Read the statements concerning the basic characteristics of skeletal muscle cells:
I. Skeletal muscles are closely associated with the skeletal components of the body. II. Skeletal muscle cells have a striped or striated appearance under the microscope. III. Activities of skeletal muscles are voluntary, being under the control of the autonomic nervous system. IV. Skeletal muscle is a specialized tissue of mesodermal origin.
Explanation: Statement I is correct because skeletal muscles are closely associated with skeletal components. Statement II is correct because they have a striped appearance under the microscope and are called striated muscles. Statement III is incorrect because skeletal muscles are under the voluntary control of the somatic nervous system, not the autonomic nervous system. Statement IV is correct because muscle is a specialized tissue of mesodermal origin.
Question 72 of 100
📘 CLASS XI
Identify the correct statements concerning visceral and cardiac muscles:
I. Visceral muscles are smooth and non-striated because they do not exhibit any striation. II. Visceral muscle activities are involuntary, assisting in food transport through the digestive tract. III. Cardiac muscle cells assemble in a branching pattern to form the heart musculature. IV. Cardiac muscles are striated in appearance and voluntary in nature.
Explanation: Statement I is correct because visceral muscles are non-striated and smooth in appearance. Statement II is correct because they are involuntary and assist in the transport of food and gametes. Statement III is correct because cardiac muscle cells assemble in a branching pattern to form cardiac muscle. Statement IV is incorrect because cardiac muscles are involuntary in nature, as the nervous system does not control them directly.
Question 73 of 100
📘 CLASS XI
Consider the statements regarding the anatomical structure of skeletal muscle bundles:
I. Each organized skeletal muscle consists of several muscle bundles or fascicles. II. Fascicles are held together by a common collagenous connective tissue layer called fascia. III. Each fascicle contains a number of muscle fibres. IV. The plasma membrane lining a muscle fibre is called the sarcolemma, and it encloses the sarcoplasm.
Explanation: All statements are correct. Organized skeletal muscle contains muscle bundles (fascicles) held together by a collagenous connective tissue called fascia. Each bundle contains multiple muscle fibres, which are lined by the sarcolemma and enclose the sarcoplasm.
Question 74 of 100
📘 CLASS XI
Which of the following statements about the muscle fibre sarcoplasm and myofibrils are correct?
I. The muscle fibre is a syncytium because its sarcoplasm contains many nuclei. II. Sarcoplasmic reticulum is the storehouse of calcium ions. III. Sarcoplasm contains parallelly arranged myofibrils which exhibit alternate dark and light bands. IV. The light bands are called 'A' bands, and the dark bands are called 'I' bands.
Explanation: Statement I is correct because the skeletal muscle fibre is a syncytium containing many nuclei. Statement II is correct because the sarcoplasmic reticulum stores calcium ions. Statement III is correct because myofibrils have alternate light and dark bands. Statement IV is incorrect because the light bands are called 'I' or Isotropic bands, while the dark bands are called 'A' or Anisotropic bands.
Question 75 of 100
📘 CLASS XI
Read the statements regarding the active sites and regulatory proteins in skeletal muscles:
I. In the resting state, the active binding sites for myosin on the actin filaments are masked by troponin. II. Tropomyosin filaments run close to the 'F' actins throughout its length. III. Troponin is a complex protein distributed at regular intervals on the tropomyosin. IV. Calcium ions released during contraction bind directly to a subunit of tropomyosin.
Explanation: Statement I is correct because in the resting state, a subunit of troponin masks the active binding sites for myosin on the actin filaments. Statement II is correct because tropomyosin filaments run close to F-actins throughout its length. Statement III is correct because troponin is a complex protein distributed at regular intervals on tropomyosin. Statement IV is incorrect because calcium ions bind to a subunit of troponin (not tropomyosin), which causes troponin to shift and remove the mask from the active sites.
Question 76 of 100
📘 CLASS XI
Read the following statements regarding the types of muscle tissues and their origin:
I. Muscle is a specialized tissue of mesodermal origin. II. Skeletal muscles are voluntary in nature and are closely associated with skeletal components. III. Visceral muscles are non-striated, smooth in appearance, and involuntary in nature. IV. Cardiac muscles are striated in appearance and voluntary in nature.
Explanation: Statements I, II, and III are correct as muscle is of mesodermal origin, skeletal muscle is voluntary, and visceral muscle is smooth and involuntary. Statement IV is incorrect because cardiac muscles are involuntary in nature as the nervous system does not control their activities directly.
Question 77 of 100
📘 CLASS XI
Consider the following statements about myofilaments and structural lines of a myofibril:
I. Each myofibril has alternate dark and light bands composed of actin and myosin. II. The light 'I' band contains actin, while the dark 'A' band contains myosin. III. In the center of each 'I' band is an elastic fiber called the 'Z' line which bisects it. IV. Thick filaments in the 'A' band are held together in the middle of this band by an elastic 'Z' line.
Explanation: Statements I, II, and III are correct. Myofibrils have alternate 'A' (Anisotropic) and 'I' (Isotropic) bands and the elastic 'Z' line bisects each 'I' band. Statement IV is incorrect because the thick filaments in the 'A' band are held together in the middle of the band by a thin fibrous membrane called the 'M' line, not the 'Z' line.
Question 78 of 100
📘 CLASS XI
Read the statements regarding the molecular structure of the thin filament (actin):
I. Each actin filament is made of two filamentous 'F' actins helically wound to each other. II. Each 'F' actin is a polymer of monomeric 'G' (Globular) actins. III. Two filaments of another protein, tropomyosin, run close to the 'F' actins throughout its length. IV. Troponin is a complex protein distributed at regular intervals on the 'F' actin filaments.
Explanation: Statements I, II, and III are correct as F-actin is a polymer of G-actin and is helically wound with tropomyosin. Statement IV is incorrect because troponin is distributed at regular intervals on the tropomyosin filaments, not directly on the F-actin filaments.
Question 79 of 100
📘 CLASS XI
Which of the following statements regarding the thick filament monomer (meromyosin) are correct?
I. Each meromyosin monomer has a globular head with a short arm (HMM) and a tail (LMM). II. The heavy meromyosin (HMM) component projects outwards at regular distance and angle, forming the cross arm. III. The globular head acts as an active ATPase enzyme. IV. The light meromyosin (LMM) tail contains active binding sites for ATP and thin filaments.
Explanation: Statements I, II, and III are correct. Meromyosin is split into HMM and LMM, and HMM projects out to form the cross arm. Statement IV is incorrect because the globular head of HMM contains the active ATPase enzyme and the binding sites for ATP and active sites for actin, not the tail (LMM).
Question 80 of 100
📘 CLASS XI
Read the following statements concerning the neuromuscular junction (NMJ):
I. The neuromuscular junction is the point of contact between a motor neuron and the sarcolemma of the muscle fiber. II. A motor neuron along with the muscle fibers connected to it constitute a motor unit. III. A neural signal reaching this junction releases acetylcholine, generating an action potential in the sarcolemma. IV. The action potential spreads through the muscle fiber and triggers sodium release from the sarcolemma.
Explanation: Statements I, II, and III are correct. Motor neuron signals reach the NMJ, release acetylcholine, and generate a sarcolemma action potential. Statement IV is incorrect because the spread of the action potential through the muscle fiber triggers the release of calcium ions from the sarcoplasmic reticulum (not sodium from the sarcolemma).
