Class 9 SELINA Solutions Biology Chapter 12: Movement And Locomotion

(ii) Cartilage

(iv) Hip

(i) Cervical - 7

(ii) Ear ossicles 

(iii) Ligaments 

(ii) Calcium and phosphorus 

(iv) Osteocytes

(iii) Periosteum

(i) Striped

(iii) Iris

1. External Ear

2. Tip of the nose

(a) Bones, Cartilages and Ligaments

(b) Axial skeleton and Appendicular skeleton

(c) Skull, Vertebral column, Ribs and Sternum

(d) Cervical, Thoracic, Lumbar, Sacrum and Coccyx

(e) Gliding joint, Pivot joint, Hinge joint and Ball and socket joint

(a) Freely movable joint / Synovial joint

(b) Cervical vertebra (Atlas)

(c) Foramen magnum

(d) Antagonistic muscles

(e) Synovial fluid

(a) Humerus : Glenoid cavity :: Femur : Articular cavity (Acetabulum)

(b) Thoracic vertebrae : 12 :: Cervical vertebrae : 7

(c) Wrist : Carpals :: Ankle : Tarsals

(d) Biceps : Flexor :: Triceps : Extensor

(e) Brain : Cranium :: Spinal cord : Vertebral column (Spinal column/Backbone)

(a) Patella

(b) Scapula

(c) Clavicle

(d) Sternum

(e) Metacarpals

(a) Skeletal system is the body's central framework. It consists of bones and connective tissue, including cartilage, tendons, and ligaments.

(b) Bone marrow is the soft, spongy tissue found in the centre of most bones and contains many blood vessels.

(c) Gristle or intervertebral disc is a pad of cartilage that forms a kind of cushion between two vertebrae.

(d) Pivot joint is a type of movable joint in which one bone is rotated over a pivot-like end of another bone.

(e) A structure that has been moved by a muscle cannot be returned to its original position without the action of another muscle. Such muscles which cause opposing movements are called antagonistic muscles.

Muscles pull the structure. A muscle has two ends; a fixed end where the muscle originates and a movable end that pulls some other part. The movable end is drawn out to form a tough structure known as a tendon that is attached to the bone. When a muscle is stimulated by a nerve, it contracts and becomes shorter and thicker and this pulls the bone at its movable end. Muscles can only contract and relax, they cannot lengthen.

Once a structure has been moved by a muscle, it cannot return to its original position without another muscle acting on it. Muscles that cause opposing movements are known as antagonistic muscles.

Example of antagonistic muscles:

When you flex your arm at the elbow, the muscle that lies above the upper arm, i.e. the biceps is seen and felt bulging. This muscle bulges due to contraction and becomes smaller in length, stiffer and thicker. Contraction of biceps draws the forearm towards the upper arm. However, relaxation of biceps cannot push the forearm back to its original position. When the arm is extended or straightened, the muscle at the back of the upper arm, i.e. the triceps contracts. The two muscles work antagonistically or in opposite directions to bend or flex and straighten the arm at the elbow. 

(a) A bone consists of both organic as well as inorganic constituents. When a bone is treated with weak hydrochloric acid, the inorganic salts in the bone get dissolved, and the organic framework is left behind. such a bone is called decalcified bone. It is soft and flexible and can even be tied into a knot.

(b) Joint movement gets stiffer and less flexible in old age because the amount of synovial fluid inside the joints diminishes, and the cartilage becomes thinner. Ligaments also tend to shorten and lose some flexibility, causing joints to feel tight. Hence, people in old age complain of stiff joints.

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

(d) Bones are living, growing tissues because they are supplied with nerves and blood arteries and are made of living cells called osteocytes, which aid in their development and repair.

(e) The vertebral column is curved to maintain the balance of the body in an erect position. The curve absorbs pressure and shock while walking, running and protects the column from breaking. 

(a) Thigh

(b) Middle ear

(c) Backbone

(d) Bones of the cranium

(e) Middle of the front part of the chest

(a) Differences between true ribs and floating ribs:

(b) Differences between ligaments and tendons:

(c) Differences between hinge joint and gliding joint:

(d) Differences between voluntary muscles and involuntary muscles:

(e) Differences between bone and cartilage:

Uses of skeleton:

(i) Support and shape: The skeletal system provides a framework to the body. It provides support to all soft parts and gives a definite shape to the body and all body parts.

(ii) Protection: The skeleton protects the internal delicate and important organs of the body. For example in human beings, the skull protects the brain, ribs protect the heart and lungs, vertebral column protects the spinal cord, etc.

(iii) Movement: The skeletal system helps in movement.It co-ordinates the movement of attached bones and muscles to bring about locomotion.

(iv) Leverage: Some bones and joints of the skeletal system form levers and help in magnifying, either the movement or the force. For example, slight contraction of biceps moves the hand to a distance of about a foot.

(v) Formation of blood cells: The skeleton is the site of haematopoiesis. Various types of blood cells like red blood cells, white blood cells and platelets are formed in the bone marrow of some long bones.

(vi) Storehouse for minerals: The bones are a storehouse of calcium and phosphorus for the rest of the body.

(a) Thoracic vertebra

(b) Thoracic vertebra is located in the centre of the upper and middle back which begins at the base of the neck (cervical spine) and ends around the bottom of the rib cage.

(c) 1 - Neural spine, 2 - Neural canal, 3 - Body or centrum

Internal structure of a long bone

1: Cranium/Skull; 2: Clavicle, Scapula; 3: Sternum; 4: Humerus:

5: Ulna; 6: Coccyx; 7: Ribs; 8: Radius; 9: Femur; 10: Fibula; 11: Tibia