1. Xerophytes & Transpiration Factors

2. xerophytes A plant adapted to live in dry conditions
They have a range of adaptations to reduce the loss of water vapour by transpiration.
A plant adapted for survival in soil with a limited supply of water. Capillary water is absent from the surface horizons of the soil for extended periods of time. Some xerophytes, such as cacti and succulents, store water in their stems to survive extended periods of extreme drought. Cactus spines are modified leaves which provide protection against browsing animals. Because photosynthetic leaves are absent from most mature cactus plants, photosynthesis occurs within chloroplasts in the stems. In addition, cactus plants typically inhabit well-drained alluvial slopes and have shallow, surface roots to absorb the scant rainfall.

3. xerophytes Leaves Small to reduce the surface area
Thick to reduce surface area: volumes ratio

4. xerophytes
Sunken Stomata

5. xerophytes
Stomata
Set deep inside the leaf so that they are at the base of a depression full of water vapour
Some plants open their stomata at night to store and absorb CO2

6. xerophyte
Thick waxy cuticles
reduce water loss through the epidermis

7. Xerophytes Rolling up of leaves
Lower surface faces inside and traps humid air next to the stomata
Varies with conditions

8. Xerophytes Leaf hairs Trap damp air Reduces air movement
Cut down transpiration

9. Factors Affecting Transpiration

10. Potometer Measures the water absorption
Estimate the rate of transpiration
Air/water tight
Water transpired
Water entering to xylem

11. Factors affecting rate of transpiration
Light intensity:
Affects the opening and closing of the stomata
ROT
Indirect effect

12. Factors affecting rate of transpiration
Humidity:
Humid atmosphere
Contains a lot of H2O molecules
Reduction of the water potential gradient between the air spaces and atmosphere
ROT decreases
Low humidity increases ROT

13. Factors affecting rate of transpiration
Temperature:
Temperature
kinetic energy
Rate of diffusion through the stomata pores
Air is able to hold more water molecules at higher temperatures
ROT

14. Factors affecting rate of transpiration
Wind speed:
Still air makes the H2O molecules to accumulate around the stomata pores (leaves)
Reduces the H2O potential gradient and slows the ROT
Wind disperse H2O molecules
gradient in H2O potential ROT