1. CYCLES

2. Generalized Cycle
There are several natural cycles within an ecosystem.
Materials are continually being reused
There is no net loss of materials
Therefore life within the ecosystem is not challenged.

3. Materials in Living Animals
Plants
Materials in Living Animals
Dead
Dead Animals
Absorption through roots
Animal Excreta
Reservoir of Minerals in soil moisture
Air
Soil
Feeding
Decomposition
Generalized Mineral Cycle in Nature

4. Mineral cycles also operate in both marine and fresh water aquatic habitats
Minerals in solution are absorbed by aquatic plants which are eaten by animals
Decomposers return the minerals to the water as they break down dead plants and animals.

5. Carbon Cycle

6. Carbon Cycle
Green plants take Carbon Dioxide and manufacture food in the form of carbohydrates.
This is how carbon enters the cycle
Carbohydrates form the major substrate for synthesis of other carbon based compounds
Animals obtain carbon compounds when they feed directly or indirectly on plants
Decomposers obtain carbon compounds when they break down and feed on dead bodies
The process of decay returns carbon to the cycle

7. Carbon Cycle
Both animals and plants when they respire return carbon dioxide to the environment
The actions of acids on the carbonates that make up shells and corals and other skeletons also return carbon dioxide to the environment
Dead bodies of animals and plants become buried in the earth’s crust and over millions of years becomes fossil fuels.
Burning of fossil fuels return carbon that was stored back into the environment

8. Nitrogen Cycle 1

9. Nitrogen Cycle 2

10. Nitrogen Cycle Proteins require nitrogen for their synthesis.
Nitrogen in abundant in the air (79%)
However nitrogen has to be ‘fixed’ i.e. converted to compounds that plants can use.
Plants take nitrogen from the soil largely in the form of nitrates.
In nature nitrogen fixation takes place two ways:
Lightning discharges ( cause nitrogen to combine with oxygen to form oxides of nitrogen. These oxides dissolve in rain water to form nitric acid. Nitric acid combines with ions in the soil to form nitrates.)
Nitrogen-fixing bacteria are present in the soil and root nodules of leguminous plants eg. Black-eyed peas, soy beans and pigeon peas. These bacteria combine nitrogen with oxygen to form nitrates.

11. Nitrogen Cycle
Animals get protein from plants. They digest these proteins and use the amino acids obtained to build their own body proteins
Dead plants and animals and animal waste are acted upon by decay bacteria ( putrefying bacteria) to produce ammonia in the soil.
Nitrifying bacteria in the soil convert ammonia to nitrites and nitrates which plants absorb.
Nitrogen is returned to the atmosphere by the action of denitrifying bacteria.

12. Summary
These cycles illustrate the interdependence of organisms and their physical environment
The cycles also show that there exists a very delicate balance between the components of any ecosystem and that of the whole earth
Stress is placed on the cycle of nature when materials are removed from one stage too quickly for them to be replenished by normal means
Excess of particular materials are added so rapidly that they cannot be used up and accumulate.
Disruption of the cycles also take place when materials are converted into forms which are no longer biodegradable.

13. Return

14. Return

15. Task 1 You will be divided into groups of 8
Use the materials given to each group to construct a chart of either the nitrogen or carbon cycle.
Elect a group leader who would make a brief presentation to the class about their groups cycle.

16. Task 2 (Home Work) 1 Materials in living Plants
Materials in Living Animals
Air
Dead
Plants
Dead Animals 3 2
Animal Excreta
Reservoir of Minerals in soil moisture
Soil
Generalized Mineral Cycle in Nature

17. Answer the following questions based on the diagram for task 2
Name one natural cycle that shows a similar pattern to that illustrated in the diagram (1)
State the processes that occur at each of the numbered stages 1,2,3 (3)
Name the group of organisms that operate at 2 (1)
Give two reasons why the cycle you named might be important (2)
Describe how the cycle you named might be disrupted (2)
Describe two steps which can be taken to compensate for disruption to the cycle named (4)