CBSE Class 10 Science Control and Coordination Notes

1. Introduction — What is Control and Coordination?

Every living organism, from a tiny amoeba to a complex human being, must be able to detect changes in its environment and respond to them appropriately. This ability to sense and respond is fundamental to survival. Control and Coordination refers to all the mechanisms by which an organism detects stimuli (changes in the internal or external environment) and produces a coordinated response that helps it survive, function, and maintain internal balance.

In animals, this control and coordination is achieved by two major systems working in close partnership — the Nervous System, which sends rapid electrical signals through a network of specialised cells, and the Endocrine System, which sends slower but longer-lasting chemical messages through hormones released into the bloodstream. In plants, which have no nervous system, coordination is achieved entirely through chemical signals called plant hormones or phytohormones.

2. The Nervous System in Animals

The nervous system is the body's rapid communication network. Think of it like the internet — it allows different parts of the body to send and receive messages almost instantly. This system is made up of billions of specialised cells called neurons, organised into a vast network that extends from the brain to every corner of the body.

2.1 The Neuron — Structure and Function

The neuron (or nerve cell) is the structural and functional unit of the nervous system. It is specifically designed to receive, process, and transmit information in the form of electrical impulses. Each neuron has three main parts:

•         Cell Body (Cyton / Soma): Contains the nucleus and most of the cell's organelles. This is the control centre of the neuron where most of the metabolic activity occurs. Multiple thread-like extensions arise from the cell body.

•         Dendrites: Short, branched extensions that arise from the cell body. They receive incoming nerve impulses from other neurons or from sense organs and carry them toward the cell body. The word 'dendrite' comes from the Greek word for 'tree' — they look like branches.

•         Axon: A long, single extension that carries impulses away from the cell body toward other neurons, muscles, or glands. Axons can be very long — the axon from your spinal cord to your toes is nearly a metre long! Many axons are covered by a fatty insulating layer called the myelin sheath, which speeds up the transmission of impulses.

2.2 Types of Neurons

2.3 The Synapse

Neurons do not physically touch each other. There is a tiny gap between the axon terminal of one neuron and the dendrite of the next. This gap is called the synapse (or synaptic cleft). When an electrical impulse reaches the end of an axon, it cannot jump the gap electrically. Instead, the axon terminal releases chemical messengers called neurotransmitters into the synapse. These chemicals diffuse across the gap and bind to receptors on the next neuron's dendrite, triggering a new electrical impulse in that neuron.

2.4 Organisation of the Nervous System

3. Reflex Action and the Reflex Arc

A reflex action is a rapid, involuntary, and stereotyped response to a stimulus that does not require conscious thought. The key word is involuntary — you do not decide to perform a reflex; it happens automatically and almost instantly. Reflexes protect the body from harm and allow rapid responses when there is no time to consult the brain.

Classic example: When you accidentally touch a hot object, you pull your hand away before you even feel the pain consciously. The withdrawal reflex is complete before the pain signal has even reached your brain. This is because the signal is processed in the spinal cord and a motor response is sent to the muscles without waiting for the brain's instruction.

3.1 The Reflex Arc — Pathway of a Reflex

The reflex arc is the specific neural pathway through which a reflex action is completed. It is the shortest and most direct path between a stimulus and a response, and it does not require the brain's conscious involvement.

3.2 Types of Reflexes

4. The Human Brain

The human brain is the most complex organ in the body — a roughly 1.4 kg structure containing approximately 86 billion neurons, each forming thousands of connections with other neurons. It is protected by the skull (cranium) and surrounded by three layers of membranes called the meninges, with cerebrospinal fluid (CSF) circulating between them. The CSF acts as a shock absorber, protecting the brain from mechanical injury.

The brain is divided into three main regions, each with distinct structures and functions: the Forebrain, the Midbrain, and the Hindbrain. For CBSE Class 10, you need to know the three major parts — the Cerebrum, the Cerebellum, and the Medulla Oblongata — and their functions in detail.

4.1 The Forebrain — Cerebrum

The Cerebrum is the largest part of the brain, making up about 85% of its total weight. It is divided into two halves called the left and right cerebral hemispheres, connected by a thick band of nerve fibres called the corpus callosum. The outer surface is called the cerebral cortex — highly folded to increase surface area, giving the brain its characteristic wrinkled appearance.

•         Sensory functions: Receives and interprets information from all sense organs — sight, hearing, smell, taste, and touch.

•         Motor functions: Controls all voluntary movements of the body — walking, writing, speaking, picking up objects.

•         Higher functions: Seat of intelligence, reasoning, memory, emotion, language, creativity, and conscious thought. These abilities make humans unique among animals.

•         Association areas: Integrate information from different senses and coordinate complex behaviours.

4.2 The Hindbrain — Cerebellum and Medulla

4.3 Hypothalamus and Other Key Regions

•         Hypothalamus: Controls body temperature, hunger, thirst, sleep, and emotional responses. Also controls the pituitary gland — linking the nervous system to the endocrine system. Sometimes called the 'master regulator'.

•         Thalamus: Acts as a relay station — receives sensory signals from the body and routes them to the correct areas of the cerebral cortex.

•         Limbic System: Involved in emotion, memory, and motivation. Includes the hippocampus (memory formation) and amygdala (emotional responses like fear).

4.4 Protection of the Brain and Spinal Cord

•         Skull (Cranium): Hard bony case that surrounds and protects the brain from physical injury.

•         Vertebral Column (Backbone): Bony column of vertebrae that protects the spinal cord.

•         Meninges: Three layers of membranes (dura mater, arachnoid mater, pia mater) that surround both the brain and spinal cord.

•         Cerebrospinal Fluid (CSF): Clear fluid that fills the space between the meninges. Acts as a shock absorber, provides nutrients, and removes waste products from the brain.

5. The Endocrine System — Chemical Coordination

While the nervous system uses rapid electrical signals, the endocrine system uses chemical messengers called hormones to coordinate body functions. Hormones are chemical substances produced by specialised glands called endocrine glands (or ductless glands) and secreted directly into the bloodstream. They travel through the blood and act on specific target organs or cells, producing slower but longer-lasting effects compared to nerve impulses.

Why 'ductless' glands? Unlike exocrine glands (e.g., sweat glands, salivary glands) which release their products through ducts (tubes) to specific locations, endocrine glands have no ducts — they release hormones directly into the blood, allowing the hormone to travel to its target anywhere in the body.

5.1 Major Endocrine Glands and Their Hormones

5.2 Adrenaline — The Emergency Hormone

Adrenaline (also called epinephrine) is produced by the adrenal glands (the medulla region). It is released rapidly during times of stress, danger, excitement, or emergency — preparing the body for 'fight or flight'. Understanding adrenaline's effects is a favourite CBSE question topic.

5.3 Insulin and Diabetes — A Frequently Tested Topic

Insulin is produced by the beta cells of the islets of Langerhans in the pancreas. It is the hormone that allows cells to absorb glucose from the blood. After a meal, blood glucose levels rise, and insulin is released to bring them back to normal. Without sufficient insulin, glucose cannot enter cells and accumulates in the blood — causing Diabetes Mellitus.

6. Nervous System vs Endocrine System — Comparison

This comparison is one of the most commonly asked questions in CBSE board exams — often as a 3-mark tabular question. Memorise this table thoroughly.

7. Coordination in Plants — Plant Hormones (Phytohormones)

Plants do not have a nervous system or a circulatory system — yet they must respond to changes in their environment. They do so through chemical signals called plant hormones or phytohormones. These are chemical substances produced in one part of the plant that are transported to other parts where they cause specific effects. Plant responses are generally slower than animal responses but are beautifully precise.

The two-category system: Plant hormones are broadly classified as growth promoters (auxins, gibberellins, cytokinins) — which stimulate growth and development — and growth inhibitors (abscisic acid) — which inhibit growth and help the plant cope with stress. Ethylene occupies a special position as it acts as both a growth regulator and a ripening agent.

7.1 Auxin

What it is: Auxins (most commonly Indole-3-Acetic Acid / IAA) are produced at the growing tips of shoots and roots (the apical meristems). They are the most studied plant hormones and were the first to be discovered, by Charles Darwin through experiments on bending of grass shoots toward light.

•         Promotes cell elongation: Auxin causes cells to take in more water and elongate. This is the mechanism behind phototropism and geotropism.

•         Phototropism: When a plant is illuminated from one side, auxin migrates from the lit side to the shaded side. The shaded side has more auxin → cells elongate more on the shaded side → plant bends toward the light source.

•         Apical dominance: High concentration of auxin at the tip suppresses growth of side buds. Removing the tip (pruning) reduces auxin → side branches grow.

•         Root vs Shoot response: Auxin promotes growth in shoots at high concentrations but actually inhibits root growth at the same concentration. Roots are far more sensitive to auxin than shoots.

7.2 Gibberellins

•         Promote stem elongation: Gibberellins stimulate internode elongation — making plants grow taller. Plants treated with gibberellins can grow to extraordinary heights.

•         Seed germination: Stimulate germination of seeds (especially those that need cold treatment) by promoting the production of enzymes that break down stored food in seeds.

•         Flowering: Can trigger flowering in plants that normally require long days, even under short-day conditions.

•         Fruit development: Promote fruit growth — commercially used to produce larger seedless grapes.

7.3 Cytokinins

•         Promote cell division: Cytokinins stimulate cell division (cytokinesis) — they are produced mainly in regions of active cell division such as roots and developing seeds.

•         Delay ageing (senescence): Cytokinins slow down the breakdown of chlorophyll and proteins in leaves, delaying yellowing and ageing.

•         Work with auxin: The ratio of auxin to cytokinin determines what kind of growth occurs in tissue culture — high auxin/low cytokinin promotes root formation; low auxin/high cytokinin promotes shoot formation.

7.4 Abscisic Acid (ABA)

•         Growth inhibitor — 'stress hormone': ABA inhibits growth and is sometimes called the plant's stress hormone because it helps the plant respond to unfavourable conditions like drought, cold, and waterlogging.

•         Stomatal closure: During drought, ABA triggers the guard cells to close the stomata, preventing water loss by transpiration.

•         Seed dormancy: ABA keeps seeds dormant until conditions are favourable for germination. As ABA levels fall (due to rain or warmth), seeds germinate.

•         Leaf fall (abscission): ABA promotes the formation of the abscission zone at the base of leaf stalks, leading to leaf fall in deciduous plants.

7.5 Ethylene

•         Fruit ripening: Ethylene is a gas hormone uniquely responsible for triggering and accelerating fruit ripening. Commercially, ethylene is used to ripen bananas, tomatoes, and other fruits during transport.

•         Abscission: Promotes leaf, flower, and fruit drop.

•         Triple response in seedlings: Causes shortening and thickening of the stem, and horizontal growth — a response to mechanical obstruction in the soil.

8. Movements in Plants — Tropic and Nastic Movements

Plants cannot move from one place to another, but parts of a plant can move in response to stimuli. These movements are classified based on whether they are directional (depend on the direction of the stimulus) or non-directional.

8.1 Tropic Movements (Tropisms)

A tropic movement (or tropism) is a directional growth movement where the direction of movement is determined by the direction of the stimulus. They are caused by unequal growth on the two sides of an organ due to unequal distribution of hormones (mainly auxin).

8.2 Nastic Movements

Nastic movements are non-directional responses to stimuli — the direction of movement is not determined by the direction of the stimulus. They are typically caused by changes in turgor pressure (water content) in cells rather than growth differences.

•         Thigmonasty (Seismonasty): Touch-induced movement. Classic example: Mimosa pudica (touch-me-not or 'Chhui-Mui') — when touched, leaves fold rapidly due to sudden loss of water from cells in the pulvinus (swollen base of leaf stalk). This is reversible — leaves open again after a few minutes.

•         Photonasty: Response to change in light intensity (day/night) rather than direction. Example: flowers of some plants opening in day and closing at night.

•         Thermonasty: Response to temperature changes. Example: tulips open on warm days and close on cold days.

9. Feedback Mechanisms in Hormone Regulation

The body does not just release hormones and forget about them — it has sophisticated feedback mechanisms to ensure hormone levels remain within a precise range. The most common is negative feedback, where the product of a hormone's action feeds back to inhibit further hormone release.

This same negative feedback principle applies to blood glucose regulation (insulin/glucagon), reproductive hormones, adrenal hormones, and virtually every other hormone system. It ensures that no hormone is produced in excess or deficiency for sustained periods — maintaining homeostasis.

10. Common Mistakes to Avoid

11. Key Definitions and Summary Table

12. Key Points to Remember

•         Impulse direction: Dendrite → Cell Body → Axon → Next Neuron. Always one-way.

•         Synapse: Gap between neurons bridged by chemical neurotransmitters. Ensures one-way signal transmission.

•         Reflex arc: Spinal cord is the integration centre. Response happens BEFORE brain registers sensation.

•         Cerebrum: Intelligence, memory, voluntary movement. Cerebellum: balance. Medulla: involuntary functions.

•         Pituitary = master gland: Controls other endocrine glands. Located at base of brain, controlled by hypothalamus.

•         Insulin vs Glucagon: Insulin ↓ blood glucose. Glucagon ↑ blood glucose. Both from pancreas.

•         Adrenaline: Fight-or-flight hormone. ↑ heart rate, ↑ breathing, ↑ blood glucose. From adrenal medulla.

•         Goitre: Caused by iodine deficiency → insufficient thyroxine → thyroid gland enlarges.

•         Auxin: Phototropism — accumulates on dark side → more elongation → bending toward light.

•         ABA: Only major growth INHIBITOR. Causes stomatal closure, dormancy, leaf fall.

•         Tropism vs Nastic: Tropism = directional growth. Nastic = non-directional turgor movement.

•         Nervous system: Fast, short-lived, electrical. Endocrine: slow, long-lasting, chemical.

13. Practice Questions

These questions are modelled on actual CBSE board exam patterns. Write complete, structured answers — definitions first, then explanation, then example where relevant. Diagram questions must always include proper labels.

13.1 — 1 Mark Questions (VSA)

1.       Name the structural and functional unit of the nervous system.

2.       Which part of the brain controls balance and posture?

3.       Name the hormone produced by the adrenal gland during emergency situations.

4.       What is the function of the synapse in nerve impulse transmission?

5.       Name the plant hormone responsible for fruit ripening.

6.       Which gland is called the 'master gland' and why?

7.       What type of movement is shown by the roots of a plant growing toward water?

8.       Name the hormone that regulates blood glucose levels and the gland that produces it.

13.2 — 3 Mark Questions (SA)

9.       Draw a labelled diagram of a neuron. Briefly explain the function of each part.

10.   Explain the mechanism of a reflex action with an example. Why is a reflex arc considered an advantage to the organism?

11.   Compare the nervous system and endocrine system in tabular form (any three points of difference).

12.   Explain phototropism in plants. What is the role of auxin in this process?

13.   What is the role of iodine in the human body? What disease results from its deficiency? Explain the mechanism.

14.   Differentiate between tropic movements and nastic movements in plants with one example each.

13.3 — 5 Mark Questions (LA)

15.   Describe the structure and functions of the human brain. Draw a neat labelled diagram of the human brain and label the cerebrum, cerebellum, and medulla oblongata. State the functions of each.

16.   (a) What are plant hormones? Name any four plant hormones. (b) Describe the role of auxin in causing the bending of a plant shoot toward light. (c) How does abscisic acid differ from auxin in its role in plant growth?

17.   Describe the human endocrine system. Name any four endocrine glands, the hormones they produce, and their functions. What happens when insulin production is insufficient in the body?

18.   (a) Define reflex action and reflex arc. (b) Draw a labelled diagram of the reflex arc showing all five components. (c) Explain why the knee-jerk reflex does not involve the brain.

19.   Explain how coordination is achieved in plants without a nervous system. Describe any three types of tropic movements with examples and the hormones involved. Why are these movements considered directional?