Class 11 Biology

Locomotion Movement

NCERT Solution

Question 1: Draw the diagram of a sarcomere of skeletal muscle showing different regions.

Answer: Sacromere of Skeletal Muscle

actin and myosin filaments

Question 2: Define sliding filament theory of muscle contraction.

Answer: Sliding Filament Theory of Muscle Contraction

Mechanism of muscle contraction is best explained by the sliding filament theory which states that contraction of a muscle fibre takes place by the sliding of the thin filaments over the thick filaments.

Question 3: Describe the important steps in muscle contraction.

Answer: Muscle contraction is initiated by a signal sent by the central nervous system (CNS) via a motor neuron. A motor neuron alongwith the muscle fibres connected to it constitute a motor unit. The junction between a motor neuron and the sarcolemma of the muscle fibre is called the neuromuscular junction or motor-end plate. A neural signal reaching this junction releases a neurotransmitter (Acetyl choline) which generates an action potential in the sarcolemma. This spreads through the muscle fibre and causes the release of calcium ions into the sarcoplasm. Increase in Ca++ level leads to the binding of calcium with a subunit of troponin on actin filaments and thereby remove the masking of active sites for myosin.

Utilising the energy from ATP hydrolysis, the myosin head now binds to the exposed active sites on actin to form a cross bridge. This pulls the attached actin filaments towards the centre of ‘A’ band. The ‘Z’ line attached to these actins are also pulled inwards thereby causing a shortening of the sarcomere, i.e., contraction.

The process continues till the Ca++ ions are pumped back to the sarcoplasmic cisternae resulting in the masking of actin filaments. This causes the return of ‘Z’ lines back to their original position, i.e., relaxation.

Question 4: Write true or false. If false change the statement so that it is true.

  1. Actin is present in thin filament
  2. H-zone of striated muscle fibre represents both thick and thin filaments.
  3. Human skeleton has 206 bones.
  4. There are 11 pairs of ribs in man.
  5. Sternum is present on the ventral side of the body.

Answer:(a) True, (b) False, H-zone represents thick filaments, (c) True, (d) False, There are 12 pairs of ribs in man, (e) True

Question 5: Write the difference between:

(a) Actin and Myosin


Actin filaments are thinner.Myosin filaments are thicker.
Actin filament is composed of polymer of monomeric globular actins.Myosin filament is composed of polymer of a protein called meromyosin.

(b) Red and White muscles


Red MuscleWhite Muscle
Red muscle contains red-coloured oxygen storing pigment (myoglobin).Myoglobin is absent in white muscle.
They can use a large amount of oxygen for ATP production.They cannot use plenty of oxygen.
Is called aerobic muscle.Is calle anaerobic muscle.
Only aerobic respiration takes place in red muscle.Anaerobic respiration also takes place in white muscles.

(c) Pectoral and Pelvic girdle


Pectoral GirdlePelvic Girdle
Is present in anterior portion of body.Is present in posterior portion of body.
Articulates with forelimbsArticulates with hind limbs.
Is composed of clavicle and scapula.Is composed of ilium, ischium and pubis.

Question 6: What are the different types of movements exhibited by the cells of human body?

Answer: Cells of the human body exhibit three main types of movements, namely, amoeboid, ciliary and muscular.

Amoeboid Movement: Some specialised cells in our body exhibit amoeboid movement. Such movement is affected by pseudopodia formed by the streaming of protoplasm. Cytoskeletal elements like microfilaments are also involved in amoeboid movement too.

Ciliary Movement: Ciliary movement occurs in most of our internal tubular organs which are lined by ciliated epithelium. The coordinated movements of cilia in the trachea help us in removing dust particles and some of the foreign substances inhaled alongwith the atmospheric air. Passage of ova through the female reproductive tract is also facilitated by the ciliary movement.

Muscular Movement: Movement of our limbs, jaws, tongue, etc. requires muscular movement. The contractile property of muscles is effectively used for locomotion and other movements by human beings and majority of multicellular organisms. Locomotion requires a perfect coordinated activity of muscular, skeletal and neural systems.

Question 7: How do you distinguish between a skeletal muscle and a cardiac muscle?


Skeletal MuscleCardiac Muscle
Are striated.Are striated.
Is unbranched.Is branched.
Present in voluntary organs.Present in heart.
Gets tired within a short span of time.Never gets tired and keeps on contracting throughout the life.

Question 8: Name the type of joint between the following:

  1. Atlas/axis
  2. Carpal/metacarpal of thumb
  3. Between phalanges
  4. Femur/acetabulum
  5. Between cranial bones
  6. Between pubic bones in the pelvic girdle

Answer: (a) Pivot joint, (b) saddle joint, (c) gliding joint, (d) ball and socket joint, (e) fibrous joint, (f) cartilaginous joint