Biochemical Cycles

1. Biochemical Cycles Matter is conserved, it is neither created nor destroyed only changed from one form to another

2. Biochemical cycles

3. Biochemical Cycles • Besides energy, all organisms require water and various nutrients. The elements of primary importance in these nutrients are carbon, nitrogen, oxygen, and phosphorus. Nutrients, unlike energy, are recycled through ecosystems in nutrient (biogeochemical) cycles. For each element, the cycle may involve 1) a reservoir, in which the nutrient is present but is temporarily unavailable, 2) an exchange pool, which is the primary source of nutrients, and 3) the biotic community, which consists of the organisms through which nutrients pass. Human activities have altered nutrient cycles.

4. Carbon Cycle

5. Carbon Cycle • The Carbon Cycle: All living things are composed of organic molecules, which are carbon-based compounds. Therefore, the carbon cycle is extremely important. The exchange pool for carbon is the atmosphere where the carbon resides in the form of carbon dioxide. Carbon enters the biotic community through the process of photosynthesis in which CO2 is removed from the air and used to make carbohydrates. The numbers in boxes in the diagram indicate the amount of carbon present in reservoirs, and the numbers with the arrows indicate the amount transferred between reservoirs.

6. Carbon Cycle • Carbon may return directly to the atmosphere when plants respire, which produces CO2, or carbon may travel to the next trophic level when the plant is eaten by a herbivore. The carbon may continue through to the next higher trophic level or to decomposers. At each level most of the carbon returns to the atmosphere as CO2 when the organisms at each level respire. The ocean also holds a large amount of carbon in the form of bicarbonates. Burning fossil fuels has significantly increased the amount of CO2 in the atmosphere by about 30% in just 40 years.

7. Carbon Cycle continued • There are 3 main reservoirs through which carbon moves: the atmosphere, terrestrial organisms, referred to as the biota, and the ocean. The atmosphere plays a central role in the carbon cycle. Here, carbon is found as carbon dioxide. Atmospheric carbon dioxide enters terrestrial food chains through plants when they perform photosynthesis. Some of the carbon picked up by plants returns to the atmosphere as carbon dioxide when plants respire. The rest of the carbon is used to build plant tissues. The carbon then either moves through the food chain, beginning with herbivores when they eat plants, or to decomposers, when plants die. Animals and decomposers return the carbon to the atmosphere as carbon dioxide when they respire. Oceans play a major role in determining carbon dioxide levels in the atmosphere. Carbon dioxide dissolves in ocean water and returns to the atmosphere when it spontaneously comes out of solution. Carbon leaves the water when it enters aquatic food chains via photosynthesis. The carbon is returned to the water when aquatic organisms respire. The burning of fossil fuels releases carbon dioxide from carbon stores long-buried in the earth. This adds to the levels of carbon dioxide in the atmosphere, increasing the greenhouse effect, and contributing to global warming.

8. Water Cycle

9. Water Cycle • The Water Cycle: Water covers the majority of the earth's surface. The water cycle is driven by solar energy that causes evaporation. Gravity plays a role in the movement of water from one place to another. Water enters the atmosphere as a result of transpiration from plants and evaporation from standing water and other surfaces. Water returns to the surface of the earth from the atmosphere when precipitation occurs. Much of the water that enters the soil percolates into the groundwater and slowly flows through pores into bodies of water. The numbers in the figure indicate water flow in km2/yr.

10. Phosphorous Cycle

11. Phosphorus Cycle • The Phosphorus Cycle: Phosphorus is important to living things because it is a component of cell membranes and DNA. In the phosphorus cycle, rocks and soil are the source. Producers pick up phosphorus from the soil and it is then passed on to consumers and decomposers. Consumers return phosphorus to the soil through their wastes and when their bodies decompose

12. Nitrogen Cycle

13. Nitrogen Cycle • The Nitrogen Cycle: Nitrogen is an important element for living things because it is a component of proteins and DNA. Although nitrogen gas, N2, in the atmosphere is plentiful, it must be converted by soil bacteria into compounds that plants can use. Plants use the nitrogen to produce proteins and other organic molecules. The nitrogen moves through the ecosystem as organisms consume other organisms, either living or dead. Some bacteria convert the nitrogen compounds in the soil back to N2, which then enters the atmosphere. Human activities, such as agriculture and industry, have introduced additional nitrogen into the cycle.

14. Nitrogen Cycle • Many essential nutrients recycle through ecosystems. The nitrogen cycle is one example of this process. All organisms require nitrogen for proteins and nucleic acids. How does this element enter living systems? The atmosphere is about 80% nitrogen gas. Nitrogen is unavailable to plants and animals in this form. In terrestrial communities, nitrogen-fixing bacteria live in the soil or in nodules on the roots of some groups of plants. These bacteria convert nitrogen gas into ammonia, which they use to synthesize the nitrogenous compounds they require. Excess ammonia is released into the soil where nitrifying bacteria convert it into nitrite and nitrate. Nitrate is absorbed by plants and used to produce protein and other important molecules. Now the nitrogen can move through the food chain as plants are consumed by animals. When plants and animals produce wastes or die, the process of decomposition releases nitrogen into the soil as ammonia. There are also denitrifying bacteria. They convert nitrate into nitrogen gas, thus completing the cycle.