In each of the following cases (A, B, C and D), choose the correct option as given below:
(a) Both (A) and (R) are true, and (R) is the correct explanation of (A).
(b) Both (A) and (R) are true, but (R) is not the correct explanation of (A).
(c) (A) is true but (R) is false.
(d) (A) is false but (R) is true.
(A) Assertion (A): Epithelium is well-suited for gas exchange in the lungs.
Reason (R): It consists of multiple layers of tall cells that slow down diffusion.
(B) Assertion (A): Cardiac muscle can contract continuously without fatigue.
Reason (R): Cardiac muscle cells have a high number of mitochondria and an abundant blood supply.
(C) Assertion (A): Tendons connect bone to bone and allow joint movement.
Reason (R): Tendons are made of tough connective tissue that transmits force from muscle to bone.
(D) Assertion (A): In a hinge joint, movement occurs primarily in one plane.
Reason (R): The bone ends are shaped to allow sliding in all directions.
(A) (c) (A) is true but (R) is false.
Explanation: The epithelium lining the alveoli of the lungs is well adapted for gas exchange. The alveoli are lined by a single layer of thin, flat squamous epithelial cells, not multiple layers of tall cells. This thin structure reduces the diffusion distance and allows rapid exchange of oxygen and carbon dioxide. Multiple cell layers would increase the diffusion distance and slow down diffusion.
(B) (a) Both (A) and (R) are true, and (R) is the correct explanation of (A).
Explanation: Cardiac muscles work continuously and rhythmically throughout life and are highly resistant to fatigue under normal conditions. This is because their cells contain a large number of mitochondria and receive a rich blood supply. These features ensure a constant supply of oxygen and ATP required for continuous contraction, along with efficient removal of metabolic wastes.
(C) (d) (A) is false but (R) is true.
Explanation: Tendons do not connect bone to bone; they connect muscles to bones. Bones are connected to each other by ligaments, which provide stability to joints and prevent excessive movement.
Tendons are tough, fibrous connective tissues that transmit the force generated by muscle contraction to bones, thereby helping in movement at the joints.
(D) (c) (A) is true but (R) is false.
Explanation: In a hinge joint, movement occurs mainly in one plane, such as bending (flexion) and straightening (extension). However, the bone ends are not designed to allow sliding in all directions. Instead, they are shaped in a way that restricts movement to a single plane and provides controlled movement with stability. Sliding movement occurs in gliding joints, while movement in multiple directions is a characteristic of ball and socket joints.
