A Plant Bends Towards Light Without Any Muscles
Separate tropic from nastic movements and classify a plant response, see what each of the four plant hormones does, match a hormone to its gland and its target, and follow the feedback loop that controls blood sugar.
How can a plant respond to its surroundings with no nerves at all?
A shoot on a windowsill leans towards the light. A root finds its way down through the soil and towards a damp patch. A touch-me-not plant folds its leaves the moment you brush against it.
None of those movements uses a nerve or a muscle, because a plant has neither. What a plant has instead is chemistry and growth, and it turns out that the two are enough — provided the response does not need to be fast.
That gives plants two quite different ways of moving:
- Movements that depend on growth, which are slow, permanent and directed by where the stimulus is coming from
- Movements that do not depend on growth, which are quick, reversible and take no notice of direction
Animals have both a nervous system and a chemical one, and the second works in exactly the way a plant's does: a substance made in one place travels in the bloodstream and acts somewhere else. Those substances are hormones, and they reach cells that no nerve arrives at.
So this part of the chapter completes the picture. Nervous control is fast, precise and short-lived; chemical control is slower, spread over the whole body and long-lasting. A plant manages with only the second; an animal uses both.
This page covers the second part of the CBSE Class 10 Science chapter on control and coordination: tropic and nastic movements, the plant hormones, the endocrine glands, and feedback regulation.
None of those movements uses a nerve or a muscle, because a plant has neither. What a plant has instead is chemistry and growth, and it turns out that the two are enough — provided the response does not need to be fast.
That gives plants two quite different ways of moving:
- Movements that depend on growth, which are slow, permanent and directed by where the stimulus is coming from
- Movements that do not depend on growth, which are quick, reversible and take no notice of direction
Animals have both a nervous system and a chemical one, and the second works in exactly the way a plant's does: a substance made in one place travels in the bloodstream and acts somewhere else. Those substances are hormones, and they reach cells that no nerve arrives at.
So this part of the chapter completes the picture. Nervous control is fast, precise and short-lived; chemical control is slower, spread over the whole body and long-lasting. A plant manages with only the second; an animal uses both.
This page covers the second part of the CBSE Class 10 Science chapter on control and coordination: tropic and nastic movements, the plant hormones, the endocrine glands, and feedback regulation.
What is the difference between a tropic and a nastic movement?
A tropic movement is a growth response whose direction is set by the stimulus; a nastic movement is a quick, reversible change that has no relation to the direction of the stimulus.
Nastic movement — the touch-me-not. Brush a leaf of the Mimosa plant and it folds within seconds. Nothing has grown; water has moved out of certain cells at the base of each leaflet, so those cells lose their firmness and the leaflet drops. Wait a while and the water returns and the leaf reopens.
Two features mark it out:
- It is fast and reversible, because it is only a movement of water
- It happens the same way whichever side you touch — the direction of the stimulus does not decide the direction of the response
Tropic movement — growth towards or away from something. These are slow, one-way and permanent, and they are named after the stimulus:
- Phototropism — response to light. A shoot grows towards light, which is positive phototropism; a root grows away from it, which is negative
- Geotropism — response to gravity. A root grows downward, which is positive geotropism; a shoot grows upward, which is negative
- Hydrotropism — response to water. Roots grow towards moisture, which is why roots spread towards a leaking pipe or a damp patch of soil
- Chemotropism — response to a chemical. The pollen tube grows towards the ovule down the style, guided by chemicals — the link back to the reproduction chapter
Worked classification. Name the response in each case.
- A sunflower seedling on a windowsill leaning towards the window — positive phototropism
- A germinating seed sending its root down whichever way the seed was placed — positive geotropism
- Roots of a plant growing sideways towards a wet drain — hydrotropism
- The pollen tube travelling down the style — chemotropism
- A touch-me-not folding its leaves — nastic, not a tropism at all
The classification trap. The Mimosa response looks like the most dramatic plant movement in the syllabus, and it is the one most often called a tropism by mistake. It is not, because nothing grew and the direction of the touch made no difference. Ask two questions — did it involve growth, and did the direction of the stimulus set the direction of the response — and the classification follows.
A boundary case worth knowing. A shoot that has bent towards light cannot bend back if the light moves; it can only grow a new bend. Growth-based responses are permanent, which is why a plant that has leaned towards a window stays crooked even after being turned around — and why nastic movements exist at all for situations that need reversing.
Nastic movement — the touch-me-not. Brush a leaf of the Mimosa plant and it folds within seconds. Nothing has grown; water has moved out of certain cells at the base of each leaflet, so those cells lose their firmness and the leaflet drops. Wait a while and the water returns and the leaf reopens.
Two features mark it out:
- It is fast and reversible, because it is only a movement of water
- It happens the same way whichever side you touch — the direction of the stimulus does not decide the direction of the response
Tropic movement — growth towards or away from something. These are slow, one-way and permanent, and they are named after the stimulus:
- Phototropism — response to light. A shoot grows towards light, which is positive phototropism; a root grows away from it, which is negative
- Geotropism — response to gravity. A root grows downward, which is positive geotropism; a shoot grows upward, which is negative
- Hydrotropism — response to water. Roots grow towards moisture, which is why roots spread towards a leaking pipe or a damp patch of soil
- Chemotropism — response to a chemical. The pollen tube grows towards the ovule down the style, guided by chemicals — the link back to the reproduction chapter
Worked classification. Name the response in each case.
- A sunflower seedling on a windowsill leaning towards the window — positive phototropism
- A germinating seed sending its root down whichever way the seed was placed — positive geotropism
- Roots of a plant growing sideways towards a wet drain — hydrotropism
- The pollen tube travelling down the style — chemotropism
- A touch-me-not folding its leaves — nastic, not a tropism at all
The classification trap. The Mimosa response looks like the most dramatic plant movement in the syllabus, and it is the one most often called a tropism by mistake. It is not, because nothing grew and the direction of the touch made no difference. Ask two questions — did it involve growth, and did the direction of the stimulus set the direction of the response — and the classification follows.
A boundary case worth knowing. A shoot that has bent towards light cannot bend back if the light moves; it can only grow a new bend. Growth-based responses are permanent, which is why a plant that has leaned towards a window stays crooked even after being turned around — and why nastic movements exist at all for situations that need reversing.
What does each of the four plant hormones do?
Three promote growth in different ways, and one holds it back.
Auxin — cell elongation, and the hormone behind phototropism. Auxin is made at the tip of a growing shoot and helps the cells behind the tip grow longer.
Here is the mechanism that explains a bending shoot. When light falls on one side of a shoot, the auxin diffuses away from the bright side to the shady side. There is now more auxin on the shady side, so those cells elongate more than the cells facing the light — and a stem whose one side is growing faster than the other must bend. It bends towards the light, which is exactly what is observed.
Notice how much that explains. The bending is a growth response, so it is slow and permanent; the direction is set by where the light is; and the response is strongest just behind the tip, where the cells are still able to elongate. One hormone moving sideways accounts for all three features of phototropism.
Gibberellin — stem growth. It works alongside auxin and promotes the growth of the stem.
Cytokinin — cell division. It promotes cells to divide rather than merely elongate, and it is found in greater concentration in areas of rapid division such as fruits and seeds.
Abscisic acid — the inhibitor. Unlike the other three, it slows growth down, and among its effects is the wilting of leaves — it closes the stomata and reduces water loss.
So the four divide two ways:
- Promoters — auxin, gibberellin and cytokinin
- Inhibitor — abscisic acid
Why a plant needs an inhibitor at all. Growth is expensive and sometimes unwise. A plant short of water gains nothing by growing and would lose the water it has left through open stomata, so a signal that stops growth and shuts the pores keeps it alive until conditions improve. The inhibitor is as important as the promoters, which is the point of including it in the list of four.
And a limitation to note. These hormones move through the plant slowly, mostly from cell to cell, and they are not delivered by any pumped system. That is why plant responses take hours or days, while the Mimosa's water movement takes seconds — and why a plant can never respond as quickly as an animal.
Auxin — cell elongation, and the hormone behind phototropism. Auxin is made at the tip of a growing shoot and helps the cells behind the tip grow longer.
Here is the mechanism that explains a bending shoot. When light falls on one side of a shoot, the auxin diffuses away from the bright side to the shady side. There is now more auxin on the shady side, so those cells elongate more than the cells facing the light — and a stem whose one side is growing faster than the other must bend. It bends towards the light, which is exactly what is observed.
Notice how much that explains. The bending is a growth response, so it is slow and permanent; the direction is set by where the light is; and the response is strongest just behind the tip, where the cells are still able to elongate. One hormone moving sideways accounts for all three features of phototropism.
Gibberellin — stem growth. It works alongside auxin and promotes the growth of the stem.
Cytokinin — cell division. It promotes cells to divide rather than merely elongate, and it is found in greater concentration in areas of rapid division such as fruits and seeds.
Abscisic acid — the inhibitor. Unlike the other three, it slows growth down, and among its effects is the wilting of leaves — it closes the stomata and reduces water loss.
So the four divide two ways:
- Promoters — auxin, gibberellin and cytokinin
- Inhibitor — abscisic acid
Why a plant needs an inhibitor at all. Growth is expensive and sometimes unwise. A plant short of water gains nothing by growing and would lose the water it has left through open stomata, so a signal that stops growth and shuts the pores keeps it alive until conditions improve. The inhibitor is as important as the promoters, which is the point of including it in the list of four.
And a limitation to note. These hormones move through the plant slowly, mostly from cell to cell, and they are not delivered by any pumped system. That is why plant responses take hours or days, while the Mimosa's water movement takes seconds — and why a plant can never respond as quickly as an animal.
Which endocrine gland makes which hormone, and what does it act on?
An endocrine gland pours its hormone straight into the blood, which carries it to every cell — but only cells with the right receptor respond.
- Pituitary gland — secretes growth hormone, acting on the whole body, controlling the growth of bones and tissues. Too little in childhood causes dwarfism; too much causes gigantism
- Thyroid gland — secretes thyroxine, which regulates the metabolism of carbohydrates, proteins and fats. Iodine is essential for making it, and a shortage of iodine in the diet causes the swelling of the gland called goitre
- Pancreas — secretes insulin, which regulates the blood sugar level. Too little insulin causes diabetes, treated with insulin injections
- Adrenal gland — secretes adrenaline, acting on the heart, blood vessels and diaphragm, and preparing the body for emergency action
- Testis — secretes testosterone, producing the male secondary sexual characters at puberty
- Ovary — secretes oestrogen, producing the female secondary sexual characters
How hormonal control differs from nervous control.
- Delivery: nerves reach only the cells they connect to; hormones reach every cell through the blood
- Speed: nervous control is almost instant; hormonal control takes longer
- Duration: a nervous response ends as soon as the impulse stops; a hormonal effect lasts much longer
- Quantity: hormones act in very small amounts, which is why an excess or a shortage has such large effects
Why the blood does not simply deliver chaos. Every hormone reaches every cell, so something must decide which cells obey. Only cells carrying the matching receptor respond — which is why thyroxine adjusts metabolism everywhere while testosterone acts only where its receptors are. The address is on the cell, not on the message.
Worked matching. Name the gland and the effect for each of these.
- A child who has not grown as expected — pituitary, growth hormone
- Swelling at the front of the neck in an area where the soil lacks iodine — thyroid, thyroxine, goitre
- A person whose blood sugar stays high after a meal — pancreas, insulin, diabetes
- A pounding heart before a race — adrenal, adrenaline
The iodine point is worth stating fully. Thyroxine cannot be made without iodine, and iodine reaches us only through food and water. Where the local soil is poor in iodine, adding it to common salt supplies it directly — which is why iodised salt is sold and why the deficiency is preventable rather than treatable.
One misconception to clear. Hormones are not carried by nerves and they are not the same as enzymes. A hormone is a chemical messenger carried by blood; an enzyme is a catalyst that speeds up a reaction where it already is. The pancreas happens to make both — insulin as a hormone and digestive enzymes as a juice — and telling them apart is a standard question.
- Pituitary gland — secretes growth hormone, acting on the whole body, controlling the growth of bones and tissues. Too little in childhood causes dwarfism; too much causes gigantism
- Thyroid gland — secretes thyroxine, which regulates the metabolism of carbohydrates, proteins and fats. Iodine is essential for making it, and a shortage of iodine in the diet causes the swelling of the gland called goitre
- Pancreas — secretes insulin, which regulates the blood sugar level. Too little insulin causes diabetes, treated with insulin injections
- Adrenal gland — secretes adrenaline, acting on the heart, blood vessels and diaphragm, and preparing the body for emergency action
- Testis — secretes testosterone, producing the male secondary sexual characters at puberty
- Ovary — secretes oestrogen, producing the female secondary sexual characters
How hormonal control differs from nervous control.
- Delivery: nerves reach only the cells they connect to; hormones reach every cell through the blood
- Speed: nervous control is almost instant; hormonal control takes longer
- Duration: a nervous response ends as soon as the impulse stops; a hormonal effect lasts much longer
- Quantity: hormones act in very small amounts, which is why an excess or a shortage has such large effects
Why the blood does not simply deliver chaos. Every hormone reaches every cell, so something must decide which cells obey. Only cells carrying the matching receptor respond — which is why thyroxine adjusts metabolism everywhere while testosterone acts only where its receptors are. The address is on the cell, not on the message.
Worked matching. Name the gland and the effect for each of these.
- A child who has not grown as expected — pituitary, growth hormone
- Swelling at the front of the neck in an area where the soil lacks iodine — thyroid, thyroxine, goitre
- A person whose blood sugar stays high after a meal — pancreas, insulin, diabetes
- A pounding heart before a race — adrenal, adrenaline
The iodine point is worth stating fully. Thyroxine cannot be made without iodine, and iodine reaches us only through food and water. Where the local soil is poor in iodine, adding it to common salt supplies it directly — which is why iodised salt is sold and why the deficiency is preventable rather than treatable.
One misconception to clear. Hormones are not carried by nerves and they are not the same as enzymes. A hormone is a chemical messenger carried by blood; an enzyme is a catalyst that speeds up a reaction where it already is. The pancreas happens to make both — insulin as a hormone and digestive enzymes as a juice — and telling them apart is a standard question.
How does feedback keep blood sugar at the right level?
The level being controlled is itself what switches the control on and off. That circular arrangement is called feedback.
Follow a meal.
- You eat, and the digested food raises the sugar level in the blood
- Cells in the pancreas detect that rise directly — nothing had to tell them
- The pancreas secretes more insulin
- Insulin makes body cells take up glucose from the blood and the liver store it
- The blood sugar level falls back towards normal
- The pancreas, detecting the lower level, secretes less insulin
The output of the system reduces the cause of the output. That is what makes it a feedback loop, and it is why no external instruction is needed: the pancreas is measuring the very thing it is correcting.
Why the design is used everywhere. A fixed instruction cannot work, because the correction needed depends on the meal, the activity and the moment. Feedback adjusts automatically to a situation nobody planned for, and it does so continuously.
What happens when the loop breaks. If the pancreas secretes too little insulin, the blood sugar cannot be brought down and stays high — that is diabetes, and the treatment is to supply the missing insulin by injection. The loop is repaired from outside, which is why the dose has to be matched to the meal, exactly as the pancreas would have done.
The same principle controls the other hormones. The timing and the amount of every hormone are regulated by feedback: when the effect has been achieved, the signal that produced it is reduced. Nothing in the body is switched on permanently, and a hormone that could not be switched off would be as dangerous as one that could not be switched on.
A familiar non-biological comparison. A ceiling fan's regulator has to be set by a person; a refrigerator's thermostat sets itself, because it measures the temperature it is controlling. The pancreas is a thermostat for sugar, and a diabetic person on injections is working the regulator by hand.
One boundary case worth naming. Feedback works within a range. If the disturbance is too large or too fast, the loop cannot keep up — which is why a very sugary meal produces a bigger swing than a balanced one, and why the advice in a diabetic diet is about the size and timing of meals rather than about sugar alone. Understanding the loop explains the advice, which is the real payoff of this section.
Follow a meal.
- You eat, and the digested food raises the sugar level in the blood
- Cells in the pancreas detect that rise directly — nothing had to tell them
- The pancreas secretes more insulin
- Insulin makes body cells take up glucose from the blood and the liver store it
- The blood sugar level falls back towards normal
- The pancreas, detecting the lower level, secretes less insulin
The output of the system reduces the cause of the output. That is what makes it a feedback loop, and it is why no external instruction is needed: the pancreas is measuring the very thing it is correcting.
Why the design is used everywhere. A fixed instruction cannot work, because the correction needed depends on the meal, the activity and the moment. Feedback adjusts automatically to a situation nobody planned for, and it does so continuously.
What happens when the loop breaks. If the pancreas secretes too little insulin, the blood sugar cannot be brought down and stays high — that is diabetes, and the treatment is to supply the missing insulin by injection. The loop is repaired from outside, which is why the dose has to be matched to the meal, exactly as the pancreas would have done.
The same principle controls the other hormones. The timing and the amount of every hormone are regulated by feedback: when the effect has been achieved, the signal that produced it is reduced. Nothing in the body is switched on permanently, and a hormone that could not be switched off would be as dangerous as one that could not be switched on.
A familiar non-biological comparison. A ceiling fan's regulator has to be set by a person; a refrigerator's thermostat sets itself, because it measures the temperature it is controlling. The pancreas is a thermostat for sugar, and a diabetic person on injections is working the regulator by hand.
One boundary case worth naming. Feedback works within a range. If the disturbance is too large or too fast, the loop cannot keep up — which is why a very sugary meal produces a bigger swing than a balanced one, and why the advice in a diabetic diet is about the size and timing of meals rather than about sugar alone. Understanding the loop explains the advice, which is the real payoff of this section.
Exam tip
What layout keeps a hormones answer complete?
Give the gland, the hormone, the target and the effect — four items, every time. A hormone named without its target earns half the mark.
- Name the deficiency disease where there is one: dwarfism, goitre, diabetes. These are frequently the actual question
- **Say iodine in the thyroxine answer, and connect it to iodised salt
- For a plant response, name the tropism and its sign**: positive phototropism, negative geotropism. The sign carries a mark
- Test a movement with two questions — did it involve growth, and did the direction of the stimulus set the direction — before calling it a tropism
- Give the auxin mechanism in full: auxin diffuses to the shady side, those cells elongate more, and the shoot bends towards the light
- Group the plant hormones as three promoters and one inhibitor
- For feedback, write the loop as a cycle ending where it began, and say that the pancreas detects the level it corrects
- Compare nervous with hormonal control on four points: delivery, speed, duration and quantity
The misconception to name. Hormones do not travel along nerves and they are not enzymes. A hormone is carried in the blood to a distant target; an enzyme catalyses a reaction where it is. The pancreas makes both, which is exactly why that question is set — and the answer is that insulin goes into the blood while the digestive enzymes go into the duodenum.
- Name the deficiency disease where there is one: dwarfism, goitre, diabetes. These are frequently the actual question
- **Say iodine in the thyroxine answer, and connect it to iodised salt
- For a plant response, name the tropism and its sign**: positive phototropism, negative geotropism. The sign carries a mark
- Test a movement with two questions — did it involve growth, and did the direction of the stimulus set the direction — before calling it a tropism
- Give the auxin mechanism in full: auxin diffuses to the shady side, those cells elongate more, and the shoot bends towards the light
- Group the plant hormones as three promoters and one inhibitor
- For feedback, write the loop as a cycle ending where it began, and say that the pancreas detects the level it corrects
- Compare nervous with hormonal control on four points: delivery, speed, duration and quantity
The misconception to name. Hormones do not travel along nerves and they are not enzymes. A hormone is carried in the blood to a distant target; an enzyme catalyses a reaction where it is. The pancreas makes both, which is exactly why that question is set — and the answer is that insulin goes into the blood while the digestive enzymes go into the duodenum.
Did you know
Why does your heart pound before you have even started running?
Something startles you on a dark road. Before you have worked out what it was, your heart is racing, your breathing has quickened, your hands are unsteady and you feel a jolt in your stomach.
None of that was decided. Adrenaline has been released from the adrenal glands straight into the blood, and within seconds it has reached the heart, the blood vessels, the diaphragm and the muscles. Its job is to prepare the body to act, and it does so on several fronts at once:
- The heart beats faster, so more oxygenated blood reaches the muscles
- The blood vessels around the digestive system and skin contract, diverting blood to where it is needed
- The breathing rate rises, as the diaphragm and rib muscles work harder to take in more oxygen
- The muscles are supplied and ready
Every one of those changes is preparation for running or fighting, which is why the response is called fight-or-flight — and it is the same response in a deer and in a person, produced by the same hormone.
Notice the timing. It is far too fast to be a considered decision and far too widespread to be a single nerve, and that combination is the signature of a hormone: one message in the blood, many targets, all at once.
And notice why it is a hormone and not a reflex. A reflex produces one action in one place. Adrenaline changes the setting of the whole body, and it keeps it changed for minutes after the danger has passed — which is why you remain shaky for a while and why the feeling takes time to subside. Nervous control ends when the signal stops; hormonal control lingers.
The same system explains the exam-hall version. A rise in adrenaline before something important is the body preparing for exertion that is not going to happen, so the energy has nowhere to go and is felt as restlessness. Breathing slowly and deliberately works because it directly opposes one of adrenaline's effects, and the rest of the response follows the breathing down.
The general lesson of the chapter. The body has two messaging systems, and it uses whichever fits: a nerve when the target is one place and the timing is critical, a hormone when the target is everywhere and the effect must last.
None of that was decided. Adrenaline has been released from the adrenal glands straight into the blood, and within seconds it has reached the heart, the blood vessels, the diaphragm and the muscles. Its job is to prepare the body to act, and it does so on several fronts at once:
- The heart beats faster, so more oxygenated blood reaches the muscles
- The blood vessels around the digestive system and skin contract, diverting blood to where it is needed
- The breathing rate rises, as the diaphragm and rib muscles work harder to take in more oxygen
- The muscles are supplied and ready
Every one of those changes is preparation for running or fighting, which is why the response is called fight-or-flight — and it is the same response in a deer and in a person, produced by the same hormone.
Notice the timing. It is far too fast to be a considered decision and far too widespread to be a single nerve, and that combination is the signature of a hormone: one message in the blood, many targets, all at once.
And notice why it is a hormone and not a reflex. A reflex produces one action in one place. Adrenaline changes the setting of the whole body, and it keeps it changed for minutes after the danger has passed — which is why you remain shaky for a while and why the feeling takes time to subside. Nervous control ends when the signal stops; hormonal control lingers.
The same system explains the exam-hall version. A rise in adrenaline before something important is the body preparing for exertion that is not going to happen, so the energy has nowhere to go and is felt as restlessness. Breathing slowly and deliberately works because it directly opposes one of adrenaline's effects, and the rest of the response follows the breathing down.
The general lesson of the chapter. The body has two messaging systems, and it uses whichever fits: a nerve when the target is one place and the timing is critical, a hormone when the target is everywhere and the effect must last.
Exam relevance
Why does NEET keep returning to hormones and tropisms?
This is foundation work for two Class 11 Biology chapters, one on each half of the topic.
Where the endocrine glands lead. Class 11 Chemical Coordination and Integration covers the same glands with far more detail: the hypothalamus and its releasing hormones, the two lobes of the pituitary, the parathyroid, the pineal and the thymus, and the mechanism by which a hormone acts on its receptor. The gland-hormone-target-effect table you build here is the skeleton of that chapter, and NEET sets match-the-column questions on it repeatedly.
Where feedback leads. The insulin loop becomes the general principle of negative feedback, applied to thyroxine through the hypothalamus and pituitary, and then to the menstrual cycle in the reproduction chapter. Assertion-reason items on feedback are standard, and the wording NEET uses is exactly the wording of this section.
Where the plant half leads. Class 11 Plant Growth and Development expands the four hormones into five, adding ethylene, and treats each with its discovery, its transport and its commercial applications — auxin for rooting, gibberellin for stem elongation and seedless fruit, cytokinin for delaying leaf senescence, abscisic acid for dormancy. The three-promoters-and-one-inhibitor grouping is the frame, and the auxin explanation of phototropism is repeated there almost unchanged.
Where the deficiency diseases lead. Goitre, dwarfism, gigantism and diabetes are all revisited in Class 11 and in NEET, usually as a symptom-to-cause matching question. Naming the hormone and the gland together is what those questions need.
Question types to expect. At this level: classify the movement, name the hormone, state the target, trace the feedback loop. In competitive papers: match gland to hormone to effect, assertion-reason items on feedback and on the auxin mechanism, and diagram-based questions on the endocrine system.
The single trap that costs marks. Calling the touch-me-not response a tropism. It is nastic — no growth is involved and the direction of the touch is irrelevant. NEET sets this as a distractor because the movement is so much more visible than any real tropism.
A second trap. Saying that auxin accumulates on the lit side. It moves away from the light to the shady side, and the shady side therefore grows faster. Getting the direction backwards reverses the whole explanation and gives a shoot bending away from light, which is not what happens.
Board versus competitive emphasis. The CBSE paper marks the named hormone with its target and the labelled loop; a competitive paper marks a matched pair or a single correct statement. The transferable asset is the four-column table — gland, hormone, target, effect — because every later question is a row of it.
Where the endocrine glands lead. Class 11 Chemical Coordination and Integration covers the same glands with far more detail: the hypothalamus and its releasing hormones, the two lobes of the pituitary, the parathyroid, the pineal and the thymus, and the mechanism by which a hormone acts on its receptor. The gland-hormone-target-effect table you build here is the skeleton of that chapter, and NEET sets match-the-column questions on it repeatedly.
Where feedback leads. The insulin loop becomes the general principle of negative feedback, applied to thyroxine through the hypothalamus and pituitary, and then to the menstrual cycle in the reproduction chapter. Assertion-reason items on feedback are standard, and the wording NEET uses is exactly the wording of this section.
Where the plant half leads. Class 11 Plant Growth and Development expands the four hormones into five, adding ethylene, and treats each with its discovery, its transport and its commercial applications — auxin for rooting, gibberellin for stem elongation and seedless fruit, cytokinin for delaying leaf senescence, abscisic acid for dormancy. The three-promoters-and-one-inhibitor grouping is the frame, and the auxin explanation of phototropism is repeated there almost unchanged.
Where the deficiency diseases lead. Goitre, dwarfism, gigantism and diabetes are all revisited in Class 11 and in NEET, usually as a symptom-to-cause matching question. Naming the hormone and the gland together is what those questions need.
Question types to expect. At this level: classify the movement, name the hormone, state the target, trace the feedback loop. In competitive papers: match gland to hormone to effect, assertion-reason items on feedback and on the auxin mechanism, and diagram-based questions on the endocrine system.
The single trap that costs marks. Calling the touch-me-not response a tropism. It is nastic — no growth is involved and the direction of the touch is irrelevant. NEET sets this as a distractor because the movement is so much more visible than any real tropism.
A second trap. Saying that auxin accumulates on the lit side. It moves away from the light to the shady side, and the shady side therefore grows faster. Getting the direction backwards reverses the whole explanation and gives a shoot bending away from light, which is not what happens.
Board versus competitive emphasis. The CBSE paper marks the named hormone with its target and the labelled loop; a competitive paper marks a matched pair or a single correct statement. The transferable asset is the four-column table — gland, hormone, target, effect — because every later question is a row of it.
Key takeaways
What should you know about chemical coordination?
Two kinds of plant movement, four plant hormones, six glands and one loop.
- Tropic movements depend on growth and their direction is set by the stimulus; nastic movements are quick, reversible water movements with no relation to direction
- Positive phototropism in shoots, negative in roots; positive geotropism in roots, negative in shoots; hydrotropism towards water; chemotropism of the pollen tube towards the ovule
- The touch-me-not is nastic, not a tropism
- Auxin causes cell elongation and, by moving to the shady side, makes a shoot bend towards light
- Gibberellin promotes stem growth, cytokinin promotes cell division, and abscisic acid inhibits growth and causes wilting — three promoters and one inhibitor
- Pituitary — growth hormone, whole body, dwarfism and gigantism; thyroid — thyroxine, metabolism, needs iodine, goitre; pancreas — insulin, blood sugar, diabetes; adrenal — adrenaline, heart and vessels, emergency action; testis — testosterone; ovary — oestrogen
- Hormones travel in the blood to every cell, but only cells with the matching receptor respond
- Hormonal control is slower, wider and longer-lasting than nervous control, and works in tiny amounts
- Feedback: a rise in blood sugar makes the pancreas release insulin, the level falls, and less insulin is released — the system measures what it corrects
- A hormone is not an enzyme and is not carried by nerves
The sharpest self-test is the auxin explanation. Describe in three sentences why a shoot bends towards light, naming where the auxin is made, which way it moves and which side grows faster.
- Tropic movements depend on growth and their direction is set by the stimulus; nastic movements are quick, reversible water movements with no relation to direction
- Positive phototropism in shoots, negative in roots; positive geotropism in roots, negative in shoots; hydrotropism towards water; chemotropism of the pollen tube towards the ovule
- The touch-me-not is nastic, not a tropism
- Auxin causes cell elongation and, by moving to the shady side, makes a shoot bend towards light
- Gibberellin promotes stem growth, cytokinin promotes cell division, and abscisic acid inhibits growth and causes wilting — three promoters and one inhibitor
- Pituitary — growth hormone, whole body, dwarfism and gigantism; thyroid — thyroxine, metabolism, needs iodine, goitre; pancreas — insulin, blood sugar, diabetes; adrenal — adrenaline, heart and vessels, emergency action; testis — testosterone; ovary — oestrogen
- Hormones travel in the blood to every cell, but only cells with the matching receptor respond
- Hormonal control is slower, wider and longer-lasting than nervous control, and works in tiny amounts
- Feedback: a rise in blood sugar makes the pancreas release insulin, the level falls, and less insulin is released — the system measures what it corrects
- A hormone is not an enzyme and is not carried by nerves
The sharpest self-test is the auxin explanation. Describe in three sentences why a shoot bends towards light, naming where the auxin is made, which way it moves and which side grows faster.