NCERT Class 11 Biology Chapter 20 Notes Locomotion And Movement- Download PDF Notes

Download NCERT Notes for Class 11 Biology Chapter 17 PDF

To download the PDF for Locomotion and Movement, students can click on the link provided. These notes explain key topics like types of muscles, muscle contraction, and the skeletal system. The NCERT notes for class 11 Biology chapter 17 PDF can be accessed offline for quick learning. Diagrams and short summaries make it easy to understand and revise. The NCERT Notes for Class 11 Biology are a valuable resource for understanding the basic and difficult concepts.

Locomotion and Movement Class 11 Notes

This chapter includes topics like types of movement, the structure of muscles, and the skeletal system. The Locomotion and Movement Class 11 Notes explain the mechanism of muscle contraction in a simple way. These are helpful for quick revision and better understanding during exams.

Introduction

Movement is important for survival as it helps in searching for food, escaping predators, and reproduction in animals. Locomotion is carried out by a well-organised, muscular, and skeletal system controlled by the nervous system. Different organisms have evolved various forms of movement.

Types of Movement

The types of movement are described below-

Amoeboid:

Amoeboid movement is seen in unicellular organisms like Amoeba and in certain cells of multicellular organisms, such as leucocytes. It involves the formation of temporary projections called pseudopodia, which help in engulfing food and movement.

Ciliary:

Ciliary movement is by small hair-like structures called cilia that beat in a coordinated manner. This type of movement is seen in the respiratory tract and the reproductive tract. Paramecium, a unicellular organism, uses cilia for locomotion in water.

Muscular:

Muscular movement is the most advanced form of movement seen in higher animals, including humans. It is based on the contraction and relaxation of muscle fibres and is responsible for various functions such as walking, running, breathing, and pumping blood.

Muscle

Muscles are made up of muscle fibres, which are composed of protein filaments called actin and myosin. These proteins play an important role in muscle contraction. Muscles are classified based on their structural function into three types:

Skeletal muscles: These are voluntary muscles attached to bones and help in movement.

Visceral Muscles: These are involuntary muscles found in internal organs like the stomach and intestine.

Cardiac Muscles: These are involuntary muscles found only in the heart and help in continuous contraction for pumping blood.

Structure of Skeletal Muscle in Detail

Skeletal muscle is a striated, voluntary muscle responsible for body movement. It is made up of muscle fibres, which are long, cylindrical, and multinucleate cells. These fibres are grouped into bundles surrounded by connective tissues like epimysium, perimysium, and endomysium. Each muscle fibre contains myofibrils that are further composed of repeating units called sarcomeres- the functional unit of contraction. Sarcomere contains thick(myosin) and thin(actin) filaments arranged in an overlapping pattern that gives skeletal muscles a striated appearance. Skeletal muscles are richly supplied with nerves and blood vessels, ensuring proper contraction and oxygen supply. It is attached to bones by tendons, enabling movement through contraction and relaxation.

Structure of Sarcomere

The sarcomere is the functional unit of a striated muscle fibre responsible for muscle contraction. It is composed of a thick filament arranged in a highly organised repeating pattern between two lines and consists of different bands and zones that contribute to muscle contraction. Z lines are dark, thin protein bands that define the boundary of a sarcomere. Thin filaments are made up of actin, troponin, and tropomyosin proteins. Actin filaments are attached to the Z line and extend to the centre of the sarcomere. Thick filaments are made up of myosin molecules with globular heads that form cross-bridges with actin during contraction. I-band(Isotropic band) is the region containing only thin filaments and shortens during muscle contraction. A-band(Anisotropic band) is the region containing the entire length of the thick filament and remains constant during contraction. The central region of the A-band contains only thick filaments called the H-zone and disappears during muscle contraction as actin slides over myosin. The M-line of the sarcomere holds the thick filament together and provides structural support to the myosin filaments.

Structure Of Contractile Protein:-

The two main contractile proteins in muscles are actin(thin filaments) and myosin(thick filaments). Actin filaments are made up of globular actin(G-actin) subunits that polymerise to form filamentous actin(F-actin). These filaments are associated with regulatory proteins like troponin and tropomyosin, which control muscle contraction and consist of myosin molecules, each with a tail and head. The myosin head has ATPase activity, which provides energy for contraction. During contraction, the myosin heads bind to actin filaments, forming cross-bridges that pull actin towards the sarcomere's center, leading to the shortening of the muscle fibre.

Mechanism of Muscle Contraction (Sliding Filament Theory):-

• A motor neuron releases the neurotransmitter acetylcholine at the neuromuscular junction.

• Acetylcholine binds to the receptors on the muscle fibre, triggering an action potential across the muscle membrane.

• The action potential travels through T-tubules, reaching the sarcoplasmic reticulum, which releases calcium ions into the sarcoplasm.

• Calcium ions play an important role in initiating muscle contraction by binding to troponin, a protein on actin filaments.

• Troponin undergoes a conformational change, causing tropomyosin to move away, exposing the myosin binding sites on actin.

• The myosin heads are attached to the exposed binding sites and actin filaments, forming cross-bridges.

• Myosin is in an energised state, carrying ATP that is hydrolysed into ADP and inorganic phosphate.

• Once the cross-bridge is formed, myosin heads pivot, pulling the actin filament toward the centre of the sarcomere.

• This action is called a power stroke, which results in muscle contraction.

• A new ATP molecule binds to myosin, causing it to detach from actin, which prevents continuous binding and allows relaxation.

• The ATP bound to myosin is hydrolysed, re-energising the myosin to return to its original position.

• Once the nerve impulse stops, calcium ions are pumped back into the sarcoplasmic reticulum.

• Troponin and Tropomyosin cover the myosin binding sites again, preventing further cross-bridge formation.

Skeletal System

• Consists of a framework of bones and a few cartilages.

• The human skeletal system consists of 206 bones: Axial skeleton- 80 bones, and Appendicular skeleton– 126 bones

Axial Skeleton:

The axial skeleton forms a central framework of the body consisting of 80 bones. It includes the skull, vertebral, column, ribs, and sternum. The skull has 22 bones, protects the brain, and houses sensory organs. The vertebral column has 33 vertebrae, providing structural support and flexibility and allowing movement while protecting the spinal cord. The rib cage has 12 pairs of ribs and a sternum that protect vital organs like the heart and lungs. The skeleton maintains posture, protects vital organs, and serves as an attachment for muscles involved in the movement.

Ribs- 12 Pairs

• 1st to 7th pair: True ribs(Vertebro sternal ribs)
• 8,9,10th pair: Vertebro- chondral ribs
• 11th, and 12th pairs: Vertebral ribs (Floating ribs)
• Thoracic Vertebrae, ribs, and Sternum form the rib cage.

Appendicular Skeleton:

The appendicular skeleton consists of 126 bones that facilitate movement and include the limbs and girdles. The. The pectoral girdle consists of clavicles and scapulae connecting the upper limbs to the axial skeleton. The upper limbs include the humerus, radius, ulna, carpal, metacarpals, and phalanges. The pelvic girdle supports the body's weight and consists of hip bones(ilium, ischium, and pubis). The lower limbs include the femur, tibia, fibula, tarsal, metatarsal, and phalanges. The skeleton plays an important role in locomotion and the manipulation of objects.

Joints

Joints are the points of articulation between two or more bones, facilitating movement and flexibility. They are classified based on structure and function:

Fibrous joints, for example, sutures in the skull, are immovable.

Cartilaginous joints, for example, the intervertebral disc, allow limited movement

Synovial joints, for example, in the knee and shoulder, are highly movable and contain synovial fluid, which lubricates the joint and reduces friction. They are further categorised into hinge joints(elbow), ball and socket joints(the hip and shoulder), pivot joints(neck), gliding joints(wrist), and saddle joints(thumb). Joints play a critical role in the movement, providing stability and flexibility to the skeletal system.

Disorders of The Skeletal System

The disorders of the muscular and skeletal system are given below:

• Tetany: A medical condition characterised by involuntary muscle contractions and spasms that are usually caused by low calcium levels in the blood.

• Muscular dystrophy: A genetic condition leading to progressive muscle degeneration.

• Myasthenia gravis: An autoimmune disorder that weakens muscles by blocking nerve signals.

• Arthritis: Inflammation of joints, causing pain and stiffness.

• Osteoporosis: A condition where bones become weak and brittle due to calcium deficiency.

• Gout: A form of arthritis is caused by the accumulation of uric acid crystals in the joints, leading to severe pain, swelling, and inflammation.

Also, Read

• NCERT Notes for Class 11 Physics
• NCERT Notes for Class 11 Chemistry
• NCERT Notes for Class 11 Mathematics

Chapter 17 Biology: Previous Year Questions and Answers

The previous year’s questions given below help students understand the question pattern and check how well they are prepared. The NCERT Class 11 Biology Chapter 17 Notes Locomotion and Movement make revision easier and help students strengthen their conceptual clarity.

Question 1: Muscles with characteristic striations and involuntary are

Option 1. Muscles in the wall of the alimentary canal

Option 2. Muscles of the heart

Option 3. Muscles assisting locomotion

Option 4. Muscles of the eyelids

Answer:

Cardiac muscles are the primary tissue of the heart wall and are involuntary, striated muscles. With blood supplied by the coronary circulation, the cardiac muscle (myocardium) forms a thick middle layer between the inner layer (the endocardium) and the outer layer (the pericardium) of the heart wall.

Hence, the correct answer is option (2), Muscles of the heart

Question 2: Macrophages and leucocytes exhibit

Option 1. Ciliary movement

Option 2. Flagellar movement

Option 3. Amoeboid movement

Option 4. Gliding movement

Answer:

Macrophages and leucocytes move using amoeboid movement, which helps them squeeze through small spaces. This movement is similar to how an amoeba moves by forming temporary extensions called pseudopodia. It allows these cells to reach infection sites quickly. This type of movement is important for immune responses.

Hence, the answer is option (3), Amoeboid movements

Question 3: Which one of the following is not a disorder of bone?

Option 1. Arthritis

Option 2. Osteoporosis

Option 3. Rickets

Option 4. Atherosclerosis

Answer:

The accumulation of fatty deposits, cholesterol, and other materials on the inner walls of arteries is known as atherosclerosis, and it has an impact on the cardiovascular system. Arterial stiffness is the result of these buildups forming plaques, which can impede blood flow and cause the arteries to stiffen and narrow. As the illness worsens, the decreased blood flow may deprive critical tissues and organs, including the brain and heart, of nutrition and oxygen.

Hence, the correct answer is option (4)Atherosclerosis.

Also Read:

• NCERT Solution

• NCERT Solutions for Class 11

• NCERT Solutions for Class 11 Biology

Features of the Class 11 Biology Chapter 17 Notes

The notes provide a structured way to revise important topics quickly and effectively. They have several features, some of which are listed below:

• Explanations of every topic are provided in detail in the Class 11 Biology Chapter 17 Notes.

• The notes are available in the PDF format so that students can access them easily.

• Colourful and well-labelled diagrams are included to make the learning effective.

• The Class 11 Biology Chapter 17 Notes are based on the latest syllabus.

• These notes are short and concise, which saves a lot of time during exams.

Chapter-Wise NCERT Class 11 Notes Biology

Given below are the notes for each chapter, which are designed to simplify the concepts and help students grasp key topics quickly for effective exam preparation.