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Locomotion and Movement

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CBSE Gujarat Board Haryana Board

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Class 10 Class 12

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 ?


(a) Shortening of muscle is due to the sliding of actin filament over myosin filament. According to sliding filament theory, the cross bridges take energy from ATP molecules and get rotated inward. Thus sarcomeres contract as Z-lines come closer. Due to contraction of sarcomeres finally whole muscle fibre contracts. During relaxation link between cross bridges and actin filaments get broken and cross bridge rotate outward. Thus sarcomeres expand as Z-lines get apart resulting in increase in the length of the mucle fibre.

(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.



how many pairs of floating ribs are present in humns?


What is the rib cage made of ?

The thoracic vertebrae, ribs and sternum together form the rib cage. 

Total number of pair of ribs?


What is gout ?

Gout is the inflammation of joints due to accumulation of uric acid crystals. 

Which pairs are called false ribs?

8th, 9th and 10th pairs of ribs are called as false ribs or vertebrondral ribs.