1. Food Chain

2. Food Webs Many individual food chains are interlocked into a food web

3. Oxygen, Carbon dioxide and Nitrogen cycles The food chain thus return simple forms of carbon to the soil and atmosphere. Oxygen, Carbon dioxide, nitrogen and water are cycling continously between the animal and plant worlds.

4. Oxygen Cycle Almost all living things need oxygen. They use this oxygen during the process of creating energy in living cells. Just as water moves from the sky to the earth and back in the hydrologic cycle, oxygen is also cycled through the environment. Just as water moves from the sky to the earth and back in the hydrologic cycle, oxygen is also cycled through the environment. Plants mark the beginning of the oxygen cycle. Plants mark the beginning of the oxygen cycle.

5. How do living organism use oxygen to produce energy? How do living organism use oxygen to produce energy?

8. These pathways must be followed by the respiratory chain located at the inner membrane of the mitochondria for oxygen to be consumed to produce energy These pathways must be followed by the respiratory chain located at the inner membrane of the mitochondria for oxygen to be consumed to produce energy(ATP)

9. Let us go back to deal with Oxygen cycle Let us go back to deal with Oxygen cycle

10. Plants are able to use the energy of sunlight to convert carbon dioxide and water into carbohydrates and oxygen in a process called photosynthesis. CO 2 + H 2 O+ energy………. O2+carbohydrates CO 2 + H 2 O+ energy………. O2+carbohydrates This means that plants "breathe" in carbon dioxide and "breathe" out oxygen. This means that plants "breathe" in carbon dioxide and "breathe" out oxygen.

11. Animals form the other half of the oxygen cycle. We breathe in oxygen which we use to break carbohydrates down into energy in a process called respiration (Previously demonstrated). O 2 + CHO……………CO 2 + H 2 O+ Energy O 2 + CHO……………CO 2 + H 2 O+ Energy Carbon dioxide produced during respiration is breathed out by animals into the air. Carbon dioxide produced during respiration is breathed out by animals into the air.

14. Nitrogen Cycle Nitrogen is an essential constituent of animal and plant matter as it forms proteins, which are the building blocks of life.

15. The ultimate source of nitrogen is atmospheric nitrogen but neither plants nor animals are capable of assimilating free nitrogen. Thus the process of converting atmospheric nitrogen to useful nitrogenous compounds by plants, passing it to animals and then the decomposition of these compounds to give back free nitrogen in the atmospheres is called Nitrogen Cycle. It is because of the nitrogen cycle that the percentage of nitrogen remains constant in the air.

18. A) How does nitrogen enter the soil? Biological nitrogen fixation When nitrogen fixation is brought about by micro-organisms the process is called biological nitrogen fixation. When nitrogen fixation is brought about by micro-organisms the process is called biological nitrogen fixation. Examples: Rhizobium, a nitrogen fixing bacteria present in the roots of some plants, fixes atmospheric nitrogen to the soil. Azotobacter and Clostridium are other free-living nitrogen fixing bacteria. Examples: Rhizobium, a nitrogen fixing bacteria present in the roots of some plants, fixes atmospheric nitrogen to the soil. Azotobacter and Clostridium are other free-living nitrogen fixing bacteria.

19. B) How does nitrogen enter the body of plants and animals? The nitrates in the soil are absorbed by plants as mineral salts. Plants convert the inorganic nitrates to organic proteins. The proteins from the plants enter the body of animals in form of food.

20. C) How is nitrogen returned to the soil? When plants and animals die their bodies decompose. The organic proteins undergo a series of chemical changes, brought about by micro-organisms e.g. ammonifying bacteria, nitrosomonas, nitrosococcus. These changes convert the proteins back to inorganic nitrates. In humans and animals some proteins are broken down to ammonia and carbon dioxide, which forms urea and is excreted out as urine. Their waste matter is also treated by micro-organisms to convert it into inorganic nitrates.

21. Micro-organisms involved in Nitrogen Cycle