Locomotion and Movement
NCERT Class 11 Biology • Chapter 17 Solutions
Muscle Structure & Contraction
1. Draw the diagram of a sarcomere showing different regions.
Description of regions:
- Z-line: Elastic fibre that bisects the I-band. Boundary of a sarcomere.
- A-band (Anisotropic): Dark band containing the entire length of thick filaments (Myosin) and overlapping thin filaments.
- I-band (Isotropic): Light band containing only thin filaments (Actin).
- H-zone: The central part of the A-band where thin filaments do not overlap thick filaments (only Myosin present).
- M-line: A thin fibrous membrane in the middle of the A-band holding thick filaments together.
2. Define sliding filament theory of muscle contraction.
Sliding Filament Theory:
It states that contraction of a muscle fibre takes place by the sliding of thin filaments (Actin) over the thick filaments (Myosin), which shortens the sarcomere and thus the muscle fibre.
It states that contraction of a muscle fibre takes place by the sliding of thin filaments (Actin) over the thick filaments (Myosin), which shortens the sarcomere and thus the muscle fibre.
3. Describe the important steps in muscle contraction.
[Image of Muscle Contraction Steps]
- Excitation: A neural signal reaches the neuromuscular junction, releasing acetylcholine, which generates an action potential in the sarcolemma.
- Calcium Release: The potential spreads to the T-tubules, triggering the release of $Ca^{++}$ from the Sarcoplasmic Reticulum into the sarcoplasm.
- Unmasking: Calcium binds to Troponin on actin filaments, changing its shape and unmasking the active binding sites for myosin.
- Cross-Bridge Formation: Energized myosin heads bind to the exposed active sites on actin to form a cross-bridge.
- Power Stroke: Myosin pulls the attached actin filaments towards the centre of the A-band (M-line), causing the Z-lines to move closer (Shortening/Contraction). ADP and Pi are released.
- Relaxation: A new ATP binds to the myosin head, breaking the cross-bridge. Calcium is pumped back into the SR, masking the active sites, and the muscle relaxes.
Comparisons & Facts
4. True or False Statements (with corrections).
- (a) Actin is present in thin filament. $\rightarrow$ True.
- (b) H-zone of striated muscle fibre represents both thick and thin filaments. $\rightarrow$ False. (Correction: H-zone represents only thick filaments).
- (c) Human skeleton has 206 bones. $\rightarrow$ True.
- (d) There are 11 pairs of ribs in man. $\rightarrow$ False. (Correction: There are 12 pairs of ribs).
- (e) Sternum is present on the ventral side of the body. $\rightarrow$ True.
5. Write the differences between (a) Actin & Myosin (b) Red & White Muscle (c) Pectoral & Pelvic Girdle.
| (a) Actin | (a) Myosin |
|---|---|
| Thin filament protein. | Thick filament protein. |
| Contains Troponin and Tropomyosin. | Has a globular head (ATPase activity) and tail. |
| (b) Red Muscle | (b) White Muscle |
|---|---|
| High myoglobin content (Red). | Low myoglobin content (Pale/White). |
| Rich in mitochondria (Aerobic). | Few mitochondria (Anaerobic). |
| Does not fatigue easily. | Fatigues quickly (Lactic acid accumulation). |
| (c) Pectoral Girdle | (c) Pelvic Girdle |
|---|---|
| Shoulder girdle. | Hip girdle. |
| Consists of Clavicle and Scapula. | Consists of two Coxal bones (Ilium, Ischium, Pubis). |
| Glenoid cavity articulates with Humerus. | Acetabulum articulates with Femur. |
6. Match Column I with Column II.
| Column I | Column II |
|---|---|
| (a) Smooth muscle | (iv) Involuntary |
| (b) Tropomyosin | (ii) Thin filament |
| (c) Red muscle | (i) Myoglobin |
| (d) Skull | (iii) Sutures |
Joints & Bones
7. Different types of movements exhibited by human body cells?
- Amoeboid Movement: Exhibited by Leucocytes (WBCs) and Macrophages (using pseudopodia).
- Ciliary Movement: Exhibited by cells in trachea (removing dust) and oviducts (transporting ova).
- Muscular Movement: Exhibited by limbs, jaws, tongue, etc., using contractile property of muscles.
8. Distinguish between skeletal muscle and cardiac muscle.
| Feature | Skeletal Muscle | Cardiac Muscle |
|---|---|---|
| Location | Attached to bones. | Heart walls. |
| Control | Voluntary. | Involuntary. |
| Structure | Cylindrical, unbranched, multinucleate (syncytium). | Cylindrical, branched, uninucleate. |
| Junctions | Absent. | Intercalated discs (Communication junctions). |
9. Name the type of joint.
[Image of Types of Joints]
- (a) Atlas/Axis: Pivot Joint.
- (b) Carpal/Metacarpal of thumb: Saddle Joint.
- (c) Between phalanges: Hinge Joint.
- (d) Femur/Acetabulum: Ball and Socket Joint.
- (e) Between cranial bones: Fibrous Joint (Sutures).
- (f) Between pubic bones: Cartilaginous Joint (Pubic Symphysis).
10. Fill in the blank spaces.
(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 Tropomyosin and Troponin.
(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 8 bones.