Consider the following statements regarding sarcomere structure and muscle contraction:
I. The functional unit of contraction, the sarcomere, is defined as the region between two successive Z lines. II. During contraction, the I band shortens while the A band remains unchanged in length. III. In a resting muscle, the H zone consists of only thick filaments that are not overlapped by thin filaments. IV. The M line is a thin fibrous membrane that runs through the center of the I band to hold thin filaments together.
Explanation: Statement I is correct because the portion of the myofibril between two successive Z lines is considered the functional unit of contraction, called a sarcomere. Statement II is correct because during shortening of the muscle, the I bands get reduced, whereas the A bands retain their length. Statement III is correct because the central part of the thick filament not overlapped by thin filaments is called the H zone, containing only thick (myosin) filaments. Statement IV is incorrect because the M line is located in the middle of the A band, holding thick filaments together, while the Z line bisects the I band.
Question 52 of 100
📘 CLASS XI
Select the correct combination of statements concerning the structural proteins of skeletal muscle:
I. Actin and myosin are the two primary proteins responsible for the striated appearance of myofibrils. II. Actin filaments are thicker than myosin filaments, which is why they are called thick filaments. III. Myosin is a polymerized protein composed of monomeric units called meromyosins. IV. Troponin is a complex protein distributed at regular intervals on the tropomyosin filaments.
Explanation: Statement I is correct because the striated appearance of the myofibril is due to the distribution pattern of actin and myosin. Statement II is incorrect because actin filaments are thinner than myosin filaments, hence are called thin and thick filaments respectively. Statement III is correct because myosin is a polymerized protein consisting of monomeric meromyosins. Statement IV is correct because troponin is a complex protein distributed at regular intervals on tropomyosin.
Question 53 of 100
📘 CLASS XI
Analyze the statements about the sliding-filament theory and cross-bridge cycle:
I. A cross-bridge is formed when the myosin head binds to the exposed active site on actin using energy from ATP hydrolysis. II. The binding of a new ATP molecule to the myosin head causes the cross-bridge to break. III. ADP and inorganic phosphate are released from the myosin head before it returns to its relaxed state. IV. Re-masking of active sites on actin occurs immediately when calcium ions are actively pumped out of the sarcoplasm back into the sarcoplasmic cisternae.
Explanation: Statement I is correct because the myosin head binds to the exposed active sites on actin using energy from ATP hydrolysis to form a cross-bridge. Statement II is correct because when a new ATP binds, the cross-bridge is broken. Statement III is correct because myosin releases the ADP and inorganic phosphate to go back to its relaxed state. Statement IV is correct because when calcium is actively pumped back into the sarcoplasmic cisternae, it results in the masking of actin filaments.
Question 54 of 100
📘 CLASS XI
Read the statements regarding skeletal muscle fatigue and energy metabolism:
I. Repeated activation of a muscle can lead to the accumulation of lactic acid, which causes muscle fatigue. II. Lactic acid accumulation is the result of the aerobic breakdown of glycogen in muscles. III. Red muscle fibres contain plenty of mitochondria and high levels of myoglobin, allowing them to perform aerobic respiration. IV. White muscle fibres have low myoglobin, few mitochondria, but a high amount of sarcoplasmic reticulum, depending on anaerobic energy processes.
Explanation: Statement I is correct because repeated activation of the muscles leads to the accumulation of lactic acid, causing fatigue. Statement II is incorrect because lactic acid is formed due to the anaerobic breakdown of glycogen, not aerobic. Statement III is correct because red muscle fibres have high myoglobin, plenty of mitochondria, and utilize oxygen for aerobic ATP production. Statement IV is correct because white fibres have less myoglobin, few mitochondria, high sarcoplasmic reticulum, and rely on anaerobic processes for energy.
Question 55 of 100
📘 CLASS XI
Which of the following statements about the axial skeleton divisions are correct?
I. The axial skeleton comprises 80 bones distributed along the main axis of the body. II. The skull, vertebral column, sternum, and ribs are the four major components of the axial skeleton. III. The skull region contains cranial and facial bones, totaling 22 bones. IV. The hyoid bone is a single, U-shaped bone located at the base of the buccal cavity and is part of the appendicular skeleton.
Explanation: Statement I is correct because the axial skeleton comprises 80 bones distributed along the main longitudinal axis of the body. Statement II is correct because the skull, vertebral column, sternum, and ribs constitute the axial skeleton. Statement III is correct because the skull is composed of two sets of bones: cranial and facial, totaling 22 bones. Statement IV is incorrect because the hyoid bone, although located at the base of the buccal cavity, is considered part of the axial skeleton, not the appendicular skeleton.
Question 56 of 100
📘 CLASS XI
Identify the correct statements regarding the regional differentiation of the vertebral column in humans:
I. The vertebral column is made of 26 serially arranged, dorsally placed vertebrae. II. The vertebral column is divided into cervical, thoracic, lumbar, sacral, and coccygeal regions starting from the skull. III. In an adult, both sacral and coccygeal vertebrae are represented as fused single bones (1 fused sacrum and 1 fused coccyx). IV. The number of cervical vertebrae is highly variable among mammalian species, with humans having 7 and other mammals having 12.
Explanation: Statement I is correct because the vertebral column is formed by 26 serially arranged units called vertebrae and is dorsally placed. Statement II is correct because the column is differentiated into cervical, thoracic, lumbar, sacral, and coccygeal regions starting from the skull. Statement III is correct because in adults, sacral (1-fused) and coccygeal (1-fused) vertebrae are represented as fused units. Statement IV is incorrect because the number of cervical vertebrae is seven in almost all mammals, including humans.
Question 57 of 100
📘 CLASS XI
Read these statements regarding the structural parts of a typical vertebra and its functions:
I. Each vertebra has a central hollow portion called the neural canal through which the spinal cord passes. II. The first cervical vertebra is the axis, which articulates directly with the occipital condyles. III. The vertebral column protects the spinal cord and supports the head. IV. The vertebral column serves as the point of attachment for the ribs and musculature of the back.
Explanation: Statement I is correct because each vertebra has a central hollow portion (neural canal) through which the spinal cord passes. Statement II is incorrect because the first vertebra is the atlas (not the axis), and it articulates with the occipital condyles. Statement III is correct because the vertebral column protects the spinal cord and supports the head. Statement IV is correct because it serves as the point of attachment for the ribs and musculature of the back.
Question 58 of 100
📘 CLASS XI
Consider the following statements about human ribs and the rib cage:
I. There are 12 pairs of ribs in human beings, each being a thin flat bone. II. Ribs are bicephalic because they have two articulation surfaces on their dorsal ends. III. False ribs (8th, 9th, and 10th pairs) join the sternum directly with elastic cartilages. IV. The rib cage is formed by the thoracic vertebrae, ribs, and the ventral flat bone, the sternum.
Explanation: Statement I is correct because there are 12 pairs of ribs. Statement II is correct because each rib has two articulation surfaces on its dorsal end and is hence called bicephalic. Statement III is incorrect because the 8th, 9th, and 10th ribs (false ribs) do not articulate directly with the sternum but join the 7th rib with the help of hyaline cartilage. Statement IV is correct because the thoracic vertebrae, ribs, and sternum together form the rib cage.
Question 59 of 100
📘 CLASS XI
Select the correct statements regarding the appendicular bones of the human upper limb (hand):
I. Each upper limb consists of exactly 30 bones. II. The hand bones include the humerus, radius, and ulna in the arm. III. There are 8 wrist bones called carpals and 5 palm bones called metacarpals. IV. The fingers (digits) are made up of 14 phalanges.
Explanation: All statements are correct. Each human limb is composed of 30 bones. For the upper limb, these include the humerus, radius, and ulna, 8 carpals (wrist bones), 5 metacarpals (palm bones), and 14 phalanges (digits).
Question 60 of 100
📘 CLASS XI
Analyze the statements about the bones of the human lower limb (leg):
I. Femur is the thigh bone and is the longest bone in the human body. II. The leg contains the tibia and fibula, while the ankle has 8 tarsals. III. The sole contains 5 metatarsals and the digits contain 14 phalanges. IV. The patella is a cup-shaped bone (knee cap) that covers the knee dorsally.
Explanation: Statement I is correct because the femur is the thigh bone and the longest bone in the body. Statement II is incorrect because ankle bones (tarsals) are 7 in number (unlike wrist carpals which are 8). Statement III is correct because there are 5 metatarsals and 14 phalanges in the foot. Statement IV is incorrect because the patella is a cup-shaped bone that covers the knee ventrally (knee cap), not dorsally.
