Answer the following briefly :
(a) How does a muscle shorten during its contraction and lengthen during its relaxation?
(b) What biological functions are served by the skeletal system ?
(c) Why a red muscle fibre can work for a prolonged period while a white musule fibre suffers from fatigue after a shorter work ?
(b) Functions of skeletal system :
1. It provides mechanical support.
2. It protects the essential organs as heart, brain, spinal cord etc.
3. It plays role in breathing.
4. It helps in locomotion.
5. It checks entry of food into glottis at the time of swallowing of food.
(c) Red muscle fibres contain myoglobin which stores oxyen as oxymyoglobin and it also has more number of mitochondria. Due to sufficient supply of oxygen little lactic acid is formed. These muscles contract slowly and remain in the contracted state for a long time. TDue to more energy and less lactic acid these muscles do not fatigue in less time.
White muscle fibres have no myoglobin. So, lactic acid is formed in them. Moreover, their contraction is fast, thus they get fatigued.