Control and Coordination

Have you ever touched a hot object and immediately pulled your hand away? Have you noticed how your eyes adjust to changing light, how plants bend towards sunlight, or how your body maintains balance while walking? These activities are possible because living organisms can detect changes in their surroundings and respond appropriately.

The chapter Control and Coordination explains how the nervous system and hormones regulate the activities of the human body and how plants coordinate their responses to environmental stimuli. It connects important concepts from neurons, reflex actions, the brain, the spinal cord, hormones, plant movements, and chemical coordination.

Understanding this chapter requires more than memorising definitions. You should know how a message travels through the body, why some responses are extremely fast, how hormones differ from nerve impulses, and how plants respond despite not having a nervous system.

These notes follow the core concepts of the NCERT Class 10 Science chapter and are designed for conceptual understanding, school examinations, and revision.

1. Meaning of Control and Coordination

Control and coordination are processes that regulate the activities of an organism and help different organs work together in response to internal and external changes.

Control means regulating an activity so that it occurs appropriately.
Coordination means working together in an organised manner to produce a suitable response.

For example, when you run, your brain, nerves, muscles, heart, and respiratory system work together. Your muscles produce movement, your heart pumps blood faster, and your breathing rate increases to supply the additional oxygen required.

Why do living organisms need control and coordination?

Living organisms constantly experience changes called stimuli. A stimulus is any detectable change that can produce a response.

Examples include:

Bright light falling on the eyes.
Touching a hot utensil.
The smell of food.
A sudden loud noise.
A plant receiving light from one direction.
A change in blood glucose concentration.

The ability to detect and respond to stimuli helps organisms survive, maintain internal balance, and perform essential life processes.

Types of coordination in living organisms

Type	Main mechanism	Example
Nervous coordination	Electrical impulses and chemical neurotransmitters	Withdrawing a hand from a hot object
Hormonal coordination	Chemical messengers called hormones	Regulation of blood glucose by insulin
Plant coordination	Plant hormones and changes in growth or movement	A shoot bending towards light

Important: Animals use both nervous and hormonal coordination. Plants also coordinate their responses, primarily through chemical signalling and changes in growth or cell movements, but they do not possess a nervous system like animals.

2. Control and Coordination in Animals

Animals require a system that can receive information, interpret it, and produce an appropriate response. In humans, two major systems perform this work:

Nervous system: Transmits information rapidly through nerve impulses and chemical signals between neurons.
Endocrine system: Releases hormones into the blood to regulate processes such as growth, metabolism, reproduction, and responses to stress.

These systems work together. For example, when you encounter danger, the nervous system helps you recognise the threat, while hormones such as adrenaline prepare your body for rapid action.

3. The Human Nervous System

The nervous system is a network of specialised cells and structures that receives information, processes it, and coordinates responses.

It helps us:

Detect changes in the environment.
Think, learn, remember, and make decisions.
Control voluntary movements.
Produce rapid protective responses.
Regulate several involuntary activities of the body.

3.1 Main components of the nervous system

The human nervous system is commonly divided into the following parts.

Component	Main parts	Main function
Central Nervous System (CNS)	Brain and spinal cord	Receives and integrates information and coordinates responses
Peripheral Nervous System (PNS)	Nerves connecting the CNS with the rest of the body	Carries sensory information towards the CNS and motor commands away from it

The peripheral nervous system includes cranial nerves, which arise from the brain, and spinal nerves, which arise from the spinal cord.

3.2 Receptors and effectors

For a response to occur, the body must detect a stimulus and communicate with the structures that perform the response.

Receptors are specialised cells or sensory structures that detect particular stimuli.

Examples:

Photoreceptors: Detect light in the retina of the eye.
Auditory receptors: Detect sound-related vibrations in the inner ear.
Olfactory receptors: Detect chemicals responsible for smell.
Taste receptors: Detect chemicals associated with taste.
Touch and temperature receptors: Detect mechanical contact, temperature, and related sensations.

Effectors are muscles or glands that carry out a response.

For example, when you touch a hot object, sensory receptors detect the harmful stimulus, the nervous system processes the information, and muscles in your arm contract to withdraw your hand.

The basic sequence is:

Stimulus → Receptor → Sensory neuron → CNS → Motor neuron → Effector → Response

This is a simplified pathway. The exact route depends on the type of response.

4. Neuron: The Structural and Functional Unit of the Nervous System

A neuron is a specialised cell that receives and transmits information. Neurons are also called nerve cells.

They are adapted to carry signals over distances and communicate with other neurons, muscles, or glands.

4.1 Structure of a neuron

structure of nerve cell

The major parts of a neuron are:

1. Dendrites

Short, branched extensions of the neuron.
Receive signals from receptors or other neurons.
Carry signals towards the cell body in a typical neuron.

2. Cell body (cyton)

Contains the nucleus and most of the cell’s cytoplasm and organelles.
Maintains the neuron’s normal activities.
Integrates incoming signals.

3. Axon

A long extension that carries electrical impulses away from the cell body.
May be covered by a myelin sheath, which insulates the axon and helps many types of nerve fibres transmit impulses faster.

4. Axon terminals

The branched endings of an axon.
Help transmit information to another neuron, muscle cell, or gland cell.

4.2 How does a neuron transmit a nerve impulse?

A nerve impulse is an electrical signal produced by changes in the electrical properties of a neuron’s cell membrane.

The process can be understood step by step:

A suitable stimulus activates a receptor or neuron.
Electrical changes are generated in the cell membrane.
The signal travels along the neuron.
When the signal reaches the axon terminal, it may trigger the release of chemical messengers.
These messengers can stimulate the next cell, allowing the signal to continue through the pathway.

The signal travels within a neuron through electrical changes. Communication across most ordinary neuron-to-neuron junctions occurs chemically.

Important examination point: A nerve impulse is not simply a stream of electrons travelling through a wire. It involves coordinated movements of ions across the cell membrane.

4.3 Types of neurons according to function

Type of neuron	Function	Example
Sensory neuron	Carries information from sensory receptors towards the CNS	Carries information about heat from the skin
Relay neuron (interneuron)	Connects and processes information within the CNS	Links sensory and motor pathways in many reflexes
Motor neuron	Carries commands from the CNS towards effectors	Sends a signal to an arm muscle

A complete response often requires communication between these different types of neurons.

5. Synapse: The Junction Between Neurons

A synapse is a specialised junction through which one neuron communicates with another cell. In the typical chemical synapse taught at this level, a tiny gap called the synaptic cleft separates the communicating cells.

How does a chemical synapse work?

An electrical impulse reaches the axon terminal of the first neuron.
Chemical messengers called neurotransmitters are released.
The neurotransmitters cross the synaptic cleft.
They bind to suitable receptors on the next cell.
This produces a response that may generate a new electrical signal.

structure of synapse

Why is a synapse important?

It allows information to pass between neurons.
It helps regulate whether a signal excites or inhibits the next cell.
It enables complex information processing in the nervous system.
Chemical transmission at a typical synapse generally makes transmission directional.

Remember: The gap between two communicating neurons is called the synaptic cleft, while the specialised junction as a whole is called the synapse.

Electrical transmission versus chemical transmission

Feature	Within a typical neuron	Across a chemical synapse
Main mechanism	Electrical changes in the membrane	Release and reception of neurotransmitters
Direction	Along the neuron’s conducting membrane	Usually from the presynaptic cell to the postsynaptic cell
Key structure	Axon and cell membrane	Axon terminal, synaptic cleft, and postsynaptic receptors

6. Reflex Action and Reflex Arc

Imagine that you accidentally touch a hot pan. You pull your hand away almost immediately, often before you have consciously thought about the danger.

This is an example of a reflex action.

6.1 Definition of reflex action

A reflex action is a rapid, automatic response to a stimulus that occurs through a reflex pathway without requiring a deliberate decision.

Examples include:

Withdrawing a hand from a painful, hot object.
Blinking when something approaches the eye.
The knee-jerk response tested by a doctor.
Constriction of the pupil in bright light.

Not every quick or automatic action uses the same pathway. For instance, different reflexes involve different combinations of sensory neurons, interneurons, motor neurons, and brain or spinal cord circuits.

6.2 What is a reflex arc?

A reflex arc is the neural pathway through which a reflex response is produced.

The usual sequence in a simple withdrawal reflex is:

Stimulus → Receptor → Sensory neuron → Spinal cord relay → Motor neuron → Muscle → Withdrawal

Step-by-step explanation:

Stimulus: The skin comes into contact with a dangerously hot object.
Receptor: Sensory endings detect the harmful stimulus.
Sensory neuron: The signal travels towards the spinal cord.
Integration: Neurons in the spinal cord connect the sensory input to an appropriate motor pathway.
Motor neuron: A command travels towards the relevant muscles.
Effector: The muscles contract.
Response: The hand is withdrawn.

The information also reaches the brain, allowing the person to become consciously aware of the pain. The spinal reflex can begin before conscious awareness is complete.

6.3 Why are reflex actions important?

Protection: They help reduce exposure to potentially harmful stimuli.
Speed: The pathway can produce a response without waiting for a deliberate decision.
Efficiency: A relatively simple neural circuit can coordinate a rapid response.
Automatic regulation: Certain reflexes help maintain posture and regulate internal functions.

6.4 Does the brain have no role in reflex actions?

This is a common misconception.

In many familiar spinal withdrawal reflexes, the spinal cord integrates the initial reflex pathway. However, the brain receives information and can influence many reflexes. Other reflexes are coordinated through brain circuits; for example, some eye and head reflexes involve the brainstem.

Therefore, it is inaccurate to say that all reflex actions are controlled only by the spinal cord.

6.5 Reflex action versus voluntary action

Basis	Reflex action	Voluntary action
Nature	Automatic response	Deliberate, goal-directed action
Initial control	Reflex circuit in the spinal cord or brainstem, depending on the reflex	Involves brain processes responsible for planning and movement
Typical speed	Often very rapid	Usually involves more processing before action
Example	Withdrawing a hand from a hot object	Choosing to write a sentence
Awareness	Does not require a prior conscious decision	Generally involves conscious intention

Exam tip: Do not define a reflex action merely as an action performed quickly. Its essential features are that it is automatic and occurs through a reflex neural pathway.

7. The Human Brain

The brain is the main coordinating centre of the nervous system. It receives and interprets sensory information, controls voluntary activities, and regulates many involuntary processes.

It also supports memory, learning, reasoning, emotions, and decision-making.

The brain is protected by:

The skull (cranium), which provides hard external protection.
The meninges, which are protective membranes surrounding the brain and spinal cord.
Cerebrospinal fluid (CSF), which cushions the central nervous system and helps protect it from mechanical shocks.

7.1 Major regions of the brain

At the Class 10 level, the brain is commonly studied through three broad regions: the forebrain, midbrain, and hindbrain.

A. Forebrain

The forebrain includes the cerebrum and other structures involved in sensory processing, regulation, and higher functions.

Cerebrum

The cerebrum is the largest part of the human brain. It is involved in:

Thinking and reasoning.
Learning and memory.
Interpreting sensory information.
Planning and making decisions.
Controlling many voluntary movements.

For example, when you solve a mathematics problem, read a passage, or decide to pick up a pen, the cerebrum plays an important role.

Hypothalamus

The hypothalamus helps regulate internal conditions such as body temperature, hunger, thirst, and sleep-related functions. It also connects nervous regulation with hormonal control through its interaction with the pituitary gland.

B. Midbrain

The midbrain participates in several pathways related to visual and auditory information and helps coordinate certain reflex responses and movements.

It forms part of the brainstem, which connects major brain regions with the spinal cord.

C. Hindbrain

The hindbrain includes the cerebellum, pons, and medulla oblongata.

1. Cerebellum

The cerebellum helps coordinate movements and maintain balance and posture.

Its functions include:

Improving the precision of voluntary movements.
Coordinating the timing of muscle activity.
Helping maintain balance.
Supporting smooth, controlled movement.

For example, walking on a straight line, writing neatly, or riding a bicycle requires coordinated activity involving the cerebellum.

2. Pons

The pons is part of the brainstem. It helps relay information between brain regions and participates in regulating breathing and other functions.

3. Medulla oblongata

The medulla oblongata regulates several essential involuntary functions, including important aspects of:

Breathing.
Heart rate.
Blood pressure.
Swallowing and vomiting reflexes.

Damage to the brainstem can therefore interfere with life-sustaining functions.

7.2 Functions of important brain regions

Brain region	Major function	Example
Cerebrum	Thinking, memory, sensory interpretation, voluntary movement	Solving a problem
Hypothalamus	Regulation of internal conditions and hormonal links	Regulation of thirst
Midbrain	Certain visual and auditory reflex pathways	Orienting responses to sensory stimuli
Cerebellum	Coordination, balance, posture	Maintaining balance while cycling
Pons	Relay functions and participation in breathing regulation	Coordination of respiratory activity
Medulla oblongata	Important involuntary functions	Regulation of breathing and heart rate

7.3 Voluntary and involuntary actions

Voluntary actions are performed with conscious intention. Examples include writing, choosing to stand up, and deliberately moving your hand.

Involuntary actions occur without deliberate conscious control. Examples include the automatic regulation of heart rate, many aspects of digestion, and certain reflexes.

However, the distinction is not always absolute. Breathing, for example, is automatically regulated but can also be consciously controlled for a limited time.

7.4 How does the nervous system make muscles move?

Muscles respond to signals from motor neurons.

The nervous system processes the information.
Motor commands travel along motor neurons.
At the neuromuscular junction, chemical neurotransmitters communicate the signal to the muscle.
The muscle fibres respond and contract.
Coordinated contraction and relaxation produce movement.

Neuromuscular junction is the specialised communication point between a motor neuron and a muscle fibre.

This explains how an electrical signal in the nervous system can ultimately produce a physical movement.

8. How Does Nervous Coordination Differ from Hormonal Coordination?

Both systems help coordinate the body, but their mechanisms are different.

Feature	Nervous coordination	Hormonal coordination
Messenger	Nerve impulses and neurotransmitters	Hormones
Route	Neurons and their connections	Usually blood circulation
Typical response	Often rapid	Often slower to begin
Duration	Often brief, depending on the response	Often longer-lasting, depending on the hormone
Target	Specific connected cells and circuits	Cells with the appropriate receptors
Example	Pulling a hand away from a hot object	Insulin regulating blood glucose

These are general patterns, not absolute rules. Some hormonal responses are rapid, and some nervous effects can persist.

9. Coordination in Plants

Plants cannot run away from danger, but they can detect changes in light, gravity, water availability, and touch. They respond through changes in growth, cell expansion, and other physiological processes.

Unlike animals, plants do not have a brain or a nervous system made of neurons. Their coordination depends largely on plant hormones, chemical signalling, and changes in cell activity.

Examples include:

Shoots growing towards a light source.
Roots growing downwards in response to gravity.
Roots growing towards regions with available water.
Tendrils coiling around a support.

Two important types of plant movement are tropic movements and nastic movements.

9.1 Tropic movements

A tropic movement is a directional growth response of a plant part to an external stimulus.

The direction of growth is related to the direction from which the stimulus acts.

Positive tropism: Growth towards the stimulus.
Negative tropism: Growth away from the stimulus.

For example, a shoot that grows towards light exhibits positive phototropism.

9.2 Types of tropic movements

Types of tropic movements

1. Phototropism — response to light

A plant shoot commonly bends towards a light source. In many shoots, auxin promotes greater cell elongation on the shaded side, causing the shoot to curve towards the light.

phototropism explained with illustrative image

2. Geotropism (gravitropism) — response to gravity

Roots generally show positive gravitropism by growing in the direction of gravity, while shoots generally show negative gravitropism by growing against it.

3. Hydrotropism — response to water

Roots can grow towards regions with greater water availability. This helps the plant access water required for essential life processes.

4. Thigmotropism — response to touch

Tendrils of climbing plants coil around a suitable support after contact. This helps the plant climb and obtain better access to light.

5. Chemotropism — response to chemicals

The growth of a pollen tube towards the ovule is a standard example of chemotropism, involving chemical signals associated with the female reproductive tissues.

Important distinction: Tropism is a directional growth response. It is not simply any movement made by a plant.

9.3 How does a shoot bend towards light?

Consider a plant placed near a window where light enters from one side.

The shoot detects directional light.
The distribution and activity of the plant hormone auxin change in the growing region.
In a typical shoot, auxin promotes greater elongation on the shaded side.
The shaded side grows faster than the illuminated side.
This unequal growth causes the shoot to bend towards the light.

This process is called phototropism.

The difference in growth rates, rather than the shoot simply moving like an animal’s limb, explains the bending.

9.4 Nastic movements

A nastic movement is a plant response in which the direction of movement is not determined by the direction of the stimulus.

For example, the leaves of Mimosa pudica (the touch-me-not plant) fold when touched.

This movement involves changes in the water content and pressure of specialised cells, rather than ordinary directional growth alone.

Other examples include the opening and closing of some flowers in response to light or temperature.

Tropic movement versus nastic movement

Feature	Tropic movement	Nastic movement
Direction of response	Depends on stimulus direction	Does not depend on stimulus direction in the same way
Common mechanism	Directional growth	Changes in cell pressure or growth
Example	Shoot bending towards light	Touch-me-not leaves folding when touched
Typical pattern	Often relatively slow	May be relatively rapid, as in Mimosa pudica

9.5 Why do plants respond to stimuli?

Plant responses help them:

Obtain sufficient light for photosynthesis.
Absorb water and mineral nutrients.
Climb and gain structural support.
Respond to environmental changes.
Carry out reproductive processes successfully.

Plant movements may be slower than many animal responses, but they are essential for growth and survival.

10. Plant Hormones

Plant hormones, also called phytohormones, are chemical messengers that regulate plant growth, development, and responses to environmental stimuli.

They may be produced in one region of a plant and act in the same or another region. Their effects depend on the hormone, its concentration, the tissue involved, and the plant’s developmental stage.

The five major plant hormones commonly discussed in the Class 10 NCERT chapter are auxins, gibberellins, cytokinins, abscisic acid, and ethylene.

10.1 Major plant hormones and their functions

Plant hormone	Major functions	Example or significance
Auxin	Promotes cell elongation in many tissues and helps regulate directional growth	Unequal elongation causes a shoot to bend towards light
Gibberellins	Promote stem elongation and influence seed germination and other growth processes	Helps in the growth of stems
Cytokinins	Promote cell division and influence shoot development	Important in actively dividing tissues
Abscisic acid (ABA)	Often inhibits growth and helps plants respond to stress	Promotes stomatal closure during water stress
Ethylene	A gaseous plant hormone involved in fruit ripening and other developmental responses	Helps regulate the ripening of many fruits

Remember: Abscisic acid is commonly described as a growth-inhibiting hormone at this level, but its functions also include important stress responses. Plant hormones can have several effects, so their actions should not be reduced to a single function in every situation.

10.2 Auxin and phototropism

Auxin is particularly important for understanding the bending of shoots.

When light falls more strongly on one side of a typical shoot, auxin activity and distribution contribute to faster elongation on the shaded side. This unequal growth bends the shoot towards the light.

Exam connection: If a question asks why a plant shoot bends towards light, explain the role of auxin and the unequal growth of the two sides. Merely writing “because the plant needs sunlight” does not explain the mechanism.

10.3 Why are plant hormones important?

Plant hormones coordinate many activities without a nervous system. They help regulate:

Cell division and cell elongation.
Root and shoot development.
Directional growth responses.
Seed germination.
Fruit development and ripening.
Responses to environmental stress.

11. Hormones in Animals

The nervous system is useful for rapid communication, but many body activities require regulation over a longer period and across multiple organs. For these functions, animals use hormones.

A hormone is a chemical messenger produced by specialised cells or glands that influences target cells possessing the appropriate receptors.

11.1 What is the endocrine system?

The endocrine system consists of glands and hormone-producing tissues that release hormones into the bloodstream or surrounding body fluids.

Unlike many exocrine glands, endocrine glands do not use ducts to deliver their hormones to a body surface or into a cavity. Their secretions enter the blood or nearby fluid and reach target tissues.

Examples of endocrine glands include:

Pituitary gland
Thyroid gland
Adrenal glands
Pancreas (its hormone-producing islets)
Testes
Ovaries

11.2 How do hormones work?

Hormonal coordination generally follows this sequence:

A gland or hormone-producing cell releases a hormone.
The hormone enters the blood or surrounding body fluid.
It reaches tissues throughout the body.
Only cells with suitable receptors respond directly to that hormone.
Changes in cell activity produce the physiological response.

For example, insulin released by the pancreas acts on target tissues and helps regulate blood glucose.

Important: A hormone may circulate throughout the body, but this does not mean that every cell responds to it. The response depends on the presence of appropriate receptors and the cell’s ability to respond.

12. Major Endocrine Glands and Their Hormones

12.1 Pituitary gland

The pituitary gland is a small endocrine gland located at the base of the brain. It releases several hormones involved in growth, reproduction, and the regulation of other endocrine glands.

Growth hormone (GH) is secreted by the anterior pituitary gland and promotes growth and development.

Too little growth hormone during childhood can lead to reduced growth.
Excessive growth hormone during childhood can cause excessive linear growth.

The pituitary is often called the master gland because several of its hormones regulate other endocrine glands. However, its activity is itself controlled by signals from the hypothalamus and by feedback from hormones and other body conditions.

12.2 Thyroid gland

The thyroid gland is located in the front of the neck.

It produces thyroxine (T4) and the more biologically active thyroid hormone triiodothyronine (T3). At the Class 10 level, thyroxine is especially important.

Functions of thyroid hormones include:

Regulating the body’s metabolic rate.
Supporting normal growth and development.
Influencing how the body uses nutrients for energy.

Role of iodine: Iodine is required to make thyroid hormones. If the diet does not provide sufficient iodine, thyroid hormone production may be impaired, and the thyroid gland may enlarge, causing goitre in some cases.

This is one reason iodised salt is recommended as a practical public-health measure in regions where iodine deficiency is a concern.

12.3 Adrenal glands

The adrenal glands are located above the kidneys. They produce several hormones, including adrenaline.

Adrenaline helps prepare the body for an immediate challenge, commonly described as the fight-or-flight response.

When a person faces a threatening situation, adrenaline can:

Increase heart rate.
Increase the availability of energy for muscles.
Influence blood flow to different organs.
Support an increase in breathing and other responses needed for rapid action.

These changes help the body respond to a sudden challenge.

12.4 Pancreas

The pancreas has both digestive and endocrine functions. Its hormone-producing islets release hormones including insulin and glucagon.

Insulin helps lower blood glucose by promoting glucose uptake in many tissues and by supporting glucose storage and other metabolic processes.

Glucagon helps raise blood glucose, particularly by stimulating the liver to release glucose into the blood.

At this level, insulin is especially important because its deficiency or ineffective action can lead to persistently elevated blood glucose, as seen in diabetes mellitus.

12.5 Testes

The testes are male reproductive glands that produce sperm and secrete testosterone.

Testosterone contributes to:

Development of male reproductive organs.
Development of secondary sexual characteristics during puberty.
Regulation of sperm production and other reproductive functions.

Examples of secondary sexual characteristics include facial hair growth and a deepening voice during male puberty.

12.6 Ovaries

The ovaries are female reproductive glands that release egg cells and produce hormones including oestrogens and progesterone.

Oestrogens contribute to the development of female secondary sexual characteristics and help regulate the reproductive cycle. Progesterone plays an important role in preparing and maintaining the uterine lining during the menstrual cycle and pregnancy.

12.7 Important hormone table for examinations

Endocrine gland or tissue	Hormone	Major function
Pituitary gland	Growth hormone	Promotes body growth
Thyroid gland	Thyroxine	Regulates metabolism and supports growth and development
Adrenal glands	Adrenaline	Helps prepare the body for sudden challenges
Pancreas	Insulin	Helps regulate and lower blood glucose
Pancreas	Glucagon	Helps raise blood glucose
Testes	Testosterone	Supports male reproductive development and functions
Ovaries	Oestrogens	Supports female reproductive development and functions
Ovaries	Progesterone	Helps regulate the reproductive cycle and supports pregnancy

13. Feedback Mechanism in Hormonal Coordination

Hormones must be released in appropriate amounts and at suitable times. A feedback mechanism helps regulate their production and release according to the body’s requirements.

13.1 Negative feedback

Negative feedback occurs when a change in a regulated condition triggers responses that oppose the original change.

A familiar example is the regulation of blood glucose.

Blood glucose rises

Pancreatic beta cells release more insulin

Cells take up more glucose where insulin promotes uptake; the liver and other tissues help store or use glucose

Blood glucose moves towards its normal range

As glucose regulation improves, the stimulus for additional insulin release decreases.

The body does not simply switch insulin secretion completely on or off. Secretion adjusts continuously in response to blood glucose and other signals.

13.2 Why is feedback important?

It helps maintain stable internal conditions.
It prevents unnecessary or excessive hormone secretion.
It adjusts the body’s response as conditions change.
It coordinates processes that must remain within suitable ranges.

The regulation of internal conditions is related to homeostasis, the maintenance of relatively stable internal conditions despite changes inside or outside the body.

14. Nervous Coordination and Chemical Coordination in Plants and Animals

It is useful to compare the systems studied in this chapter.

Feature	Nervous system in animals	Hormonal coordination in animals	Coordination in plants
Main mechanism	Nerve impulses and neurotransmitters	Hormones	Plant hormones and other cellular signalling processes
Main structures	Neurons, brain, spinal cord, nerves	Endocrine glands and hormone-producing tissues	Growing regions and other responsive plant tissues
Typical response	Often rapid	Often slower and longer-lasting	Frequently involves growth; some movements are rapid
Example	Withdrawal reflex	Adrenaline response	Shoot bending towards light
Nervous system present?	Yes	Works alongside the nervous system	No animal-like nervous system

These mechanisms are different, but they share a common purpose: detecting or responding to changes and coordinating biological activities.

15. Common Misconceptions and Important Corrections

1. Misconception: All rapid responses are reflex actions.

Correction: Reflex actions are automatic responses produced through reflex pathways. A rapid response may also involve other neural processes.

2. Misconception: The brain is not involved in reflex actions.

Correction: Many spinal reflexes begin through spinal circuits, but the brain receives sensory information and influences many responses. Some reflexes are coordinated by brain circuits.

3. Misconception: All hormones act on every cell.

Correction: Hormones act directly on target cells with appropriate receptors.

4. Misconception: Plants do not coordinate their activities because they have no brain.

Correction: Plants coordinate growth and responses through hormones, chemical signals, and changes in cellular activity.

5. Misconception: Every plant movement is a tropic movement.

Correction: Tropisms are directional growth responses. Nastic movements, such as the folding of touch-me-not leaves, do not depend on the direction of the stimulus in the same way.

6. Misconception: Auxin always inhibits growth.

Correction: Auxin can promote cell elongation in shoots, while its effects vary according to tissue, concentration, and developmental conditions.

7. Misconception: The pituitary gland functions independently of the rest of the body.

Correction: Its activity is regulated by the hypothalamus and feedback signals, even though it controls several other endocrine glands.

8. Misconception: Hormones and nerve impulses are identical.

Correction: They use different mechanisms and operate on different timescales, although both contribute to coordinated responses.

9. Misconception: Plants and animals use exactly the same hormones.

Correction: Plants and animals have different hormonal signalling systems. Plant hormones such as auxin and gibberellins are distinct from animal hormones such as insulin and adrenaline.

10. Misconception: Iodine directly acts as a hormone.

Correction: Iodine is an essential nutrient used by the thyroid gland to synthesise thyroid hormones.

Quick Revision Notes

Control and coordination help organisms detect changes and produce suitable responses.
A stimulus is a detectable change that can produce a response. A receptor detects the stimulus, while an effector carries out the response.
The nervous system uses nerve impulses and neurotransmitters to communicate information.
A neuron is a specialised nerve cell. Its main parts are dendrites, cell body, axon, and axon terminals.
A synapse is a specialised junction between communicating cells; the synaptic cleft is the gap at a typical chemical synapse.
Sensory neurons carry sensory information towards the CNS, relay neurons connect neural pathways, and motor neurons carry commands towards effectors.
A reflex action is an automatic response produced through a reflex pathway.
A reflex arc commonly includes a receptor, sensory neuron, spinal cord circuit, motor neuron, and effector.
The CNS consists of the brain and spinal cord. The PNS connects the CNS with the rest of the body.
The cerebrum is involved in thinking, memory, sensory interpretation, and voluntary movement.
The cerebellum helps coordinate movements, posture, and balance.
The medulla oblongata regulates important involuntary functions such as breathing and heart rate.
Tropic movements are directional growth responses to stimuli. Nastic movements do not depend on stimulus direction in the same way.
Phototropism is a response to light; gravitropism is a response to gravity; hydrotropism is a response to water; thigmotropism is a response to touch; and chemotropism is a response to chemicals.
Auxin helps regulate cell elongation and phototropism. Gibberellins promote stem elongation, cytokinins promote cell division, abscisic acid helps regulate stress responses, and ethylene helps regulate fruit ripening.
Hormones are chemical messengers that act on suitable target cells.
The pituitary gland releases growth hormone and several hormones that regulate other endocrine glands.
The thyroid gland produces thyroid hormones, including thyroxine, which regulates metabolism. Iodine is required for thyroid hormone synthesis.
Adrenaline prepares the body for sudden challenges. Insulin helps lower blood glucose, while glucagon helps raise it.
Testosterone, oestrogens, and progesterone contribute to reproductive development and functions.
Negative feedback helps regulate hormone secretion and maintain stable internal conditions.
Homeostasis is the maintenance of relatively stable internal conditions despite changing circumstances.

Practice MCQs

Choose the correct answer for each question before reading its explanation.

1. Which statement best describes the function of a receptor?

A. It always produces hormones.

B. It detects a stimulus and initiates sensory signalling.

C. It contracts whenever the body moves.

D. It stores all the information received by the brain.

Correct Answer: B. It detects a stimulus and initiates sensory signalling.

Explanation: Receptors detect particular stimuli, such as light, temperature, or touch, and help initiate sensory signalling. Muscles and glands act as effectors.

2. Which part of a neuron generally carries impulses away from the cell body?

A. Dendrite

B. Nucleus

C. Axon

D. Synaptic cleft

Correct Answer: C. Axon

Explanation: The axon typically conducts impulses away from the cell body towards the axon terminals. Dendrites commonly receive incoming signals.

3. What is the correct sequence for a typical spinal withdrawal reflex?

A. Receptor → sensory neuron → spinal cord circuit → motor neuron → muscle

B. Muscle → receptor → motor neuron → sensory neuron → brain

C. Sensory neuron → muscle → receptor → spinal cord → motor neuron

D. Brain → receptor → muscle → sensory neuron → spinal cord

Correct Answer: A. Receptor → sensory neuron → spinal cord circuit → motor neuron → muscle

Explanation: The sensory pathway carries information towards the spinal cord, where a neural circuit activates a motor pathway. The muscle then contracts to produce withdrawal.

4. Which structure is primarily responsible for coordinating balance and the precision of voluntary movements?

A. Thyroid gland

B. Cerebrum alone

C. Medulla oblongata alone

D. Cerebellum

Correct Answer: D. Cerebellum

Explanation: The cerebellum coordinates muscle activity and helps maintain posture, balance, and the precision of movement.

5. The gap between two neurons at a typical chemical synapse is called the:

A. Axon

B. Synaptic cleft

C. Dendrite

D. Cell body

Correct Answer: B. Synaptic cleft

Explanation: The synaptic cleft is the tiny gap across which neurotransmitters travel during chemical communication between cells.

6. Why can a reflex action help protect the body from injury?

A. It always requires a conscious decision.

B. It prevents sensory receptors from working.

C. It can produce a rapid automatic response through a reflex pathway.

D. It stops the brain from receiving information.

Correct Answer: C. It can produce a rapid automatic response through a reflex pathway.

Explanation: A reflex circuit can initiate an appropriate response without waiting for a deliberate conscious decision, reducing exposure to some harmful stimuli.

7. A shoot bends towards light because:

A. The shaded side of a typical shoot elongates more than the illuminated side.

B. The illuminated side always stops growing completely.

C. Gravity disappears when light falls on the plant.

D. The plant moves its entire body towards the window.

Correct Answer: A. The shaded side of a typical shoot elongates more than the illuminated side.

Explanation: Auxin contributes to greater elongation on the shaded side of a typical shoot, producing a bend towards the light.

8. Which plant hormone is particularly associated with cell division?

A. Adrenaline

B. Insulin

C. Thyroxine

D. Cytokinin

Correct Answer: D. Cytokinin

Explanation: Cytokinins promote cell division and influence plant growth and development. The other listed substances are animal hormones.

9. The leaves of Mimosa pudica fold when touched. This is an example of:

A. Positive phototropism

B. A nastic movement

C. Positive hydrotropism

D. Negative gravitropism

Correct Answer: B. A nastic movement

Explanation: The touch-induced folding of touch-me-not leaves is a nastic response involving changes in cell turgor. Its direction is not determined by the direction of the touch.

10. Which of the following is an example of positive gravitropism?

A. A shoot bending towards light

B. A tendril coiling around a support

C. A root growing in the direction of gravity

D. A flower opening in response to light

Correct Answer: C. A root growing in the direction of gravity

Explanation: Positive gravitropism means growth towards gravity. Roots commonly show this response.

11. Which statement about hormones is correct?

A. Hormones can act only on cells with suitable receptors.

B. Hormones always act faster than nerve impulses.

C. Hormones are released only by the brain.

D. Hormones travel exclusively through neurons.

Correct Answer: A. Hormones can act only on cells with suitable receptors.

Explanation: A hormone produces its direct effects in target cells that possess the appropriate receptors and cellular response mechanisms.

12. Which gland produces thyroxine?

A. Adrenal gland

B. Pancreas

C. Pituitary gland

D. Thyroid gland

Correct Answer: D. Thyroid gland

Explanation: The thyroid gland produces thyroxine (T4), which contributes to the regulation of metabolism, growth, and development.

13. Why is iodised salt recommended in regions where iodine deficiency is a concern?

A. Iodine directly replaces insulin.

B. Iodine is needed for the synthesis of thyroid hormones.

C. Iodine is the main component of adrenaline.

D. Iodine prevents all hormonal disorders.

Correct Answer: B. Iodine is needed for the synthesis of thyroid hormones.

Explanation: Iodine is an essential component of thyroid hormone synthesis. Insufficient iodine intake can impair thyroid function and may contribute to goitre.

14. Which hormone helps prepare the body for a sudden threatening situation?

A. Cytokinin

B. Auxin

C. Adrenaline

D. Thyroxine only

Correct Answer: C. Adrenaline

Explanation: Adrenaline, secreted by the adrenal glands, supports the fight-or-flight response by changing heart activity, energy availability, and other physiological functions.

15. Which hormone helps lower blood glucose?

A. Insulin

B. Glucagon

C. Adrenaline only

D. Growth hormone

Correct Answer: A. Insulin

Explanation: Insulin helps lower blood glucose by promoting glucose uptake in many tissues and supporting glucose storage and metabolism. Glucagon generally has the opposite effect on blood glucose.

16. Which statement correctly distinguishes nervous and hormonal coordination?

A. Nervous coordination uses only hormones, while hormonal coordination uses only axons.

B. Both systems always produce responses of identical speed and duration.

C. Hormones act only on the organ in which they are produced.

D. Nervous signalling often produces rapid responses, whereas hormonal effects can be more prolonged.

Correct Answer: D. Nervous signalling often produces rapid responses, whereas hormonal effects can be more prolonged.

Explanation: Nervous signalling is often rapid and precisely directed through neural pathways. Hormonal effects may develop more slowly and last longer, although both systems show exceptions.

17. Which hormone is secreted by the testes and contributes to male secondary sexual characteristics?

A. Oestrogen

B. Testosterone

C. Insulin

D. Thyroxine

Correct Answer: B. Testosterone

Explanation: Testosterone is produced mainly by the testes in males and contributes to reproductive development and secondary sexual characteristics.

18. A plant root grows towards a region with greater water availability. This response is called:

A. Phototropism

B. Chemotropism

C. Hydrotropism

D. Thigmotropism

Correct Answer: C. Hydrotropism

Explanation: Hydrotropism is a growth response to water availability. Roots can grow towards regions where water is more accessible.

19. What happens during negative feedback in the regulation of blood glucose?

A. A rise in blood glucose can stimulate insulin release, helping glucose move towards its normal range.

B. Insulin always increases blood glucose.

C. The pancreas permanently stops releasing hormones after one meal.

D. Blood glucose can never change after insulin is released.

Correct Answer: A. A rise in blood glucose can stimulate insulin release, helping glucose move towards its normal range.

Explanation: As blood glucose rises, insulin secretion generally increases. Insulin promotes glucose uptake and storage, helping oppose the initial rise. As regulation improves, the stimulus for additional insulin release decreases.

20. Which statement about coordination in plants is correct?

A. Plants use a brain and spinal cord to control all movements.

B. All plant movements are caused by muscles.

C. Plant hormones are identical to human hormones.

D. Plants can coordinate growth and responses through hormones and cellular signalling without an animal-like nervous system.

Correct Answer: D. Plants can coordinate growth and responses through hormones and cellular signalling without an animal-like nervous system.

Explanation: Plants use chemical signals, plant hormones, and changes in cell activity to coordinate growth, development, and environmental responses.

Frequently Asked Questions (FAQs)

1. What is control and coordination in Class 10 Science?

Control and coordination are processes that regulate the activities of an organism and ensure that different organs work together. In animals, the nervous and endocrine systems play major roles. Plants coordinate their responses through hormones and cellular signalling.

2. What is the difference between a reflex action and a voluntary action?

A reflex action is an automatic response produced through a reflex pathway, such as withdrawing a hand from a hot object. A voluntary action is a deliberate action, such as choosing to write or pick up a book. Reflex actions do not require a prior conscious decision.

3. Why are nerve impulses transmitted electrically within neurons but chemically across typical synapses?

Within a neuron, the impulse travels through electrical changes in the cell membrane. At a typical chemical synapse, the arrival of an impulse causes the release of neurotransmitters, which cross the synaptic cleft and communicate with the next cell.

4. What is the difference between the cerebrum and cerebellum?

The cerebrum is involved in thinking, memory, sensory interpretation, decision-making, and voluntary movement. The cerebellum helps coordinate movement, maintain balance, and regulate posture. Both are important, but their major functions differ.

5. Why do plant shoots bend towards sunlight?

Plant shoots commonly exhibit positive phototropism. Auxin contributes to greater cell elongation on the shaded side of the growing shoot, so that side grows faster and the shoot bends towards the light.

6. Which plant hormones should Class 10 students remember?

The five major plant hormones discussed in this chapter are:

Auxin: Helps regulate cell elongation and directional growth.
Gibberellins: Promote stem elongation and influence germination.
Cytokinins: Promote cell division.
Abscisic acid (ABA): Helps regulate stress responses and can inhibit growth.
Ethylene: Helps regulate fruit ripening and other developmental processes.

7. Why is the pituitary gland called the master gland?

The pituitary gland is often called the master gland because several of its hormones regulate the activity of other endocrine glands. However, it is not completely independent: the hypothalamus and feedback mechanisms help regulate its activity.

8. Why is insulin important for the human body?

Insulin is a hormone produced by the beta cells of the pancreas. It helps regulate blood glucose by promoting glucose uptake in many tissues and supporting the storage and use of glucose. Insufficient insulin production or ineffective insulin action can contribute to diabetes mellitus.

9. What is the difference between tropic and nastic movements?

A tropic movement is a directional growth response related to the direction of a stimulus, such as a shoot bending towards light. A nastic movement does not depend on stimulus direction in the same way, as seen when touch-me-not leaves fold after being touched.

10. How does the body control the amount of hormone released?

The body uses feedback mechanisms to adjust hormone secretion according to its needs. In negative feedback, a change triggers a response that opposes the original change. For example, rising blood glucose generally stimulates insulin release, helping blood glucose move towards its normal range.

Conclusion

The chapter Control and Coordination explains how living organisms respond to changes and organise their activities. In humans, the nervous system enables rapid communication through neurons and reflex pathways, while hormones regulate growth, metabolism, reproduction, and other essential functions. In plants, hormones and cellular signalling coordinate growth responses such as phototropism, gravitropism, and other movements.

For effective revision, focus on understanding the pathway of a reflex arc, the functions of the major brain regions, the differences between tropic and nastic movements, the functions of plant hormones, and the major animal endocrine glands.

Do not memorise these facts as disconnected lists. Try to explain what causes a response, how the signal travels, which structure or hormone is involved, and what happens next. That approach will help you apply the concepts to unfamiliar questions as well as answer direct textbook questions.