Question

Give scientific reasons.
a. Oxygen is necessary for complete oxidation of glucose.
b. Fibers are one of the important nutrients.
c. Cell division is one of the important properties of cells and organisms.
d. Sometimes, higher plants and animals too perform anaerobic respiration.
e. Kreb's cycle is also known as citric acid cycle.

Answer 1

a. Glucose can be used by two pathways i.e. aerobic and anaerobic respiration. Glucose is completely oxidised only in the presence of oxygen and results in the release of energy. It undergoes three steps to finally reach its fate - glycolysis, Kreb's cycle and electron transport chain reaction. In anaerobic respiration, glucose undergoes partial oxidation and results in the release of energy which is comparitvely less to the energy released during aerobic respiration.

b. Fibers are one of the imporatant nutrients beacuse they help in the digestion of foods although they themselves are not digestable. They help in the egestion of undigested substannces which is also a reason why we are advised to have fiber rich food in case of constipation. Fibers are naturally present in leafy vegetables, fruits, cereals, etc.

c. Cell division is is one of the important properties of cells and organisms because:

• it is the means of asexual reproduction in unicellular organisms
• the zygote which is formed of single cell, transforms into an adult composed of millions of cells formed by successive divisions
• it is the basis of repair for old and worn out tissues
• it also results regeneration of organisms
• it forms the basis of evolution to various life forms

d. When availability of oxygen is limited, higher animals and plants can also show anaerobic respiration. For example, during exercise the availability of oxygen to the muscles is limited, as a result of which they undergo anaerobic respiration and results in the production of lactic acid. Similarly plants may also show anaerobic respiration in case of water logged roots and result in the production of ethyl alcohol, carbon dioxide and energy. Althought the energy obatained through anerobic respiration is less as compared to the energy released during aerobic respiration.

e. Krebs cycle is also known as citric acid cycle because the first product formed during the cycle is citric acid. Citric acid is formed by the condensation of an acetyl group with oxaloacetic acid and water.