NCERT Solutions for Class 11 Science Biology Chapter 20 - Locomotion And Movement

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There are 12 pair of ribs. Each rib is a thin flat bone that is attached dorsally to the vertebral coloumn and ventrally to the sternum.
Hence, the correct answer is option B.

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Pivot joint is a synovial joint present between atlas and axis. Synovial joints are characterised by the presence of synovial fluid between the articulating surfaces of the two bones. This joint allows the movement in one plane only. 
Hence, the correct answer is option A.

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The globular head of the myosin is an active ATPase enzyme. It has binding sites far ATP and active sites for actin.
Hence, the correct answer is option C.

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There are 24 intervertebral disc found in the spine of human. They act as an shock absorber present between each of the vertebrae and the spinal coloumn. They keep the vertebrae separate during the activity. They provide protection to the nerves that run from the brain and the spine.
Hence, the correct answer is option C.

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The vertebral coloumn is formed by 26 serially arranged units called vertebrae. It is placed dorsally. The vertebral coloumn is differentiated into cervical (7), thoracic (12), lumbar (5), sacral (1-fused) and coccygeal (1-fused) regions starting from the skull.
The correct sequential order is :-
Cervical $\to$ thoracic $\to$ lumbar $\to$ sacral $\to$coccygeal.
Hence, the correct answer is option D.

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Ball and socket joint is present between humerus and pectoral girdle while hinge joint is a knee joint.
Hence, the correct answer is option A.

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Knee joint and elbow joint are the examples of Hinge Joint. It allows movement in one plane. Spoon like surface of one bone fits into the concave surface of another bone. 
Hence, the correct answer is option D.

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Marophages and leucocytes are some specialised blood cells in the body that exhibit amoeboid movement. This movement occurs due to the streaming of protoplasm.
Hence, the correct answer is option C.

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Atherosclerosis is a heart disorder caused due to the deposition of calcium, fat, cholesterol and fibrous tissue, that makes the lumen of the arteries narrower.
Hence, the correct answer is option D.

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Visceral muscles are located in the inner walls of hollow visceral organs such as alimentary canal, reproductive tract. These muscles do not exhibit any striation and are smooth in appearance. They are also called smooth or non-striated muscle.
Hence, the correct answer is option B.

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The glenoid cavity is a depression present below the acromion. It articulates with the head of the humerus to form the shoulder joint in the pectoral girdle.
Hence, the correct answer is option B.

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Cardiac muscles or the heart muscle are striated and involuntary in nature. Whereas, muscles of the alimentary canal are smooth and involuntary, while skeletal muscles are voluntary muscles with striations. Eyelids are involuntary but sometimes may be under our control so  voluntary as well.
Hence, the correct answer is option B.

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Correct Match:
 

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a. Exhibit ameboid movement:- Macrophages and leucocytes are some specialised blood cells that exhibit amoeboid movement.
b. Exhibit ciliary movement:- Ciliary movement occurs in internal tubular organ that are lined by ciliated epithelium.
For example:- The passage of ova through the female reproductive tract is facilitated by ciliary movement.

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Locomotion requires a perfect coordinated activity of muscular, skeletal, nervous systems.

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Each muscle fibre is lined by the plasma membrane called sarcolema enclosing the sarcoplasm (just like cytoplasm). The endoplasmic reticulum in muscle fibre is called sarcoplasmic reticulum. These names refer to muscle cell.

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The correct sequence of three tiny bones of the ear are:-
Malleus $\to$ Incus $\to$ Stapes

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Both bones and cartilage are specialised connective tissue. Bone has hard matrix because of the calcium salts whereas cartilage has slightly pliable matrix because of chondroitin salts.

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Myasthenia gravis is an auto-immune disorder that affects the neuromuscular junction that results in fatigue, weakening and paralysis of skeletal muscle.

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The bone joints function without grinding noise and pain because of the presence of synovial fluid that is filled in the synovial cavity.

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The ball and socket joint is a synovial joint present between humerus and pectoral girdle.

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Humerus, radius and ulna are the three different bones of fare arm.

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a. Bicephalic ribs:- They are called bicephalic because it has two articulation surface on its dorsal end.
b. True ribs:- The first seven pair of ribs are called true ribs. They are dorsally attached to the thoracic vertebrae and ventrally connected to the sternum with the help of hyaline cartilage.
c. Floating ribs:- They are last two pairs such as 11^th and 12^th of ribs that are not connected ventrally.

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Osteoporosis is an age-related disorder and affected individuals are suffer from stiff and inflamed joints. This disorder is characterised by the decreased bone mass and increased chances of fractures. It is commonly caused due to a decreased level of oestrogen in females, after menopause.

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a. Thyrocalcitonin hormone will lower the calcium level when more calcium ion is present in extracellular fluid. This hormone decreases the calcium level by suppressing the release of calcium ions from the bones. It promotes the accumulation of calcium in the bones.
b. If less amount of calcium is in extracellular fluid then parathyroid hormone will promote the release of calcium from the bones.

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Thyrocalcitonin hormone secreted from parafollicular cells of thyroid hormone, decreases the level of calcium ion in the blood. On the other hand, Parathyroid hormone increases the level of calcium ion in the blood as this hormone will mobilize the release of calcium ion from the bones.

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The weight gain is due to an increase in muscle mass and less fat. The myofibrils become thickened due to increased amount of sarcoplasm resulting in enlargement of the skeletal muscles. It occurs due to protein synthesis and mitochondria due to which muscles become more dense. Hence, the correct answer is option b.

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(a) Strenuous exercise increases the strain on the muscles because they have to perform more work.
(b) The breathing rate of Radha changed due to increased energy consumption by the muscles. The oxygen demand also increased by the muscles and it can be fulfilled by an increased blood supply to the muscles. So, the heart and lungs work faster to fulfill the increased demand of the muscles.

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Gout is caused due to accumulation of uric acid crystals. It is a form of arthritis and is characterised by inflammation of joints, swelling and redness in joints. This makes the movement more painful and difficult.

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ATP (Adenosine Triphosphate) is the source of energy for muscle contraction. ATPase enzyme is present on the globular head of the myosin that breaks down ATP into ADP and inorganic phosphate in the presence of magnesium and calcium ions. The energy is released in the head of myosin.
ATP $\to$ ADP + P_i + Energy

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The pelvic girdle consists of two coxal bones and is formed by the fusion of three bones ilium, ischium and pubis. The point of fusion of three bones is a cavity called acetabulum to which the thigh bone articulates. In pectoral girdle, the glenoid cavity is a depression present below the acromion and articulates with the head of the humerus to form the shoulder joint.

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The calcium ions play an important role in the process of muscle contraction. This process is initiated by a signal sent by the central nervous system through a motor neuron. A motor neuron alongwith a muscle fibres connected to it constitute a motor unit. The junction between a motor neuron and the sarcolemina of the muscle fibre is called the neuromuscilar junction.
A neural signal when reaches at neuromuscular junction releases a neurotransmitter (acetylcholine) that generates an action potential in the sarcolemma. This action potential spreads through the muscle fibre results in the release of calcium ions into the sarcoplasm. Increase in calcium ion level results in the binding of calcium with a subunit of troponin on actin filaments and remove the masking of active site for myosin. Calcium ion facillitates the sliding of actin and myosin filament towards each other and results in muscle contraction.
When calcium ions are released from the muscle cells. The binding sites get covered and the actin and myosin filaments are move back to their original positions resulting in relaxation of muscles. Tetany is caused due to low level of calcium ion in the body fluid. It occurs due to decrease in the function of parathyroid gland. As this gland is involved in the secretion of parathyroid hormone responsible for regulating the calcium levels in the blood. In case of tetany, a rapid spasm (wild contraction) in the muscles occurs due to low level of calcium ion.

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A slipped disc is a medical condition caused due to the displacement of intervertebral disc from its original position. It causes muscle weakness. Numbness in the body and pain in the muscles of arms and legs as well as in the lower back is also caused in this condition. Affected individual feels difficulty in walking and standing for a while. If this condition is left untreated for longer time, it would cause permanent nerve damage and paralysis.

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The mechanism of muscle contraction is explained by sliding filament theory.
This theory states that the contraction of a muscle fibre takes place by the sliding of the thin filament over the thick filament. This process is initiated by a signal sent by the central nervous system (CNS) through a motor neuron. A motor unit is formed by the connection between a motor neuron alongwith the muscle fibres. 
Neuromuscular junction is the junction between a motor neuron and the sarcolemna of the muscle fibre. This junction is also
called motor-end-plate.
A neural signal reaching at the neuromuscular junction releases a acetylchline neurotransmitter that generates an action potential in the sarcolemma.
This action potential spreads through the muscle fibre and results in the release of calcium ions into the Sarcoplasm. Increase in the level of calcium ions leads to the binding of calcium with a subunit of troponin on actin filaments and remove the masking of active sites for myosin. The energy is utilised by the hydrolysis of ATP and the myosin head now gets binds to the exposed active sites on actin to form a cross bridge. This pulls the attached actin filaments towards the centre of 'A' band. The 'Z' line are attached to these actins are pulled inward results in shortening of sarcomere i.e., contraction. During contraction, the 'I' bands get reduced, whereas the 'A' bands retain the length. The myosin, releasing the ADP and Pi return back to its relaxed state. This process continues till the calcium ions are pumped back to the sarcoplasmic cisternae that results in the masking of actin filaments. It causes the return of 'z' lines back to their original position, i.e., relaxation.

 

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Muscle contraction is initiated by a signal sent by the central nervous system (CNS) via a motor neuron. A motor neuron alongwith the muscle fibres connected to it constitute a motor unit. The junction between a motor neuron and the sarcolemma of the muscle fibre is called the neuromuscular junction or motor-end plate. A neural signal reaching this junction releases a 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 Ca++ 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. This pulls the attached actin filaments towards the centre of ‘A’ band. The ‘Z’ line attached to these actins are also pulled inwards thereby causing a shortening of the sarcomere, i.e., contraction. It is clear from the above steps, that during shortening of the muscle, i.e., contraction, the ‘I’ bands get reduced, whereas the ‘A’ bands retain the length. The myosin, releasing the ADP and Pi goes back to its relaxed state. A new ATP binds and the cross-bridge is broken. The ATP is again hydrolysed by the myosin head and the cycle of cross bridge formation and breakage is repeated causing further sliding. The process continues till the Ca++ ions are pumped back to the sarcoplasmic cisternae resulting in the masking of actin filaments. This causes the return of ‘Z’ lines back to their original position, i.e., relaxation.

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Calcium ion plays an important role in muscle contraction as it facilitates the binding of calcium with a subunit of troponin on the actin filaments and removes the masking of the active site of myosin. It stimulates the binding of the myosin head with the active site of the actin and results in the formation of a cross-bridge. 

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Pectoral girdle-

• Consists of clavicle (collar bone) and scapula
• Scapula is a triangular flat bone with a slightly elevated ridge called the spine, projecting as a flat, expanded process called acromion.
• Clavicle articulates with acromion.
• Below acromion, a depression called glenoid cavity is present. Here, humerus articulates to form the shoulder joint.

• Has 2 coxal bones formed by the fusion of ilium, ischium and pubis
• Acetabulum is a cavity formed at the point of fusion of these three bones where the thigh bone articulates
• Two halves of the pelvic girdle meet ventrally to form Pubic Symphysis (contains fibrous cartilage)