Ecology

ECOLOGY & ECOSYSTEMS

• Need to know definitions:
• Population - all the organisms of a particular species found in an ecosystem at any one time.
• Community - the population of all species (animals, plants and decomposers) found in a particular ecosystem at any one time.
• Habitat - a part of the ecosystem that can provide food, water, shelter and a breeding sight for a living organism.
• Only about 10% of the energy entering a trophic level is passed on to the next trophic level; this is why a very small number of food chains have more than 5 trophic levels. There just isn't enough energy left for another trophic level.
• 100% -- 10% -- 1% -- 0.1% -- 0.01%
• Losses of energy:
• Respiration
• Form of heat
• Excretion and decomposition
• Digested
• Used in the body
• There is a term known as "food chain" for "food web" that describes the relationship between living organisms in an ecosystem. Members of the food chain are such of producers, consumers, secondary consumers, tertiary consumers and eventually a top predator.

Carbon Cycle

• Carbon is a compound of all major biological molecules. It is obtained through carbon dioxide in the atmosphere by plants and transferred through the food chain. It remains (the carbon dioxide concentration) relatively constant at 0.04%. It is removed and restored as it may.
• Release of Carbon Dioxide in the Atmosphere:
• Respiration: organisms respire, and carbon dioxide released.
• Combustion: burning of fossil fuels.
• Decomposition: decaying of living organisms is done by decomposers (fungi, bacteria). End products of decomposition include carbon dioxide and respiration of decomposers has also.
• The carbon cycle ensures a continuous supply of carbon dioxide to carry out photosynthesis. It enables a linear flow of energy. The carbon compounds pass through the trapped solar energy passes from organism to organism in the food chains of an ecosystem.
• Carbon Dioxide Removal:
• During photosynthesis, the green plants absorbs carbon dioxide from the atmosphere and use it to manufacture glucose. Glucose maybe changed to other organic compounds like fats and proteins. When animals feed on green plants, the carbon compounds become part of the bodies of these animals. The carbon compounds may be preserved in fossil fuels such as coal, natural gas and oil.

Nitrogen Cycle

• 1) Fixation: this is the first step in the process of making nitrogen useable for plants. Here nitrogen is changed into ammonium and other nitrogen containing compounds by the following:
• Lightening - converts nitrogen in the air to oxides of nitrogen.
• Bacteria - free living nitrogen-fixing bacteria converts nitrogen gas into ammonia and used by bacteria to make proteins. When the bacteria die, their proteins release ammonia into the soil. Rhizobium (e.g.) usually live in root nodules of leguminous plants. Ammonia is used up by plants making amino acids.
• Heber's process - 30% of total fixed nitrogen is produced industrially using high temperatures and pressure to convert nitrogen and hydrogen into ammonia.
• 2) Nitrification: this is the process by which ammonium gets changed into nitrates by bacteria. Nitrates are the compounds that the plants can then absorb.
• 3) Assimilation: this is how plants get nitrogen; they absorb nitrates from the soil into their roots which are used by the plant. This nitrogen is then passed along food chains through feeding.
• 4) Ammonification: decomposition by bacteria and fungi produces ammonia from decay of organic compounds and re-enter the nitrogen cycle.
• 5) De-Nitrification: de-nitrifying bacteria use nitrates in the soil as an energy source and convert them into nitrogen gas that enters the air.
• Exam Qs:
• 1) Nitriication affects plants: -nitrifying bacteria
• -ammonia changes to nitrites
• -nitrites to nitrates
• -used as plant protien
• 2) How nitrates absorbed: -active transport
• -against concentration gradient
• -root hair cell absorbs them

Water Cycle