NCERT Solutions Class 11 Biology Chapter 20 Locomotion and Movement

Question. Draw the diagram of a sarcomere of skeletal muscle showing different regions.
Answer        

Question. Define sliding filament theory of muscle contraction.
Answer Sliding filament theory of muscle contraction states that contraction of a muscle fibre takes place by the sliding of the thin filaments over the thick filaments.

Question. Describe the important steps in muscle contraction.
Answer The important steps muscle contraction:
-- Muscle contraction is initiated by a signal sent by the central nervous system (CNS) via a motor neuron and reach the neuromuscular junction. As a result, neurotransmitter (Acetyl choline) which generates an action potential in the sarcolemma.
-- This spreads through the muscle fibre and causes the release of calcium ions into the sarcoplasm.
-- Increase in Calcium level leads to the binding of calcium with a subunit of troponin on actin filaments and thereby remove the masking of active sites for myosin. Utilising the energy from ATP hydrolysis, the myosin head now binds to the exposed active sites on actin to form a cross bridge.
-- The actin filaments are pulled. As a result, the H-zone reduces. It is at this stage that the contraction of the muscle occurs.
-- After muscle contraction, the myosin head pulls the actin filament and releases ADP along with inorganic phosphate. ATP molecules bind and detach myosin and the cross bridges are broken and decreases the calcium ions contraction. As a result, masking the actin filaments and leading to muscle relaxation.

Question. Write true or false. If false change the statement so that it is true.

(a) Actin is present in thin filament
-- True

(b) H-zone of striated muscle fibre represents both thick and thin filaments.
-- False, H -zone of striated muscle fibre represents thick filament.

(c) Human skeleton has 206 bones.
-- True

(d) There are 11 pairs of ribs in man.
-- False, There are 12 pairs of ribs in man.

(e) Sternum is present on the ventral side of the body.
-- True

Question. Write the difference between:
(a) Actin and Myosin
(b) Red and White muscles
(c) Pectoral and Pelvic girdle
Answer 
(a) Actin and Myosin

(b) Red and White muscles

(c) Pectoral and Pelvic girdle

Question. Match Column I with Column II:
      Column I                 Column II
(a) Smooth muscle      (i) Myoglobin
(b) Tropomyosin         (ii) Thin filament
(c) Red muscle           (iii) Sutures
(d) Skull                     (iv) Involuntary
Answer 
(a) - (iv) 
(b) - (ii)
(c) - (i) 
(d) - (iii) 

Question. What are the different types of movements exhibited by the cells of human body?
Answer Movement is one of the significant features of living beings. The different types of movements exhibited by the cells of human body are:
-- Amoeboid movement: Some specialised cells in our body like macrophages and leucocytes in blood exhibit amoeboid movement. It is effected by pseudopodia formed by the streaming of protoplasm (as in Amoeba). Cytoskeletal elements like microfilaments are also involved in amoeboid movement.
-- Ciliary Movement: It occurs in most of our internal tubular organs which are lined by ciliated epithelium. The coordinated movements of cilia in the trachea help us in removing dust particles and some of the foreign substances inhaled alongwith the atmospheric air. Passage of ova through the female reproductive tract is also facilitated by the ciliary movement.
-- Muscular movement: Muscle cells show muscular movement such as limbs, jaws, tongue, etc,

Question. How do you distinguish between a skeletal muscle and a cardiac muscle?
Answer 

Question. Name the type of joint between the following:-

(a) atlas/axis
-- Pivotal joint

(b) carpal/metacarpal of thumb
-- Saddle joint

(c) between phalanges
Hinge joint

(d) femur/acetabulum
-- Ball and Socket joint

(e) between cranial bones
-- Fibrous

(f) between pubic bones in the pelvic girdle
-- Cartilaginous joint

Question.Fill in the blank spaces:

(a) All mammals (except a few) have __________ cervical vertebra.
-- seven

(b) The number of phalanges in each limb of human is __________
-- 14

(c) Thin filament of myofibril contains 2 'F' actins and two other proteins namely __________ and__________.
-- troponin, tropomyosin

(d) In a muscle fibre Ca++ is stored in __________
-- sarcoplasmic reticulum

(e) __________ and __________ pairs of ribs are called floating ribs.
-- 11th and 12th

(f) The human cranium is made of __________ bones.
-- eight