ICSE Class 10 Biology: Transpiration in Plants Explained

Ever wonder why a leaf looks like it’s sweating on a hot day?

💡 In Simple Words: Transpiration is the way plants lose water through tiny holes in their leaves. It’s like a natural air‑conditioner that helps the plant stay cool and pull nutrients from the roots.

What is Transpiration?

Transpiration is the loss of water vapor from the aerial parts of a plant, mainly the leaves. The water comes from the soil, travels up through the plant, and then evaporates into the air.

Think of a plant as a straw that drinks water from the ground. The water climbs up the straw (the plant’s xylem – the tubes that carry water) and then sneaks out through tiny doors called stomata (singular: stoma). When the water leaves, it turns into vapor, just like steam from a kettle.

How Transpiration Happens – The Steps

Here’s the simple chain of events, broken down into bite‑size pieces:

• Water absorption: Roots soak up water from the soil.
• Upward transport: Water moves up the xylem thanks to capillary action and pressure differences.
• Stomatal opening: Light triggers the stomata to open, creating a gateway.
• Evaporation: Inside the leaf, water reaches the air spaces and turns into vapor.
• Diffusion: Water vapor diffuses out of the leaf and into the surrounding air.
• Cooling effect: The loss of water cools the leaf, much like sweating cools our skin.

Factors That Influence Transpiration

Just like we sweat more on a hot, windy day, plants change their water loss rate based on a few key factors.

Why Transpiration Matters for the Plant

• Uptake of minerals: As water climbs, it drags dissolved nutrients from the soil to the leaves.
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• Cooling: Evaporation removes excess heat, preventing leaf burn.
• Maintaining turgor: A steady flow of water keeps cells firm, helping the plant stay upright.
• Creating a pull: The loss of water creates a negative pressure (like sucking on a straw) that draws more water upward.

Quick Summary

• Transpiration = water vapor loss, mainly through stomata.
• Roots → xylem → leaf → stomata → air.
• Light, temperature, wind, and humidity control the rate.
• Helps transport nutrients, cools the plant, and maintains structure.

📝 Likely Exam Questions

1. Define transpiration.
   Answer: Transpiration is the loss of water vapor from the aerial parts of a plant, especially through stomata in the leaves.
2. List two factors that increase the rate of transpiration and explain why.
   Answer: Light intensity – it causes stomata to open, allowing more water to escape. Wind speed – moving air removes saturated vapor near the leaf surface, increasing the gradient for diffusion.
3. Explain how transpiration helps in the upward movement of water.
   Answer: As water evaporates from the leaf, it creates a negative pressure (tension) in the xylem, pulling more water up from the roots, similar to sucking on a straw.
4. Why is transpiration considered a cooling mechanism?
   Answer: The phase change from liquid water to vapor absorbs heat from the leaf surface, lowering its temperature.
5. Describe the role of stomata in transpiration.
   Answer: Stomata are microscopic pores on leaf surfaces that open to allow gas exchange. When open, they provide a pathway for water vapor to escape, driving transpiration.