GSEB Class 11 Biology Solutions Chapter 20 Locomotion and Movement

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

Exam Tip: Practice drawing the sarcomere with accurate labels for the Z-line, A-band, I-band, and H-zone, as the arrangement of these bands is crucial for understanding muscle contraction.

Question 2. Define sliding filament theory of muscle contraction.
Answer: The mechanism of muscle contraction is best explained by the sliding filament theory, which states that muscle fiber contraction occurs by the thin filaments gliding over the thick filaments.
In simple words: The sliding filament theory explains how muscles work by saying that thin threads inside muscle cells slide past thicker threads, making the muscle shorter and causing it to contract.

Exam Tip: When defining the sliding filament theory, emphasize the movement of thin filaments over thick filaments, as this is the core concept.

Question 3. Describe the important steps in muscle contraction.
Answer: Muscle contraction starts with a signal sent by the central nervous system (CNS) through a motor neuron. A motor neuron, along with the muscle fibers it connects to, forms a motor unit. The point where a motor neuron and the muscle fiber's sarcolemma meet is called the neuromuscular junction or motor-end plate. A neural signal reaching this area releases a neurotransmitter, which then creates an action potential in the sarcolemma. This potential spreads across the muscle fiber and triggers the release of calcium ions into the sarcoplasm.
An increase in \( \text{Ca}^{++} \) levels causes calcium to bind with a troponin subunit on actin filaments, thereby uncovering the active sites for myosin. Using energy from ATP hydrolysis, the myosin head then attaches to these exposed active sites on actin filaments, moving towards the center of the 'A' band. The Z-lines linked to these actins are also pulled inward, leading to a shortening of the sarcomere, which is contraction. During this process, the I-bands become smaller, while the 'A' bands keep their length.
The ATP is again broken down by the myosin head, and the cross-bridge cycle of formation and breakage repeats, causing further sliding. This process continues until the \( \text{Ca}^{++} \) ions are pumped back into the sarcoplasmic cisternae, which results in the masking of actin filaments. This action causes the Z-lines to return to their original position, meaning relaxation occurs.
In simple words: Muscle contraction begins with a brain signal. This signal releases calcium, which uncovers binding spots on thin filaments. Myosin heads then grab these spots, pull the thin filaments inward, and use energy from ATP to repeat the pulling, causing the muscle to shorten. When calcium is pumped back, the muscle relaxes.

Exam Tip: Clearly outline the sequence of events: neural signal, neurotransmitter release, action potential, calcium release, binding of calcium to troponin, myosin binding to actin, ATP hydrolysis, filament sliding, and calcium reuptake for relaxation. Mentioning the specific bands (A-band, I-band, Z-line) and their changes is important.

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 fiber represents both thick and thin filaments.
3. The human skeleton has 206 bones.
4. There are 11 pairs of ribs in man.
5. The sternum is present on the ventral side of the body.
Answer:
1. True
2. True
3. True
4. False. There are 12 pairs of ribs in man.
5. True
In simple words: This question asks to identify true or false statements about muscles and the human body. One statement about the number of rib pairs in humans is false and needs correction from 11 to 12.

Exam Tip: For true/false questions, read each statement carefully. If a statement is false and requires correction, make sure your corrected version is factually accurate and clearly reverses the error in the original statement.

Question 5. Write the difference between:
1. Actin and myosin
2. Red and white muscles
3. Pectoral and Pelvic girdle
Answer:
(1) Differences between Actin and Myosin:
Actin:
1. These are thin filaments.
2. Actin has low molecular weight filamentous protein.
3. It occurs in two forms: monomeric G-actin and polymeric F-actin.
4. The thin filaments also contain the contractile protein called tropomyosin.
5. It is a rod-shaped fibrous protein.
Myosin:
1. These are thick filaments.
2. Myosin has high molecular-weight, small globular proteins.
3. It covers the active sites of F actin.
4. Each myosin molecule has two parts: a tail, and a head.
5. It is a globular protein.

(2) Differences between Red and White muscles:
Red muscles:
1. They are smaller in diameter.
2. Mitochondria are more numerous.
3. Blood capillaries are more.
4. The sarcoplasmic reticulum is less.
5. They contain a very high amount of myoglobin.
White muscles:
1. They are bigger in diameter.
2. Mitochondria are less in number.
3. Blood capillaries are less.
4. The sarcoplasmic reticulum is more.
5. They contain a very low amount of myoglobin.

(3) Differences between the Pectoral and Pelvic girdle:
Pectoral girdle:
1. Pectoral bones assist in the articulation of the upper and the lower limbs, respectively, with the axial skeleton.
2. The pectoral girdle is made of two halves.
3. Each half of the pectoral girdle consists of a clavicle and a scapula.
4. The scapula is a large, triangular flat bone located in the posterior part of the thorax, between the second and seventh ribs.
5. The posterior, flat, triangular body of the scapula has a slightly raised ridge called the spine, which extends as a flat, expanded process called the acromion.
6. The clavicle connects with this. Below the acromion is a depression called the glenoid cavity, which connects with the humerus head to form the shoulder joint.
7. Each clavicle is a long, slender bone with two curvatures. This bone is commonly known as the collarbone.
Pelvic girdle:
1. The pelvic girdle also helps in the articulation of the upper and the lower limbs, respectively, with the axial skeleton.
2. The pelvic girdle consists of two coxal bones.
3. Each coxal bone is formed by the fusion of three bones: ilium, ischium, and pubis.
4. At the point where these bones join, there is a cavity called the acetabulum, to which the thigh bone connects.
5. Anteriorly, the two halves of the pelvic girdle meet to form the pubic symphysis, which contains fibrous cartilage.
In simple words: This answer explains the key differences between various biological components: Actin and Myosin (thin vs. thick muscle filaments), Red and White muscles (slow vs. fast twitch characteristics), and Pectoral and Pelvic girdles (shoulder vs. hip structures).

Exam Tip: For "difference between" questions, always present your answer in a comparative format, either using a table or by listing corresponding points for each item to ensure clarity and easy comparison.

Question 6. Match column I with column II:
Column I
(i) Smooth muscle
(ii) Tropomyosin
(iii) Red muscle
(iv) Skull
Column II
(a) Myoglobin
(b) Thin filament
(c) Sutures
(d) Involuntary.
Answer:
1. d
2. b
3. a
4. c
In simple words: This question asks us to link items from one list to their correct match in another list. The correct pairs connect smooth muscle to involuntary movement, tropomyosin to thin filaments, red muscle to myoglobin, and the skull to sutures.

Exam Tip: When matching, identify the most obvious pairs first, and then use elimination for the remaining options. Double-check each match to ensure it is accurate.

Question 7. What are the different types of movements exhibited by the cells of the human body?
Answer: Human body cells show three main kinds of movements: amoeboid, ciliary, and muscular. Some specialized cells, such as macrophages and leucocytes in the blood, display amoeboid movement. This movement is influenced by pseudopodia, which form due to streaming protoplasm.
Ciliary movement happens in most of our internal tubular organs, which are covered by ciliated epithelium. The movement of cilia in the trachea helps remove dust particles and other foreign matter. The passage of ova through the female reproductive tract is also aided by ciliary movement. Movements of our limbs, jaws, tongue, and so on, require muscular movement. The ability of muscles to contract is effectively utilized for both locomotion and other movements by humans.
In simple words: Human cells move in three ways: amoeboid (like white blood cells), ciliary (like tiny hairs moving things in tubes), and muscular (for bigger body movements like walking or talking).

Exam Tip: When discussing types of cell movement, provide a clear definition or characteristic for each type (amoeboid, ciliary, muscular) and give specific examples of where they occur in the human body.

Question 8. How do you distinguish between a skeletal muscle and a cardiac muscle?
Answer:

Exam Tip: When comparing muscle types, focus on key differentiating features like voluntary/involuntary nature, location, presence/absence of striations, number and position of nuclei, and specific structures like intercalated discs.

Question 9. Name the type of joint between the followings.
1. Atlas/ Axis
2. Carpal/ metacarpal of the thumb
3. between phalanges
4. Femur/acetabulum
5. between cranial bones
6. between pubic bones in the pelvic girdle.
Answer:
1. Pivot joint
2. Ball and socket
3. Saddle joint
4. Fibrous joint
5. Gliding joint
6. Ball and socket
In simple words: This question asks to identify the type of joint found between different bones. Each pair of bones listed connects in a specific way, like a pivot joint for the neck, ball-and-socket for the thumb, and fibrous joints for the skull.

Exam Tip: For questions about joints, memorize the common types of joints (pivot, ball-and-socket, hinge, gliding, saddle, fibrous) and associate them with specific examples of bones where they occur in the body.

Question 10. Fill in the blank spaces:
Answer:
1. All mammals (except a few) have seven cervical vertebrae.
2. The number of phalanges in each limb of a human is 14.
3. The thin filament of a myofibril contains 2 'F' actins and two other proteins, namely Tropomyosin and Troponin.
4. In a muscle fiber, \( \text{Ca}^{++} \) is stored in Sarcoplasm.
5. 11th and 12th pairs of ribs are called floating ribs.
6. The human cranium is made of 8 bones.
In simple words: This answer provides facts about the body, such as the number of cervical vertebrae in mammals, phalanges in human limbs, the proteins in thin muscle filaments, where calcium is stored in muscle fibers, the name for the last two rib pairs, and the number of bones in the human cranium.

Exam Tip: For fill-in-the-blank questions, recall specific numerical facts and key terminology related to anatomy and physiology. Ensure accuracy in spelling and numerical values.