- The flow of water into a root, up the stem (xylem) and out of the leaves.
- Most transpiration happens at the leaves
You will have to know these structures and their roles in transpiration in I/GCSE Biology
- There are cells on the surface of plant roots which grow into hairs and stick out of the soil.
- Each part of the root will contain millions of microscopic hairs.
- This gives the plant a large surface area for absorbing water and mineral ions from the soil.
- The concentration of mineral ions is usually higher in the root cells than in the soil around them, so mineral ions are absorbed by active transport. Water, however, is absorbed by my osmosis.
- Phloem is long elongated living cells with small pores in the end walls to all0w things to flow through.
- They transport food substances (sucrose) made in the leaves to the rest of the plant for immediate use (e.g. in growing regions) or for storage.
- This process is called translocation and it requires energy from respiration, Transport happens in both directions.
- Xylem tubes are made of dead cells joined end to end with no cell walls between them and a hole down the middle. They are strengthened with a material called lignin.
- They carry water and mineral ions from the roots to the stem and leaves.
- The movement of water from the roots, through the xylem and out of the leaves is called transpiration stream.
- Ions are moved against their concentration gradient into the plant's roots by active transport.
- This makes the water potential in the roots lower.
- Water moves into the xylem joining the transpiration stream.
- As this moves up the xylem, from the roots all the way up to the leaves.
- This movement of water out of the leaves pulls on the water in the transpiration stream.
- Water evaporates in the leaves, leaving through the stomata.
- Rate of Transpiration = distance moved by bubble (cm) / time taken (mins)
Drafted by Catrina (Biology)