Control and Coordination is one of the most concept-heavy chapters in CBSE Class 10 Biology — it connects the nervous system, hormones, reflex actions, and plant movements into one unified idea: how living organisms sense and respond to their environment. Board papers regularly draw diagram-based and comparison-based questions directly from this chapter, especially on the neuron structure, reflex arc, and human brain.
At Convex Classes Jaipur, we teach this chapter with a focus on comparisons — because most exam questions here ask you to differentiate between two similar-sounding concepts (reflex vs. voluntary action, nervous vs. hormonal control, tropism vs. nastic movement). Below you’ll find complete NCERT solutions along with extra theory to make each comparison crystal clear.
Chat with Convex Classes Jaipur Get Class 10 Science batch details on WhatsApp Chat Now →What Is Control and Coordination? (Concept Overview)
All living organisms need to detect changes in their surroundings (called stimuli) and respond to them appropriately in order to survive. This ability is called control and coordination. In animals, this is achieved through two closely linked systems:
- Nervous system – uses electrical impulses via neurons for fast, short-lived responses
- Endocrine (hormonal) system – uses chemical messengers (hormones) via the bloodstream for slower, longer-lasting responses
Plants, which lack a nervous system, coordinate their responses purely through chemical substances called plant hormones (phytohormones) and through changes in turgor pressure, movement, and growth patterns.
A key exam-relevant idea: coordination is necessary because different parts of a multicellular body need to work together — a stimulus detected in one part (eyes, skin, roots) often requires a response in a completely different part (muscles, glands, stem).
Q1. What is the difference between a reflex action and walking?
Answer:
| Basis | Reflex Action | Walking |
|---|---|---|
| Nature | Automatic, involuntary, unconscious response | Voluntary, conscious, learned movement |
| Control centre | Spinal cord (via reflex arc); brain informed later | Cerebellum and cerebral cortex of the brain |
| Speed | Extremely fast — happens before conscious thought | Slower, involves continuous planning and adjustment |
| Purpose | Protects the body from sudden harm (e.g., touching a hot object) | Purposeful locomotion from one place to another |
| Example | Withdrawing hand from a flame, blinking at bright light | Walking to school, climbing stairs |
Deeper theory: A reflex action follows a fixed pathway called the reflex arc: stimulus → receptor → sensory neuron → relay neuron (in the spinal cord) → motor neuron → effector (muscle/gland) → response. Since the signal doesn’t have to travel all the way to the brain and back, the reaction time is drastically reduced — this is precisely why reflexes are the body’s chosen mechanism for handling danger.
Walking, in contrast, requires continuous feedback: the cerebellum constantly receives input about balance, muscle tension, and joint position, and fine-tunes motor signals to keep the body upright and moving smoothly. This is a much more complex, higher-order brain function compared to a simple reflex.
Exam tip (Convex Classes Jaipur): Always mention “reflex arc” and name at least 3 of its components — CBSE examiners specifically award marks for naming sensory neuron, relay/interneuron, and motor neuron.
Q2. What happens at the synapse between two neurons?
Answer: A synapse is the tiny junction/gap between the axon terminal of one neuron and the dendrite of the next. The signal transmission at a synapse happens in this sequence:
- An electrical impulse travels along the axon of the first (presynaptic) neuron.
- On reaching the axon terminal, it triggers the release of chemical messengers called neurotransmitters into the synaptic cleft (the tiny gap between the two neurons).
- These neurotransmitters diffuse across the gap and bind to specific receptors on the membrane of the next (postsynaptic) neuron.
- This binding regenerates an electrical impulse in the second neuron, and the signal continues its journey.
Why this matters: This chemical-to-electrical conversion at every synapse means a nerve impulse always travels in one direction only — from dendrite to cell body to axon — which is why nervous coordination is so precise and specific compared to hormonal coordination.
Q3. Which part of the brain maintains the posture and equilibrium of the body?
Answer: The cerebellum, a part of the hindbrain, is responsible for maintaining posture, balance, and equilibrium of the body. It works by:
- Receiving continuous sensory information from the inner ear (balance), eyes, and proprioceptors (stretch receptors in muscles and joints).
- Comparing this incoming data with the intended movement.
- Sending corrective signals to skeletal muscles to ensure smooth, precise, and well-coordinated voluntary movements.
Damage to the cerebellum typically results in loss of balance and jerky, uncoordinated movements — a fact that helps illustrate its role in board-exam answers.
Q4. How do we detect the smell of an agarbatti (incense stick)?
Answer: Smell detection follows this pathway:
- Odour molecules released by the incense stick enter the nasal cavity and are detected by specialised olfactory receptor cells present in the lining of the nose.
- These receptors generate an electrical signal (nerve impulse) on binding with odour molecules.
- The signal travels via the olfactory nerve to the olfactory bulb, located at the base of the brain.
- From the olfactory bulb, the signal is relayed to the olfactory cortex in the forebrain, where it is finally interpreted and we consciously perceive the smell.
Q5. What is the role of the brain in reflex action?
Answer: A reflex action itself is executed by the spinal cord without direct involvement of the brain — this is what makes it so fast. However, the brain is not entirely excluded:
- A copy of the sensory information about the reflex event is simultaneously sent to the brain.
- The brain registers and stores this information, allowing the organism to become consciously aware that the reflex occurred.
- This awareness helps in learning and future avoidance of similar harmful stimuli — for example, remembering not to touch a hot vessel again.
Q6. What are plant hormones?
Answer: Plant hormones, also called phytohormones, are chemical substances synthesised in one part of the plant and transported to another part where they regulate growth, development, and response to stimuli. The five major plant hormones are:
| Hormone | Main Function |
|---|---|
| Auxin | Promotes cell elongation; controls phototropism and apical dominance |
| Gibberellins | Promote stem elongation, seed germination, and flowering |
| Cytokinins | Promote cell division; delay leaf senescence (ageing) |
| Abscisic acid (ABA) | Growth inhibitor; promotes seed dormancy and stress/wilting response (also called stress hormone) |
| Ethylene | Gaseous hormone; promotes fruit ripening and leaf/flower abscission |
Q7. How is the movement of leaves of a sensitive plant different from the movement of a shoot towards light?
Answer:
| Feature | Sensitive Plant (Mimosa pudica — “touch-me-not”) | Shoot Towards Light (Phototropism) |
|---|---|---|
| Stimulus | Touch (mechanical) | Light (directional) |
| Type of movement | Nastic movement — independent of the direction of the stimulus | Tropic movement — directional, growth is towards/away from stimulus |
| Mechanism | Rapid change in turgor pressure in specialised motor cells (pulvinus) at the base of leaflets | Differential growth — cells on the shaded side elongate more (due to auxin accumulation) than the illuminated side |
| Speed | Very fast (seconds) | Slow (hours to days) |
| Growth involved? | No growth — purely a pressure-based movement | Yes — actual cell elongation/growth occurs |
Key distinction for exams: Nastic movements are not related to the direction of the stimulus and don’t involve growth, while tropic movements are directional and growth-dependent. This single line answers most “differentiate” style questions correctly.
Q8. Give an example of a plant hormone that promotes growth.
Answer: Auxin is a classic example — synthesised at the shoot tip, it promotes cell elongation and is responsible for phototropic bending of shoots towards light. Gibberellins are another growth-promoting hormone, responsible for stem elongation and breaking seed/bud dormancy.
Q9. How do auxins promote the growth of a tendril around a support?
Answer: When a tendril touches a support (like a fence or stick):
- Auxin accumulates on the side of the tendril away from the point of contact (the outer side).
- This higher auxin concentration causes cells on that side to elongate faster than the cells on the side touching the support.
- This unequal (differential) growth causes the tendril to curve and coil around the support, allowing the climbing plant to hold on and grow upward.
This is a form of tropism called thigmotropism (response to touch).
Q10. Design an experiment to demonstrate hydrotropism.
Answer:
Aim: To show that plant roots grow in the direction of water (positive hydrotropism).
Materials required: A plastic tray/pot with soil, a few soaked seeds/germinated seedlings, a small perforated earthen (porous) pot filled with water.
Procedure:
- Fill a large tray with dry, loosely packed soil and sow a few seeds in the centre so they germinate.
- Bury a small porous pot filled with water at some horizontal distance from the seedlings, without directly wetting the surrounding soil surface.
- Keep the setup undisturbed for several days, watering only lightly from the top (not near the porous pot).
Observation: After a few days, on carefully removing the soil, the roots of the seedling are found to have grown and bent towards the porous pot (the side with more moisture) rather than growing straight down.
Conclusion: This proves hydrotropism — the directional growth of roots towards a source of water, driven by uneven distribution of moisture-sensing growth hormones.
Q11. How does chemical coordination take place in animals?
Answer: Chemical coordination in animals occurs through the endocrine system:
- Specialised ductless (endocrine) glands — such as the pituitary, thyroid, adrenal, and pancreas — secrete chemical messengers called hormones directly into the bloodstream.
- Hormones travel throughout the body via blood and reach target organs/tissues possessing specific receptors for them.
- On binding to these receptors, hormones trigger a specific physiological response — regulating growth, metabolism, reproduction, or stress response.
Examples: Thyroxine (regulates metabolism), insulin (regulates blood sugar), adrenaline (fight-or-flight response), growth hormone (regulates body growth).
Q12. Why is the use of iodised salt advisable?
Answer: Iodine is an essential raw material required by the thyroid gland to synthesise the hormone thyroxine, which regulates the body’s basal metabolic rate, growth, and development. A deficiency of iodine in the diet leads to:
- Goitre – abnormal enlargement of the thyroid gland
- Hypothyroidism – symptoms include fatigue, weight gain, and slowed metabolism
- In severe cases during pregnancy, iodine deficiency can affect the physical and mental development of the child
Since iodine is not naturally abundant in most inland diets, iodised salt provides a simple, reliable, and inexpensive way to ensure adequate iodine intake and prevent these disorders.
Q13. How does our body respond when adrenaline is secreted into the blood?
Answer: Adrenaline (epinephrine), secreted by the adrenal glands during stress, fear, or excitement, prepares the body for a “fight or flight” response:
- Heart rate increases — pumping more blood to muscles and vital organs
- Breathing rate increases — supplying more oxygen for quick energy release
- Blood is diverted away from digestion and towards skeletal muscles
- Blood glucose levels rise as adrenaline stimulates the breakdown of glycogen into glucose in the liver, providing an instant energy boost
This entire response happens rapidly and prepares the body to either confront the danger or flee from it.
Q14. Why are some patients of diabetes treated by giving injections of insulin?
Answer: Diabetes mellitus occurs when the pancreas fails to produce sufficient insulin, or the body’s cells become resistant to it. Insulin is the hormone responsible for:
- Facilitating the uptake of glucose from blood into body cells for use as energy
- Converting excess glucose into glycogen for storage in the liver and muscles, thereby lowering blood glucose levels
Without adequate insulin, blood glucose levels remain persistently high, which can damage blood vessels, nerves, kidneys, and eyes over time. Patients with Type 1 diabetes, in particular, cannot produce their own insulin at all, so insulin injections are given externally to regulate their blood sugar and prevent these complications.
Q15. How are involuntary actions and reflex actions different from each other?
Answer:
| Basis | Reflex Actions | Involuntary Actions |
|---|---|---|
| Control | Spinal cord (via reflex arc) | Medulla/brainstem, hypothalamus |
| Nature of stimulus | Sudden, external, requiring an immediate response | Ongoing internal regulation |
| Speed | Very fast (milliseconds) | Continuous / rhythmic, not necessarily “fast” |
| Example | Withdrawing hand from a hot object, knee-jerk, blinking | Heartbeat, peristalsis (movement of food in gut), salivation |
| Conscious control | Cannot be consciously controlled | Also mostly not under conscious control, though a few (like breathing rate) can be partly influenced |
Q16. Compare and contrast nervous and hormonal mechanisms for control and coordination in animals.
Answer:
| Aspect | Nervous System | Hormonal (Endocrine) System |
|---|---|---|
| Mode of transmission | Electrical impulses via neurons | Chemical messengers (hormones) via blood |
| Speed | Very fast, almost instantaneous | Comparatively slow |
| Specificity | Highly specific — targets exact muscles/glands | General — can affect multiple organs simultaneously |
| Duration of effect | Short-lived | Long-lasting |
| Best suited for | Quick responses (e.g., reflexes, movement) | Long-term processes (e.g., growth, metabolism, puberty) |
Why both are needed: The body requires both quick, precise nervous responses (like pulling away from fire) and slow, sustained hormonal responses (like growth during puberty) — this is why organisms have evolved both systems working together rather than relying on just one.
Q17. What is the difference between the manner in which movement takes place in a sensitive plant and the movement in our legs?
Answer:
| Feature | Sensitive Plant Movement | Movement in Our Legs |
|---|---|---|
| Type | Nastic movement (non-directional, no growth) | Voluntary, directional movement |
| Mechanism | Rapid change in turgor pressure in pulvinus cells | Coordinated contraction and relaxation of skeletal muscles, controlled by nerves |
| Control | No nervous system — purely a mechanical/chemical response | Controlled by the brain (cerebrum, cerebellum) via motor neurons |
| Speed | Very fast (seconds) | Comparatively slower, purposeful |
| Purpose | Defence against herbivores/physical disturbance | Locomotion, posture, purposeful action |
Control and Coordination Class 10 – Quick Revision Notes
- Nervous system = brain + spinal cord + nerves; uses electrical impulses via neurons; fast and specific
- Reflex arc = receptor → sensory neuron → spinal cord (relay neuron) → motor neuron → effector
- Endocrine system = ductless glands secreting hormones directly into blood; slow but long-lasting
- Plant hormones = auxin, gibberellins, cytokinins, abscisic acid, ethylene
- Tropic movements = directional, growth-based (phototropism, geotropism, hydrotropism, thigmotropism)
- Nastic movements = non-directional, pressure-based, no growth (e.g., Mimosa pudica)
Frequently Asked Questions (FAQs)
Q1. What is the role of the nervous system in control and coordination?
Ans. The nervous system detects environmental changes through sensory receptors, processes this information in the brain and spinal cord, and sends signals to muscles or glands to produce an appropriate, rapid response.
Q2. What are reflex actions, and how do they work?
Ans. Reflex actions are involuntary, immediate responses to a stimulus that occur without conscious thought, controlled via a fixed pathway called the reflex arc, involving sensory neurons, the spinal cord, and motor neurons.
Q3. How do plants exhibit control and coordination without a nervous system?
Ans. Plants coordinate their activities through chemical substances called plant hormones (auxins, gibberellins, cytokinins, abscisic acid, ethylene) and through changes in turgor pressure, resulting in tropic movements (like phototropism) and nastic movements (like the folding of Mimosa leaves).
Q4. Is Control and Coordination an important chapter for CBSE Class 10 board exams?
Ans. Yes, it is one of the most frequently tested Biology chapters, with regular diagram-based questions on neurons and the human brain, plus comparison-based questions (reflex vs. voluntary, nervous vs. hormonal, tropic vs. nastic).
Q5. How can Convex Classes Jaipur help me prepare this chapter better?
Ans. At Convex Classes Jaipur, our faculty break down every comparison-based concept in this chapter with clear diagrams, structured tables, and CBSE marking-scheme-aligned answer writing practice, along with regular tests and doubt-clearing sessions.
This content has been prepared by the academic team at Convex Classes Jaipur for educational purposes, strictly following the CBSE/NCERT Class 10 Science syllabus.
