a nodule that has been opened.

8. Ecological Significance: Bacteria are Decomposers Decay is brought about chiefly by vast armies of saprophytic bacteria, though larger fungi contribute to the process. If there were no decay, the remains of dead plants and animals and the waste of cities would accumulate so fast that they would soon interfere with the life of new generations. The saprophytes also enrich the soil by returning minerals to it and release carbon dioxide into the air for plants to use. Thus the balance of nature is maintained.

9. Nitrogen Cycles Through the Environment Sketch the nitrogen cycle and describe what each arrow means in the cycle.

10. Phosphorous Cycles Through the Environment

11. Phosphorus Cycles through the Environment §Phosphorus occurs in the rocks of the earth’s surface. Erosion releases phosphate, a molecular combination of phosphorus and oxygen. Dissolved in water, this is taken up by plants in order to form proteins. §As animals eat the plants, phosphorus cycles through the food chain. Decomposers eventually consume the organisms and return the phosphorus to the soil. §Soils are carried by erosion down rivers where they are eventually deposited in deltas and the ocean floor and are incorporated into sedimentary rocks. Alternatively, phosphorus in the water can be taken up by plankton and cycle through an oceanic food chain. §Phosphorus is an essential to plant growth. This is why phosphorus is used on farms for fertilizer. Phosphorus in water can cause algae to bloom in massive quantities and lead to the loss of dissolved oxygen and the massive death of fish in the water

12. Phosphorus Cycles through the Environment Sketch the diagram and describe what each arrow is doing.