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

One of the significant attributes of living beings is movement, and of all the living beings plants and animals show a wide range of movements. And, such voluntary movements are known as locomotion. The different forms of locomotory movement are walking, climbing, running, swimming, and flying. Locomotory structures are different from those that help in other types of movements. The methods through which animals perform locomotion changes with the demand of their situation and their habitats.

Also covered in this chapter are the reasons that explain why locomotion is required, which are to find shelter, food, appropriate breeding grounds, mating partner, to hide from predators, or in search of favourable climatic conditions. The topics in this chapter are explained below.

• Different types of movement
• Muscle
• Skeleton System
• Joints
• Disorders in Skeleton and Muscular System

Except for plants which are immobile, every other living organism exhibits locomotion and movement function. This chapter's inclusion in class 11 has been made to enlighten the students about movement and its functionality exhaustively. Animals have different methods of locomotion compared to plants.

This chapter will explain to the students the various structures used for locomotion and their mechanism, the skeletal system, functions of joints and bones, muscular system, and the disarray in the skeletal system, like arthritis. Even the concepts of voluntary and involuntary action of muscles have been incorporated in this chapter.

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

Answer:


 

Q2. Define the 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 the shortening of the myofibrils.

2. Each muscle fiber possesses alternate light and dark bands, which contains a specialized 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 fiber specialized 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.

Q3. Describe the important steps in muscle contraction.

Answer: During striated muscle contraction, the thick filament slides over the skinny filament by a recurrent binding and releases myosin on the filament. This whole method happens consecutively.

Step 1: Muscle contraction is initiated by signals that move the nerve fiber and reach the myoneural junction or motor endplate. The myoneural junction may be a junction between a somatic cell and also the membrane of the muscle fiber. As a result, a neurotransmitter (acetylcholine) is discharged into the junction cleft by generating an action potential on the sarcolemma.

Step 2: The generation of this action potential releases metallic element ions from the cytoplasmic reticulum within the sarcoplasm.

Step 3: The exaggerated metallic element ions within the cytoplasm cause the activation of simple protein sites. metallic element ions bind to the troponin on simple protein filaments and take away the tropomyosin, wrapped around simple protein filaments. Hence, active actin sites are exposed and this enables myosin heads to connect to the present site.

Step 4: In this stage, the myosin head attaches to the exposed site of simple actin and forms cross bridges by utilizing energy from ATP. The actin filaments are pulled. As a result, the H-zone reduces. It's at this stage that the contraction of the muscle happens.

Step 5: After shortening, the myosin head pulls the actin filament and releases ADP at the side of orthophosphate. ATP molecules bind and detach myosin and also the cross-bridges are broken.

Step 6: This method of formation and breaking down of cross-bridges continues till there's a visit to the stimulant, which causes a rise in metallic elements. As a result, the concentration of metallic element ions decreases, thereby masking the actin filament and resulting in muscle relaxation.

Q4. Write true or false. If false change the statement so that it is true.
a. Actin is present in the thin filament.
b. H-zone of striated muscle fiber represents both thick and thin filaments.
c. The human skeleton has 206 bones.
d. There are 11 pairs of ribs in man.
e. The sternum is present on the ventral side of the body.

Answer:
a. Actin is present in the thin filament.  (True).
b. H-zone of striated muscle fiber represents both thick and thin filaments. (False).
- H -zone of striated muscle fiber is the central part of the thick filament that is not overlapped by the thin filament.
c.The human skeleton has 206 bones. (True).
d. There are 11 pairs of ribs in man. (False).
- There are 12 pairs of ribs in a man.
e.The sternum is present on the ventral side of the body. (True).

Q5. Write the difference between :
a. Actin and Myosin
b. Red and White muscles
c. Pectoral and Pelvic girdle

Answer:
a. The differences between actin and myosin are as follows:

b. The differences between Red and White muscles are as follows:

c. The differences between the Pectoral and Pelvic girdle are as follows:

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

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

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:

Q9. Name the type of joint between the following:-
a. atlas/axis
b. carpal/metacarpal of the thumb
c. between phalanges
d. femur/acetabulum
e. between cranial bones
f. between pubic bones in the pelvic girdle

Answers:
a.The joint between the atlas/axis is pivotal joint
b. The joint between the carpal/metacarpal of the thumb is saddle joint
c. There is a hinge joint in between phalanges.
d. Femur/acetabulum possesses a ball and socket joint.
e. The joint between cranial bones are fibrous joints.
f. The joints between pubic bones in the pelvic girdle are the ball and socket joints.

Q10. Fill in the blank spaces:
a. All mammals (except a few) have ______ cervical vertebra.
b. The number of phalanges in each limb of humans is ______.
c. The thin filament of myofibril contains 2 ‘F’ actins and two other proteins namely _______ and ______.
d. In a muscle fiber, 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 vertebrae.
b. The number of phalanges in each limb of a human is 14.
c. The specialized thin filament of myofibril contains 2 ‘F’ actins and two other proteins namely troponin and tropomyosin.
d. In a muscle fiber, Ca++ is stored in the sarcoplasmic reticulum.
e. The 11th and 12th pairs of ribs are called floating ribs.
f. The human cranium is made of eight bones.
 

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