Question 2.
Define sliding filament theory of muscle contraction.
Answer:
The sliding filament theory states that muscle contraction occurs when the thin filaments (actin) slide over the thick filaments (myosin), resulting in the shortening of the sarcomere, which ultimately leads to the contraction of the muscle fiber.

Question 3.
Describe the important steps in muscle contraction.
Answer:
Steps in Muscle Contraction:

1. A nerve impulse arriving at the neuromuscular junction initiates the contractile response.
2. A neurotransmitter released at the junction enters the sarcomere through its membrane channels.
3. The opening of these channels allows Na⁺ ions to flow into the sarcomere, generating an action potential that travels along the entire muscle fiber.
4. The sarcoplasmic reticulum releases Ca²⁺ ions, which bind to troponin on the thin filament.
5. This binding causes conformational changes in troponin, exposing the active sites on F-actin.
6. The myosin heads attach to these active sites, forming cross-bridges.
7. The cross-bridges pull the actin filaments past the myosin filaments, shortening the sarcomere.
8. When thousands of actin and myosin filaments interact simultaneously, the entire muscle cell contracts.

This process is explained by the sliding filament theory of muscle contraction.

Question 4.
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) True – Actin is present in thin filaments.
(b) False – Correct statement: H-zone of a striated muscle fibre contains only thick filaments.
(c) True – Human skeleton has 206 bones.
(d) False – Correct statement: There are 12 pairs of ribs in man.
(e) True – Sternum is present on the ventral side of the body.

Question 5.
Write the difference between:
(a) Actin and Myosin
(b) Red and White muscles

(c) Pectoral and Pelvic girdle
Answer:

(a) Actin and Myosin

1. Actin Filaments:

• Thinner compared to myosin filaments.
• Exist in two forms: Globular actin (G-actin) and Fibrous actin (F-actin).
• Contain proteins tropomyosin and troponin.

1. Myosin Filaments:

• Composed of two portions: Head and Tail.
• Head is formed of Heavy Meromyosin (HMM) and tail of Light Meromyosin (LMM).
• Myosin head has contractile property and ATPase activity, enabling muscle contraction.

(b) Red and White Muscles

(c) Pectoral and Pelvic Girdle

Question 6.
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:

Question 7.
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: amoeboid, ciliary, and muscular.

1. Amoeboid Movement:

• Seen in specialized cells like macrophages and leukocytes in blood.
• Movement occurs by pseudopodia formed through the streaming of protoplasm (similar to Amoeba).
• Cytoskeletal elements, such as microfilaments, play an important role in this type of movement.

2. Ciliary Movement:

• Occurs in internal tubular organs lined by ciliated epithelium.
• Coordinated ciliary movements help remove dust and foreign particles from the trachea.
• Also facilitates the passage of ova through the female reproductive tract.

3. Muscular Movement:

• Responsible for movements of limbs, jaws, tongue, and other body parts.
• Achieved through the contractile property of muscles.
• Locomotion requires coordinated activity of the muscular, skeletal, and neural systems

I can also make a simple diagram showing amoeboid, ciliary, and muscular movements to visually explain

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

Skeletal muscle: Skeletal muscles are closely associated with the skeletal components of the body. They have a striped appearance under the microscope and hence are called striated muscles. As their activities are under the voluntary control of the nervous system, they are known as voluntary muscles. They are primarily involved in locomotory actions and changes in body posture.

Cardiac muscle: Cardiac muscles are the muscles of the heart. Many cardiac muscle cells assemble in a branching pattern to form a cardiac muscle. Based on appearance, cardiac muscles are striated. They are involuntary in nature, as the nervous system does not control their activities directly.