Cycles of Matter

1. Cycles of Matter Chapter 2 Section 2

2. Recycling Matter • The way matter is recycled in ecosystems is similar to the way the metal in old cars is recycled. • Like the supply of metal for building cars, the supply of matter in an ecosystem is limited. • If matter could not be recycled, ecosystems would quickly run out of the raw materials necessary for life.

3. Energy • Energy, on the other hand, is not recycled. • You must constantly supply a car with energy in the form of gasoline. • Ecosystems also must be constantly supplied with energy, in the form of sunlight. • Gasoline and the sun’s energy cannot be recycled. They must be constantly supplied.

4. Energy and the Ecosystem • Energy enters an ecosystem from the producers to the consumers to the decomposers. • In contrast, matter cycles through an ecosystem over and over. • Matter in an ecosystem includes: water, oxygen, carbon, nitrogen and many other substances.

5. The Water Cycle • Water is recycled through the water cycle. • The water cycle is the continuous process by which water moves from Earth’s surface to the atmosphere and back. • The process of evaporation, condensation, and precipitation make up the water cycle.

7. Evaporation • The process by which molecules of liquid water absorb energy and change to the gas state is evaporation. • In the water cycle, liquid water evaporates from Earth’s surface and forms water vapor, a gas, in the atmosphere. • Most water evaporates from the surfaces of oceans and lakes. • The energy for evaporation comes from the sun.

9. Condensation • As the water vapor rises higher in the atmosphere, it cools down. • When it cools to a certain temperature the vapor turns back into tiny drops of liquid water. • The process by which a gas changes to a liquid is called condensation. • The water droplets collect around particles of dust in the air, eventually forming clouds.

11. Precipitation • As more water vapor condenses, the drops of water in the cloud grow larger and heavier. • Eventually the heavy drops fall back to the Earth in a form of precipitation – rain, snow, sleet, or hail. • Most precipitation falls back into oceans or lakes. • The precipitation that falls on land may soak into the soil and become groundwater. • Or the precipitation may run off the land, ultimately flowing into a river or ocean once again.

13. The Carbon and Oxygen Cycle • Two other chemicals necessary for life are carbon and oxygen. • The processes by which they are recycled are linked together. • Carbon is the building block for the matter that makes up the bodies of living things. • It is present in the atmosphere in the gas carbon dioxide. • Producers take in carbon dioxide from the atmosphere during photosynthesis.

15. Photosynthesis • In this process, the producers use carbon from the carbon dioxide to produce other carbon containing molecules. • These molecules include sugars and starches. • To obtain energy from these molecules, consumers break them down into simpler molecules. • Consumers release water and carbon dioxide as waste products.

16. The Nitrogen Cycle • Like carbon, nitrogen is a necessary building block in the matter that makes up living things. • Since the air around you is about 78 percent nitrogen, you might think that it would be easy for living things to obtain nitrogen. • Most organisms cannot use the nitrogen in the air. • Nitrogen gas is called “free” nitrogen, meaning it is not combined with other kinds of atoms. • Most organisms can use nitrogen only once it has been “fixed” or combined with other elements to form nitrogen-containing compounds.

18. Nitrogen Fixation • The process of changing free nitrogen gas into a usable form of nitrogen in called nitrogen fixation. • Most nitrogen fixation is performed by certain kinds of bacteria. • These bacteria live in buds called nodules on the roots of certain plants. • These plants, known as legumes, include clover, beans, peas, alfalfa, and peanuts.

19. Legumes and Nitrogen • The relationship between the legumes and the bacteria is an example of mutualism. • Both the bacteria and the plant benefit from this relationship. • The bacteria feed on the plant’s sugars and plant is supplied with nitrogen in a usable form.

20. Farmers • Many farmers make use of the nitrogen fixing bacteria in legumes to enrich their fields. • Every few years, a farmer may plant a legume such as alfalfa in a field. • The bacteria in the alfalfa roots build up a new supply of nitrogen compounds in the soil. • The following year, the new crops planted in the field benefit from the improved soil.

21. Return of Nitrogen to the Environment • Once the nitrogen is fixed into chemical compounds, it can be used by organisms to build proteins and other complex substances. • Decomposers break down these complex compounds in animal wastes and in the bodies of dead organism. • This returns simple nitrogen compounds to the soil. • Nitrogen can cycle from the soil to producers and consumers many times. • At some point, bacteria break down the nitrogen compounds completely. • These bacteria release free nitrogen back into the air and the cycle starts again.