BiologyICSE Class 10 · Chemical Coordination in Plants

Tropic Movements in Plants: Photo-, Geo-, Hydro-, Thigmo- and Chemotropism (ICSE Class 10 Biology)

Updated 16 October 2026 · Fact-checked

A tropic movement (tropism) is a slow, directional growth movement of a plant part in response to a stimulus. Growth towards the stimulus is positive and away from it is negative. Shoots are positively phototropic, roots positively geotropic and hydrotropic, tendrils thigmotropic, and pollen tubes chemotropic. Auxin controls bending.

Notice the shoot grows towards light and the roots grow towards gravity and water; auxin on the shaded side makes the shoot bend.

Illustration drawn for QuestionBuddy.

Understand Tropic Movements in Plants

What a tropism is. Plants cannot walk to light or water, but their organs can grow in a chosen direction. A tropic movement is a directional growth movement of a plant part in response to an external stimulus coming from one direction. Three keywords earn marks in any definition: growth, stimulus, direction. Tropisms are slow (hours to days) and permanent, because new cells are added or lengthened.

Positive and negative. Growth towards the stimulus is positive; growth away from it is negative. The same stimulus can produce opposite responses in root and shoot.

The five tropisms in the syllabus.

Tropism	Stimulus	Response and example
Phototropism	light	shoots grow towards light (+); roots away from light (−); a house plant on a windowsill leans to the window
Geotropism (gravitropism)	gravity	roots grow downwards (+); shoots grow upwards (−)
Hydrotropism	water	roots grow towards moist soil or a leaking pipe (+)
Thigmotropism	touch or contact	tendrils of pea, cucumber, gourd and grapevine coil around a support
Chemotropism	chemicals	the pollen tube grows down the style towards the ovule (+)

Why each response helps the plant. Shoots reach light for photosynthesis; roots anchor the plant and reach water and minerals; tendrils lift weak stems towards light without spending material on a thick trunk; the pollen tube delivers male gametes to the egg for fertilisation.

How auxin causes phototropism. Auxin is made at the shoot tip and moves down.
1. Light falls on the shoot from one side.
2. Auxin moves to the shaded side.
3. Cells on the shaded side elongate more than those on the lit side.
4. Unequal growth bends the shoot towards the light.
If the tip is cut off or covered with an opaque cap, no bending occurs, showing that the tip senses light. In roots, the same high auxin level slows elongation, which is why a root and a shoot can bend in opposite directions.

Thigmotropism in a tendril. The side of the tendril touching the support grows less than the outer side, so the tendril curls around the support. The structure is a tendril, not 'stem' or 'creeper'.

Tropic versus other plant movements (a contrast only). The folding of touch-me-not (Mimosa) leaves is quick, reversible and not directed by where the touch came from; it is not a growth movement, so it is not a tropism. Use it only as a contrast.

Clinostat (an idea). A slowly rotating stand turns a seedling so that gravity or one-sided light acts equally on all sides. The seedling then grows straight, showing that a one-sided stimulus causes the bending.

Flow chart. One-sided stimulus → detected (shoot tip or root tip) → auxin redistributed → unequal elongation on two sides → organ bends → towards stimulus (+) or away (−).

Draw-and-label checklist: phototropism. A pot with a seedling inside a box with a slit on one side; arrows for light entering the slit; the shoot bent towards the slit; label: light source, shoot (positively phototropic), shaded side (more auxin, more elongation), root (positively geotropic).

Tropic Movements in Plants: key facts

Tropism, stimulus, example: Phototropism light, shoot bends to window
Geotropism gravity, root grows down
Hydrotropism water, root to moist soil
Thigmotropism touch, pea tendril coils
Chemotropism chemicals, pollen tube to ovule; Learn as a three-column table.
Signs for root and shoot: $S h oo t : + p h o t o t r o p i c, - g eo t r o p i c ∣ R oo t : + g eo t r o p i c, + h y d r o t r o p i c, - p h o t o t r o p i c$; Towards = positive; away = negative.
Auxin and bending: One-sided light
Auxin to shaded side
Shaded cells elongate more
Shoot bends to light; The tip senses light and makes the auxin.

Phototropism	light, shoot bends to window
Geotropism	gravity, root grows down
Hydrotropism	water, root to moist soil
Thigmotropism	touch, pea tendril coils
Chemotropism	chemicals, pollen tube to ovule

How to answer Tropic Movements in Plants questions

ICSE gives a picture or a case (a climbing plant, a bent seedling, a table of tropisms) and asks you to name the tropism, define it, name the structure, state the stimulus and say whether the response is positive or negative.

1Find the stimulus first: light, gravity, water, touch or chemical.
2Name the tropism from the stimulus, then the plant part (shoot, root, tendril, pollen tube).
3State positive or negative by checking whether the part grows towards or away.
4In a definition, include 'growth movement', 'stimulus' and 'direction'.
5If asked how, explain auxin moving to the shaded side and unequal elongation.

Tropic Movements in Plants in real life

The idea, met in an everyday situation. Answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Roots around a dripper

Suppose a farmer in a dry district uses drip irrigation, with water dripping at the base of each plant, and when he digs one up he finds most of its roots crowded around the dripper instead of spreading widely.

Name the response and explain why the roots are crowded there.

Try it first, then show the solutionSolution

The soil near the dripper stays moist while the rest is dry.
Root tips grow faster towards the moist side.
This is positive hydrotropism.
With a steady water supply there, most new roots keep growing in that zone.

Answer: Positive hydrotropism: roots grew towards the moist soil around the dripper.

Memory hook: Hydro = water; roots chase water.

Potato sprouts in a cupboard

Suppose potatoes stored in a dark cupboard sprout, and the pale shoots all grow towards a thin crack of light under the cupboard door.

Name the response and explain how the shoots bend towards the crack.

Try it first, then show the solutionSolution

Light enters only through the crack, so it reaches each shoot from one side.
Auxin made at the shoot tip moves to the shaded side.
Cells on the shaded side elongate more than those on the lit side.
The shoots bend towards the light: positive phototropism.

Answer: Positive phototropism: auxin on the shaded side makes it grow more, so the shoots bend towards the crack of light.

Memory hook: Shoots follow the light, even in a cupboard.

Tricks to remember Tropic Movements in Plants

Short memory aids. Say each one aloud once, then use it on a question the same day.

Ph-G-H-Th-Ch = Light, Earth, Water, Touch, Chemical
Photo = light, Geo = Earth (gravity), Hydro = water, Thigmo = touch, Chemo = chemical.
Use it when: Matching tropism to stimulus.
Roots go down to the ground water
Roots are positive for the two 'down there' stimuli: gravity and water.
Use it when: Signs of root responses.
Auxin hides in the shade
Auxin runs from the light to the shaded side; the shaded side grows longer.
Use it when: Explaining phototropism.

Tropic Movements in Plants: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Match the stimulus · 1 mark · MCQBoard level

The growth of a pollen tube through the style towards the ovule is an example of:
(a) hydrotropism (b) thigmotropism (c) chemotropism (d) geotropism
(A tropism-stimulus table was asked in 2025.)

Try it first, then show the solutionSolution

The pollen tube is guided by chemicals from the ovule: chemotropism.

Answer: (c) chemotropism.

Example 2: Which side grows faster? · 3 marks · Short answerBoard level

A gourd tendril touches a bamboo pole on its left side and, over a few days, curls to the left around the pole. (a) Which side of the tendril grows faster: the side touching the pole or the outer side? (b) Explain why this makes it curl round the pole. (c) Why does a tendril that never touches a support stay fairly straight? (A climbing-plant case was asked in 2024.)

Try it first, then show the solutionSolution

(a) The outer side, away from the pole (1 mark).
(b) Unequal growth: the outer side lengthens more than the touching side, so the tendril bends towards and coils round the support; this is thigmotropism (1 mark).
(c) Without a touch stimulus on one side, both sides grow about equally, so it does not curl (1 mark).

Answer: (a) The outer side. (b) Faster growth on the outer side bends the tendril round the pole (thigmotropism). (c) No one-sided touch, so growth stays even.

Example 3: One stimulus, opposite responses · 2 marks · Short answerHarder board level

A seedling laid on its side has its root bending down and its shoot bending up, both responding to gravity. Explain how auxin can cause these opposite responses.

Try it first, then show the solutionSolution

Gravity makes auxin collect on the lower side of both the root and the shoot (1 mark).
In the shoot, more auxin speeds elongation, so the lower side grows more and the shoot bends up (negative geotropism); in the root, more auxin slows elongation, so the upper side grows more and the root bends down (positive geotropism) (1 mark).

Answer: Auxin gathers on the lower side; it speeds growth in the shoot (bends up) but slows it in the root (bends down).

Example 4: Collar or clear cap · 3 marks · Short answerHarder board level

Two oat seedlings are lit from the left. Seedling A has a foil collar around the stem 1 cm below the tip, leaving the tip exposed. Seedling B has a transparent cap over its tip. Predict what happens to each and explain.

Try it first, then show the solutionSolution

A bends towards the light, because its tip is still exposed to light (1 mark).
B also bends towards the light, because the transparent cap lets light reach the tip (1 mark).
The tip senses one-sided light and sends auxin down the shaded side; neither the collar below the tip nor a clear cap prevents this (1 mark).

Answer: Both bend towards the light, since in each the tip can still sense light and redistribute auxin.

Example 5: Measuring the bend · 3 marks · Case-basedHOTS / competency

Suppose, in a shoot lit from one side, cells on the shaded side measure 60 µm long and cells on the lit side measure 40 µm. (a) How many times longer are the shaded-side cells? (b) In which direction does the shoot bend? (c) Name the hormone responsible and where it is made.

Try it first, then show the solutionSolution

(a) 60 ÷ 40 = 1.5 times (1 mark).
(b) Towards the lit side, because the longer shaded side pushes the shoot over (1 mark).
(c) Auxin, made at the shoot tip (1 mark).

Answer: (a) 1.5 times. (b) Towards the light. (c) Auxin, from the shoot tip.

Example 6: Seedling in space · 2 marks · Short answerHOTS / competency

Suppose bean seeds are germinated in a dark box on board a space station, where there is almost no gravity. Predict how the root and shoot would grow, and give a reason.

Try it first, then show the solutionSolution

Without gravity or light to give direction, root and shoot cannot show geotropism or phototropism (1 mark).
They would grow in random, irregular directions (roots may still grow towards a moist surface by hydrotropism) (1 mark).

Answer: Roots and shoots grow in random directions because no one-sided stimulus guides them.

Where students lose marks in Tropic Movements in Plants

The slips examiners see most often, and what to write instead.

Mistake: Phototropism written for a climbing pea
CISCE examiners' comments (2024): candidates wrote phototropism for pea plants using a support, missed the keywords touch stimulus and growth movement in the definition, and named the structure as stem, vine or creeper instead of tendril.
Do this: Coiling around a support = touch = thigmotropism; the structure is a tendril.
Usually costs: 1-2 marks.
Mistake: Leaving 'growth' out of the definition
A tropism is a growth movement; without the word, the definition could describe any movement.
Do this: Write 'directional growth movement in response to a stimulus'.
Usually costs: 1 mark.
Mistake: Reversing signs for the shoot
Shoots grow up against gravity, so they are negatively geotropic, not positively.
Do this: Towards the stimulus = positive; away = negative.
Usually costs: 1 mark.
Mistake: Auxin on the lit side
Students guess that the lit side 'grows towards' the light; the shaded side actually grows faster.
Do this: Auxin moves to the shaded side; that side elongates more.
Usually costs: 1 mark.

Exam tips

Stimulus first, then tropism, then plant part, then sign.
Tendril = thigmotropism; pollen tube = chemotropism.
Definition: growth movement + stimulus + direction.
Auxin on the shaded side; shaded side grows longer.

Practice questions on Tropic Movements in Plants

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · MCQBoard level
A tropic movement is:
(a) a quick, reversible movement (b) a directional growth movement in response to a stimulus (c) movement of the whole plant (d) movement caused only by light
Hint
Growth and direction.
Answer
(b).
Q2 · 1 mark · Very short answerBoard level
A root in a dark pot of evenly moist soil still grows straight down. Name the stimulus guiding it and the tropism shown.
Hint
No light, no dry patch: what is left?
Answer
Gravity; positive geotropism.
Q3 · 1 mark · Assertion-reasonHarder board level
Assertion (A): A shoot lit from one side bends towards the light.
Reason (R): Auxin accumulates on the lit side and makes those cells elongate more.
(a) (A) is true and (R) is false.
(b) (A) is false and (R) is true.
(c) Both (A) and (R) are true, and (R) is the correct explanation of (A).
(d) Both (A) and (R) are true, but (R) is not the correct explanation of (A).
Hint
Which side gets the auxin?
Answer
(a). Auxin moves to the shaded side.
Q4 · 2 marks · Short answerHarder board level
Define phototropism and state the type of phototropism shown by roots.
Hint
Growth, light, direction.
Answer
Phototropism is the directional growth movement of a plant part in response to light. Roots show negative phototropism (they grow away from light).
Q5 · 2 marks · Short answerHarder board level
State how each tropism helps the plant: (a) positive geotropism of roots; (b) chemotropism of the pollen tube.
Hint
Anchorage; fertilisation.
Answer
(a) Roots grow down into the soil for anchorage and absorption of water and minerals. (b) The pollen tube reaches the ovule and delivers male gametes for fertilisation.
Q6 · 2 marks · Short answerHarder board level
Why is the folding of touch-me-not leaves not called thigmotropism?
Hint
Growth? Direction?
Answer
It is a quick, reversible movement caused by changes in turgor, not growth, and it does not depend on the direction of the touch, so it is not a tropic movement.
Q7 · 2 marks · Short answerHarder board level
What is a clinostat, and what does a seedling growing on a rotating clinostat show?
Hint
Equal stimulus all round.
Answer
A slowly rotating stand that turns the seedling so a stimulus such as gravity acts equally on all sides; the seedling grows without bending, showing that a one-sided stimulus causes tropic bending.
Q8 · 3 marks · Case-basedHOTS / competency
Read and answer.
Suppose a potted bean plant is kept in a box with a single hole on its right side, and after three days its shoot tip points to the hole while its root has grown straight down.
(a) Name the two tropisms seen. (1)
(b) State whether each is positive or negative. (1)
(c) Predict the shoot's shape if the hole were moved to the left side for the next three days. (1)
Hint
Two stimuli, then reverse one.
Answer
(a) Phototropism (shoot) and geotropism (root). (b) Shoot: positive phototropism; root: positive geotropism. (c) The new growth at the top bends to the left, giving an S-shaped or zig-zag shoot.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.What is the stimulus in geotropism?Show answer
Gravity.
2.Which plant part shows thigmotropism?Show answer
Tendrils (of pea, cucumber, grapevine).
3.Is a shoot positively or negatively geotropic?Show answer
Negatively.
4.Name the hormone that causes phototropic bending.Show answer
Auxin.
5.Name the tropism of a pollen tube.Show answer
Chemotropism.

Tropic Movements in Plants: frequently asked questions

Is gravitropism the same as geotropism?

Yes. Both mean the growth response to gravity; ICSE uses geotropism.

Do I need the details of experiments by Darwin or Went?

No. A basic understanding of the five tropisms with examples and the role of auxin is enough.

Are tropisms controlled by nerves?

No. Plants have no nerves; tropisms are coordinated chemically, mainly by auxin.

Can a root show phototropism?

Yes, but negatively: roots grow away from light.