Where Mindful Learning Begins
Where Mindful Learning Begins
Class 10 Science NCERT Solutions Chapter 6 (CBSE 2026-27) — every in-text question, every embedded Activity question, and all 12 back-of-chapter Exercises on this one page, solved with the reasoning behind each answer.
Control and Coordination follows on from Life Processes and asks how organisms actually detect and respond to their environment. It moves from the nervous system in animals — neurons, synapses, reflex arcs, and the three regions of the human brain — through coordination in plants without any nerves or muscles at all (immediate responses in the sensitive plant, and slower tropic growth movements driven by hormones like auxin), to the endocrine system in animals, where hormones like adrenaline, thyroxin, insulin and growth hormone coordinate the body chemically. These NCERT solutions work through every Activity-based question — the taste-and-smell test, the phototropism experiment, the endocrine gland table — and the full 12-question Exercise set in detail, making this one of the most conceptually rich chapters in the biology portion of the Class 10 Science syllabus.
Control and Coordination asks a simple question with a genuinely layered answer: how does a living organism detect a change in its environment and respond to it correctly? For animals, the chapter builds the answer from the neuron upward — a receptor detects a stimulus, an electrical impulse travels along the dendrite, cell body and axon, crosses a synapse as a chemical signal, and either triggers a fast reflex arc through the spinal cord or reaches the brain for conscious thought, with muscle proteins finally doing the physical work of movement. Plants, with no nerves or muscles at all, solve the same problem completely differently — through rapid water-driven movements (as in the sensitive plant) and slower, hormone-driven tropic growth (phototropism, geotropism, hydrotropism, chemotropism). The chapter closes with the endocrine system, where hormones like adrenaline, thyroxin, growth hormone and insulin provide a second, chemical channel of coordination in animals, regulated by feedback mechanisms. Every question woven through the chapter is solved here, section by section, in the order the textbook presents it: the three "QUESTIONS" boxes after Sections 6.1 through 6.3, the questions embedded directly inside Activities and diagrams, and the full 12-question Exercise set at the end.
Neurons, synapses, reflex arcs, the three regions of the human brain, and how nervous impulses finally cause muscles to move.
The sensitive plant's rapid water-driven response, and the slower, auxin-driven tropic growth movements — phototropism, geotropism, hydrotropism, chemotropism.
Adrenaline, thyroxin, growth hormone, testosterone, oestrogen and insulin — the endocrine glands that secrete them, and the feedback mechanisms that regulate them.
A reflex action is a sudden, automatic, involuntary response to a stimulus that doesn't involve conscious thought — it is controlled by the spinal cord via a reflex arc, giving a very fast response (e.g., pulling your hand away from a hot object). Walking is a voluntary action, consciously controlled and coordinated by the brain (particularly the cerebellum, which maintains balance and posture), and involves thinking and decision-making, even though it becomes automatic with practice.
At the end of one neuron's axon, the electrical impulse triggers the release of chemicals (neurotransmitters). These chemicals cross the gap — the synapse — between the two neurons and set off a new electrical impulse in the dendrite of the next neuron, allowing the nerve impulse to pass onward.
The cerebellum (part of the hind-brain).
The smell is detected by olfactory receptors — specialised nerve cell tips in the nose sensitive to smell. When stimulated, they generate an electrical impulse that travels along the nerve to the brain, where it is processed and interpreted as that specific smell.
In a reflex action, the immediate response is controlled by the spinal cord via a reflex arc, without needing the brain's direct involvement, allowing a very quick response. However, information about the stimulus is also sent to the brain at the same time, so the brain becomes aware of what happened — even though it did not control the immediate reflex response itself.
Plant hormones are chemical compounds synthesised in one part of a plant that diffuse to another part to coordinate growth, development, and responses to the environment.
The sensitive plant's leaf movement is rapid and involves no growth — it happens due to a change in the amount of water in specific cells (causing them to swell or shrink), so it happens quickly and is reversible. A shoot's movement towards light (phototropism) is slow and growth-dependent — it happens due to unequal growth of cells on different sides of the shoot (driven by the hormone auxin), and once this growth occurs, it isn't reversible in the same way.
Auxin (promotes cell elongation, e.g., at the shoot tip). Gibberellins (stem growth) and cytokinins (cell division) are also correct examples.
When a tendril touches a support, the part in contact with the object grows more slowly than the part away from it, because auxin accumulates more on the side away from the point of contact. This faster growth on the outer side makes the tendril curve/circle around the object and cling to it.
Take a small pot with germinated seedlings and place it inside a larger tray. Fix a small perforated earthen pot filled with water at an angle to one side of the tray (not directly above the seedlings), and fill the rest of the tray with dry sawdust or soil, so the roots have no water source except seepage from the perforated pot. After a few days, observe the direction the roots grow in — if they bend and grow towards the water-filled pot rather than growing straight down, this demonstrates hydrotropism.
Through hormones, secreted by endocrine glands directly into the bloodstream. The blood carries these hormones to specific target organs/tissues throughout the body, where they bring about the required changes. Unlike the nervous system, this method is slower but can reach every cell of the body with widespread, sustained effects.
Iodine is essential for the thyroid gland to synthesise thyroxin, which regulates carbohydrate, protein and fat metabolism for balanced growth. A deficiency of iodine can lead to insufficient thyroxin production, causing goitre (a swollen neck). Iodised salt ensures adequate iodine intake, preventing this deficiency.
Adrenaline prepares the body for a "fight or flight" response: the heart beats faster (supplying more oxygen to muscles), blood flow to the digestive system and skin is reduced (diverting blood to skeletal muscles), and the breathing rate increases (via contraction of the diaphragm and rib muscles) — together enabling the body to react quickly.
Insulin, produced by the pancreas, regulates blood sugar levels. In diabetes, the pancreas may not secrete enough insulin, causing blood sugar to rise and leading to harmful effects. Injecting insulin compensates for this deficiency and helps bring blood sugar back to a normal range.
(i) Information is acquired at the dendritic tip (dendrite) of the nerve cell.
(ii) It travels as an electrical impulse through the axon (from dendrite → cell body → axon → end of axon).
(iii) It is converted into a chemical signal at the synapse — the gap at the end of the axon, where it meets the next neuron.
Yes — food tastes much blander/less distinct when the nose is blocked. This is because much of what we perceive as "taste" (flavour) actually comes from olfactory receptors detecting aroma, working together with the tongue's gustatory receptors. Blocking the nose removes the olfactory input, so full flavour can't be appreciated, even though the tongue still detects basic tastes. This is exactly why food tastes bland when you have a cold — a congested nose reduces smell, which diminishes taste perception.
Light-sensitive receptor cells in the eye detect the bright light → this triggers a chemical reaction that creates an electrical impulse at the receptor → the impulse travels via the dendrite to the cell body, then along the axon → it reaches the spinal cord, forming a reflex arc that triggers an immediate protective response (like blinking or pupil constriction) → at the same time, information about the bright light also travels up to the brain for further processing and awareness.
Fore-brain: the main thinking part; receives sensory impulses (hearing, smell, sight, etc.), interprets them in association areas, and sends signals to motor areas that control voluntary muscle movement; also houses centres for sensations like hunger.
Mid-brain and hind-brain: control many involuntary actions such as blood pressure, salivation, and vomiting (via the medulla in the hind-brain). The cerebellum (hind-brain) is responsible for precision of voluntary actions and maintaining posture and balance.
Voluntary muscles are those we can consciously control (e.g., muscles used in walking or writing), directed by the thinking part of the brain (fore-brain). Involuntary muscles are those we cannot consciously control (e.g., heart, digestive tract muscles), regulated automatically by the mid-brain and hind-brain without requiring conscious thought.
When the flask is turned so the shoots (which had bent towards the original light) now face away from light, the old parts of the shoot and root do not change direction — they stay as already grown. But new growth occurs in the corrected direction: new shoot growth bends towards the new light position, and new root growth bends away from light. This shows that phototropic bending is a result of new/ongoing growth responding to the current direction of light, not a re-orientation of already-formed plant parts — confirming phototropism as a directional growth response.
Shoots bending towards light (positive phototropism) helps leaves receive maximum sunlight for photosynthesis. Roots bending away from light (negative phototropism, and generally growing downward) helps them grow into the soil to access the water and minerals the plant needs.
Hydrotropism: directional growth movement of a plant part (typically roots) in response to water — roots grow towards a water source.
Chemotropism: directional growth movement in response to a chemical stimulus. Example: the growth of pollen tubes towards ovules during fertilisation, guided by chemical signals from the ovule.
The thyroid gland is located in the neck region. When iodine is deficient and the thyroid can't produce enough thyroxin, it enlarges in an attempt to compensate, causing a visible swelling in the neck — exactly the symptom seen in goitre, directly correlating with the thyroid's location.
| Hormone | Endocrine Gland | Function |
|---|---|---|
| Growth hormone | Pituitary gland | Stimulates growth in all organs |
| Thyroxin | Thyroid gland | Regulates metabolism for body growth |
| Insulin | Pancreas | Regulates blood sugar level |
| Testosterone | Testes | Development of male sex organs / secondary sexual characteristics |
| Oestrogen | Ovaries | Development of female sex organs, regulates menstrual cycle, etc. |
| Adrenaline | Adrenal gland | Prepares body for "fight or flight" (faster heartbeat, breathing, etc.) |
| Releasing hormones | Hypothalamus | Stimulates pituitary gland to release hormones |
Answer: (d) Cytokinin — the other three are animal hormones.
Answer: (b) synapse
Answer: (d) all of the above
Receptors are specialised nerve cell tips (usually in sense organs like the eyes, ears, nose, tongue, and skin) that detect changes (stimuli) in the environment — light, sound, smell, taste, touch — and convert this information into electrical impulses sent to the brain/spinal cord for processing.
If receptors don't work properly (e.g., damaged eye or ear receptors), the organism cannot properly detect the corresponding stimulus — damaged visual receptors could cause blindness or poor vision, damaged auditory receptors could cause hearing loss, damaged olfactory receptors could impair smell. This would prevent the body from responding appropriately to important environmental changes, which could be dangerous — for example, not detecting a hot object or an oncoming vehicle.
A neuron consists of a cell body (containing the nucleus), dendrites (branched extensions that receive information/stimuli), and a long axon (carrying the electrical impulse away from the cell body to its end, where it connects to the next neuron or a muscle/gland via a synapse).
Function: the neuron detects information at the dendritic tip, converts it into an electrical impulse, and transmits this impulse along its length (dendrite → cell body → axon) to the next neuron or effector organ, enabling information to travel through the nervous system.
Phototropism occurs due to the unequal distribution of the hormone auxin in a plant's shoot. When light falls on the shoot from one side, auxin (synthesised at the shoot tip) diffuses towards the shadier side of the shoot. This higher auxin concentration stimulates cells on the shaded side to elongate more than cells on the illuminated side, causing the shoot to bend towards the light.
A spinal cord injury would disrupt nerve impulse transmission between the brain and the rest of the body below the point of injury, affecting: (i) reflex actions (since the spinal cord is where reflex arcs form), (ii) voluntary movements controlled by the brain (motor signals below the injury can't pass through), and (iii) sensory information from below the injury (sensory signals travelling up to the brain would also be blocked).
Through plant hormones, synthesised at specific locations and diffusing to other parts where they act, coordinating growth, development, and responses to stimuli like light, gravity, water and touch. Examples: auxin (cell elongation), gibberellins (stem growth), cytokinins (cell division), and abscisic acid (inhibits growth, causes wilting).
A system of control and coordination is needed so that an organism can detect environmental changes and respond appropriately, in a well-regulated and timely manner. This ensures the correct, specific response to each type of environmental change — protecting the organism from harm, letting it use environmental changes to its advantage, and coordinating the different tissues/organs of a multicellular body to work together effectively.
Reflex actions are sudden, immediate responses to a specific stimulus, controlled via a reflex arc in the spinal cord (e.g., pulling your hand from a hot object; blinking at bright light) — a quick, discrete response to an urgent stimulus.
Involuntary actions are ongoing, continuous bodily functions that occur automatically without conscious control or an immediate external stimulus, controlled mainly by the mid-brain and hind-brain (e.g., heartbeat, breathing, digestion, blood pressure) — they don't need a triggering event and happen continuously to maintain basic body function.
Nervous mechanism: uses electrical impulses via neurons; very fast response; effect is localised (only cells connected by nervous tissue) and short-lived (impulses need time to reset).
Hormonal mechanism: uses chemical messengers (hormones) secreted into the blood by endocrine glands; comparatively slower response; effect is widespread (reaches all cells/tissues regardless of nervous connections) and can be sustained/longer-lasting.
Both mechanisms work together in animals to provide comprehensive and complementary control and coordination.
In the sensitive plant, movement occurs due to a rapid change in the amount of water in specific cells (causing swelling or shrinking), with no nervous or muscular tissue involved and no growth — a quick mechanical/chemical response.
In our legs, movement occurs due to the contraction of specialised muscle cells (with proteins that change shape and arrangement) in response to electrical nerve impulses from the nervous system — a coordinated action involving both nervous tissue (to send the signal) and muscular tissue (to produce the movement).
Next up is Chapter 7 — How do Organisms Reproduce? Or explore the full chapter list, browse the Class 10 Science hub, or book a free demo class for personalised coaching.
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