NCERT Class 11-Biology: Chapter –20 Locomotion and Movement Part 3

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Question 8:

How do our bone joints function without grinding noise and pain?


Our bone joints function without grinding noise and pain due to the presence of synovial fluid, which is filled in the synovial cavity between the articulating surfaces of two bones. The synovial fluid reduces friction and shock between the joints and the joints function without any grinding noise or pain.

Question 9:

Give the location of a ball and socket joint in a human body


The ball and socket joint is a joint in which a ball-shaped surface of a bone is fitted into a cup-like indentation of another bone. It can move in 360 degrees. It is found between:

The humerus and Pectoral girdle (Shoulder Joint).

Femur and Acetabulum of Pelvic girdle (Hip Joint).

There are four ball and socket joints present in the human body.

Two shoulder joints and two hip joints.

Question 10:

Our fore arm is made of three different bones. Comment.


Our forearms are made up of three different types of bones. Humerus, Radius, and Ulna.

  • The humerus forms the joints at the shoulder and the elbow.

  • Radius or radial bone extends from the other side of the elbow to the side of thumb of the wrist, and it runs parallel to the ulna.

  • The ulna stretches from the elbow to the smallest finger.

Short Answer Type Questions

Question 1:

With respect to rib cage, explain the following:

a. Bicephalic ribs

b. True ribs

c. Floating ribs


a. Bicephalic ribs: It is called Bicephalic because each of the two ribs has articulating surfaces on the dorsal end and each rib is flat and thin bone which is connected vertically to the sternum and dorsally to the vertebral column.

b. True ribs: The first seven ribs known as true ribs. Ventrally they are connected to the sternum with the help of hyaline cartilage, and it is dorsally attached to the thoracic vertebrae.

c. Floating ribs: These ribs are not connected to the sternum, and they are the last two ribs (11th and 12th ribs) of the rib cage.

Question 2:

In old age, people often suffer from stiff and inflamed joints. What is this condition called? What are the possible reasons for these symptoms?


  • In old age, people often suffer from stiff and inflamed joints due to an autoimmune disease known as rheumatoid arthritis, which occurs due to the immune system attacking the cells of its own body. The cells lined in the synovial membrane of the synovial joints are attacked, which causes inflammation and stiffness in the joints.

  • Thus, the reasons for these symptoms are the inflammation in the synovial joints due to the immune system attacking its own synovial cells.

  • The trigger behind the immune system attacking itself is still unknown, but possible reasons are smoking, genetic factors, and vitamin D deficiency.

Question 3:

Exchange of calcium between bone and extracellular fluid takes place under the influence of certain hormones

a. What will happen if more of is in extracellular fluid?

b. What will happen if very less amount of is in the extracellular fluid?


a. If more of is in the extracellular fluid, then it will get accumulated into the bones under the influence of the hormone Thyrocalcitonin (TCT).

b. If very less amount of is in the extracellular fluid thin bone resorption would occur due to the Parathyroid hormone.

Question 4:

Name atleast two hormones which result in fluctuation of level.


The two hormones which results in the fluctuation of levels are:

  • Thyrocalcitonin (TCT): It lowers the levels of and in the blood and promotes the formation of bone in the body.

  • Parathyroid hormone: When the in our blood goes too low, the parathyroid glands make more parathyroid hormone. The Increased levels of Parathyroid hormone (PTH) cause the bones to release their into the blood.