1. Biocycles

2. Water Cycle

3. Nitrogen Cycle

4. Why Nitrogen?
The Nitrogen cycle is important because nitrogen is an essential element involved in protein synthesis.

5. Why a cycle?
Atmospheric Nitrogen N2(approx. 78% of the earth’s atmosphere) is not directly accessible to most plants or animals.

6. To NO2- (nitrites) which are still relatively inaccessible
In order for nitrogen to become useable (available for plants and animals), it goes through a cycle which changes it from:
N2 (gaseous nitrogen) to NH3 (urea or ammonia)
To NO2- (nitrites) which are still relatively inaccessible

7. And finally to NO3- (nitrate) which is more accessible to plants because it only has single bonds between the nitrogen and oxygen molecules, not double or triple as in the case of nitrite and N2 gas)

8. Bacteria
Bacteria play an important role in the nitrogen cycle, they are able to:
Convert N2 into NH3
Convert NH3 into NO2-
Convert NH3 and NO2- into NO3-

9. Bacteria can also fix nitrogen from N2 into the soil
Bacteria can also fix nitrogen from N2 into the soil. The nitrogen fixing bacteria are found in lumps on the roots called root nodules. The bacteria and the plant have a symbiotic relationship: the bacteria benefits by having food and shelter from the plant and the plant benefits by having nitrates produced by the bacteria.
Roots of a legume plant (peas, beans and clover).

10. Denitrifying Bacteria
Other bacteria called denitrifying bacteria also remove the nitrates and nitrites from the soil and return the nitrogen back to the atmosphere.

11. decomposition by bacteria & fungi
Nitrogen in
the air
nitrogen fixing plant
eg pea, clover
animal protein
plant made
protein
dead plants & animals
urine & faeces
denitrifying
bacteria
root nodules
(containing nitrogen
fixing bacteria)
decomposition by bacteria & fungi
nitrates absorbed
nitrates
ammonia
bacteria
nitrites
bacteria
(nitrifying bacteria)

12. Biocycles
The Phosphorus Cycle

13. Why Phosphorus?
Phosphorus is important in the molecule ATP (Adenosine TriPhosphate), an important energy carrying molecule that acts like a rechargeable battery during cell activities such as photosynthesis and respiration.

14. The cycle
Phosphates/phosphorus is a macronutrient, which means it is needed in large quantities, however it is in limited availability in most habitats, so it’s return to the cycle is very important.
Essentially plants are responsible (with the assistance of fungi) for making soil phosphorus available for animals.
Animal excretion and death returns the phosphorus to the soil so the cycle can continue.
Weathering of phosphorus rich rocks is a further source of phosphorus.

15. The cycle

16. Biocycles
The Carbon Cycle

17. Again, carbon is an essential element for life, organic molecules such as carbohydrates are built on a carbon chain backbone. The majority of carbon in the atmosphere is in the form of carbon dioxide (CO2) and is not accessible to animals.