NCERT Solutions for Class 11 Biology Chapter 20 Locomotion and Movement

Class 11 Biology Chapter 20 Question Answer

Q1. Draw the diagram of a sarcomere of skeletal muscle showing different regions.

Answer:

Q2. Define sliding filament theory of muscle contraction.

Answer:

Sliding filament theory of muscle contraction

1.The sliding filament theory was mainly proposed to explain the process of muscle contraction. This theory proposes that during muscle contraction the thin filaments slide over the thick filaments leading to shortening of the myofibrils.

2. Each muscle fibre possesses alternate light and dark bands, which contains a specialised contractile protein known as actin and myosin respectively.

3. Actin refers to a thin contractile protein present in the light band and is known as the I-band, on the other hand, myosin is a thick contractile protein present in the dark band and is known as the A-band.

4. An elastic fibre called z line bisects each I-band. to this z line, the thin filament is firmly anchored. The central part of the thick filament that is not overlapped by the thin filament is known as the H-zone.

5. During muscle contraction, the myosin heads or cross bridges come in close contact with the thin filaments causing the thin filaments to be pulled towards the middle of the sarcomere. The Z line attached to the actin filaments is also pulled leading to the shortening of the sarcomere. Hence, the length of the band remains constant as its original length and the I-band shortens and the H-zone disappears.

Chapter 20 of NCERT Solutions for Class 11 Biology

Q3. Describe the important steps in muscle contraction.

Answer:

The process of muscle contraction includes the following events

1. Depolarisation of Sarcolemma- In this event, a signal is sent by the central nervous system through a motor neuron and it reaches the neuromuscular junction or motor end plate. The neuromuscular junction refers to the junction between a motor neuron and the sarcolemma of the muscle fibre. The receiving of the signal by neuromuscular junction causes the acetylcholine which is a neurotransmitter to release and set the action potential in the sarcolemma.

2. Release of Calcium Ions- This step includes the transmission of the action potential by sarcolemma to the sarcoplasmic reticulum to release calcium ions in the sarcoplasm.

3. Conformational Changes in Actin Filaments- The calcium ions thus released binds to the troponin and tropomyosin on active filaments changing the three-dimensional shape of the actin–troponin-tropomyosin complex. This causes the active site for myosin which is found on the actin filament to be exposed.

4. Activation of Myosin Heads- Later on, the myosin heads also get activated and they release energy by the hydrolysis of ATP resulting in the binding of myosin heads to the active sites present on the actin filaments. This leads to the formation of actin-myosin cross-bridge.

5. Sliding of Actin Filaments over Myosin- After the formation of cross-bridges, the myosin head rotates to pull the actin filament towards the centre of the A-band, i.e. the H-zone. The Z-line attached to the actin filaments is also pulled inwards resulting in the contraction of the sarcomere. During contraction, the I-band shortens, while the A-band retains its length. This causes the muscles to contract.

Class 11 Locomotion and Movement NCERT Solutions

Q4. Write true or false. If false change the statement so that it is true.

(a) Actin is present in thin filament
(b) H-zone of striated muscle fibre represents both thick and thin filaments.
(c) Human skeleton has 206 bones.
(d) There are 11 pairs of ribs in man.
(e) Sternum is present on the ventral side of the body.

Answer:

(a) Actin is present in thin filament

True statement

(b) H-zone of striated muscle fibre represents both thick and thin filaments.

False statement. H -zone of striated muscle fibre is the central part of the thick filament that is not overlapped by the thin filament.

(c) Human skeleton has 206 bones

True statement.

(d) There are 11 pairs of ribs in man.

False statement. There are 12 pairs of ribs in a man.

(e) Sternum is present on the ventral side of the body.

True statement

Locomotion and Movement NCERT Solutions

Q5. Write the difference between :

(a) Actin and Myosin

Answer:

The differences between actin and myosin are as follows:

Q5. Write the difference between :

(b) Red and White muscles

Answer:

Q5. Write the difference between :

(c) Pectoral and Pelvic girdle

Answer:

Solutions for NCERT Class 11 Biology Chapter 20 Locomotion and Movement:

Q6. Match Column I with Column II :

Column I Column II
(a) Smooth muscle (i) Myoglobin
(b) Tropomyosin (ii) Thin filament
(c) Red muscle (iii) Sutures
(d) Skull (iv) Involuntary

Answer:

The correct matching is as follows: a- iv, b- ii, c- i, d- iii

Column I Column II
(a) Smooth muscle (iv) Involuntary
(b) Tropomyosin (ii) Thin filament
(c) Red muscle (i) Myoglobin
(d) Skull (iii) Sutures

Q7. What are the different types of movements exhibited by the cells of human body

Answer:

The different types of movements exhibited by the cells of the human body are as follows:

1. Amoeboid movement - The leucocytes present in the blood show amoeboid movement. During tissue damage, these blood cells move in an amoeboid manner (by forming temporary pseudopodia) from the circulatory system towards the site of injury to initiate an Immune response.

2. Ciliary movement- The reproductive cells such as sperms and ova show ciliary movement. The passage of ova through the fallopian tube towards the uterus is facilitated by this movement.

3. Muscular movement- The muscle cells of the human body show muscular movement. These contract and relax to bring about the movement. E.g. Movements of limbs, tongue and jaws are examples of muscular movements.

Class 11 Biology Chapter 20 NCERT Solutions:

Q8. How do you distinguish between a skeletal muscle and a cardiac muscle ?

Answer:

The differences between skeletal muscles and cardiac muscles are as follows:

Chapter 20 of NCERT Solutions for Class 11 Biology

Q9. Name the type of joint between the following:-

(a) atlas/axis

Answer:

(a) atlas/axis possess pivotal joint

Q9. Name the type of joint between the following:-

(b) carpal/metacarpal of thumb

Answer:

(b) carpal/metacarpal of thumb possess saddle joint

CBSE NCERT Solutions for Class 11 Biology Chapter 20 Locomotion and Movement:

Q9. Name the type of joint between the following:-

(c) between phalanges

Answer:

between phalanges hinge joint

Q9. Name the type of joint between the following:-

(d) femur/acetabulum

Answer:

femur/acetabulum possess ball and socket joint.

Q9. Name the type of joint between the following:-

(e) between cranial bones

Answer:

between cranial bones fibrous joints are present

Q9. Name the type of joint between the following:-

(f) between pubic bones in the pelvic girdle

Answer:

between pubic bones in the pelvic girdle ball and socket joints are present.

Locomotion and Movement Class 11 NCERT Solutions

10. Fill in the blank spaces:

(a) All mammals (except a few) have __________ cervical vertebra.
(b) The number of phalanges in each limb of human is __________
(c) Thin filament of myofibril contains 2 ‘F’ actins and two other proteins namely __________ and __________.
(d) In a muscle fibre Ca++ is stored in __________
(e) __________ and __________ pairs of ribs are called floating ribs.
(f) The human cranium is made of __________ bones.

Answer:

(a) All mammals (except a few) have seven cervical vertebra.
(b) The number of phalanges in each limb of human is 14.
(c) Thin filament of myofibril contains 2 ‘F’ actins and two other proteins namely troponin and tropomyosin.
(d) In a muscle fibre Ca++ is stored in sarcoplasmic reticulum.
(e) 11th and 12th pairs of ribs are called floating ribs.
(f) The human cranium is made of eight bones.