BharatNotes Why this chapter matters for UPSC: This is Chapter 6 of NCERT's Class X Science (Reprint 2026-27). It asks how a living body, plant or animal, notices a change around it and answers with the right movement, and it gives two answers: nerves, which are fast and wired, and hormones, which are slower, chemical and able to reach every cell. Prelims general science draws on its matched lists (parts of the brain and their jobs, plant hormones, glands and their hormones), and its last pages are the biology behind health questions on iodised salt, goitre and diabetes.
Contemporary hook: The International Diabetes Federation's Diabetes Atlas, 11th edition (released on 7 April 2025), counts 89.8 million adults aged 20-79 with diabetes in India in 2024, and states that "India has the second highest number of adults (20-79 years) with diabetes in the world." Diabetes is a disorder of the blood-sugar control described at the end of this chapter.
🧠 First Principles — Read This First
A response needs a message. Every movement a living thing makes in answer to its surroundings, a hand pulled back from a flame or a shoot bending towards a window, has three steps: detect the change, decide, act. The cells that detect, decide and act sit in different places, so a message has to travel between them. Control and coordination is the study of how that message travels.
There are only two ways to send it. An electrical impulse is fast, but it reaches only cells wired to the nervous tissue, and a cell needs time to reset before it can fire again. A chemical released into the body is slow, but it can reach every cell and can be kept up for a long time. Animals use both: nerves and hormones. Plants have no nerves; they pass electrical-chemical signals from cell to cell without a special tissue, and they coordinate growth with hormones.
Control needs feedback. A hormone must be released in the right amount at the right time. The body does this by letting the level of the thing being controlled switch the hormone up or down: when blood sugar rises, the pancreas makes more insulin; when it falls, less.
PART 1 — Quick Reference
Table 1: The path of a nerve impulse
| Step | What happens | Where |
|---|---|---|
| 1 | A change in the environment is detected by receptors, "the specialised tips of some nerve cells" | Sense organs: inner ear, nose, tongue and so on |
| 2 | The information sets off a chemical reaction that creates an electrical impulse | Dendritic tip of a nerve cell |
| 3 | The impulse travels from the dendrite to the cell body, then along the axon to its end | Inside one neuron |
| 4 | At the end of the axon, the impulse sets off the release of some chemicals | Axon ending |
| 5 | The chemicals cross the gap, or synapse, and start a similar impulse in a dendrite of the next neuron | Between two neurons |
| 6 | A similar synapse delivers the impulse to other cells, such as muscle cells or glands | Neuromuscular junction (Fig. 6.1 b) |
Source: NCERT, Science Class X, ch. 6, Reprint 2026-27, section 6.1 and Figure 6.1 (p. 101).
Table 2: Three kinds of nervous response
| Kind | NCERT's examples | What controls it |
|---|---|---|
| Reflex action | Pulling the hand back from a flame; change in the size of the pupil (a "simple reflex") | A reflex arc formed in the spinal cord; the information also goes on to the brain |
| Voluntary action | Writing, talking, moving a chair, clapping at the end of a programme; walking in a straight line, riding a bicycle, picking up a pencil | The fore-brain decides and its motor areas move voluntary muscles; the cerebellum gives precision, posture and balance |
| Involuntary action | Heartbeat, breathing, digesting food, the mouth watering at food we like; blood pressure, salivation, vomiting | The mid-brain and hind-brain; the medulla in the hind-brain |
Source: NCERT, Science Class X, ch. 6, Reprint 2026-27, sections 6.1.1-6.1.2 and the summary (pp. 102-104, 111).
Table 3: The human brain and spinal cord in Class X
| Part | Where | What NCERT says it does |
|---|---|---|
| Fore-brain | Brain | "The main thinking part of the brain": sensory areas for hearing, smell, sight; association areas that interpret this information; motor areas that control voluntary muscles; a hunger centre "in a separate part of the fore-brain" |
| Mid-brain | Brain | With the hind-brain, controls many involuntary actions |
| Medulla | Hind-brain | Involuntary actions including blood pressure, salivation and vomiting |
| Cerebellum | Hind-brain | "Precision of voluntary actions and maintaining the posture and balance of the body" |
| Spinal cord | Inside the vertebral column | Nerves from all over the body meet in a bundle here on their way to the brain; reflex arcs are formed here |
| Central nervous system | Brain + spinal cord | Receives information from all parts of the body and integrates it |
| Peripheral nervous system | Cranial nerves (from the brain) + spinal nerves (from the spinal cord) | Links the central nervous system with the rest of the body |
| Protection | Skull, fluid, backbone | Brain in a "bony box", inside "a fluid-filled balloon" for shock absorption; spinal cord inside the vertebral column |
Source: NCERT, Science Class X, ch. 6, Reprint 2026-27, sections 6.1.1-6.1.3 and Figure 6.3 (pp. 102-105).
Table 4: How plants move
| Movement | Needs growth? | NCERT's example | How it happens |
|---|---|---|---|
| Response to touch | No | Leaves of chhui-mui (the sensitive or touch-me-not plant) fold up and droop | Electrical-chemical signals pass from cell to cell (no specialised tissue); cells change shape by changing the amount of water in them |
| Coiling of tendrils | Yes | Pea tendrils climbing a fence | The part of the tendril touching the support grows less rapidly than the part away from it, so the tendril circles the support |
| Phototropism | Yes | Shoots bend towards light; roots bend away from it | Auxin (Table 5) |
| Geotropism | Yes | Roots grow down, shoots grow up | Response to the pull of gravity |
| Chemotropism | Yes | Pollen tubes grow towards ovules | Response to chemicals |
| Hydrotropism | Yes | Left as a question: NCERT asks for examples and for an experiment | Response to water |
Source: NCERT, Science Class X, ch. 6, Reprint 2026-27, sections 6.2-6.2.2, Activity 6.2 and the in-text questions (pp. 105-108).
Table 5: Plant hormones in Class X
| Hormone | Where it is made or found | What it does |
|---|---|---|
| Auxin | Synthesised at the shoot tip | Helps cells grow longer; with light from one side it diffuses towards the shady side, so that side grows more and the shoot bends towards light |
| Gibberellins | Not stated | Like auxins, help the growth of the stem |
| Cytokinins | Greater concentration where cells divide fast, such as fruits and seeds | Promote cell division |
| Abscisic acid | Not stated | Inhibits growth; its effects include wilting of leaves |
Source: NCERT, Science Class X, ch. 6, Reprint 2026-27, section 6.2.2 (p. 108).
Table 6: NCERT's Table 6.1, completed
NCERT prints Table 6.1 with some cells left blank on purpose: Activity 6.4 asks the student to complete it. The cells in italics below are filled in from NCERT's own text in the same chapter.
| No. | Hormone | Endocrine gland | Functions |
|---|---|---|---|
| 1 | Growth hormone | Pituitary gland | Stimulates growth in all organs |
| 2 | Thyroxin | Thyroid gland | Regulates metabolism for body growth |
| 3 | Insulin | Pancreas | Regulates blood sugar level |
| 4 | Testosterone | Testes | Changes associated with puberty in males |
| 5 | Oestrogen | Ovaries | Development of female sex organs, regulates menstrual cycle, etc. |
| 6 | Adrenaline | Adrenal gland | Prepares the body to fight or run: faster heartbeat, blood diverted to skeletal muscles, faster breathing |
| 7 | Releasing hormones | Hypothalamus | Stimulates pituitary gland to release hormones |
Source: NCERT, Science Class X, ch. 6, Reprint 2026-27, Table 6.1 and Activity 6.4 (p. 111); the filled cells are from section 6.3 and the "Do You Know?" box (pp. 109-110).
Table 7: Nerves and hormones compared
| Nervous control | Hormonal control | |
|---|---|---|
| Signal | Electrical impulse along neurons; chemicals only across the synapse | A chemical (hormone), secreted into the blood in animals |
| Reach | Only cells connected by nervous tissue | Can potentially reach all cells of the body |
| Speed | Fast | "Slower, of course" |
| Staying power | A cell must reset before it can fire again; cells cannot fire continually | "Can be done steadily and persistently" |
| NCERT's example | The hand pulled back from a flame (reflex arc) | Adrenaline preparing a squirrel to fight or run |
| Coordination | Integrated by the brain and spinal cord | Amount set by feedback (insulin and blood sugar) |
| In plants? | No nervous tissue; electrical-chemical signals pass cell to cell | Yes: auxin, gibberellins, cytokinins, abscisic acid |
Source: NCERT, Science Class X, ch. 6, Reprint 2026-27, pp. 101-102, 106, 108-109, 111. This table answers NCERT Exercise 11.
Table 8: NCERT lines to read with care
| NCERT says | The record |
|---|---|
| The sensation of feeling full comes from "a centre associated with hunger, which is in a separate part of the fore-brain" (p. 104) | Correct, but unnamed. Class XI names the part: the forebrain "consists of cerebrum, thalamus and hypothalamus", and "The hypothalamus contains a number of centres which control body temperature, urge for eating and drinking." |
| "Many of these involuntary actions are controlled by the mid-brain and hind-brain. All these involuntary actions including blood pressure, salivation and vomiting are controlled by the medulla in the hind-brain." (p. 104) | Read "all these" as the actions just listed: the sentence before gives the mid-brain a share. Class XI: "The medulla contains centres which control respiration, cardiovascular reflexes and gastric secretions." |
| Auxin, gibberellins and cytokinins promote growth; "Abscisic acid is one example of a hormone which inhibits growth" (p. 108) | NCERT says "one example", not the only one. Class XI adds ethylene: "The gaseous PGR, ethylene, could fit either of the groups, but it is largely an inhibitor of growth activities." |
| The thyroid makes "thyroxin hormone" (p. 110) | Class X names one hormone, in an older spelling. Class XI: the thyroid secretes "tetraiodothyronine or thyroxine (T4) and triiodothyronine (T3)". |
| Table 6.1 is printed with blank cells (p. 111) | Not a misprint: Activity 6.4 asks the student to complete it. Table 6 above fills them from NCERT's own text. |
| A synapse delivers impulses "to other cells, such as muscles cells or gland" (p. 101) | A slip: read it as muscle cells or glands (Fig. 6.1 b shows a neuromuscular junction). |
Source: NCERT, Science Class X, Reprint 2026-27, ch. 6 (pp. 101, 104, 108, 110-111); NCERT, Biology Class XI, ch. 13 "Plant Growth and Development", ch. 18 "Neural Control and Coordination", ch. 19 "Chemical Coordination and Integration".
PART 2 — Concepts & Narrative
Why living things need control (chapter opening)
We treat movement as a sign of life. Some of it is growth: a germinating seedling pushes the soil aside over a few days, and stops when its growth stops. Some is not: "A cat running, children playing on swings, buffaloes chewing cud". NCERT reads such movement as a controlled response to a change around the organism: the cat may be running because it has seen a mouse, and in class we whisper to a friend rather than shout. The right movement must follow the right event, and in multicellular organisms specialised tissues provide this control and coordination.
The nervous system (6.1)
In animals, control and coordination are provided by nervous and muscular tissue. All information from the environment is picked up by receptors, which are "the specialised tips of some nerve cells", usually in the sense organs. Gustatory receptors detect taste; olfactory receptors detect smell.
Neuron, dendrite, axon, synapse. A neuron (nerve cell) is the unit of nervous tissue. Information is picked up at the dendritic tip, where a chemical reaction creates an electrical impulse. The impulse travels from the dendrite to the cell body and then along the axon to its end. There it sets off the release of chemicals, which "cross the gap, or synapse" and start a similar impulse in the next neuron. So the signal is electrical inside a neuron and chemical between neurons. NCERT's question on Fig. 6.1(a) asks you to find exactly these three places: where information is acquired (dendrite), where it travels as an impulse (dendrite, cell body, axon) and where it becomes a chemical signal (the end of the axon).
Activity 6.1 asks you to taste sugar, then taste it again with your nose blocked, and to notice whether food tastes different. NCERT leaves the explanation for discussion, and asks whether something similar happens when we have a cold. The clue is on the same page: taste and smell have separate receptors.
Reflex actions (6.1.1)
In everyday speech we say we did something "reflexly" when we acted without thinking. NCERT takes the urgent case: touching a flame. If the signal had to go to the thinking part of the brain, be thought about, and come back as an order to the muscles, "it may take enough time for us to get burnt!"
Why the spinal cord, and not the brain? Thinking is a complex activity: it involves many impulses passing through dense networks of neurons in the brain, and that takes time. The design solution is to connect the nerve that detects heat directly to the nerve that moves the muscle. This connection is a reflex arc (Fig. 6.2). The best place for it is where the input and output nerves first meet: nerves from all over the body meet in a bundle in the spinal cord on their way to the brain. So "Reflex arcs are formed in this spinal cord itself, although the information input also goes on to reach the brain." NCERT gives the evolutionary reason too: "reflex arcs have evolved in animals because the thinking process of the brain is not fast enough". Many animals have little or none of the neuron network needed for thinking, and even where that network exists, reflex arcs "continue to be more efficient for quick responses".
NCERT then asks you to trace what happens when a bright light falls on the eyes. Its own next page calls the change in the size of the pupil a "simple reflex".
The human brain (6.1.2)
The spinal cord does more than reflexes: it carries the information we think about. Thinking itself is concentrated in the brain, "the main coordinating centre of the body".
Central and peripheral nervous system. The brain and spinal cord together are the central nervous system: they "receive information from all parts of the body and integrate it". The peripheral nervous system connects them to the rest of the body: cranial nerves arise from the brain and spinal nerves from the spinal cord. When we decide to write, talk or move a chair, the brain sends messages to muscles; NCERT calls this the second way in which the nervous system communicates with the muscles, the first being the reflex arc.
The brain has three regions, the fore-brain, mid-brain and hind-brain.
Fore-brain. It is "the main thinking part of the brain". Separate areas receive impulses for hearing, smell, sight and so on. Association areas interpret this information by putting it together with information from other receptors and with what is already stored. A decision is passed to motor areas, which control voluntary muscles such as those of the leg. Some sensations are different: the feeling of having eaten enough comes from a hunger centre in a separate part of the fore-brain (Class XI names it the hypothalamus; see Table 8).
Mid-brain and hind-brain. Between simple reflexes and thought-out actions lies a set of movements we cannot control by thinking: the mouth watering at food we like, the heartbeat, breathing, digestion. Many of these involuntary actions are controlled by the mid-brain and hind-brain; blood pressure, salivation and vomiting are controlled by the medulla in the hind-brain.
Cerebellum. Walking in a straight line, riding a bicycle and picking up a pencil depend on the cerebellum, a part of the hind-brain. It is "responsible for precision of voluntary actions and maintaining the posture and balance of the body". This answers NCERT's in-text question on which part maintains posture and equilibrium.
Protection, and how nerves make muscles move (6.1.3-6.1.4)
The brain sits inside a "bony box", and inside the box it is held in "a fluid-filled balloon which provides further shock absorption". The hard, bumpy structure down the middle of the back is the vertebral column, or backbone, which protects the spinal cord.
The final action is done by muscle. A muscle cell moves by changing its shape so that it shortens. NCERT's explanation is chemical: "Muscle cells have special proteins that change both their shape and their arrangement in the cell in response to nervous electrical impulses." The new arrangement gives the cell a shorter form. NCERT links this to the voluntary and involuntary muscles studied in Class IX and leaves the difference for you to work out.
Coordination in plants (6.2)
Plants have neither nerves nor muscles, yet they respond. Touch the leaves of a chhui-mui, "the 'sensitive' or 'touch-me-not' plant of the Mimosa family", and they fold up and droop. A germinating seed sends its root down and its stem up. These are two different kinds of movement: "one dependent on growth and the other independent of growth".
Immediate response (6.2.1). The sensitive plant's leaves move with no growth involved, and they move at a point different from where they were touched, so information must travel. Plants "also use electrical-chemical means to convey this information from cell to cell, but unlike in animals, there is no specialised tissue in plants for the conduction of information." In place of the special proteins of muscle, plant cells "change shape by changing the amount of water in them", swelling or shrinking.
Movement due to growth (6.2.2). Pea tendrils are sensitive to touch: the side touching a support grows less rapidly than the far side, so the tendril curls round the support. More often, plants respond by growing in a direction. Shoots bend towards light and roots away from it (phototropism); roots grow down and shoots up in response to gravity (geotropism). NCERT asks what hydrotropism and chemotropism would mean, and gives one example of chemotropism: "the growth of pollen tubes towards ovules". In Activity 6.2, freshly germinated bean seeds on a wire mesh over a flask of water, in a box whose open side faces a window, bend their shoots towards light and roots away within two or three days; NCERT then has you turn the flask and ask whether the old parts or the new growth change direction.
Speeds differ. The sensitive plant responds very quickly; the movement of sunflowers in response to day or night is "quite slow"; growth movements are slower still.
From electrical to chemical signals: plant hormones (6.2.2)
Electrical impulses are fast, but NCERT names two limits: they reach only cells connected by nervous tissue, and a cell that has fired "will take some time to reset its mechanisms" before it can fire again. So most multicellular organisms also use chemical communication: a stimulated cell releases a compound, and other cells detect it with "special molecules on their surfaces". This is slower, "but it can potentially reach all cells of the body, regardless of nervous connections, and it can be done steadily and persistently."
Plant hormones coordinate growth, development and responses to the environment. They "are synthesised at places away from where they act and simply diffuse to the area of action."
Auxin and the bending shoot. Auxin is synthesised at the shoot tip and helps cells grow longer. When light comes from one side, auxin diffuses towards the shady side of the shoot. The cells on that side grow longer, so the shoot bends towards the light. This is the hormone behind Activity 6.2. NCERT's in-text question on how auxins help a tendril grow round a support asks you to apply the same idea, uneven growth on two sides, to the tendril: the text itself gives the growth difference, not auxin's route in a tendril.
Gibberellins, like auxins, help the stem grow. Cytokinins promote cell division and are found in greater concentration where cells divide fast, as in fruits and seeds. Plants also need signals to stop growing: "Abscisic acid is one example of a hormone which inhibits growth. Its effects include wilting of leaves."
Hormones in animals (6.3)
A squirrel in danger must prepare either to fight or to run away. Both use much energy, and many tissues must work together. Nerves alone would reach only a limited set of tissues; a chemical reaches all of them. Many animals, including humans, use adrenaline, "secreted from the adrenal glands". Adrenaline is secreted directly into the blood. The heart beats faster, sending more oxygen to the muscles; blood to the digestive system and skin is reduced by "contraction of muscles around small arteries", which diverts it to the skeletal muscles; and the breathing rate rises as the diaphragm and rib muscles contract. Such hormones are part of the endocrine system, "a second way of control and coordination in our body".
Animal hormones also control growth. Animals do not bend towards light, but their growth is still carefully placed: "we do not grow fingers on our faces."
- Thyroxin. Iodine is needed by the thyroid gland to make thyroxin, which "regulates carbohydrate, protein and fat metabolism in the body so as to provide the best balance for growth". If iodine is short in the diet, goitre may follow; one symptom is a swollen neck. This is why salt packets say "iodised salt".
- Growth hormone. Secreted by the pituitary, it regulates growth and development. A deficiency in childhood leads to dwarfism.
- Sex hormones. The changes of puberty, around 10-12 years of age, are due to testosterone in males and oestrogen in females.
- Insulin. Produced by the pancreas, it helps regulate blood sugar. If it is not secreted in proper amounts, blood sugar rises with harmful effects; some patients with diabetes take insulin injections.
- Releasing factor. A "Do You Know?" box adds that the hypothalamus releases growth hormone releasing factor when growth hormone is low, which makes the pituitary release growth hormone.
Feedback: how the amount is controlled. If hormones must be secreted in precise amounts, something must set the amount. NCERT: "The timing and amount of hormone released are regulated by feedback mechanisms." When blood sugar rises, cells of the pancreas detect it and produce more insulin; as blood sugar falls, insulin secretion is reduced. The thing being controlled (blood sugar) switches its own controller (insulin) up or down. The hypothalamus box shows the same logic one step higher: a low level of growth hormone triggers the factor that releases more of it.
Did the 2020-21 edition differ?
No. In the 2020-21 edition this was Chapter 7 (pp. 114-126); in Reprint 2026-27 it is Chapter 6 (pp. 100-112). Its sections, boxes, activities and exercises read the same; the current text adds references to its figures, and the chapter's place in the book has changed.
Source: NCERT, Science Class X, 2020-21 edition (whole-book zip, Wayback Machine capture of 9 October 2021), compared with Reprint 2026-27.
Beyond the textbook: what Class XI biology adds
NCERT's Class XI Biology names the parts that Class X describes.
Brain. "The hindbrain comprises pons, cerebellum and medulla (also called the medulla oblongata)"; Table 8 gives Class XI's lines on the forebrain, the hypothalamus and the medulla.
Pituitary and hypothalamus. The posterior pituitary "stores and releases two hormones called oxytocin and vasopressin, which are actually synthesised by the hypothalamus". Vasopressin "stimulates resorption of water and electrolytes by the distal tubules" of the kidney and is also called anti-diuretic hormone (ADH): this is the hormonal side of the kidney in Chapter 5. On growth hormone, Class XI adds the excess as well as the shortage: "Over-secretion of GH stimulates abnormal growth of the body leading to gigantism and low secretion of GH results in stunted growth resulting in pituitary dwarfism"; excess in adults, especially in middle age, causes acromegaly.
Thyroid. Two hormones, "tetraiodothyronine or thyroxine (T4) and triiodothyronine (T3)". Iodine deficiency "results in hypothyroidism and enlargement of the thyroid gland, commonly called goitre".
Adrenal. The adrenal medulla secretes "adrenaline or epinephrine and noradrenaline or norepinephrine", which are "called emergency hormones or hormones of Fight or Flight". Besides a faster heartbeat and breathing, they "increase alertness, pupilary dilation, piloerection (raising of hairs), sweating etc."
Pancreas. The hormone-making part of the pancreas is about 1 to 2 million Islets of Langerhans, only 1 to 2 per cent of the pancreatic tissue. Their α-cells secrete glucagon, which raises blood glucose; their β-cells secrete insulin, which lowers it. "The glucose homeostasis in blood is thus maintained jointly by the two – insulin and glucagons." "Prolonged hyperglycemia leads to a complex disorder called diabetes mellitus which is associated with loss of glucose through urine and formation of harmful compounds known as ketone bodies. Diabetic patients are successfully treated with insulin therapy."
Plants. Class XI groups auxins, gibberellins and cytokinins as growth promoters, and puts abscisic acid with the group behind "dormancy and abscission" and responses to "wounds and stresses of biotic and abiotic origin"; ethylene is in Table 8.
Source: NCERT, Biology, Class XI, ch. 13 "Plant Growth and Development", ch. 18 "Neural Control and Coordination", ch. 19 "Chemical Coordination and Integration".
Beyond the textbook: diabetes in India, two numbers, two methods
Two different figures for diabetes in India are often quoted together. They measure different things.
A count. The International Diabetes Federation's Diabetes Atlas, 11th edition, released on 7 April 2025, estimates the number of adults aged 20-79 with diabetes in India at 32.7 million in 2000, 61.3 million in 2011 and 89.8 million in 2024, and projects 156.7 million in 2050. It states that "India has the second highest number of adults (20-79 years) with diabetes in the world." Worldwide, the IDF puts adults living with diabetes at 589 million.
A rate. The ICMR-INDIAB study, published in The Lancet Diabetes & Endocrinology in 2023, surveyed 113,043 people aged 20 and above, drawn from urban and rural areas of 31 states, union territories and the National Capital Territory, between 18 October 2008 and 17 December 2020. It found an overall weighted prevalence of diabetes of 11.4 %, and of prediabetes 15.3 %.
A count of people and a percentage of adults are not the same measure, and they come from different studies, age bands and years. Quote each with its source; do not convert one into the other. Any claim that India has the most people with diabetes in the world is not what the IDF says.
Source: International Diabetes Federation, Diabetes Atlas country page for India and IDF news release of 7 April 2025; Anjana R.M. et al., "Metabolic non-communicable disease health report of India: the ICMR-INDIAB national cross-sectional study (ICMR-INDIAB-17)", Lancet Diabetes Endocrinol 2023, PubMed 37301218.
PART 3 — UPSC Integration
Cross-paper relevance
- Prelims (general science) — neuron and synapse, the reflex arc, parts of the brain and their functions, central and peripheral nervous systems, tropisms, plant hormones, endocrine glands and their hormones, feedback.
- GS3 (Science and technology) — electrical and chemical signalling as two designs for control; plant growth hormones and their uses in agriculture rest on Table 5.
- GS2 (Health) — iodised salt, iodine deficiency and goitre; growth hormone and stunted growth; insulin, feedback and diabetes, with the IDF count and the ICMR-INDIAB prevalence quoted correctly.
Past questions on these themes: No past question in the bank is set directly on this chapter.
Frames for Mains Answers
1. Two control systems, two designs. Electrical impulses are fast but reach only wired cells and need reset time; hormones are slow but reach every cell and last. Use NCERT's squirrel: nerves alone could not prepare the whole body to fight or run; adrenaline can.
2. Feedback and disease. Blood sugar rises, the pancreas makes more insulin; it falls, insulin falls. When this control fails and blood sugar stays high, the result is diabetes mellitus (Class XI). Add the IDF count (89.8 million adults, 2024, second highest in the world) and the ICMR-INDIAB rate (11.4 %), each with its source.
3. A nutrient, a gland and a disease. Iodine is needed to make thyroxin; thyroxin balances carbohydrate, protein and fat metabolism for growth; iodine deficiency can cause goitre. This is the science behind iodised salt.
4. Plants respond without nerves. Water movement in cells for the fast touch response; hormones and uneven growth for the slow tropisms. Movement in plants is either growth-independent or growth-dependent.
Exam Strategy
Prelims fact-traps:
- The gap between two neurons is the synapse; the signal crosses it as a chemical, not as an electrical impulse.
- Reflex arcs are formed in the spinal cord, but the information still reaches the brain.
- Cerebellum: posture, balance, precision of voluntary actions. Medulla: blood pressure, salivation, vomiting.
- Association areas interpret; motor areas move voluntary muscles.
- The sensitive plant's movement is not growth; tendrils and tropisms are.
- Auxin moves to the shady side and makes that side grow more.
- Cytokinins: cell division, high in fruits and seeds. Abscisic acid: inhibits growth, wilting.
- Adrenaline comes from the adrenal glands, not the pituitary; growth hormone comes from the pituitary.
- The hypothalamus, not the pituitary, releases growth hormone releasing factor.
- IDF: India has the second highest number of adults with diabetes, not the highest.
Mains: Build answers on the contrast between the two control systems and on feedback. For health questions, start from the mechanism (iodine → thyroxin; insulin → blood sugar) and then add one dated figure with its source.
Practice Questions
Questions 1-3 are the NCERT exercise MCQs. Practice (UPSC-pattern, not past papers): questions 4-10.
1. Which of the following is a plant hormone?
(a) Insulin
(b) Thyroxin
(c) Oestrogen
(d) Cytokinin.
Answer: (d). The other three are animal hormones (NCERT Answers, p. 218).
2. The gap between two neurons is called a
(a) dendrite.
(b) synapse.
(c) axon.
(d) impulse.
Answer: (b) (NCERT Answers, p. 218).
3. The brain is responsible for
(a) thinking.
(b) regulating the heart beat.
(c) balancing the body.
(d) all of the above.
Answer: (d). Thinking is the fore-brain's job, the heartbeat is an involuntary action of the mid- and hind-brain, and balance is the cerebellum's (NCERT Answers, p. 218).
4. Consider the following statements about the reflex arc, as NCERT Class X describes it:
1. The connection between the input nerve and the output nerve is made in the spinal cord.
2. The information from a reflex action never reaches the brain.
3. Reflex arcs remain more efficient for quick responses even in animals that have complex neuron networks for thinking.
Which of the statements given above are correct?
(a) 1 and 2 only
(b) 1 and 3 only
(c) 2 and 3 only
(d) 1, 2 and 3
Answer: (b). The information input "also goes on to reach the brain".
5. Consider the following pairs:
1. Cerebellum : posture and balance of the body
2. Medulla : blood pressure, salivation and vomiting
3. Association areas of the fore-brain : movement of voluntary muscles
How many of the pairs given above are correctly matched?
(a) Only one
(b) Only two
(c) All three
(d) None
Answer: (b). Association areas interpret sensory information; the motor areas control voluntary muscles.
6. Which one of the following plant movements does not depend on growth?
(a) A shoot bending towards light
(b) A root growing downwards
(c) The leaves of chhui-mui folding up when touched
(d) A pea tendril coiling round a support
Answer: (c). The sensitive plant's cells change shape by changing their water content.
7. Consider the following statements about plant hormones:
1. Auxin is synthesised at the root tip and moves towards the lighted side of the shoot.
2. Cytokinins promote cell division and are present in greater concentration in fruits and seeds.
3. Abscisic acid inhibits growth, and its effects include wilting of leaves.
Which of the statements given above are correct?
(a) 1 and 2 only
(b) 2 and 3 only
(c) 1 and 3 only
(d) 1, 2 and 3
Answer: (b). Auxin is synthesised at the shoot tip and diffuses towards the shady side.
8. Which one of the following pairs of a hormone and its source is not correctly matched?
(a) Growth hormone releasing factor : Hypothalamus
(b) Thyroxin : Thyroid gland
(c) Testosterone : Testes
(d) Adrenaline : Pituitary gland
Answer: (d). Adrenaline is secreted by the adrenal glands.
9. Consider the following statements:
1. The International Diabetes Federation estimates that India had 89.8 million adults aged 20-79 with diabetes in 2024.
2. According to the International Diabetes Federation, India has the highest number of adults with diabetes in the world.
3. The ICMR-INDIAB study reported an overall weighted prevalence of diabetes of 11.4 % among people aged 20 and above.
Which of the statements given above are correct?
(a) 1 and 2 only
(b) 1 and 3 only
(c) 2 and 3 only
(d) 1, 2 and 3
Answer: (b). The IDF says India has the second highest number.
10. A squirrel facing danger must be ready either to fight or to run. Using this example, compare nervous and hormonal mechanisms of control and coordination in animals. (150 words)
NCERT exercises (where the answers are on this page): 4 Table 1 and Activity 6.1; 5 Table 1 and the neuron box; 6 the auxin box and Table 4; 7 Table 3 and the reflex box; 8 Table 5; 9 the First Principles; 10 Table 2; 11 Table 7; 12 Table 4 and the section on how nerves make muscles move.
📦 Revision Capsule
Hard Facts
- Impulse path: dendrite → cell body → axon → chemicals across the synapse → next neuron.
- Reflex arcs are formed in the spinal cord; the information also reaches the brain.
- Brain: fore-brain (thinking, senses, association, motor areas, hunger centre); mid-brain and hind-brain (involuntary actions); medulla (blood pressure, salivation, vomiting); cerebellum (precision, posture, balance).
- CNS = brain + spinal cord; PNS = cranial + spinal nerves.
- Plant hormones: auxin (shoot tip, cell elongation, shady side), gibberellins (stem growth), cytokinins (cell division, fruits and seeds), abscisic acid (inhibits growth, wilting).
- Adrenal glands → adrenaline; thyroid → thyroxin (needs iodine); pituitary → growth hormone; pancreas → insulin; testes → testosterone; ovaries → oestrogen; hypothalamus → releasing hormones.
Core Concepts
- Response = detect, decide, act; a message must travel between the three.
- Electrical signals are fast but wired and need reset time; chemical signals are slower but reach all cells and last.
- Plants move by changing water content (fast, no growth) or by uneven growth (slow, tropisms).
- Hormone levels are set by feedback.
Confused Pairs
- Reflex (spinal cord, no thought) vs voluntary (fore-brain decides) vs involuntary (mid- and hind-brain).
- Cerebellum (balance, precision) vs medulla (blood pressure, salivation, vomiting).
- Association areas (interpret) vs motor areas (move voluntary muscles).
- Sensitive-plant movement (no growth) vs tendril coiling (growth).
- Phototropism (light) vs geotropism (gravity) vs chemotropism (chemicals, pollen tube) vs hydrotropism (water).
- Auxin (elongation) vs cytokinins (cell division).
- Growth hormone (pituitary) vs growth hormone releasing factor (hypothalamus).
- IDF count of people vs ICMR-INDIAB percentage of adults.
Data Points
- Puberty: around 10-12 years (NCERT).
- IDF Diabetes Atlas 11th edition (7 April 2025): India 89.8 million adults aged 20-79 with diabetes (2024), second highest in the world; 156.7 million projected for 2050; 589 million worldwide.
- ICMR-INDIAB (2023 paper, survey 2008-2020): diabetes 11.4 %, prediabetes 15.3 %.
- Class XI: about 1 to 2 million islets of Langerhans, 1 to 2 per cent of the pancreas.
PYQ Pattern
- No past question in the bank matches this chapter directly.
Sources
- NCERT, Science, Textbook for Class X, ch. 6 "Control and Coordination", Reprint 2026-27 — ncert.nic.in PDF.
- NCERT, Science, Class X, Answers, Reprint 2026-27 — ncert.nic.in PDF.
- NCERT, Science, Class X, 2020-21 edition (whole-book zip), as archived on 9 October 2021 — Wayback Machine.
- NCERT, Biology, Textbook for Class XI, ch. 13 "Plant Growth and Development" — ncert.nic.in PDF.
- NCERT, Biology, Textbook for Class XI, ch. 18 "Neural Control and Coordination" — ncert.nic.in PDF.
- NCERT, Biology, Textbook for Class XI, ch. 19 "Chemical Coordination and Integration" — ncert.nic.in PDF.
- International Diabetes Federation, Diabetes Atlas, country page for India — diabetesatlas.org.
- International Diabetes Federation, "Over 250 million people worldwide unaware they have diabetes, according to new IDF research", news release, 7 April 2025.
- Anjana R.M. et al., "Metabolic non-communicable disease health report of India: the ICMR-INDIAB national cross-sectional study (ICMR-INDIAB-17)", The Lancet Diabetes & Endocrinology, 2023 — PubMed 37301218.
