Transpiration vs Translocation — Difference (with Table & FAQs)
Transpiration vs Translocation compared side by side — a 6-row comparison table, 4 key points and 7 exam FAQs. Class 10 Biology, free and no sign-up.
TL;DR: Transpiration vs Translocation compared side by side — a 6-row comparison table, 4 key points and 7 exam FAQs. Class 10 Biology, free and no sign-up.
Written & reviewed by the Syllab.in Academic Team (CBSE/NCERT subject experts) · Updated
The main difference between Transpiration and Translocation: Transpiration is water loss from leaves into atmosphere. Translocation is movement of food through phloem to all plant parts.
Transpiration vs Translocation — Comparison Table
| Basis | Transpiration | Translocation |
|---|---|---|
| Substance | Water vapor | Sugar and nutrients |
| Vessel | Through leaves into air | Through phloem |
| Direction | Unidirectional, upward and out | Bidirectional, as needed |
| Requires Energy | No, passive process | Yes, active transport |
| Purpose | Cooling, water uptake | Distribution of food |
| Rate | Higher in hot, dry conditions | Constant throughout day |
Key Points
- Transpiration pulls water up from roots
- Translocation distributes photosynthetic products
- Both are essential plant processes
- Transpiration creates water shortage in hot weather
Transpiration — losing water on purpose
Transpiration is the loss of water in the form of vapour from the aerial parts of a plant, mainly the leaves. Most of it escapes through tiny pores called stomata, each guarded by a pair of bean-shaped guard cells that open the pore when they swell with water and close it when they lose water.
It sounds wasteful — a large tree can lose hundreds of litres a day — but the plant gains three things from it. It creates the suction that pulls water up from the roots, it cools the leaf in the way sweating cools you, and it carries dissolved minerals upward with the water stream.
Translocation — moving food where it is needed
Translocation is the transport of the soluble products of photosynthesis — mainly sucrose, along with amino acids — from where they are made to where they are needed. It happens in the phloem, and unlike transpiration it costs the plant energy in the form of ATP.
The tissue that supplies the food is called the source, usually a green leaf. The part that receives it is the sink — a root, a growing shoot tip, a developing fruit or a storage organ. Because sinks exist above and below the leaves, translocation moves food both upward and downward, which is the detail students most often get wrong.
Xylem versus phloem — the two transport tissues
Almost every question on this topic reduces to knowing which tissue does what. Learn these as a contrasting pair.
- Xylem carries water and dissolved minerals. Phloem carries prepared food (sucrose).
- Xylem moves material only upward, from root to leaf. Phloem moves food in both directions, source to sink.
- Xylem is made of dead cells — tracheids and vessels with no living contents, which is why it forms hollow tubes. Phloem is made of living cells — sieve tubes and their companion cells.
- Xylem transport is passive: no energy is spent, because transpiration pull does the work. Phloem transport is active and needs ATP.
- Xylem elements are lignified for strength; phloem sieve tubes have perforated sieve plates that let material pass between cells.
How transpiration pull actually lifts water
As water evaporates from the leaf surface, it leaves the cells there slightly short of water. That creates a suction, and because water molecules stick to one another (cohesion) and to the xylem walls (adhesion), the whole column of water in the xylem is pulled upward as one continuous thread.
This suction force is called transpiration pull, and it is strong enough to raise water to the top of the tallest trees without the plant spending any energy. It is the reason transpiration is described as a necessary evil rather than simply a loss.
What changes the rate of transpiration
The factors mirror those for evaporation, because transpiration is evaporation happening through a leaf.
- Temperature — higher temperature speeds it up.
- Humidity — high humidity slows it down, since the surrounding air already holds water vapour.
- Wind speed — moving air carries vapour away and speeds it up.
- Light — stomata open in light and close in the dark, so transpiration is much higher during the day.
- Available soil water — a plant short of water closes its stomata to conserve what it has.
Transpiration vs Translocation — Worked Examples
- Water droplets inside a polythene bag tied over a leafy shoot — Transpiration. Water vapour left the leaves and condensed on the cool plastic.
- Sugar reaching a developing mango — Translocation. The fruit is a sink; sucrose made in the leaves travels to it through the phloem.
- A wilting plant at noon — Transpiration is outpacing absorption, so the cells lose turgor. The plant closes its stomata to slow the loss.
- A potato tuber swelling underground — Translocation moving food downward to a storage sink — proof that phloem transport is not one-directional.
Common Mistakes Students Make
- Saying translocation happens in the xylem. Food moves in the phloem; the xylem carries water and minerals.
- Writing that translocation only moves food downwards. It moves to any sink, above or below the leaves.
- Calling transpiration simply a waste of water. It generates the transpiration pull that lifts water and it cools the plant.
- Forgetting that phloem transport needs energy while xylem transport does not.
- Confusing guttation with transpiration — guttation is the loss of liquid water droplets from leaf margins, not water vapour.
Diagrams
Where This Shows Up in Real Life
Why farmers water at dawn or dusk
Transpiration peaks in the middle of a hot, bright, breezy day, exactly when evaporation from the soil is also highest. Irrigating at noon means much of the water is lost before roots can take it up. Watering at dawn or after sunset, when stomata are closing and the air is cooler and more humid, puts far more of it into the plant. The same reasoning underlies drip irrigation, which delivers water directly to the root zone instead of wetting the whole field surface.
Why a transplanted sapling wilts
Digging up a plant tears the fine root hairs that do almost all the absorbing. The leaves keep transpiring at the old rate while uptake has collapsed, so the plant loses turgor and droops. Gardeners counter this by removing some leaves to cut the transpiring surface, shading the sapling for a few days, and watering generously — all three reduce the gap between loss and uptake until new root hairs grow.
Ringing, and the proof that phloem carries food
If a complete ring of bark — which contains the phloem — is stripped from a tree trunk, the tissue just above the ring swells while the roots below slowly starve and the tree eventually dies. Water still reaches the leaves because the xylem is deeper and untouched, so the tree stays green for a while. This classic experiment demonstrates two things at once: food travels downward through the phloem, and water travels upward through the xylem.
Why forests bring rain
A single large tree can transpire hundreds of litres a day, and a whole forest returns an enormous volume of water vapour to the atmosphere. That vapour condenses and falls as rain, sometimes far downwind. It is a direct link between deforestation and reduced rainfall, and it is why transpiration matters at the scale of the water cycle, not just the individual plant.
Board-Style Questions with Model Answers
Differentiate between transpiration and translocation. (3 marks)
Transpiration is the loss of water in the form of vapour from the aerial parts of a plant, chiefly through the stomata of the leaves. It moves water and dissolved minerals upward only, through the xylem, which is made of dead cells, and it is a passive process requiring no energy from the plant. Translocation is the transport of the soluble products of photosynthesis, mainly sucrose, from the source where they are made to the sinks where they are used or stored. It occurs in the phloem, which is made of living sieve tubes and companion cells, it can move material both upward and downward, and it is an active process that consumes ATP.
Explain how water rises from the roots to the top of a tall tree. (5 marks)
Water enters the root hairs by osmosis, because the concentration of solutes inside the root hair cell is higher than in the surrounding soil water. It then passes cell to cell across the cortex and into the xylem vessels, which form continuous hollow tubes running the whole height of the plant. At the top, water evaporates from the surface of the mesophyll cells and escapes through the stomata as transpiration. This evaporation leaves those cells short of water and creates a suction called transpiration pull. Because water molecules are strongly attracted to one another (cohesion) and to the walls of the xylem (adhesion), the entire column of water behaves as one continuous thread and is drawn upward as a unit. Root pressure also contributes, particularly at night when transpiration is low, but transpiration pull is the main force and it requires no energy from the plant.
What is translocation? Explain the roles of source and sink. (3 marks)
Translocation is the transport of soluble food, mainly sucrose along with amino acids, through the phloem from where it is produced to where it is needed. The source is the part that supplies the food, normally a photosynthesising green leaf, and food is actively loaded into the phloem there using energy from ATP. The sink is any part that consumes or stores the food — roots, growing shoot tips, flowers, developing fruits and storage organs such as tubers. Because sinks exist both above and below the leaves, translocation can move material upward or downward, unlike the strictly upward flow in the xylem.
Why is transpiration described as a necessary evil? (3 marks)
It is called an evil because the plant loses an enormous quantity of water, far more than it uses for photosynthesis, and in dry conditions this loss can cause wilting and even death. It is called necessary because the plant gains three important things from it. First, the evaporation creates transpiration pull, the suction that raises water and dissolved minerals from the roots to the highest leaves without the plant spending energy. Second, the evaporation cools the leaf surface, protecting it from overheating in strong sunlight. Third, the upward water stream carries dissolved mineral ions from the soil to every part of the plant.
Compare the structure and function of xylem and phloem. (5 marks)
Xylem consists of tracheids and vessels, which are dead cells with thickened lignified walls and no living contents, so they form continuous hollow tubes; it also contains xylem fibres and parenchyma. It transports water and dissolved minerals in one direction only, upward from root to leaf, and the movement is passive, driven by transpiration pull with no expenditure of energy. Its lignified walls additionally provide mechanical support to the plant. Phloem consists of sieve tubes with perforated sieve plates, companion cells, phloem fibres and parenchyma, and its conducting cells are living. It transports prepared food, mainly sucrose, from source to sink in either direction, and the movement is active, requiring ATP for loading and unloading. Together the two tissues form the vascular bundle.
Assertion–Reason Questions (CBSE Format)
For each question choose: (a) both A and R are true and R is the correct explanation of A; (b) both are true but R is not the correct explanation; (c) A is true but R is false; (d) A is false but R is true.
1. Assertion (A): Transpiration helps in the upward movement of water in plants.
Reason (R): Evaporation of water from leaves creates a suction called transpiration pull.
Answer: (a) — Both are true and the reason explains the assertion. Evaporation at the leaf surface generates the suction that draws the continuous water column up the xylem.
2. Assertion (A): Translocation requires energy while xylem transport does not.
Reason (R): Phloem loading and unloading are active processes that consume ATP.
Answer: (a) — Both are true and correctly linked. Xylem transport is driven passively by transpiration pull, whereas phloem transport needs metabolic energy.
3. Assertion (A): A tree dies if a complete ring of bark is removed from its trunk.
Reason (R): The xylem is removed along with the bark, so water cannot reach the leaves.
Answer: (c) — The assertion is true but the reason is false. Ringing removes the phloem, which lies in the bark; the xylem is deeper and remains intact, so water still rises — the tree starves because food cannot reach the roots.
4. Assertion (A): Transpiration decreases when the humidity of the air increases.
Reason (R): A smaller difference in water-vapour concentration between leaf and air slows diffusion.
Answer: (a) — Both are true and correctly linked. Transpiration depends on the vapour gradient, and humid air weakens that gradient.
Quick Self-Check
Q1. Food prepared in the leaves is transported through the:
- A. Xylem
- B. Phloem
- C. Stomata
- D. Root hair
Answer: B. Phloem — Phloem carries the soluble products of photosynthesis from source to sink. Xylem carries water and minerals.
Q2. Transpiration mainly takes place through:
- A. Roots
- B. Stomata
- C. Xylem vessels
- D. Sieve tubes
Answer: B. Stomata — Stomata are the pores on leaves through which most water vapour escapes.
Q3. Which statement about xylem is correct?
- A. It is made of living cells
- B. It transports food
- C. It is made of dead cells and moves water upward
- D. It requires ATP
Answer: C. It is made of dead cells and moves water upward — Xylem consists of dead, lignified tracheids and vessels, and moves water upward passively using transpiration pull.
Q4. Translocation requires energy because:
- A. Food is heavier than water
- B. It is an active process using ATP
- C. Phloem cells are dead
- D. It works against transpiration pull
Answer: B. It is an active process using ATP — Phloem loading and unloading are active processes that consume ATP, unlike passive xylem transport.
Key Terms Glossary
- Transpiration
- The loss of water as vapour from the aerial parts of a plant, mainly through stomata.
- Translocation
- The transport of soluble food, mainly sucrose, through the phloem from source to sink.
- Xylem
- Dead, lignified conducting tissue carrying water and minerals upward only. Transport is passive.
- Phloem
- Living conducting tissue carrying prepared food in both directions. Transport is active and needs ATP.
- Stomata
- Tiny pores, mainly on leaves, through which gases and water vapour pass. Each is bounded by two guard cells.
- Guard cells
- Bean-shaped cells that open the stomatal pore when turgid and close it when they lose water.
- Transpiration pull
- The suction generated by evaporation at the leaf surface, which lifts the water column up the xylem.
- Cohesion
- The mutual attraction between water molecules that keeps the xylem water column continuous.
- Adhesion
- The attraction between water molecules and the xylem walls, helping the column resist breaking.
- Source
- The plant part that supplies food for translocation, normally a photosynthesising leaf.
- Sink
- Any plant part that uses or stores translocated food — roots, fruits, growing tips, tubers.
- Guttation
- Loss of LIQUID water droplets from leaf margins, usually at night. Not the same as transpiration.
One-Minute Revision
- TRANSPIRATION = water vapour OUT through stomata. TRANSLOCATION = food moved through phloem.
- XYLEM: water + minerals, UPWARD only, DEAD cells, PASSIVE (no ATP).
- PHLOEM: food (sucrose), BOTH directions source→sink, LIVING cells, ACTIVE (needs ATP).
- Transpiration pull does the lifting — cohesion and adhesion keep the water column unbroken.
- Rate rises with temperature, wind and light; FALLS with humidity and low soil water.
- Called a NECESSARY EVIL: huge water loss, but it lifts water, cools the leaf and carries minerals.
- Ringing kills a tree because it removes PHLOEM (in the bark). Xylem is deeper and survives.
- Guttation = liquid droplets at leaf margins. Transpiration = water VAPOUR. Do not mix them up.
Syllabus reference: NCERT Class 10 Science, Chapter 6 — Life Processes (transport in plants); introduced in Class 7, Chapter 11.
Frequently Asked Questions
What is the difference between transpiration and translocation?
Transpiration is the loss of water vapour from the aerial parts of a plant (mainly the leaves) through stomata. Translocation is the transport of food (sugars made in the leaves) to other parts of the plant through the phloem.
Which tissues are involved in transpiration and translocation?
Transpiration involves water moving up through the xylem and evaporating from the leaves. Translocation moves prepared food through the phloem.
Does translocation move food only downwards?
No. Translocation moves food from the source (leaves) to sinks such as roots, fruits and growing tips — it can travel both upward and downward as the plant needs.
Is transpiration a necessary evil?
Yes, and that is the phrase textbooks use. The plant loses a great deal of water, which is the 'evil' part. But the loss generates the transpiration pull that raises water from the roots, cools the leaves, and carries dissolved minerals upward — so the plant cannot do without it.
What is the difference between the source and the sink in translocation?
The source is the part that makes or releases food, usually a photosynthesising leaf. The sink is any part that uses or stores it — roots, growing tips, flowers, fruits and storage organs. Food always moves from source to sink, which can be in any direction.
Why does transpiration decrease in humid weather?
The surrounding air already holds a lot of water vapour, so the difference in water-vapour concentration between the leaf and the air is small. With a weaker gradient, less water evaporates from the leaf surface.
What is guttation and how is it different from transpiration?
Guttation is the loss of liquid water as droplets from the margins of leaves, usually at night or early morning when humidity is high and root pressure is strong. Transpiration is the loss of water as vapour, mainly through stomata during the day.