Cycles in the Ecosystem

•          All matter and nutrients needed by organisms is already on the planet. There is very little new input from outer space.

•          This is why it is important to recycle all matter.

•          The important elements for organisms are carbon (C), hydrogen (H), nitrogen (N), and oxygen (O).

•          When an organism dies, it is broken down into simple compounds which can be used by other organisms.

1.         Carbon-oxygen cycle

            a.         Carbon dioxide from the atmosphere is used by plants in photosynthesis.

            b.         The sugar they make is a source of energy as well as for making other compounds such as proteins and starch.

            c.         Plants give off oxygen as a waste product, which is used by plants and animals in respiration.

            d.         In respiration, the carbon compounds are broken down into carbon dioxide.

            e.         In nature, the cycle is balanced - the amount of carbon dioxide produced by respiration is used by plants in photosynthesis.

            f.         Because of human activity, the cycle is currently out of balance.

            g.         There is more carbon dioxide being released into the atmosphere than plants can use. Most of this comes from burning fossil fuels:

                        i.         vehicles

                        ii.        factories

                        iii.       producing electricity

                        iv.       heating our homes

            h.         There are also natural sources of carbon dioxide

                        i.         volcanoes

                        ii.        forest fires

                        iii.       activity of decomposers

            i.         This is leading to a rise of carbon dioxide in the atmosphere causing global warming.

2.         Nitrogen cycle

            a.         The air is 78% nitrogen (N₂) but plants and animals cannot use nitrogen gas.

            b.         Organisms need nitrogen to make protein.

            c.         Certain bacteria are able to convert N₂ gas to a form that is useful to plants.

            d.         Animals can then get nitrogen by eating plants.

            e.         The bacteria are called “nitrogen fixers.” They convert nitrogen gas into nitrate and other bacteria convert the nitrate into ammonia.

            f.         The bacteria live in small bumps on the roots of special plants called legumes. The bumps are nodules.

            g.         Common legumes are peas, beans, clover, and alfalfa.

            h.         This is an example of mutualism. The plant provides a safe environment for the bacteria while the bacteria provide the plant with nitrogen.

            i.         When an organism dies, the nitrogen in it’s body is returned to the ecosystem by decomposers.

            j.         By using legumes, farmers can avoid buying expensive fertilizers.

3.         Mineral cycle

            a.         Most minerals on the planet are trapped in rocks.

            b.         They are released by weathering. Weathering is the wearing down of rocks by the action of:

                        i.         Wind - small particles of sand act as a sandblaster. This erodes the rocks into sand.

                        ii.        Water - Water gets into cracks in the rocks. When it freezes it expands, breaking the rock apart.

                        iii.       Changes in temperature - rapid changes in temperature can make rocks split into smaller pieces.

                        iv.       Tree roots - small roots grow into cracks in the rocks and as they get larger they break the rock apart.

                        v.         Acid rain - caused by humans, acid rain slowly dissolves rocks.

            c.         Minerals can be dissolved in water and travel through rivers to lakes and the ocean.

            d.         Mining - a human activity that interferes with the mineral cycle by removing minerals from nature. Some minerals are recycled by humans but most end up in landfills.

4.         Water cycle

            a.         The amount of water in the biosphere is fairly constant.

            b.         At different times, different amounts can be in different phases:

                        i.         Solid - called ice

                        ii.        Liquid - called water

                        iii.       Gas - called vapor

            c.         Water enters the atmosphere by transpiration and evaporation. It returns to earth as precipitation.

            d.         Most evaporation occurs over the ocean. Most precipitates over the ocean but some of the vapor is blown by wind to precipitate over land.

            e.         Some water also evaporates and precipitates over land.

            f.         Water that precipitates over land can:

                        i.         Runoff - flow off the land back toward lakes and oceans.

                        ii.        Infiltrate - soak into the ground and contribute to the groundwater.

                        iii.       Water absorbed by plants can return to the atmosphere through transpiration.