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Q1. Name the monomer of myosin filament.  

Solution

Meromyosin  

Q2. Represent diagrammatically the sliding filament theory.  

Solution

Sliding filament theory:        

Q3. Name the hormone responsible for osteoporosis.

Solution

Oestrogen

Q4. Why are skeletal muscles called striated muscles?

Solution

The skeletal muscles have a stripe-like appearance when observed under the microscope. Hence, they are called striated muscles.

Q5. Name the bone present at the base of the buccal cavity.

Solution

Hyoid bone is present at the base of the buccal cavity.

Q6. How many bones are present in the front part of the skull which protects the facial region?

Solution

14

Q7. Represent diagrammatically the anatomy of a sarcomere.

Solution

Anatomy of a Sarcomere:  

Q8. State the significance of the occipital condyles.  

Solution

The occipital condyles help the skull to articulate with the superior region of the vertebral column.  

Q9. How many bones are present in the human skeletal system?

Solution

206 bones

Q10. How many bones are present in the axial skeleton? Name the bony structures which constitute the axial skeleton?

Solution

80 bones are present in the axial skeleton. The skull, vertebral column, sternum and ribs constitute the axial skeleton.

Q11. Which bone articulates with the glenoid cavity?

Solution

The head of humerus articulates with the glenoid cavity.

Q12. Represent diagrammatically the pectoral girdle and the bones of the forelimbs.

Solution

Pectoral girdle and the bones of the forelimbs:  

Q13. Name the substance which when accumulated in muscles causes fatigue.

Solution

Lactic acid

Q14. Name the three processes which are exhibited by the cells of the human body.

Solution

The human body cells exhibit amoeboid, ciliary and muscular movements.

Q15. Give any two examples of the synovial joints.

Solution

Two examples of the synovial joints are

Joint between the humerus and the pectoral girdle

Knee joint

Q16. Describe the synovial joint.  

Solution

The synovial joint is characterised by the synovial cavity filled with the synovial fluid.     The synovial cavity is present between the articulating bones of the joint.     This arrangement and the presence of the lubricating fluid allow considerable movement.     Some examples are the knee joint and the ball and socket joint present between the glenoid cavity and head of the humerus.  

Q17. Describe the structure of actin filament.

Solution

The actin filament is made of two polymer F actins which are helically wound to each other. Each F actin is made of a monomer called globular or G actin. Two filaments of a protein called tropomyosin run close to the F actins throughout their length. At regular intervals, a protein named troponin is distributed on the tropomyosin. In the resting phase, the active binding site for myosin present on the actin filament gets masked by the troponin.

Q18. Why are the ribs called bicephalic? What are true ribs?  

Solution

Because the rib bones have two articulation surfaces on the dorsal side, they are called bicephalic.     The first seven pairs of ribs are dorsally attached to the thoracic vertebrae, and they are ventrally connected to the sternum. These ribs are called true ribs.  

Q19. State the two major divisions of the human skeletal system.

Solution

Two major divisions of the human skeletal system are

Axial skeleton

Appendicular skeleton

Q20. Draw the cross-sectional view of a muscle showing muscle fibres and bundles.

Solution

Cross-sectional view of a muscle showing muscle fibres and bundles:  

Q21. State the property of muscles which is effectively used for locomotion.

Solution

The contractile property of muscles.

Q22. Name the cartilage which helps vertebrochondral ribs to join the seventh rib.

Solution

Hyaline cartilage

Q23. Which cell organelle is abundantly present in aerobic muscles?

Solution

Mitochondrion

Q24. State the name for the plasma membrane of the muscle fibre.

Solution

Sarcolemma

Q25. Name the muscles present in the inner wall of the reproductive tract.

Solution

Smooth muscles

Q26. Explain the following disorders:

Osteoporosis

Tetany

Muscular dystrophy

Solution

Osteoporosis: A decreased level of oestrogen is the common cause. The bone mass is decreased due to which a risk of fracture increases. It usually occurs in old individuals.

Tetany: Rapid spasms are experienced in muscles due to a low calcium ion level in body fluids.

Muscular dystrophy: It is a genetic disorder. The skeletal muscles degenerate progressively.

Q27. Explain the structure of the myofibril.  

Solution

Structure of Myofibril:           The myofibril is a unit filament of a muscle fibre.     It is made of two kinds of bands - dark band and light band.     A dark band is also known as an A or anisotropic band (myosin filament) and contains myosin, while the light band is also known as an I or isotropic band (actin filament) and contains actin.     Both the bands or filaments are arranged parallel to each other.     Actin filaments are thinner than myosin filaments and are hence also called thin and thick filaments, respectively.     At the centre of each I band is an elastic fibre called Z-line to which thin filaments are firmly attached.     The thick filaments in the A band are held together by an M line.     The portion of the myofibril between two successive Z lines is considered functional and is called a sarcomere.     In the resting state, the edges of thin filaments partially overlap the free ends of thick filaments on either side leaving the central parts of the thick filament non-overlapped; this is called the H zone.  

Q28. Name the two bones of the pectoral girdle.

Solution

Scapula and clavicle

Q29. What are the bones of the palm called?

Solution

Metacarpals

Q30. Name the joints which do not allow any movement.

Solution

Fibrous joints

Q31. Name the embryonic layer from which the muscles originate.

Solution

Mesoderm

Q32. Name the central hollow portion of the vertebra.

Solution

Neural canal

Q33. Name the bones which form the rib cage.

Solution

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

Q34. Which pairs of ribs are called false ribs? Why?

Solution

The 8^th, 9^th and 10^th pairs of ribs are called false ribs. These three pairs of ribs do not articulate directly with the sternum. Instead they are joined to the 7^th pair by the hyaline cartilage.

Q35. Name the vertebra which articulates with the occipital condyles.

Solution

Atlas

Q36. Name the filaments found arranged parallel in a muscle fibre.

Solution

Myofibrils

Q37. Explain the contraction and relaxation of muscles by the sliding filament theory.

Solution

Muscle contraction is initiated by the signal sent by the central neural system to the motor end-plate. As soon as the motor end-plate receives the single, acetylcholine is released at the end-plate which sets the action potential in the sarcolemma. As the action potential spreads through the fibre, it causes the sarcoplasm to release calcium ions. Increase in the calcium level results in binding of calcium with the troponin present on the actin filament. The binding of calcium with the troponin unmasks the active binding site for myosin which is present on the actin filament. Myosin binds with the active site forming the cross-bridge. The energy required for the binding of myosin is obtained from the hydrolysis of ATP. Formation of the cross-bridge pulls the attached actin filaments towards the centre of the A band, and the Z lines are pulled inwards, resulting in the contraction of the sarcomere. As soon as ADP and iP are formed from ATP, myosin goes back to its relaxed state and the cross-bridge is broken. At some point, calcium ions are pumped back to the sarcoplasmic cisternae, which results in the masking of the active binding sites of myosin, resulting in the relaxation of muscle fibre.

Q38. Which is the binding site for calcium ions in the sarcoplasm?  

Solution

The subunit of troponin on the active filament is the binding site for calcium ions in the sarcoplasm.  

Q39. What is a sarcomere?

Solution

Sarcomere is the functional region of the myofibril between two successive Z lines.

Q40. State the symptom of gout.

Solution

Symptom of gout: Inflammation of joints

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