NCERT Solutions for Class 11 Biology Chapter 20: Locomotion and Movement
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1. Draw the diagram of a sarcomere of skeletal muscle showing different regions.
Ans. The diagram of a sarcomere of skeletal muscle is as below:
2. Define the sliding filament theory of muscle contraction.
Ans. According to sliding filament theory, muscle’s fibre contraction occurs due to the sliding of the thin actin filaments over the thick myosin filaments.
3. Describe the important steps in muscle contraction.
Ans. Mechanism of muscle contraction:
Step-1.Depolarization of Sarcolemma: At this stage, the Central Nervous System sends a signal through a motor neuron which arrives at the junction of muscle and neuron i.e., neuromuscular junction. When the signal arrives, a neurotransmitter acetylcholine is triggered and the action potential in the sarcolemma is set by this release.
Step-2. Release of Ca++ ions: The sarcolemma transmits the action potential to the sarcoplasmic reticulum in order to release the calcium ions in the sarcoplasm.
Step-3. Conformational changes occur in the Actin filaments: The released calcium ions tend to bind to the troponin and tropomyosin located on the active filaments. This causes a modification in the three-dimensional structure of the actin-troponin-tropomyosin complex. The active site for myosin which is located on the actin filament is exposed.
Step-4. Activation of Myosin heads: The calcium ions release causes the myosin heads to get activated which in turn causes the release of energy in the form of ATP. Hydrolysis of ATP releases energy which causes the binding of myosin heads to the active sites found on the actin filaments hence forming a crossbridge.
Step-5. Actin Filaments slide over Myosin: The myosin head rotates due to the formation of a cross-bridge, pulling the actin filaments to the centre of the A-band which is the H-zone. The Z-line which is attached to the actin filaments is pulled inwards too. Contraction of sarcomere occurs when the actin filaments are pulled in the opposite ends. During the process of contraction, the I-band shortens whereas the A-band maintains its length causing the muscles to contract.
4. Write true or false. If false, change the statement so that it is true.
(a) Actin is present in thin filament.
(b) H-zone of striated muscle fibre represents both thick and thin filaments.
(c) Human skeleton has 206 bones.
(d) There are 11 pairs of ribs in man.
(e) Sternum is present on the ventral side of the body.
Ans. (a) True.
(b) False.
Corrected statement: H-Zone of striated muscle fibres represents only thick filaments.
(c) True.
(d) False.
Corrected statement: There are 12 pairs of ribs in man.
(e) True.
5. Write the difference between:
(a) Actin and Myosin
(b) Red and White muscles
(c) Pectoral and Pelvic girdle
Ans. (a) Difference between Actin and Myosin:
| Actin | Myosin |
| This is made up of thick and heavier protein called myosin. |
| Longer than actin. |
| It consists of two proteins: myosin and meromyosin. |
| It is found only in A band of sarcomere. |
| Cross bridges are present, hence have rough surface. |
| It does not slide during contraction. |
(b) Difference between Red and White muscles:
| Red muscles | White muscles |
| They are thicker. |
| The numbers of mitochondria are less and glycogen granules are abundant. |
| Due to the presence of very few myoglobin pigments, they are white. |
| It can’t store oxygen. |
| Get energy for contraction mainly by anaerobic respiration. |
| Get fatigued with work. |
| Accumulates lactic acid when gets strained due to excessive work. |
(c) Difference between Pectoral and Pelvic girdle:
| Pectoral girdle | Pelvic girdle |
| It has three bones: Ilium, ischium and pubis. |
| Acetabulum cavity found. |
| Its position is in the hip region. |
| It’s articulated to hindlimb bones. |
| Its function is to provide articulation to leg bones. |
6. Match column I with column II.
| (a) Smooth muscle | (i) Myoglobin |
| (b) Tropomyosin | (ii) Thin filament |
| (c) Red muscle | (iii) Sutures |
| (d) Skull | (iv) Involuntary |
7. What are the different types of movements exhibited by the cells of human body?
Ans. The different types of movements exhibited by the cells of the human body are as follows:
(a) Amoeboid movement: The leucocytes present in the blood show amoeboid movement. During tissue damage, these blood cells move in an amoeboid manner (by forming temporary pseudopodia) from the circulatory system towards the site of injury to initiate an immune response. Cytoskeletal elements like microfilaments are also involved in the amoeboid movement.
(b) Ciliary movement: The reproductive cells such as sperms and ova show ciliary movement. The passage of the ova through the fallopian tube towards the uterus is facilitated by this movement. Cilia in the trachea helps in removing dust particles and foreign substances inhaled along with atmospheric air.
(c) Muscular movement: The muscle cells of the human body show muscular movement. These contract and relax to bring about the movement. E.g., Movements of limbs, tongue and jaws are examples of muscular movements.
8. How do you distinguish between a skeletal muscle and a cardiac muscle?
Ans. Difference between a Skeletal muscle and a Cardiac muscle:
| Skeletal muscle | Cardiac muscle |
| It's from the heart. |
| The cells of cardiac muscles are branched. |
| Faint bands are present. |
| Comparatively smaller than skeletal muscle. |
| It is controlled by the autonomic nervous system. |
| Single nucleus is found in the cell. |
| Endomysium is more dense than skeletal muscle. |
9. Name the type of joint between the following:
(a) Atlas/axis
(b) Carpal/metacarpal of thumb
(c) Between phalanges
(d) Femur/acetabulum
(e) Between cranial bones
(f) Between pubic bones in the pelvic girdle
Ans. (a) Atlas/axis = Pivot 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 joint.
(f) Between pubic bones in the pelvic girdle = Ball and socket joint.
10. Fill in the blank spaces:
(a) All mammals (except a few) have __________ cervical vertebra.
(b) The number of phalanges in each limb of human is __________
(c) Thin filament of myofibril contains 2 ‘F’ actins and two other proteins namely __________ and __________.
(d) In a muscle fibre Ca++ is stored in _________.
(e) __________ and __________ pairs of ribs are called floating ribs.
(f) The human cranium is made of __________ bones.
Ans. (a) All mammals (except a few) have seven cervical vertebra.
(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 Troponin and Tropomyosin.
(d) In a muscle fibre Ca++ is stored in sarcoplasmic reticulum.
(e) 11th and 12th pairs of ribs are called floating ribs.
(f) The human cranium is made of eight bones.
