What is transpiration in plants?

Transpiration in botany is a plant's loss of water, mainly through the stomata of leaves. Stomata facilitate carbon dioxide intake and oxygen release during photosynthesis; transpiration is thus seen as an unavoidable side effect. Transpiration may provide the energy to transport water and help dissipate heat in sunlight, though these ideas are debated. Excessive transpiration can harm plants, retarding growth and causing death by dehydration when water loss surpasses intake. Stephen Hales first measured transpiration, finding that plants emit significant water vapor from their leaves, encouraging a continuous flow of water and nutrients from the roots. As much as 99% of water taken in by a plant's roots is released as water vapor. Stomata regulate transpiration by opening and closing in response to environmental cues. Adaptations like smaller leaves, waxy cuticles, and alternative photosynthetic pathways also help reduce water loss.

Why do plants need to transpire?

Plants transpire because the stomata in their leaves must open to allow carbon dioxide to enter for photosynthesis and oxygen to exit. Transpiration is the process where plants lose water, mainly through the stomata of leaves. While generally unavoidable, transpiration may also help plants by providing the energy to transport water and aiding in heat dissipation in direct sunlight. However, excessive transpiration can be harmful, retarding growth and leading to dehydration if water loss exceeds intake. Plants have developed adaptations such as closing stomata, waxy cuticles, and alternative photosynthetic pathways to reduce water loss.

Which part of a plant is mainly responsible for transpiration?

The part of a plant mainly responsible for transpiration is the stomata of leaves . Stomata are small pores on leaf surfaces formed by two guard cells. These cells regulate the opening and closing of the stomata in response to environmental stimuli, thereby controlling the rate of transpiration to reduce water loss.

How does water move from the roots to the leaves during transpiration?

During transpiration, water ascends from the roots to the leaves via the xylem, a specialized vascular tissue. This process is primarily driven by the cohesion-tension theory , where water molecules are pulled up the plant due to a pressure gradient. Transpiration, the evaporation of water from the leaves, creates a tension or pull, drawing water up the xylem. The water molecules adhere to the walls of the xylem and cohere to each other, forming a continuous column from the roots to the leaves. This cohesion and adhesion allow water to be pulled upward against gravity, facilitating its movement from the roots to the leaves, where it is used in photosynthesis and other processes.

What factors can increase or decrease the rate of transpiration?

Transpiration, a plant's loss of water, happens mainly through the stomata of leaves. Several factors can influence the rate of transpiration: Light: Illumination tends to open stomata and increase transpiration. Water Supply: Ample water supply opens stomata and increases transpiration, while internal water deficit tends to close stomata and decrease it. Temperature: Optimum temperatures open stomata and increase transpiration. Many plants close their stomata under high temperatures to reduce evaporation. Wind: Transpiration increases with wind speed. Humidity: The evapotranspiration rate decreases with increasing humidity. Plants also have adaptations to reduce water loss, such as small leaves, waxy cuticles, and sunken stomata.

How does transpiration benefit both the plant and the environment?

Transpiration, the loss of water from a plant, mainly through leaf stomata, benefits both the plant and the environment. For the plant, transpiration aids in transporting water and dissolved nutrients from the roots to the rest of the plant. It can also help in cooling the plant through evaporation, preventing overheating in direct sunlight. For the environment, the water transpired by plants is released into the atmosphere, eventually returning to the surface as precipitation, contributing to "recycled rainfall". Transpiration helps maintain rainfall in continental regions , especially far from oceanic water sources.

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Introduction References & Edit History Related Topics

Images & Videos

Discover how water moves through plants, including osmosis and transpiration

Diagram showing the process of water movement through a tree, with labeled sections for absorption in the roots, cohesion in the trunk, and transpiration in the leaves. Insets illustrate water uptake by root hairs, upward movement through xylem, and evaporation from leaf stomata.

Compare differences in the leaf structures and environments of flowering dicots, ferns, pine trees, and cacti

Quick Facts

Key People:: Julius von Sachs; Stephen Hales; Henry Horatio Dixon

Related Topics:: stomate; What causes a drought?; transpiration pull

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transpiration

botany

Written by

Melissa Petruzzello

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Last updated

Oct. 10, 2026 •History

Top Questions

What is transpiration in plants?
Transpiration in botany is a plant's loss of water, mainly through the stomata of leaves. Stomata facilitate carbon dioxide intake and oxygen release during photosynthesis; transpiration is thus seen as an unavoidable side effect.

Transpiration may provide the energy to transport water and help dissipate heat in sunlight, though these ideas are debated. Excessive transpiration can harm plants, retarding growth and causing death by dehydration when water loss surpasses intake.

Stephen Hales first measured transpiration, finding that plants emit significant water vapor from their leaves, encouraging a continuous flow of water and nutrients from the roots. As much as 99% of water taken in by a plant's roots is released as water vapor.

Stomata regulate transpiration by opening and closing in response to environmental cues. Adaptations like smaller leaves, waxy cuticles, and alternative photosynthetic pathways also help reduce water loss.
2 Britannica Sources
1. photosynthesis: Water
2. transpiration
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
Why do plants need to transpire?
Plants transpire because the stomata in their leaves must open to allow carbon dioxide to enter for photosynthesis and oxygen to exit. Transpiration is the process where plants lose water, mainly through the stomata of leaves.

While generally unavoidable, transpiration may also help plants by providing the energy to transport water and aiding in heat dissipation in direct sunlight. However, excessive transpiration can be harmful, retarding growth and leading to dehydration if water loss exceeds intake. Plants have developed adaptations such as closing stomata, waxy cuticles, and alternative photosynthetic pathways to reduce water loss.
3 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
Which part of a plant is mainly responsible for transpiration?
The part of a plant mainly responsible for transpiration is the stomata of leaves. Stomata are small pores on leaf surfaces formed by two guard cells. These cells regulate the opening and closing of the stomata in response to environmental stimuli, thereby controlling the rate of transpiration to reduce water loss.
2 Britannica Sources
1. transpiration
2. angiosperm: Process of xylem transport
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
How does water move from the roots to the leaves during transpiration?
During transpiration, water ascends from the roots to the leaves via the xylem, a specialized vascular tissue. This process is primarily driven by the cohesion-tension theory, where water molecules are pulled up the plant due to a pressure gradient.

Transpiration, the evaporation of water from the leaves, creates a tension or pull, drawing water up the xylem. The water molecules adhere to the walls of the xylem and cohere to each other, forming a continuous column from the roots to the leaves. This cohesion and adhesion allow water to be pulled upward against gravity, facilitating its movement from the roots to the leaves, where it is used in photosynthesis and other processes.
5 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
What factors can increase or decrease the rate of transpiration?
Transpiration, a plant's loss of water, happens mainly through the stomata of leaves. Several factors can influence the rate of transpiration:
- Light: Illumination tends to open stomata and increase transpiration.
- Water Supply: Ample water supply opens stomata and increases transpiration, while internal water deficit tends to close stomata and decrease it.
- Temperature: Optimum temperatures open stomata and increase transpiration. Many plants close their stomata under high temperatures to reduce evaporation.
- Wind: Transpiration increases with wind speed.
- Humidity: The evapotranspiration rate decreases with increasing humidity.
Plants also have adaptations to reduce water loss, such as small leaves, waxy cuticles, and sunken stomata.
5 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
How does transpiration benefit both the plant and the environment?
Transpiration, the loss of water from a plant, mainly through leaf stomata, benefits both the plant and the environment. For the plant, transpiration aids in transporting water and dissolved nutrients from the roots to the rest of the plant. It can also help in cooling the plant through evaporation, preventing overheating in direct sunlight.

For the environment, the water transpired by plants is released into the atmosphere, eventually returning to the surface as precipitation, contributing to "recycled rainfall". Transpiration helps maintain rainfall in continental regions, especially far from oceanic water sources.
5 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

transpiration, in botany, a plant’s loss of water, mainly through the stomata of leaves. Stomatal openings are necessary to admit carbon dioxide to the leaf interior and to allow oxygen to escape during photosynthesis. Hence, transpiration is generally considered to be merely an unavoidable phenomenon that accompanies the real functions of the stomata. It has been proposed that transpiration provides the energy to transport water in the plant and may aid in heat dissipation in direct sunlight (by cooling through evaporation of water), though these theories have been challenged. Excessive transpiration can be extremely injurious to a plant. When water loss exceeds water intake, it can retard the plant’s growth and ultimately lead to death by dehydration.

Transpiration was first measured by Stephen Hales (1677–1761), an English botanist and physiologist. He noticed that plants “imbibe” and “perspire” significant amounts of water compared to animals and created a novel method for measuring the emission of water vapour by plants. He found that transpiration occurred from the leaves and that this process encouraged a continuous upward flow of water and dissolved nutrients from the roots. Modern research has shown that as much as 99 percent of the water taken in by the roots of a plant is released into the air as water vapour.

Leaf stomata are the primary sites of transpiration and consist of two guard cells that form a small pore on the surfaces of leaves. The guard cells control the opening and closing of the stomata in response to various environmental stimuli and can regulate the rate of transpiration to reduce water loss. Darkness and internal water deficit tend to close stomata and decrease transpiration; illumination, ample water supply, and optimum temperature open stomata and increase transpiration. Many plants close their stomata under high temperature conditions to reduce evaporation or under high concentrations of carbon dioxide gas, when the plant likely has sufficient quantities for photosynthesis.

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Water and its Varying Forms

A number of other adaptations also help to reduce water loss from transpiration. Physically, plants that live in areas with low humidity commonly have leaves with less surface area so that evaporation is limited. Conversely, plants in humid areas, especially those in low light conditions like understory vegetation, may have large leaves because the need for adequate sunlight is heightened and the risk of detrimental water loss is low. Many desert plants have minute leaves that are deciduous during drought periods, which nearly eliminates water loss during the dry season, and cacti lack leaves altogether. Waxy cuticles, trichomes (leaf hairs), sunken stomata, and other leaf adaptations also help reduce transpiration rates by keeping the leaf surface cool or protecting it from air currents that increase evaporation. Finally, some plants have evolved alternative photosynthetic pathways, like crassulacean acid metabolism (CAM), to minimize transpiration losses. These plants, including many succulents, open their stomata at night to take in carbon dioxide and close them during the day when conditions are commonly hot and dry.

Melissa Petruzzello

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