Consider the following statements about muscular and skeletal system disorders:
I. Myasthenia gravis is an auto-immune disorder that affects the neuromuscular junction, causing fatigue, weakening, and paralysis of skeletal muscle. II. Muscular dystrophy is characterized by progressive degeneration of skeletal muscle and is mostly a genetic disorder. III. Tetany consists of rapid, wild spasms in muscles caused by excessively high calcium levels in body fluids. IV. Osteoporosis is an age-related disorder marked by decreased bone mass and is commonly caused by decreased estrogen levels.
Explanation: Statements I, II, and IV are correct. Myasthenia gravis is autoimmune and targets the neuromuscular junction, muscular dystrophy is a genetic degeneration of skeletal muscle, and osteoporosis is an age-related loss of bone mass linked to low estrogen. Statement III is incorrect because tetany is characterized by rapid spasms in muscle due to low Ca++ (calcium) levels in body fluids, not high levels.
Question 32 of 100
📘 CLASS XI
Analyze the statements about the sliding filament theory during muscle contraction:
I. Muscle contraction takes place when thin filaments slide over thick filaments. II. During shortening of the muscle, both the I band and the A band undergo a major reduction in their horizontal lengths. III. The Z lines attached to actin filaments are pulled inwards, causing the sarcomere to shorten. IV. Sarcoplasmic calcium ions return to the sarcoplasmic cisternae, leading to the re-masking of actin filaments and subsequent muscle relaxation.
Explanation: Statements I, III, and IV are correct. Contraction occurs by the sliding of thin filaments over thick filaments, pulling the Z lines inwards to shorten the sarcomere. Active calcium uptake by sarcoplasmic cisternae re-masks the actin to bring about relaxation. Statement II is incorrect because during muscle shortening, the I bands get reduced, whereas the A bands retain their length.
Question 33 of 100
📘 CLASS XI
Which of the following statements about red and white muscle fibres are correct?
I. Red muscle fibres contain high amounts of myoglobin, giving them a reddish appearance. II. Red muscle fibres contain plenty of mitochondria that utilize stored oxygen to produce ATP aerobically. III. White muscle fibres have a very high concentration of myoglobin and many mitochondria. IV. White fibres possess a highly developed and abundant sarcoplasmic reticulum and rely on anaerobic processes for energy.
Explanation: Statements I, II, and IV are correct because red fibres are rich in myoglobin and mitochondria for aerobic ATP production, while white fibres have high sarcoplasmic reticulum and rely on anaerobic pathways. Statement III is incorrect because white muscle fibres possess very less quantity of myoglobin and few mitochondria.
Question 34 of 100
📘 CLASS XI
Read these statements regarding the matrix of human skeletal components:
I. Bone and cartilage are specialized connective tissues. II. Bone has a highly pliable matrix due to the presence of calcium salts. III. Cartilage has a slightly pliable matrix due to the presence of chondroitin salts. IV. In adult human beings, the entire skeletal system comprises 206 bones and a few cartilages.
Explanation: Statements I, III, and IV are correct. Bones and cartilages are specialized connective tissues making up the 206 bones of the adult skeletal system, with cartilage having a slightly pliable matrix due to chondroitin salts. Statement II is incorrect because bone has a very hard, non-pliable matrix due to calcium salts.
Question 35 of 100
📘 CLASS XI
Which of the following statements about the human skull bones are true?
I. The skull consists of two sets of bones: cranial (8 bones) and facial (14 bones), totaling 22 bones. II. Cranial bones form the hard protective outer covering, the cranium, for the brain. III. Facial bones form the front part of the skull and are 14 in number. IV. The skull region is bicephalic because it articulates with the vertebrae via two lateral condyles.
Explanation: Statements I, II, and III are correct because the skull has 22 bones divided into 8 cranial bones (forming the cranium) and 14 facial bones (forming the front of the skull). Statement IV is incorrect because while the skull articulates using two occipital condyles, this makes it dicondylic, not bicephalic; ribs are bicephalic.
Question 36 of 100
📘 CLASS XI
Consider the statements about the human vertebral column:
I. The vertebral column is dorsally placed and consists of 26 serially arranged units called vertebrae. II. The spinal cord passes through the central hollow portion of each vertebra, called the neural canal. III. The first cervical vertebra is the atlas, which articulates with the occipital condyles of the skull. IV. The vertebral column is differentiated into cervical (7), thoracic (12), lumbar (5), sacral (5-fused), and coccygeal (4-fused) regions in adults.
Explanation: Statements I, II, and III are correct because the vertebral column contains 26 dorsal vertebrae with a central neural canal, with the first being the atlas which articulates with the occipital condyles. Statement IV is incorrect because in adults, the column is differentiated into sacral (1-fused) and coccygeal (1-fused) regions.
Question 37 of 100
📘 CLASS XI
Read the statements regarding the structure of the myosin monomer (meromyosin):
I. Each meromyosin monomer has a globular head with a short arm (HMM) and a tail (LMM). II. The HMM component projects outwards at a regular distance and angle, forming the cross arm. III. The globular head acts as an active ATPase enzyme. IV. The tail (LMM) contains the active binding sites for ATP and thin actin filaments.
Explanation: Statements I, II, and III are correct. Meromyosin is composed of HMM (globular head and short arm) which forms the cross arm, and LMM (tail). The head functions as an active ATPase. Statement IV is incorrect because the active binding sites for ATP and active sites for actin are located on the globular head of HMM, not on the LMM tail.
Question 38 of 100
📘 CLASS XI
Select the correct statements regarding the molecular components of thin filaments:
I. Each actin filament is formed by two F actins helically wound around each other. II. F actin is a polymer made up of monomeric G (globular) actins. III. Two filaments of another protein, troponin, run close to the F actins throughout its length. IV. In the resting state, a subunit of troponin masks the active binding sites for myosin on the actin filaments.
Explanation: Statements I, II, and IV are correct. An actin filament contains two helical F actin chains made of G actin monomers, and in a resting state, a troponin subunit masks the active myosin-binding sites. Statement III is incorrect because the two filaments running close to F actin throughout its length are tropomyosin; troponin is a complex protein distributed at regular intervals on the tropomyosin.
Question 39 of 100
📘 CLASS XI
Identify the correct statements regarding the neuromuscular junction (NMJ):
I. The neuromuscular junction is the junction between a motor neuron and the sarcolemma of a muscle fibre. II. A motor neuron along with the muscle fibres connected to it is termed a motor unit. III. A neural signal reaching the NMJ releases adrenaline, which depolarizes the sarcolemma. IV. The generation of an action potential in the sarcolemma is the critical event that initiates calcium release into the sarcoplasm.
Explanation: Statements I, II, and IV are correct. The NMJ is the connection between a motor neuron and the sarcolemma, forming part of a motor unit, where an action potential triggers sarcoplasmic calcium release. Statement III is incorrect because the neural signal releases acetylcholine (not adrenaline).
Question 40 of 100
📘 CLASS XI
Analyze these statements about calcium homeostasis in sarcoplasmic structures:
I. Sarcoplasmic reticulum of the muscle fibres is a cellular reservoir storing calcium ions. II. Sarcoplasmic calcium levels must rise to initiate muscle contraction. III. Calcium ions bind to a subunit of troponin to remove the masking of active sites on actin. IV. Active pumping of calcium back into the sarcoplasmic cisternae allows muscle relaxation to proceed.
Explanation: All four statements are correct. The sarcoplasmic reticulum stores calcium ions. Neural signals cause calcium levels to rise and bind to troponin, removing the actin mask to contract the muscle, and active transport of calcium back into the cisternae is required for relaxation.
