Locomotion and MovementClass 11 Biology NCERT Solutions
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Q1Exercises
Draw the diagram of a sarcomere of skeletal muscle showing different regions.
Solution
A diagram of a sarcomere shows the functional unit of a myofibril, located between two successive 'Z' lines. A labelled diagram would include the following regions and structures, as depicted in Figure 17.2 of the textbook:
- Z line: An elastic fibre that bisects the I-band. The thin filaments are firmly attached to the Z line.
- I-band (Isotropic band): The light band, which contains only the thin filaments (actin).
- A-band (Anisotropic band): The dark band, which contains the entire length of the thick filaments (myosin). The outer edges of the A-band have overlapping thin and thick filaments.
- H-zone: The central part of the A-band, where only thick filaments are present and are not overlapped by thin filaments.
- M line: A thin fibrous membrane in the middle of the A-band that holds the thick filaments together.
During muscle contraction, the thin filaments slide over the thick filaments, causing the Z lines to move closer together, the I-bands to shorten, and the H-zone to disappear. The length of the A-band remains unchanged.
Q2Exercises
Define sliding filament theory of muscle contraction.
Solution
The sliding filament theory is the most widely accepted explanation for the mechanism of muscle contraction. It states that the contraction of a muscle fibre occurs by the sliding of the thin filaments (actin) over the thick filaments (myosin) within the sarcomere. This sliding movement pulls the Z lines closer together, causing the sarcomere to shorten, which in turn leads to the contraction of the entire muscle fibre. The lengths of the actin and myosin filaments themselves do not change during contraction.
Q3Exercises
Describe the important steps in muscle contraction.
Solution
The important steps in the mechanism of muscle contraction, according to the sliding filament theory, are as follows:
- Initiation by Neural Signal: The process begins when a signal is sent from the central nervous system (CNS) via a motor neuron to the neuromuscular junction (motor-end plate).
- Neurotransmitter Release: The arrival of the neural signal at the junction causes the release of a neurotransmitter, acetylcholine, which generates an action potential in the sarcolemma (the muscle fibre's plasma membrane).
- Release of Calcium Ions: The action potential spreads throughout the muscle fibre and triggers the sarcoplasmic reticulum to release stored calcium ions () into the sarcoplasm.
- Activation of Actin: The increased level of in the sarcoplasm leads to the binding of calcium with a subunit of troponin on the actin filaments. This binding causes a conformational change in troponin and tropomyosin, which unmasks the active binding sites for myosin on the actin filaments.
- Cross-Bridge Formation: Utilising energy from the hydrolysis of ATP (), the energised myosin head binds to the exposed active site on the actin filament, forming a cross-bridge.
- Power Stroke: The myosin head then pulls the attached actin filament towards the centre of the A-band. This is known as the power stroke. The Z lines attached to these actin filaments are also pulled inwards, causing the sarcomere to shorten, which is contraction. The ADP and inorganic phosphate () are released during this process.
- Cross-Bridge Detachment: A new ATP molecule binds to the myosin head, causing the cross-bridge to break.
- Reactivation of Myosin Head: The ATP is again hydrolysed by the ATPase activity of the myosin head, which re-energises it for the next cycle of cross-bridge formation.
This cycle of cross-bridge formation, power stroke, and detachment continues as long as calcium ions and ATP are available, causing further sliding of the filaments and sustained muscle contraction.
Q4Exercises
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.
Solution
(a) True.
(b) False. The correct statement is: H-zone of a striated muscle fibre represents only thick filaments.
(c) True.
(d) False. The correct statement is: There are 12 pairs of ribs in man.
(e) True.
Q5Exercises
Write the difference between :
(a)
Actin and Myosin
(b)
Red and White muscles
(c)
Pectoral and Pelvic girdle
Solution
(a) Difference between Actin and Myosin:
| Feature | Actin (Thin Filament) | Myosin (Thick Filament) |
|---|---|---|
| Structure | Made of two filamentous ('F') actins helically wound. Also contains troponin and tropomyosin. | A polymerised protein made of many monomeric units called meromyosins. Each has a globular head and a tail. |
| Location | Forms the light I-band and is also present in the A-band (except the H-zone). | Forms the dark A-band. |
| Function | Provides the active sites for myosin heads to bind during contraction. | The myosin heads bind to actin and pull it, causing sliding. The head has ATPase activity. |
| Thickness | Thinner filament. | Thicker filament. |
(b) Difference between Red and White Muscles:
| Feature | Red Muscles (Red Fibres) | White Muscles (White Fibres) |
|---|---|---|
| Myoglobin Content | High, giving them a reddish appearance. | Very low, giving them a pale or whitish appearance. |
| Mitochondria | Numerous (plenty). | Few. |
| Sarcoplasmic Reticulum | Less amount. | High amount. |
| Metabolism | Depend on aerobic respiration for ATP production. | Depend on anaerobic process for energy. |
| Fatigue | Do not fatigue quickly. Suited for sustained work. | Fatigue quickly due to lactic acid accumulation. Suited for fast, short-duration work. |
(c) Difference between Pectoral and Pelvic Girdle:
| Feature | Pectoral Girdle | Pelvic Girdle |
|---|---|---|
| Location | Located in the shoulder region. | Located in the hip region. |
| Function | Articulates the upper limbs (forelimbs) with the axial skeleton. | Articulates the lower limbs (hind limbs) with the axial skeleton. |
| Bones | Each half consists of a clavicle (collar bone) and a scapula (shoulder blade). | Each half (coxal bone) is formed by the fusion of three bones: ilium, ischium, and pubis. |
| Articulation Cavity | The glenoid cavity of the scapula articulates with the head of the humerus. | The acetabulum is a cavity to which the head of the femur articulates. |
| Strength | Lighter and allows for greater mobility of the arm. | Stronger and more robust to support body weight and provide stability for locomotion. |
Q6Exercises
Match Column I with Column II : Column I (a) Smooth muscle (b) Tropomyosin (c) Red muscle (d) Skull Column II
(i)
Myoglobin
(ii)
Thin filament
(iii)
Sutures
(iv)
Involuntary
Solution
The correct matches are:
- (a) Smooth muscle - (iv) Involuntary (Smooth muscles, like those in the digestive tract, are not under voluntary control.)
- (b) Tropomyosin - (ii) Thin filament (Tropomyosin is a protein that is a component of the actin or thin filament.)
- (c) Red muscle - (i) Myoglobin (Red muscles get their colour from a high content of the oxygen-storing pigment, myoglobin.)
- (d) Skull - (iii) Sutures (The flat bones of the skull are joined by fibrous joints called sutures.)
Q7Exercises
What are the different types of movements exhibited by the cells of human body?
Solution
The cells of the human body exhibit three main types of movements:
-
Amoeboid Movement: This movement is effected by pseudopodia formed by the streaming of protoplasm. It is seen in specialised cells like macrophages and leucocytes (white blood cells) in the blood. Cytoskeletal elements like microfilaments are also involved in this movement.
-
Ciliary Movement: This movement is caused by the coordinated motion of cilia. It occurs in most of our internal tubular organs that are lined by ciliated epithelium. For example, cilia in the trachea help remove dust particles, and ciliary movement in the female reproductive tract facilitates the passage of the ovum.
-
Muscular Movement: This is a more complex movement involving the contraction and relaxation of muscles. It is responsible for the movement of our limbs, jaws, tongue, etc., and is essential for locomotion and changes in body posture.
Q8Exercises
How do you distinguish between a skeletal muscle and a cardiac muscle?
Solution
A skeletal muscle can be distinguished from a cardiac muscle based on the following characteristics:
| Feature | Skeletal Muscle | Cardiac Muscle |
|---|---|---|
| Location | Attached to the skeletal components of the body. | Found only in the walls of the heart. |
| Control | Voluntary (under the conscious control of the nervous system). | Involuntary (not under direct conscious control). |
| Appearance | Striated (striped appearance under a microscope). Fibres are unbranched and arranged in parallel bundles. | Striated. Cells are arranged in a branching pattern, forming a network. |
| Structure | Muscle fibres are long, cylindrical, and multinucleated (syncytium). | Muscle cells are shorter, cylindrical, and typically uninucleated. They are interconnected by intercalated discs. |
| Function | Primarily involved in locomotory actions and changes in body posture. | Responsible for the rhythmic contraction and relaxation of the heart to pump blood throughout the body. |
Q9Exercises
Name the type of joint between the following:-
(a)
atlas/axis
(b)
carpal/metacarpal of thumb
(c)
between phalanges
(d)
femur/acetabulum
(e) between cranial bones
(f) between pubic bones in the pelvic girdle
Solution
(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 in the pelvic girdle: Cartilaginous joint (pubic symphysis)
Q10Exercises
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.
Solution
(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) 11 and 12 pairs of ribs are called floating ribs.
(f) The human cranium is made of 8 bones.