Red or dark muscles store myoglobin and hence, oxygen for meeting the gap between supply and consumption during continuous activity. Therefore, these muscles can continuously work and respire aerobically for long periods. High proportion of these muscles allow athletes to participitate in long duration events like cycling, swimming and distance running etc.

(i) The anaerobic respiration occurs even in organisms that live in aerobic condition like human beings and angiosperms under conditions of oxygen scarcity that happens in the muscle tissue. Under intense use, muscles demand too much energy (ATP) and consume much more oxygen to produce that energy.
(ii) This high consumption leads to oxygen scarcity and the muscle cells begin to make lactic acid by anaerobic respiration trying to fulfill their energetic needs.
(iii) Similarly, yeast cells under deficient conditions carry out anaerobic respiration.

(i) Photosynthesis RuBP carboxylase, hexokinase and cytochrome oxidase.
(ii) Respiration Pyruvate dehydrogenase, ATPase, lactate dehydrogenase and cytochrome oxidase.

(i) Cellular respiration.
(ii) It is an amphibolic pathway, which involves both anabolism and catabolism.
(iii) Carbohydrates, proteins, fats and organic acids can be the raw material; but glucose is the form that ultimately enters the pathway.

(i) Stepwise oxidative breakdown The series of reactions transfers the energy of glucose to ATP.
(ii) Organic substances (used as substrates) The organic substances, which are catabolised in the living cells to release energy are called as respiratory substrates. Though any food stuff, carbohydrate, fat or protein may act as a respiratory substrate, the common respiratory substrate is glucose because it can be oxidised easily and is present abundantly.