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Locomotion and Movement – CBSE NCERT Study Resources

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11th

11th - Biology

Locomotion and Movement

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Overview of the Chapter

This chapter explores the concepts of locomotion and movement in living organisms, focusing on the mechanisms, types, and significance of these processes. It covers the skeletal system, muscles, and various types of movements in humans and other organisms.

Locomotion and Movement

Locomotion refers to the movement of an organism from one place to another, while movement is a broader term that includes any change in position or posture.

Types of Movement

Movement can be classified into three main types:

  • Amoeboid Movement: Seen in amoeba and some white blood cells, involving the formation of pseudopodia.
  • Ciliary Movement: Occurs in ciliated organisms like Paramecium and in the respiratory tract of humans.
  • Muscular Movement: Involves the contraction and relaxation of muscles, as seen in humans and higher animals.

Human Skeletal System

The human skeletal system consists of 206 bones and is divided into two parts:

  • Axial Skeleton: Includes the skull, vertebral column, and rib cage.
  • Appendicular Skeleton: Comprises the limbs and girdles (pectoral and pelvic).

Joints are the points where two or more bones articulate, allowing movement. They are classified into fibrous, cartilaginous, and synovial joints.

Muscles and Their Types

Muscles are responsible for movement and are of three types:

  • Skeletal Muscles: Attached to bones, voluntary in action.
  • Smooth Muscles: Found in internal organs, involuntary in action.
  • Cardiac Muscles: Found in the heart, involuntary and striated.

Mechanism of Muscle Contraction

Muscle contraction occurs through the sliding filament theory, involving actin and myosin filaments. Calcium ions and ATP play crucial roles in this process.

Disorders of Muscular and Skeletal System

Some common disorders include:

  • Arthritis: Inflammation of joints.
  • Osteoporosis: Decrease in bone density.
  • Muscular Dystrophy: Progressive degeneration of skeletal muscles.

All Question Types with Solutions – CBSE Exam Pattern

Explore a complete set of CBSE-style questions with detailed solutions, categorized by marks and question types. Ideal for exam preparation, revision and practice.

Very Short Answer (1 Mark) – with Solutions (CBSE Pattern)

These are 1-mark questions requiring direct, concise answers. Ideal for quick recall and concept clarity.

Question 1:
Name the protein that forms the thin filaments in muscle fibers.
Answer:

Actin

Question 2:
What is the functional unit of a myofibril?
Answer:

Sarcomere

Question 3:
Which joint allows movement in all planes?
Answer:

Ball and socket joint

Question 4:
Name the bone present in the thigh region.
Answer:

Femur

Question 5:
What is the role of troponin in muscle contraction?
Answer:

Binds calcium and moves tropomyosin

Question 6:
Which neurotransmitter triggers muscle contraction?
Answer:

Acetylcholine

Question 7:
Name the type of muscle found in the heart.
Answer:

Cardiac muscle

Question 8:
What is the energy source for muscle contraction?
Answer:

ATP

Question 9:
Which mineral is essential for muscle contraction?
Answer:

Calcium

Question 10:
Name the bone that forms the upper jaw.
Answer:

Maxilla

Question 11:
What is the function of the synovial fluid?
Answer:

Reduces friction in joints

Question 12:
Which muscle is responsible for arm flexion?
Answer:

Biceps brachii

Question 13:
Name the vertebrae that support the skull.
Answer:

Atlas

Question 14:
What is the role of the sarcoplasmic reticulum?
Answer:

Stores and releases calcium ions

Question 15:
Name the contractile proteins in muscle fibers.
Answer:

Actin and myosin.

Question 16:
Which ion is essential for muscle contraction?
Answer:

Calcium (Ca²⁺).

Question 17:
What is the role of ATP in muscle contraction?
Answer:

Provides energy for contraction.

Question 18:
Which protein stores oxygen in muscles?
Answer:

Myoglobin.

Question 19:
What is the function of ligaments?
Answer:

Connect bones at joints.

Question 20:
Which disease causes weakening of bones?
Answer:

Osteoporosis.

Question 21:
What is the sliding filament theory?
Answer:

Explains muscle contraction.

Question 22:
Name the enzyme that breaks down acetylcholine.
Answer:

Acetylcholinesterase.

Question 23:
Which gland regulates calcium levels in bones?
Answer:

Parathyroid gland.

Question 24:
Define locomotion in biology.
Answer:

Movement of an organism from one place to another.

Question 25:
Name the protein responsible for muscle contraction.
Answer:

Actin and myosin.

Question 26:
What is the functional unit of a muscle fiber?
Answer:

Sarcomere.

Question 27:
Which joint allows movement in all directions?
Answer:

Ball and socket joint.

Question 28:
Name the disorder caused by the degeneration of skeletal muscles.
Answer:

Muscular dystrophy.

Question 29:
Which ion is essential for muscle contraction?
Answer:

Calcium (Ca²⁺).

Question 30:
What is the function of synovial fluid?
Answer:

Reduces friction in joints.

Very Short Answer (2 Marks) – with Solutions (CBSE Pattern)

These 2-mark questions test key concepts in a brief format. Answers are expected to be accurate and slightly descriptive.

Question 1:
Define sarcomere and state its functional unit.
Answer:
Sarcomere: Structural unit of myofibril.
Functional unit: Actin and myosin filaments between two Z-lines.
Question 2:
Name the type of joint between skull bones and its function.
Answer:
Type: Fibrous joint (suture).
Function: Provides rigidity and protection to the brain.
Question 3:
Differentiate between tendons and ligaments.
Answer:
Tendons: Connect muscle to bone (inelastic).
Ligaments: Connect bone to bone (elastic).
Question 4:
What is the role of calcium ions in muscle contraction?
Answer:
Role: Binds to troponin, exposing actin sites for myosin cross-bridge formation.
Question 5:
Identify the type of muscle found in the heart and its feature.
Answer:
Type: Cardiac muscle.
Feature: Involuntary, striated, and branched with intercalated discs.
Question 6:
Name the protein storing oxygen in muscles and its function.
Answer:
Protein: Myoglobin.
Function: Stores oxygen for aerobic respiration during muscle activity.
Question 7:
State the disorder caused by vitamin D deficiency in bones.
Answer:
Disorder: Rickets (in children) or osteomalacia (in adults).
Effect: Softening and weakening of bones.
Question 8:
What is the function of the synovial fluid in joints?
Answer:
Function: Lubricates joints, reduces friction, and nourishes articular cartilage.
Question 9:
Name the bone in the human body that does not articulate with any other bone.
Answer:
Bone: Hyoid bone.
Location: Neck, supporting the tongue and larynx.
Question 10:
Identify the type of movement shown by the cilia in the trachea.
Answer:
Movement: Ciliary movement.
Function: Clears mucus and foreign particles from the respiratory tract.
Question 11:
What is the role of ATP in muscle contraction?
Answer:
Role: Provides energy for myosin head movement and detachment from actin filaments.
Question 12:
Name the vertebral column disorder causing sideways curvature.
Answer:
Disorder: Scoliosis.
Feature: Abnormal lateral curvature of the spine.
Question 13:
Name the contractile proteins present in the sarcomere of a muscle fiber.
Answer:

The contractile proteins in the sarcomere are actin (thin filament) and myosin (thick filament). These proteins slide past each other during muscle contraction, leading to shortening of the sarcomere.

Question 14:
What is the role of calcium ions in muscle contraction?
Answer:

Calcium ions bind to troponin, causing a conformational change that moves tropomyosin away from the actin binding sites. This allows myosin heads to attach to actin, initiating muscle contraction.

Question 15:
Differentiate between red and white muscles based on their myoglobin content.
Answer:
  • Red muscles have high myoglobin content, giving them a reddish appearance and enabling sustained aerobic activity.
  • White muscles have low myoglobin, appear pale, and are adapted for short bursts of anaerobic activity.
Question 16:
Which joint allows movement in all directions? Give an example.
Answer:

The ball and socket joint allows movement in all directions. An example is the shoulder joint (between humerus and scapula).

Question 17:
What is the function of the synovial fluid in joints?
Answer:

Synovial fluid acts as a lubricant, reducing friction between cartilage-covered bone surfaces in synovial joints. It also supplies nutrients and removes waste from joint tissues.

Question 18:
Name the type of movement shown by the cilia in the respiratory tract.
Answer:

The cilia exhibit rhythmic, coordinated beating, known as ciliary movement, which helps in clearing mucus and foreign particles from the respiratory tract.

Question 19:
What is the significance of the H-zone in a sarcomere?
Answer:

The H-zone is the central region of the A-band where only myosin filaments are present. It shortens during muscle contraction as actin filaments slide inward.

Question 20:
Identify the type of muscle found in the wall of the stomach and intestine.
Answer:

The smooth (involuntary) muscle is found in the walls of the stomach and intestine. It helps in peristalsis for food movement.

Question 21:
What causes fatigue in muscles after prolonged activity?
Answer:

Fatigue occurs due to:
1. Accumulation of lactic acid from anaerobic respiration.
2. Depletion of ATP and energy reserves.
3. Reduced oxygen supply leading to incomplete breakdown of glucose.

Question 22:
Name the bone that forms the forehead in the human skull.
Answer:

The frontal bone forms the forehead and the upper part of the eye sockets in the human skull.

Question 23:
What is the role of troponin in muscle contraction?
Answer:

Troponin is a regulatory protein that binds calcium ions. When calcium binds, it causes tropomyosin to shift, exposing active sites on actin for myosin attachment, triggering contraction.

Short Answer (3 Marks) – with Solutions (CBSE Pattern)

These 3-mark questions require brief explanations and help assess understanding and application of concepts.

Question 1:
Explain the role of calcium ions in muscle contraction.
Answer:

During muscle contraction, calcium ions play a crucial role in initiating the sliding filament mechanism.

1. When a nerve impulse reaches the muscle, it releases acetylcholine, causing depolarization of the sarcolemma.
2. This triggers the release of calcium ions from the sarcoplasmic reticulum into the sarcoplasm.
3. Calcium binds to troponin, causing a conformational change that moves tropomyosin away from actin-binding sites.
4. This exposes active sites on actin filaments, allowing myosin heads to bind and form cross-bridges, leading to muscle contraction.

Question 2:
Differentiate between tendons and ligaments based on their structure and function.
Answer:

Tendons and ligaments are both connective tissues but serve different purposes:

  • Tendons: Made of dense, fibrous connective tissue. They attach muscles to bones and transmit mechanical force for movement. They are highly resistant to tension.
  • Ligaments: Composed of elastic connective tissue. They connect bone to bone at joints, providing stability and limiting excessive movement. They are more flexible than tendons.

Question 3:
Describe the sliding filament theory of muscle contraction.
Answer:

The sliding filament theory explains how muscles contract at the molecular level:

1. Myosin heads bind to exposed active sites on actin filaments, forming cross-bridges.
2. Using energy from ATP hydrolysis, myosin heads pull actin filaments toward the center of the sarcomere.
3. This shortens the sarcomere, causing the Z-lines to come closer together.
4. The H-zone and I-band reduce in size, but the A-band remains constant.
5. The process repeats as long as calcium and ATP are available.

Question 4:
What is the significance of the synovial fluid in joints?
Answer:

Synovial fluid is a viscous, lubricating fluid found in synovial joints. Its functions include:

  • Reducing friction between articular cartilage during movement.
  • Providing nutrients and oxygen to chondrocytes in cartilage.
  • Absorbing shocks to protect joint surfaces.
  • Removing metabolic waste products from the joint cavity.
Without synovial fluid, joints would wear out quickly due to excessive friction.

Question 5:
How does the vertebral column contribute to locomotion and movement?
Answer:

The vertebral column plays multiple roles in movement:

  • Provides structural support for the body and maintains upright posture.
  • Protects the spinal cord while allowing flexibility.
  • The intervertebral discs act as shock absorbers during walking or running.
  • Different regions (cervical, thoracic, lumbar) allow various movements like rotation, bending, and extension.
  • Serves as attachment points for ribs and pelvic girdle, facilitating coordinated movement.

Question 6:
Explain the importance of ATP in muscle contraction.
Answer:

ATP is essential for muscle contraction in three key ways:

1. Energy for cross-bridge cycling: ATP hydrolysis provides energy for myosin heads to bind, pivot, and detach from actin.
2. Detachment of myosin: Fresh ATP molecules are needed to break the actin-myosin cross-bridges after power stroke.
3. Calcium pump operation: ATP fuels the active transport of calcium ions back into the sarcoplasmic reticulum for muscle relaxation.
Without ATP, muscles would remain in a contracted state (rigor mortis).

Question 7:
What is the significance of the sarcomere in muscle physiology?
Answer:

The sarcomere is the functional unit of muscle contraction and has key roles:
1. Its repeating structure (between two Z-lines) gives skeletal muscles their striated appearance.
2. Contains actin (thin) and myosin (thick) filaments that slide during contraction.
3. Changes in sarcomere length (shortening) directly correlate with muscle contraction.
4. Helps in understanding disorders like muscular dystrophy where sarcomere integrity is compromised.

Question 8:
How does ATP contribute to muscle contraction and relaxation?
Answer:

ATP is essential for both contraction and relaxation:
1. Contraction: ATP binds to myosin heads, providing energy for cross-bridge formation and power strokes.
2. Relaxation: ATP is needed to detach myosin from actin and pump calcium ions back into the sarcoplasmic reticulum.
3. Without ATP, muscles remain contracted (e.g., rigor mortis).
4. ATP is regenerated via creatine phosphate and cellular respiration.

Question 9:
Explain the vertebral column's role in locomotion and protection.
Answer:

The vertebral column has dual functions:
1. Locomotion: Provides structural support and flexibility due to its 33 vertebrae separated by intervertebral discs. It anchors muscles and facilitates bending/twisting.
2. Protection: Encloses and shields the spinal cord within the vertebral canal.
3. Its S-shaped curvature absorbs shocks and maintains balance during movement.
4. Disorders like scoliosis disrupt these functions.

Long Answer (5 Marks) – with Solutions (CBSE Pattern)

These 5-mark questions are descriptive and require detailed, structured answers with proper explanation and examples.

Question 1:
Explain the sliding filament theory of muscle contraction with a labeled diagram.
Answer:
Theoretical Framework

The sliding filament theory explains how muscles contract. Our textbook shows that actin and myosin filaments slide past each other, shortening the sarcomere.

Evidence Analysis
  • Myosin heads bind to actin, forming cross-bridges.
  • ATP hydrolysis powers the 'power stroke,' pulling actin inward.
  • Calcium ions expose binding sites on actin.
Critical Evaluation

This theory is widely accepted but doesn’t fully explain fatigue. Recent studies highlight role of titin in passive force.

[Diagram: Sarcomere contraction showing overlapping filaments]
Question 2:
Compare striated, smooth, and cardiac muscles based on structure and function.
Answer:
Theoretical Framework

Muscles are classified by structure and control. Striated muscles are voluntary, while smooth and cardiac are involuntary.

Evidence Analysis
TypeStructureFunction
StriatedMultinucleated, stripedBody movement
SmoothSpindle-shapedOrgan contractions
CardiacBranched, uninucleatedHeart pumping
Critical Evaluation

Cardiac muscles have intercalated discs for synchronized contractions, unique among muscle types.

Question 3:
Describe the role of calcium ions and ATP in muscle contraction.
Answer:
Theoretical Framework

Calcium ions and ATP are critical for muscle contraction. We studied their roles in the sliding filament model.

Evidence Analysis
  • Calcium binds to troponin, exposing actin sites.
  • ATP provides energy for myosin head movement.
  • ATP also detaches myosin from actin for re-binding.
Critical Evaluation

Without ATP, muscles remain contracted (rigor mortis). Recent research shows calcium sparks regulate heart contractions.

Question 4:
Analyze the disorders of muscular and skeletal systems with two examples.
Answer:
Theoretical Framework

Disorders like myasthenia gravis and osteoporosis impair locomotion. Our textbook links them to neuromuscular or bone density issues.

Evidence Analysis
  • Myasthenia gravis: Autoimmune attack on acetylcholine receptors.
  • Osteoporosis: Reduced bone mass due to calcium deficiency.
Critical Evaluation

Treatments include immunosuppressants or bisphosphonates, but side effects exist. Current data shows rising osteoporosis cases in postmenopausal women.

Question 5:
Explain the types of joints with examples and their functional significance.
Answer:
Theoretical Framework

Joints are classified as fibrous, cartilaginous, or synovial. We studied their mobility and structure.

Evidence Analysis
  • Fibrous: Immovable (e.g., skull sutures).
  • Cartilaginous: Slightly movable (e.g., pubic symphysis).
  • Synovial: Freely movable (e.g., knee joint).
Critical Evaluation

Synovial joints are prone to arthritis. Recent studies highlight lubricin’s role in joint health.

Question 6:
Discuss the mechanism of locomotion in earthworms using hydrostatic skeleton.
Answer:
Theoretical Framework

Earthworms use a hydrostatic skeleton for locomotion. Our textbook explains how fluid pressure aids movement.

Evidence Analysis
  • Circular muscles contract to elongate segments.
  • Longitudinal muscles shorten segments.
  • Setae provide grip against soil.
Critical Evaluation

This mechanism is energy-efficient but slow. Current research explores biomimicry for soft robotics.

Question 7:
Differentiate between tendons and ligaments with their functional importance.
Answer:
Theoretical Framework

Tendons and ligaments are connective tissues with distinct roles. We studied their composition in class.

Evidence Analysis
  • Tendons: Connect muscle to bone (collagen-rich).
  • Ligaments: Connect bone to bone (elastic fibers).
Critical Evaluation

Tendon injuries heal slower due to poor blood supply. Advanced studies focus on regenerative therapies.

Question 8:
Describe the vertebral column and its role in posture and movement.
Answer:
Theoretical Framework

The vertebral column supports the body and protects the spinal cord. Our textbook outlines its 33 vertebrae.

Evidence Analysis
  • Cervical: Allows neck movement.
  • Thoracic: Supports rib cage.
  • Lumbar: Bears body weight.
Critical Evaluation

Poor posture causes disc herniation. Current data links sedentary lifestyles to spinal disorders.

Question 9:
Explain the neuromuscular junction and its role in muscle contraction.
Answer:
Theoretical Framework

The neuromuscular junction (NMJ) links motor neurons to muscles. We studied its structure in diagrams.

Evidence Analysis
  • Acetylcholine is released into the synaptic cleft.
  • Depolarization triggers action potential in muscle.
  • Enzymes like cholinesterase break down acetylcholine.
Critical Evaluation

NMJ dysfunction causes diseases like botulism. Recent research explores NMJ regeneration.

Question 10:
Analyze the energy sources for muscle contraction during exercise.
Answer:
Theoretical Framework

Muscles use ATP, creatine phosphate, and glycolysis for energy. Our textbook details their roles.

Evidence Analysis
  • ATP: Immediate source (lasts 2-3 seconds).
  • Creatine phosphate: Replenishes ATP (10-15 seconds).
  • Glycolysis: Anaerobic (30-60 seconds).
Critical Evaluation

Prolonged exercise uses aerobic respiration. Current studies emphasize lactate as fuel, not waste.

Question 11:
Explain the mechanism of muscle contraction with reference to the sliding filament theory. Include the role of calcium ions, ATP, and the sarcomere in the process.
Answer:

The mechanism of muscle contraction is explained by the sliding filament theory, which describes how muscle fibers shorten to produce movement. Here’s a step-by-step breakdown:


1. Role of Calcium Ions: When a nerve impulse reaches the muscle fiber, it triggers the release of calcium ions from the sarcoplasmic reticulum. These ions bind to troponin, causing a conformational change that moves tropomyosin away from the actin filaments, exposing the myosin-binding sites.


2. Formation of Cross-Bridges: The myosin heads attach to the exposed binding sites on actin, forming cross-bridges. This requires ATP, which provides energy for the process.


3. Power Stroke: Using the energy from ATP hydrolysis, the myosin heads pivot, pulling the actin filaments toward the center of the sarcomere. This shortens the sarcomere, leading to muscle contraction.


4. Detachment and Reset: A new ATP molecule binds to the myosin head, causing it to detach from actin. The myosin head then resets to its original position, ready for another cycle if calcium ions are still present.


5. Relaxation: When the nerve impulse stops, calcium ions are pumped back into the sarcoplasmic reticulum, tropomyosin re-covers the actin sites, and the muscle relaxes.


Key Points:

  • The sarcomere is the functional unit of contraction, with Z-lines moving closer together during contraction.
  • ATP is essential for both the power stroke and detachment of myosin heads.
  • Without calcium ions, the binding sites on actin remain blocked, preventing contraction.

Question 12:
Compare and contrast the structure and functions of skeletal, smooth, and cardiac muscles. Provide examples of where each type is found in the human body.
Answer:

The three types of muscles—skeletal, smooth, and cardiac—differ in structure and function:


  • Skeletal Muscle:
    - Structure: Striated, multinucleated, and voluntary.
    - Function: Enables locomotion, posture, and voluntary movements.
    - Example: Biceps brachii, quadriceps.

  • Smooth Muscle:
    - Structure: Non-striated, spindle-shaped, uninucleated, and involuntary.
    - Function: Controls slow, sustained contractions in internal organs.
    - Example: Walls of the stomach, intestines, and blood vessels.

  • Cardiac Muscle:
    - Structure: Striated, branched, uninucleated (sometimes binucleated), and involuntary with intercalated discs.
    - Function: Pumps blood throughout the body via rhythmic contractions.
    - Example: Heart myocardium.

Comparison Highlights:
- Control: Skeletal is voluntary; smooth and cardiac are involuntary.
- Striations: Skeletal and cardiac are striated; smooth is not.
- Location: Skeletal attaches to bones; smooth lines organs; cardiac is heart-specific.


Add-ons: Cardiac muscle has autorhythmicity (self-stimulating), while smooth muscle exhibits peristalsis (wave-like contractions).

Question 13:
Explain the sliding filament theory of muscle contraction with a labeled diagram. Discuss the role of calcium ions and ATP in this process.
Answer:

The sliding filament theory explains how muscles contract at the molecular level. According to this theory, muscle contraction occurs when the thin actin filaments slide over the thick myosin filaments, shortening the sarcomere.

Steps involved:
1. A nerve impulse triggers the release of calcium ions from the sarcoplasmic reticulum.
2. Calcium ions bind to troponin, causing a conformational change that moves tropomyosin away from the actin binding sites.
3. Myosin heads bind to the exposed actin sites, forming cross-bridges.
4. ATP hydrolysis provides energy for the myosin heads to pull the actin filaments inward, shortening the sarcomere.
5. Fresh ATP binds to myosin, causing it to detach from actin, and the cycle repeats.

Role of Calcium Ions: They initiate contraction by exposing actin binding sites.
Role of ATP: It provides energy for cross-bridge cycling and detachment of myosin heads.

Diagram: (A labeled diagram showing actin, myosin, sarcomere, Z-lines, and the sliding mechanism should be drawn.)

Question 14:
Compare and contrast the structure and function of skeletal, smooth, and cardiac muscles. Provide examples of where each type is found in the human body.
Answer:

The three types of muscles—skeletal, smooth, and cardiac—differ in structure and function, as outlined below:


  • Skeletal Muscle:
    - Structure: Striated, multinucleated, and voluntary.
    - Function: Enables locomotion, posture, and voluntary movements.
    - Example: Attached to bones (e.g., biceps, quadriceps).

  • Smooth Muscle:
    - Structure: Non-striated, spindle-shaped, uninucleated, and involuntary.
    - Function: Controls slow, sustained contractions in internal organs.
    - Example: Walls of the digestive tract, blood vessels.

  • Cardiac Muscle:
    - Structure: Striated, branched, uninucleated, and involuntary with intercalated discs.
    - Function: Pumps blood continuously; self-excitatory.
    - Example: Heart wall (myocardium).

Comparison Highlights:
- Skeletal and cardiac muscles are striated, while smooth is not.
- Cardiac and smooth muscles are involuntary, whereas skeletal is voluntary.
- Intercalated discs are unique to cardiac muscle, enabling synchronized contractions.

Question 15:
Compare and contrast the structure and function of skeletal, cardiac, and smooth muscles. Provide examples of where each type is found in the human body.
Answer:

The three types of muscles—skeletal, cardiac, and smooth—differ in structure, function, and location:


  • Skeletal Muscle:
    - Structure: Striated, multinucleated, and voluntary.
    - Function: Enables locomotion, posture, and voluntary movements.
    - Example: Biceps brachii (arm muscles), quadriceps (thigh muscles).

  • Cardiac Muscle:
    - Structure: Striated, uninucleated, branched, and involuntary with intercalated discs.
    - Function: Pumps blood throughout the body via rhythmic contractions.
    - Example: Heart (myocardium).

  • Smooth Muscle:
    - Structure: Non-striated, spindle-shaped, uninucleated, and involuntary.
    - Function: Controls slow, sustained contractions in internal organs.
    - Example: Walls of the stomach, intestines, and blood vessels.

Key Comparisons:
- Voluntary vs. Involuntary: Skeletal muscles are voluntary; cardiac and smooth are involuntary.
- Striations: Skeletal and cardiac are striated; smooth is not.
- Control: Skeletal muscles respond to somatic nerves; cardiac and smooth are regulated by the autonomic nervous system.


Add-ons: Cardiac muscle's intercalated discs allow rapid electrical signal propagation, ensuring synchronized heartbeats. Smooth muscle's elasticity is vital for organs like the bladder.

Question 16:
Explain the mechanism of muscle contraction with reference to the sliding filament theory. Include the role of calcium ions and ATP in the process.
Answer:

The mechanism of muscle contraction is explained by the sliding filament theory, which describes how actin and myosin filaments slide past each other to shorten the muscle fiber. Here's a step-by-step breakdown:


1. Neural Stimulation: A motor neuron releases acetylcholine, which triggers an action potential in the muscle fiber, leading to the release of calcium ions (Ca²⁺) from the sarcoplasmic reticulum.


2. Role of Calcium Ions: Ca²⁺ binds to troponin, causing a conformational change that moves tropomyosin away from the actin filament's binding sites. This exposes the active sites on actin, allowing myosin heads to attach.


3. Cross-Bridge Formation: The myosin head, already energized by ATP hydrolysis, binds to actin, forming a cross-bridge.


4. Power Stroke: The myosin head pivots, pulling the actin filament inward (toward the center of the sarcomere). This sliding motion shortens the muscle.


5. ATP Binding: A new ATP molecule binds to the myosin head, causing it to detach from actin. The ATP is then hydrolyzed to ADP + Pi, re-energizing the myosin head for another cycle.


6. Relaxation: When neural stimulation stops, Ca²⁺ is pumped back into the sarcoplasmic reticulum, tropomyosin reblocks actin's binding sites, and the muscle relaxes.


Key Points:

  • ATP is essential for both contraction (myosin head energization) and relaxation (detachment).
  • Calcium ions act as a switch, enabling the interaction between actin and myosin.
  • Repeated cycles of cross-bridge formation and detachment cause sarcomeres to shorten, leading to muscle contraction.

Question 17:
Explain the mechanism of muscle contraction with reference to the sliding filament theory. Include the role of actin, myosin, and regulatory proteins in the process.
Answer:

The mechanism of muscle contraction is explained by the sliding filament theory, which describes how muscle fibers shorten to generate force. Here's a step-by-step explanation:


1. Role of Actin and Myosin: Actin (thin filament) and myosin (thick filament) are the two primary proteins involved. Myosin heads bind to actin, forming cross-bridges, which pull the actin filaments inward, causing contraction.


2. Regulatory Proteins: Tropomyosin and troponin regulate the interaction. In a relaxed state, tropomyosin blocks the myosin-binding sites on actin. When calcium ions (Ca2+) are released, they bind to troponin, shifting tropomyosin and exposing the binding sites.


3. ATP Hydrolysis: Myosin heads hydrolyze ATP to ADP + Pi, providing energy for the "power stroke." This causes myosin to pull actin filaments toward the center of the sarcomere, shortening it.


4. Relaxation: When nerve stimulation stops, calcium is pumped back into the sarcoplasmic reticulum, tropomyosin re-blocks actin, and the muscle relaxes.


Application: This process is vital for voluntary movements like walking and lifting. Disorders like muscular dystrophy arise from defects in these proteins.

Question 18:
Explain the sliding filament theory of muscle contraction with a neat labeled diagram. Discuss the role of calcium ions and ATP in this process.
Answer:

The sliding filament theory explains how muscles contract at the molecular level. According to this theory, muscle contraction occurs due to the sliding of thin actin filaments over thick myosin filaments, shortening the sarcomere.

Steps involved:

  • When a nerve impulse reaches the muscle, calcium ions are released from the sarcoplasmic reticulum.
  • Calcium binds to troponin, causing a conformational change that moves tropomyosin away from actin's binding sites.
  • Myosin heads bind to actin, forming cross-bridges.
  • ATP hydrolysis provides energy for myosin heads to pull actin filaments inward (power stroke).
  • ATP also helps detach myosin heads from actin, resetting them for the next cycle.

Role of Calcium Ions: They initiate contraction by exposing actin binding sites. Without calcium, tropomyosin blocks these sites, preventing contraction.

Role of ATP: It fuels the power stroke and enables myosin detachment. Lack of ATP causes rigor mortis (muscle stiffness after death).

Diagram: A labeled sarcomere showing Z-lines, actin, myosin, and cross-bridges during contraction.

Question 19:
Compare and contrast the structure and functions of skeletal, smooth, and cardiac muscles. Provide examples of where each type is found in the human body.
Answer:

Skeletal Muscle:

  • Structure: Striated, multinucleated, voluntary, and attached to bones.
  • Function: Enables locomotion, posture, and voluntary movements.
  • Example: Biceps, quadriceps.

Smooth Muscle:

  • Structure: Non-striated, spindle-shaped, uninucleated, and involuntary.
  • Function: Controls slow, sustained contractions in internal organs.
  • Example: Walls of intestines, blood vessels.

Cardiac Muscle:

  • Structure: Striated, branched, uninucleated, and involuntary with intercalated discs.
  • Function: Rhythmic contractions to pump blood.
  • Example: Heart myocardium.

Key Differences:

  • Skeletal muscles are voluntary; smooth and cardiac are involuntary.
  • Cardiac muscles have intercalated discs for synchronized contractions.
  • Smooth muscles lack striations and contract slowly.
Question 20:
Explain the mechanism of muscle contraction with reference to the sliding filament theory. Include the role of calcium ions and ATP in the process.
Answer:

The sliding filament theory explains how muscles contract at the molecular level. According to this theory, muscle contraction occurs when the thin actin filaments slide over the thick myosin filaments, shortening the sarcomere.


Steps involved:

  • When a nerve impulse reaches the muscle, it releases acetylcholine, which depolarizes the muscle membrane.
  • This triggers the release of calcium ions from the sarcoplasmic reticulum into the sarcoplasm.
  • Calcium binds to troponin, causing a shift in tropomyosin and exposing the active sites on actin.
  • Myosin heads bind to these active sites, forming cross-bridges.
  • Using energy from ATP hydrolysis, the myosin heads pull the actin filaments inward, causing contraction.
  • ATP also helps in detaching the myosin heads, allowing the cycle to repeat.

Role of Calcium Ions: They initiate contraction by exposing actin binding sites.


Role of ATP: It provides energy for both contraction (power stroke) and relaxation (detachment of myosin heads).

Question 21:
Compare and contrast the structure and functions of skeletal, cardiac, and smooth muscles. Provide examples of where each type is found in the human body.
Answer:

The three types of muscles—skeletal, cardiac, and smooth—differ in structure and function:


1. Skeletal Muscle:

  • Structure: Striated, multinucleated, and voluntary.
  • Function: Facilitates body movement by attaching to bones.
  • Example: Biceps and triceps.

2. Cardiac Muscle:

  • Structure: Striated, uninucleated, and involuntary.
  • Function: Pumps blood throughout the body.
  • Example: Heart wall (myocardium).

3. Smooth Muscle:

  • Structure: Non-striated, uninucleated, and involuntary.
  • Function: Controls slow, sustained movements in internal organs.
  • Example: Walls of the stomach and blood vessels.

Key Differences:

  • Skeletal muscles are voluntary, while cardiac and smooth muscles are involuntary.
  • Cardiac muscles have intercalated discs for synchronized contractions, absent in others.
  • Smooth muscles contract slowly and rhythmically, unlike skeletal muscles.

Case-based Questions (4 Marks) – with Solutions (CBSE Pattern)

These 4-mark case-based questions assess analytical skills through real-life scenarios. Answers must be based on the case study provided.

Question 1:
A patient exhibits muscle fatigue and joint stiffness. Analyze the possible role of ATP depletion and synovial fluid in these symptoms.
Answer:
Case Deconstruction

The patient's muscle fatigue suggests ATP depletion, as muscles require ATP for contraction. Our textbook shows that without ATP, myosin heads cannot detach from actin filaments.

Theoretical Application
  • Synovial fluid reduces friction in joints. Its reduction causes stiffness, as seen in arthritis.
  • Example: Marathon runners experience fatigue due to ATP exhaustion.
Critical Evaluation

Evidence links ATP depletion to lactic acid buildup, worsening fatigue. Similarly, synovial fluid loss is common in aging.

Question 2:
Compare striated and smooth muscles in terms of structure and function, using examples from the human digestive system.
Answer:
Case Deconstruction

Striated muscles are voluntary and multinucleated, while smooth muscles are involuntary and spindle-shaped.

Theoretical Application
  • Example: Esophagus uses striated muscles for swallowing, while intestines rely on smooth muscles for peristalsis.
  • Smooth muscles lack sarcomeres, enabling slow, sustained contractions.
Critical Evaluation

Our textbook shows striated muscles fatigue faster due to high ATP demand, unlike smooth muscles.

Question 3:
A gymnast suffers a torn ligament. Explain how this injury affects joint stability and locomotion, referencing collagen's role.
Answer:
Case Deconstruction

Ligaments, made of collagen, connect bones. A tear compromises joint stability.

Theoretical Application
  • Example: Knee ligament tears impair walking, as seen in sports injuries.
  • Collagen provides tensile strength; its damage weakens the joint.
Critical Evaluation

Our textbook highlights that ligament injuries reduce proprioception, worsening locomotion.

Question 4:
Evaluate how osteoporosis and rickets differ in their impact on bone density and calcium metabolism.
Answer:
Case Deconstruction

Osteoporosis reduces bone density in adults, while rickets softens bones in children due to vitamin D deficiency.

Theoretical Application
  • Example: Elderly women often develop osteoporosis, whereas rickets affects malnourished children.
  • Both disorders disrupt calcium metabolism, but via different pathways.
Critical Evaluation

Evidence shows osteoporosis arises from hormonal changes, while rickets stems from dietary lack.

Question 5:
A patient exhibits muscle fatigue and joint stiffness. Analyze how ATP depletion and synovial fluid reduction contribute to these symptoms.
Answer:
Case Deconstruction

The patient's muscle fatigue arises due to ATP depletion, as studied in muscle contraction. Without ATP, myosin heads cannot detach from actin filaments.

Theoretical Application
  • Synovial fluid reduction increases friction in joints, causing stiffness.
  • Example: Marathon runners experience fatigue from ATP exhaustion.
Critical Evaluation

Our textbook shows ATP is critical for sliding filament theory. Reduced synovial fluid, as in osteoarthritis, worsens movement.

Question 6:
Compare sarcomere structure in relaxed vs. contracted muscles using I-band and A-band changes. Support with a diagram description.
Answer:
Case Deconstruction

In relaxation, the I-band is wide, while contraction shortens it. The A-band remains constant.

Theoretical Application
  • Example: Bicep flexion shows I-band narrowing.
  • [Diagram: Sarcomere with labeled zones]
Critical Evaluation

Our textbook confirms A-band stability due to myosin length. Critical analysis proves sliding filament theory.

Question 7:
A gymnast suffers a torn ligament. Explain why ligaments heal slower than muscles, referencing vascularity and satellite cells.
Answer:
Case Deconstruction

Ligaments lack vascularity, delaying nutrient supply. Muscles have satellite cells for rapid repair.

Theoretical Application
  • Example: Ankle sprains heal slower than muscle strains.
  • Satellite cells activate post-injury in muscles.
Critical Evaluation

Our textbook highlights connective tissue limitations. Evidence shows fibroblast activity is slower in ligaments.

Question 8:
Evaluate how calcium ions and troponin regulate skeletal muscle contraction. Use cross-bridge cycling in your response.
Answer:
Case Deconstruction

Calcium ions bind to troponin, exposing actin sites. This initiates cross-bridge cycling.

Theoretical Application
  • Example: Rigor mortis shows calcium's role post-mortem.
  • Our textbook confirms tropomyosin's blocking action.
Critical Evaluation

Critical analysis proves calcium's concentration dictates contraction strength, as seen in tetany.

Question 9:
Compare striated and non-striated muscles in terms of structure and voluntary control. Provide examples.
Answer:
Case Deconstruction

Striated muscles have visible bands and are voluntary (e.g., biceps), while non-striated muscles lack striations and are involuntary (e.g., stomach wall).

Theoretical Application
  • Striated: Multinucleated, attached to bones.
  • Non-striated: Spindle-shaped, found in organs.
Critical Evaluation

Our textbook shows cardiac muscles are striated but involuntary, blending features. Example: Heart contractions are automatic but structured.

Question 10:
Explain how osteoporosis and rickets disrupt bone homeostasis. Support with evidence.
Answer:
Case Deconstruction

Osteoporosis weakens bones due to calcium loss, while rickets softens them from vitamin D deficiency, disrupting bone homeostasis.

Theoretical Application
  • Osteoporosis: Common in elderly; brittle bones fracture easily.
  • Rickets: Seen in children; bowed legs due to poor mineralization.
Critical Evaluation

Our textbook links calcium absorption to vitamin D. Example: Milk fortified with vitamin D prevents rickets.

Question 11:
A gymnast performs a split. Identify the joint type involved and the muscle coordination required for flexibility.
Answer:
Case Deconstruction

The split uses a ball-and-socket joint (hip) and hinge joint (knee). Muscle coordination involves agonist-antagonist pairs like hamstrings and quadriceps.

Theoretical Application
  • Ball-and-socket: Allows multi-directional movement.
  • Example: Gymnasts train to stretch ligaments for greater flexibility.
Critical Evaluation

Our textbook shows overstretching can tear ligaments. Proper warm-ups prevent injuries during splits.

Question 12:

Rahul, a 16-year-old boy, experienced severe muscle cramps after participating in a marathon. His coach explained that this was due to the accumulation of a certain compound in his muscles. Based on this case:

  • Identify the compound responsible for muscle cramps.
  • Explain the biochemical process leading to its accumulation.
  • Suggest two measures to prevent such cramps in the future.
Answer:

The compound responsible for muscle cramps is lactic acid.

Biochemical process: During intense exercise like a marathon, the body's oxygen demand exceeds supply, leading to anaerobic respiration in muscles.
Glucose is broken down into pyruvate, which is then converted to lactic acid in the absence of oxygen.
Accumulation of lactic acid lowers pH in muscle tissues, causing fatigue and cramps.

  • Preventive measures:
  • Proper hydration before and during exercise to maintain electrolyte balance.
  • Regular training to improve muscle endurance and oxygen utilization efficiency.
Question 13:

During a biology practical, students observed the structure of a synovial joint under magnification. The teacher pointed out a fluid-filled cavity and asked:

  • Name the fluid and its function.
  • Describe two characteristic features of synovial joints.
  • How does this joint type facilitate locomotion?
Answer:

The fluid is called synovial fluid, which acts as a lubricant to reduce friction between cartilage surfaces and nourishes the joint structures.

  • Features of synovial joints:
  • Presence of articular cartilage covering bone ends to absorb shock
  • Joint cavity enclosed by fibrous articular capsule

Locomotion facilitation: Synovial joints allow free movement in multiple directions due to:
1. Smooth articular surfaces reducing friction
2. Ligaments providing stability during motion
3. Synovial fluid enabling nearly frictionless movement

Question 14:
A 45-year-old patient complains of persistent joint pain and stiffness, especially in the morning. Upon examination, the doctor observes swelling and tenderness in multiple joints.

(a) Identify the likely condition based on the symptoms.
(b) Explain the underlying cause of this condition.
(c) Suggest two lifestyle modifications to manage the symptoms.
Answer:

(a) The patient is likely suffering from rheumatoid arthritis, an autoimmune disorder affecting the joints.

(b) The condition occurs when the body's immune system mistakenly attacks the synovial membrane, leading to inflammation, swelling, and eventual damage to the cartilage and bones in the joints. Over time, this can cause joint deformity and loss of function.

(c) Two lifestyle modifications to manage symptoms include:

  • Regular low-impact exercise (e.g., swimming or yoga) to maintain joint flexibility and muscle strength.
  • Balanced diet rich in anti-inflammatory foods (e.g., omega-3 fatty acids, fruits, and vegetables) to reduce inflammation.

Question 15:
A student observes that a frog's leg muscle contracts when an electric stimulus is applied.

(a) Name the phenomenon responsible for muscle contraction.
(b) Describe the role of calcium ions and ATP in this process.
(c) Why does rigor mortis occur after death?
Answer:

(a) The phenomenon is called muscle contraction, specifically governed by the sliding filament theory.

(b)

  • Calcium ions bind to troponin, exposing active sites on actin filaments for myosin cross-bridge formation.
  • ATP provides energy for myosin heads to detach from actin and reset, enabling repeated contraction cycles.

(c) Rigor mortis occurs because after death, ATP production stops, preventing myosin heads from detaching from actin. This causes muscles to remain in a contracted state until tissue breakdown begins.

Question 16:
A 45-year-old patient complains of chronic joint pain and stiffness, especially in the knees and fingers. Upon examination, the doctor observes swelling and reduced mobility in the affected joints.

(a) Identify the likely disorder based on the symptoms.
(b) Explain the underlying cause of this disorder and its impact on joint function.
(c) Suggest two lifestyle modifications to manage the condition.
Answer:

(a) The likely disorder is osteoarthritis, a degenerative joint disease.

(b) Osteoarthritis occurs due to the breakdown of cartilage, the cushioning tissue between bones. Over time, the cartilage wears away, causing bones to rub against each other, leading to pain, swelling, and stiffness. This reduces joint flexibility and mobility.

(c) Two lifestyle modifications include:

  • Regular low-impact exercises like swimming or cycling to strengthen muscles around the joints.
  • Maintaining a healthy weight to reduce stress on weight-bearing joints like knees.
Question 17:
During a sports event, a sprinter suddenly experiences severe muscle cramps in the calf region and is unable to continue running.

(a) What could be the immediate cause of muscle cramps?
(b) Explain the role of ATP and calcium ions in muscle contraction.
(c) Suggest two measures to prevent muscle cramps during intense physical activity.
Answer:

(a) The immediate cause could be dehydration, electrolyte imbalance (especially low sodium/potassium), or overuse of muscles.

(b)

  • ATP provides energy for muscle contraction by breaking into ADP and inorganic phosphate.
  • Calcium ions bind to troponin, exposing actin binding sites for myosin, enabling the sliding filament mechanism.

(c) Preventive measures:

  • Stay hydrated and consume electrolyte-rich fluids.
  • Perform proper warm-up and stretching before exercise.

Question 18:
A 45-year-old patient complains of persistent joint pain and stiffness, especially in the morning. Upon examination, the doctor observes swelling and tenderness in multiple joints.

(a) Identify the likely condition and explain its cause.
(b) How does this condition affect the synovial joints?
(c) Suggest two ways to manage this condition.
Answer:

(a) The patient is likely suffering from rheumatoid arthritis, an autoimmune disorder where the immune system mistakenly attacks the synovial membrane, leading to inflammation.

(b) In rheumatoid arthritis, the synovial membrane becomes inflamed, causing excess synovial fluid production. This leads to:

  • Swelling and pain due to pressure on joint capsules.
  • Erosion of articular cartilage and bone over time, causing joint deformity.

(c) Management includes:

  • Medication: Anti-inflammatory drugs or disease-modifying antirheumatic drugs (DMARDs) to reduce inflammation.
  • Physical therapy: Exercises to maintain joint mobility and muscle strength.

Question 19:
A sprinter experiences a sudden, sharp pain in the back of his thigh during a race. He is unable to continue running.

(a) What type of muscle injury is this likely to be?
(b) Explain the structure of the affected muscle tissue and its role in locomotion.
(c) List two preventive measures for such injuries.
Answer:

(a) The sprinter likely has a hamstring strain, which is a tear in the skeletal muscle fibers due to overstretching or sudden contraction.

(b) The hamstring is a skeletal muscle composed of:

  • Striated fibers with alternating light and dark bands.
  • Multiple nuclei and abundant mitochondria for energy production.
It aids in locomotion by contracting and pulling on bones via tendons, enabling leg movement.

(c) Preventive measures:

  • Proper warm-up: Dynamic stretches before exercise increase muscle flexibility.
  • Strength training: Strengthening hamstrings reduces injury risk.

Question 20:
A 45-year-old patient complains of chronic joint pain and stiffness, especially in the knees and fingers. Upon examination, the doctor observes swelling and reduced mobility in the affected joints.

(a) Identify the likely disorder and explain its cause.
(b) Suggest two lifestyle modifications to manage this condition.
Answer:

(a) The patient is likely suffering from osteoarthritis, a degenerative joint disorder. It occurs due to the breakdown of cartilage, which acts as a cushion between bones. Over time, the cartilage wears away, causing bones to rub against each other, leading to pain, swelling, and stiffness. Factors like aging, obesity, and joint overuse contribute to this condition.


(b) Two lifestyle modifications to manage osteoarthritis are:

  • Weight management: Maintaining a healthy weight reduces stress on weight-bearing joints like knees and hips.
  • Regular low-impact exercise: Activities like swimming or yoga improve joint flexibility and strengthen surrounding muscles without excessive strain.
Additionally, a balanced diet rich in calcium and vitamin D supports bone health.
Question 21:
During a sports event, a sprinter suddenly experiences severe muscle cramps in the calf region and is unable to continue running.

(a) What could be the physiological reason behind this cramp?
(b) How can such cramps be prevented in athletes?
Answer:

(a) The muscle cramp is likely due to muscle fatigue and electrolyte imbalance, particularly a deficiency of sodium, potassium, or magnesium. During intense exercise, excessive sweating leads to loss of these electrolytes, disrupting muscle contraction and causing involuntary spasms. Dehydration and inadequate warm-up can also contribute.


(b) Prevention strategies include:

  • Hydration: Drinking fluids with electrolytes before, during, and after exercise maintains balance.
  • Proper warm-up and stretching: Prepares muscles for activity and reduces sudden strain.
Additionally, a diet rich in bananas (potassium) and nuts (magnesium) helps maintain electrolyte levels.
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