(a)The process involved in the breakdown of glucose in living cells occurs in two stages namely anaerobic and aerobic stages
(i) Anaerobic process: In this process, glucose is broken down into pyruvic acid in the presence of enzyme or hexokinase by a process called glycolysis. Oxygen is absent in this process. For each of the glucose respired, two molecules of ATP are released.
(ii) Aerobic process: In the mitochondria, pyruvic acid under the influence of enzymes is oxydised to Acetyl-coenzyme A (AcetylcoA) releasing carbon (iv) oxide. Acetyl COA enters the krebs cycle or citric acid cycle where series of changes take place and oxygen combines with hydrogen to form water. In the process, a large quantity of energy is generated in the form of ATP (Adenosine triphosphate). The equation for the overall process is as follows:
C\(_6\)H\(_1\)\(_2\)O\(_6\) + 6O\(_2\) → 6H\(_2\)O + 6CO\(_2\) + Energy.
In yeast cells, in the absence of oxygen, glucose is broken down into ethanol, carbon (iv) oxide and energy. C\(_6\)H\(_1\)\(_2\)O\(_6\) → 2C\(_2\)H\(_5\)OH + 2CO\(_2\). Energy. Strenuous exercise results in depletion of oxygen in the muscles. Hence, pyruvic acid is converted to lactic acid which can be oxidized further to yield energy.
(b) Glycogen can be converted to glucose during exercise when the body needs more glucose to produce sufficient energy and when one is anxious, sick, full of fear, fasting or hungry. This results in a fall in the blood sugar level.
Experiment to demonstrate that oxygen is released during Oxygen photosynthesis. Aim: To show that oxygen is released by green Test tube plant during photosynthesis.Apparatus: Two beakers, two funnels, two test tubes, water plant (Elodea).Method — Fill the beakers with Gas bubble water and place the water plant in beaker A and B. Invert a glass funnel in the beaker in order to enclose the water plant. Invert a test tube with water over the stem of the funnel. Experiment A is exposed to sunlight while B is covered with a cardboard paper or placed in the dark. Leave both experiments for sometime. Water containingObservation: Bubbles of gas appear or are noticed in experiment A. carbon IV oxide (CO2) When tested with a glowing splint, it rekindles, confirming that the Beaker gas is oxygen. This observation in A is absent in B.Conclusion: What happens in A shows that oxygen is liberated during photosynthesis.