Transpiration and Translocation
What Is Transpiration?
Transpiration is the loss of water vapour from a plant’s leaves, through tiny pores called stomata.
💡 Key Concept: Transpiration helps pull water up through the plant from the roots, transporting it to the leaves.
How Transpiration Works
1️ Water evaporates from cells inside the leaf
2️ Water vapour diffuses out through the stomata
3️ Water is pulled up through the xylem to replace it
4️ This creates a continuous stream of water = transpiration stream
Factors Affecting Transpiration Rate
Factor | Effect |
Light intensity | More light = more photosynthesis = stomata open = increased transpiration |
Temperature | Higher temp = faster evaporation = increased transpiration |
Humidity | Higher humidity = less transpiration (less diffusion gradient) |
Air movement (wind) | Wind removes water vapour = increases transpiration |
💡 Stomata play a key role – they open for gas exchange and close to reduce water loss.
What Is Translocation?
Translocation is the movement of sugars (mainly sucrose) and other dissolved substances around the plant in the phloem.
🔹 Features of Translocation:
✔ Transport is bidirectional (up and down)
✔ Moves sugars from source (e.g. leaf) to sink (e.g. root or fruit)
✔ Supports growth, storage, and energy supply
Xylem vs Phloem – Quick Comparison
Feature | Xylem | Phloem |
Transports | Water and minerals | Sugars and amino acids |
Direction | One way (up) | Both directions |
Structure | Dead, hollow tubes | Living cells with sieve plates |
Process | Transpiration | Translocation |
Questions
- What is transpiration?
- Through which vessel does water travel in a plant?
- Name one factor that increases transpiration.
- What does the phloem transport?
- What is a ‘source’ and a ‘sink’ in translocation?
Summary
- Transpiration pulls water through the plant and is affected by environmental conditions.
- Translocation moves sugars through the phloem to support growth and storage.
- Both systems are essential for transport and survival in plants.