NCERT Class 10 Science Chapter 7: Control and Coordination - A Complete Guide

Introduction to Control and Coordination

Welcome, students! In this detailed guide, we will explore Chapter 7 of the NCERT Class 10 Science syllabus, 'Control and Coordination.' Have you ever wondered how you instantly pull your hand away from a hot object, or how a plant bends towards sunlight? These actions are not random; they are the result of a highly sophisticated system of control and coordination within living organisms. All living things, from tiny plants to complex animals, respond and react to changes in their environment. This ability to respond to stimuli is a defining characteristic of life.

In multicellular organisms, specialized tissues and systems work together to provide this control and coordination. For an action to occur, information from the environment must be detected, sent to an interpreting centre, and then a corresponding message must be sent to a part of the body that can carry out the response. In animals, this is primarily achieved by two systems working in tandem: the Nervous System (using electrical impulses) and the Endocrine System (using chemical messengers called hormones). Plants, lacking a nervous system, rely entirely on chemical coordination through plant hormones. This chapter will unravel the fascinating mechanisms that allow organisms to navigate and survive in a constantly changing world.

Animals - The Nervous System

The nervous system is an intricate network of specialized cells called neurons that transmit signals between different parts of the body. It is the body's primary system for rapid communication and coordination, responsible for everything from simple reflexes to complex thoughts and emotions.

Receptors and Effectors

For the nervous system to function, it must first detect a change or stimulus from the environment. This is the job of receptors. Receptors are specialized cells or groups of cells, usually located in our sense organs, that are sensitive to specific types of stimuli.

• Photoreceptors: Detect light (in the eyes).
• Phonoreceptors: Detect sound (in the ears).
• Olfactory Receptors: Detect smell (in the nose).
• Gustatory Receptors: Detect taste (on the tongue).
• Thermoreceptors: Detect changes in temperature (in the skin).
• Mechanoreceptors: Detect touch and pressure (in the skin).

Once a stimulus is detected and processed, the nervous system sends instructions to a part of the body that can carry out the response. These parts are known as effectors. Effectors are typically muscles or glands. For example, when you touch a hot pan, the muscles in your arm (effectors) contract to pull your hand away.

Structure and Function of a Neuron

The fundamental unit of the nervous system is the neuron or nerve cell. It is responsible for transmitting information in the form of electrical signals, known as nerve impulses. A typical neuron has three main parts:

• Dendrites: These are short, branched extensions that receive information from other neurons or receptors and conduct it towards the cell body.
• Cell Body (Cyton): This is the main part of the neuron, containing the nucleus and other organelles. It processes the information received from the dendrites.
• Axon: This is a long, single extension that transmits the nerve impulse away from the cell body to another neuron or an effector (like a muscle cell). The end of the axon has several nerve endings.

The information travels along a neuron as an electrical impulse. At the end of the axon, this electrical impulse triggers the release of chemicals called neurotransmitters. These chemicals cross the gap, or synapse, between one neuron and the next, starting a similar electrical impulse in the dendrite of the next neuron. This is how information is passed from one neuron to another across the body.

Reflex Action and Reflex Arc

A reflex action is a sudden, involuntary, and rapid response to a stimulus. It is a protective mechanism that does not involve conscious thought. For example, sneezing, coughing, blinking, and withdrawing your hand from a sharp object are all reflex actions.

The pathway taken by the nerve impulses during a reflex action is called the reflex arc. Let's trace the path for the example of touching a hot object:

1. Stimulus: Heat from the object.
2. Receptor: Thermoreceptors in the skin of your hand detect the heat.
3. Sensory Neuron: The receptor triggers a nerve impulse in a sensory neuron, which carries the message towards the spinal cord.
4. Relay Neuron (in Spinal Cord): In the spinal cord, the sensory neuron passes the message to a relay neuron (or interneuron).
5. Motor Neuron: The relay neuron immediately passes the impulse to a motor neuron.
6. Effector: The motor neuron carries the instruction to the muscles in your arm (the effector).
7. Response: The muscles contract, and you pull your hand away from the hot object.

This entire process happens in a fraction of a second, often before your brain has even consciously registered the pain. The brain is informed after the action has already occurred.

The Human Brain

While the spinal cord handles many reflex actions, the brain is the ultimate command and control centre of the body. It is a complex organ responsible for thinking, memory, emotion, intelligence, and coordinating all bodily functions. The brain is well-protected inside the bony skull (cranium), and is surrounded by three membranes called meninges and a fluid called cerebrospinal fluid, which acts as a shock absorber.

The human brain is broadly divided into three main regions:

1. Forebrain

The forebrain is the largest and most complex part of the brain. It consists mainly of the cerebrum. The cerebrum is the seat of intelligence, memory, consciousness, and willpower. It is responsible for all our voluntary actions, thoughts, and logical reasoning. It has specific areas for interpreting sensory information from receptors (like hearing, sight, smell) and for sending out instructions to muscles.

2. Midbrain

The midbrain is a small region that connects the forebrain to the hindbrain. It acts as a bridge, transmitting signals between the two. The midbrain also controls certain reflex movements, such as the change in pupil size in response to light and the reflex movements of the head, neck, and trunk in response to visual and auditory stimuli.

3. Hindbrain

The hindbrain is located at the back of the head and controls many of the body's vital functions. It consists of three parts:

• Cerebellum: Located behind the cerebrum, the cerebellum is responsible for maintaining the body's posture and balance. It coordinates smooth and precise voluntary movements, such as walking, riding a bicycle, or picking up a pencil.
• Medulla Oblongata: The medulla controls all involuntary actions, which are essential for life. These include heartbeat, breathing, blood pressure, swallowing, and coughing.
• Pons: The pons relays impulses between the lower cerebellum and the cerebrum and plays a role in regulating respiration.

The Spinal Cord

The spinal cord is a long, cylindrical bundle of nerve tissue that extends from the medulla of the brain down the back. It is protected by the vertebral column (backbone). The spinal cord has two primary functions: it is the main pathway for carrying sensory information from the body to the brain and motor information from the brain to the body, and it is the control centre for most reflex actions.

How does the Nervous Tissue Cause Action?

When a nerve impulse reaches an effector, such as a muscle cell, it triggers a response. The connection point between a motor neuron and a muscle cell is called the neuromuscular junction. Here, the electrical impulse from the neuron causes the release of neurotransmitters, which stimulate the muscle cell. This stimulation causes a change in the arrangement of special proteins within the muscle cells, leading them to shorten or contract. This contraction of muscle cells, attached to bones, is what produces movement.

Coordination in Plants

Plants may not have a brain or nervous system, but they are far from static. They exhibit remarkable coordination and respond to environmental stimuli like light, gravity, water, and touch. This coordination is achieved through chemical signals in the form of plant hormones or phytohormones.

Types of Plant Movements

Plant movements can be categorized into two main types:

• Tropic Movements (Tropisms): These are directional growth movements that occur in response to a specific environmental stimulus. The direction of the movement is determined by the direction of the stimulus.
• Nastic Movements: These are non-directional movements that are not dependent on the direction of the stimulus. They are often rapid responses to stimuli like touch or light.

Tropic Movements (Tropism)

Tropisms can be positive (growth towards the stimulus) or negative (growth away from the stimulus).

• Phototropism: The movement of a plant part in response to light. Shoots and stems typically show positive phototropism (growing towards light), while roots show negative phototropism (growing away from light). This is primarily controlled by the hormone auxin.
• Geotropism: The movement of a plant part in response to gravity. Roots exhibit positive geotropism (growing downwards, with gravity), while stems show negative geotropism (growing upwards, against gravity).
• Hydrotropism: The movement of roots towards a source of water. This is a powerful tropism, essential for the plant's survival.
• Chemotropism: The movement of a plant part in response to a chemical stimulus. A classic example is the growth of the pollen tube from the stigma towards the ovule in a flower, guided by chemical signals.
• Thigmotropism: The directional growth of a plant in response to touch. This is seen in climbing plants with tendrils, which coil around any object they touch for support.

Nastic Movements

Unlike tropisms, nastic movements are independent of the stimulus's direction. The most famous example is the folding of leaves in the 'touch-me-not' plant (Mimosa pudica). When touched, the leaves rapidly droop. This is not a growth movement. Instead, it is caused by a sudden change in the amount of water (turgor pressure) in specialized cells at the base of the leaves. The plant cells rapidly lose water, causing them to go limp and the leaves to fold.

Hormones in Animals (Endocrine System)

While the nervous system provides rapid, short-term control, the endocrine system offers slower, longer-lasting coordination. It consists of several endocrine glands that produce and secrete chemical messengers called hormones directly into the bloodstream. These hormones travel throughout the body and act on specific target organs or tissues, regulating processes like growth, metabolism, and reproduction.

The secretion of hormones is precisely controlled by a feedback mechanism. For instance, if blood sugar levels rise, the pancreas secretes insulin. Insulin helps cells absorb glucose, lowering blood sugar. Once the level returns to normal, insulin secretion is reduced. This prevents excessive hormone production.

Major Endocrine Glands and Their Hormones

Importance of Iodine and the Case of Diabetes

Hormonal imbalances can lead to serious disorders. Two common examples are:

• Goitre: The thyroid gland needs iodine to produce thyroxine. If there is a deficiency of iodine in the diet, the thyroid gland enlarges in an attempt to produce more thyroxine, leading to a swelling in the neck known as goitre. This is why iodized salt is recommended.
• Diabetes: The pancreas produces insulin, a hormone that helps regulate blood sugar levels. If the pancreas does not produce enough insulin, sugar levels in the blood rise, causing a disease called diabetes mellitus. Patients with diabetes often need to take injections of insulin to manage their condition.

Hormones in Plants (Phytohormones)

Just like animals, plants use hormones to coordinate their growth, development, and responses to the environment. These are called phytohormones.

Growth Promoters

• Auxins: Synthesized at the tip of the shoot, auxins promote cell elongation and growth. They play a crucial role in phototropism. When light comes from one side, auxin diffuses to the shaded side of the shoot, causing the cells there to grow longer, which makes the shoot bend towards the light.
• Gibberellins: These hormones help in the growth of the stem, germination of seeds, and flowering. They work in conjunction with auxins to promote stem elongation.
• Cytokinins: These are found in areas of rapid cell division, like fruits and seeds. They promote cell division and also help in delaying the aging of leaves.

Growth Inhibitors

• Abscisic Acid (ABA): This hormone acts as a growth inhibitor. Its effects include causing the wilting of leaves, inducing dormancy in seeds and buds, and promoting the closing of stomata during water stress. It is often referred to as the 'stress hormone' in plants.

Important Questions and Answers

Here are some solved questions from the NCERT textbook to help you test your understanding.

Q1: What is the difference between a reflex action and walking?

Ans:

• Reflex Action: It is an involuntary action controlled by the spinal cord. It is extremely rapid and does not involve conscious thought or decision-making. It's a protective mechanism.
• Walking: It is a voluntary action that is controlled by the brain (specifically, the cerebellum for balance and the cerebrum for the conscious decision to walk). It involves thought and is a learned, complex activity requiring coordination of many muscles.

Q2: What happens at the synapse between two neurons?

Ans: At a synapse, the electrical impulse from the axon of the first neuron cannot directly jump to the dendrite of the next. Instead, when the impulse reaches the axon terminal, it triggers the release of chemical substances called neurotransmitters into the synaptic gap. These chemicals diffuse across the gap and bind to receptors on the dendrite of the second neuron, initiating a new electrical impulse in it. This ensures the one-way transmission of the nerve impulse.

Q3: Which part of the brain maintains posture and equilibrium of the body?

Ans: The cerebellum, which is part of the hindbrain, is responsible for maintaining the posture and equilibrium (balance) of the body. It also coordinates voluntary movements.

Q4: How do we detect the smell of an agarbatti (incense stick)?

Ans: When an incense stick is lit, aromatic particles diffuse into the air. These particles enter our nose and are detected by the olfactory receptors located in the nasal cavity. These receptors convert the chemical stimulus (smell) into an electrical nerve impulse. This impulse is then transmitted by the olfactory nerve to the forebrain. The forebrain interprets this signal, allowing us to perceive and identify the smell of the incense stick.

Q5: What is the role of the brain in reflex action?

Ans: In a pure reflex action, the brain does not play a direct role in the immediate response; the reflex arc is completed at the level of the spinal cord. This allows for a much faster reaction. However, the information about the stimulus and the response does eventually travel up the spinal cord to the brain. The brain then becomes aware of the event, registers sensations like pain, and can exert some conscious control over the situation if needed (for example, deciding to treat a burn or avoid the source of danger in the future).

Chapter Summary

Let's quickly recap the key concepts from this chapter:

• Control and coordination are vital processes that enable organisms to respond to stimuli and survive.
• In animals, coordination is achieved by the nervous system and the endocrine system.
• The nervous system uses neurons to transmit rapid electrical impulses. Its main components are the brain, spinal cord, and nerves.
• A reflex arc is the pathway for a rapid, involuntary response (reflex action) that is usually mediated by the spinal cord.
• The human brain has three main regions: the forebrain (thinking, voluntary actions), midbrain (reflexes), and hindbrain (balance, involuntary actions like breathing).
• Plants lack a nervous system and use chemical coordination through plant hormones (phytohormones).
• Plant movements are either directional (tropisms) like phototropism and geotropism, or non-directional (nastic movements).
• Plant hormones can be growth promoters (Auxins, Gibberellins, Cytokinins) or growth inhibitors (Abscisic Acid).
• The endocrine system in animals uses hormones secreted by endocrine glands to regulate long-term processes like growth, metabolism, and development.
• Key animal hormones include thyroxine, adrenaline, insulin, growth hormone, and sex hormones. Hormonal imbalances can cause diseases like goitre and diabetes.
• Feedback mechanisms ensure that hormones are secreted in precise quantities and at the right time.