Which of the following statements are correct regarding skeletal muscle?
A.Muscle bundles are held together by collagenous
connective tissue layer called fascicle.
B.Sarcoplasmic reticulum of muscle fibre is a store house of calcium ions.
C.Striated appearance of skeletal muscle fibre is due to distribution pattern of actin and myosin proteins.
D.M line is considered as functional unit of contraction called sarcomere.
Choose the most appropriate answer from the options given below:
AI-generated explanation. Check against your textbook.
Explanation:
Correct answer: B and C only. In skeletal muscle, sarcoplasmic reticulum stores Ca2+ ions (true). The striated appearance is due to the regular arrangement of actin and myosin within sarcomeres (true). Statement A is false because the bundle of muscle fibres is called a fascicle, which is wrapped by perimysium; fascicle itself is not the connective tissue layer. Statement D is false because the sarcomere is the functional unit of contraction; it is defined by Z-lines, not M-line (M-line is the center within a sarcomere).
🧠 Did You Know?
NCERT describes the connective tissue coverings as endomysium around each muscle fibre, perimysium around a fascicle, and epimysium around the whole muscle.
💡 NCERT Memory Line:
Sarcomere is the functional unit of contraction; its boundaries are defined by Z-lines.
Given below are two statements: one is labelled as
Assertion (A) and the other is labelled as Reason
(R). Assertion (A): Osteoporosis is characterised by decreased bone mass and increased chances of fractures. Reason (R): Common cause of osteoporosis is increased levels of estrogen.
In the light of the above statements, choose the
most appropriate answer from the options given
below:
During muscular contraction which of the following events occur?
A. 'H' zone disappears
B. 'A' band widens
C. 'I' band reduces in width
D. Myosine hydrolyzes ATP, releasing the ADP and Pi
E. Z-lines attached to actins are pulled inwards
Choose the correct answer from the options given
below.
AI-generated explanation. Check against your textbook.
Explanation:
During contraction, H-zone disappears as thin and thick filaments overlap. A-band length remains constant (does not widen). I-band shortens as filaments slide inward. Cross-bridge cycling involves myosin hydrolyzing ATP to ADP and Pi. Z-lines (at ends of sarcomeres) are pulled toward the center as actin filaments slide, bringing them inward. Hence A, C, D, E are true, B is false.
🧠 Did You Know?
In slide-filament theory, the sliding of actin filaments over myosin shortens the sarcomere without changing the length of the thick or thin filaments themselves.
💡 NCERT Memory Line:
H-zone disappears; I-band shortens; A-band retains its length; Z-lines move toward each other; ATP is hydrolyzed in the cross-bridge cycle.
Select the incorrectly matched pair from following:
AI-generated explanation. Check against your textbook.
Explanation:
Chondrocytes are the cells of cartilage, not smooth muscle. In NCERT, chondrocytes reside in cartilage matrix and maintain cartilage tissue. Neurons are nerve cells, Fibroblasts form the connective tissue fibers in areolar tissue, and Osteocytes are mature bone cells in bone tissue. Thus, option 1 is incorrect because it mismatches cartilage cells with smooth muscle cells.
🧠 Did You Know?
cartilage provides flexible support and is avascular, with chondrocytes in lacunae maintaining the matrix.
💡 NCERT Memory Line:
Chondrocytes are the cells of cartilage; osteocytes are bone cells; neurons are nerve cells; fibroblasts form fibers in connective tissues like areolar tissue.