Give reason:

(a) Decalcified bones become soft and flexible.

(b) People in old age complain of stiff joints.

(c) In the female skeleton, the pelvis or hip bone is wider and trough-shaped.

(d) Bones are considered to be a living tissue.

(e) Vertebral column is curved.

(a) Two-third of entire bone mass is made of calcium and phosphorous. It gives strength and hardness to bones. Therefore, when these inorganic substance are lost or the bone is decalcified, they become soft and flexible.

(b) The freely movable joints are well lubricated by synovial fluid to remove friction between the joint surfaces. With age, the production and quality of synovial fluid decreases, leading to less effective lubrication. This coupled with degeneration of cartilage and ligaments causes stiff joints in old age.

(c) In the female skeleton, the pelvis or hip bone is wider and trough-shaped to adapt for accommodating the foetus in the uterus during pregnancy.

(d) Bones are made up of living cells (osteocytes) that are responsible for their growth, maintenance, and repair. They receive blood supply through a network of blood vessels and they produce red and white blood cells within the bone marrow. Therefore, the bones are considered to be a living tissue.

(e) Vertebral column is curved in order to provide correct posture and balance to our body. It's curvature enables us to minimize all the stress on bones and muscles that arises due to activities.