Experiment No.9

1. Experiment No.9 Preparation of temporary mount of leaf epidermis to study the structure of stomata Measurement of transpiration rate using Ganong’spotometer

2. Temporary mount of stomata • This is not the exact image. • The dark dots represent stomatal pore surrounded by two bean shaped guard cells. Stomata • Peel can be taken from either surface as Aloe verais a monocot( equal distribution of stomata) • Place a drop of water on the epidermal peel kept on the slide and visualize under the microscope

3. Transverse section of leaf Structure of stomata Stomatal pore acts as a site for diffusion of gases in and out of leaf surface

4. Definitions • Transpiration is the process of water movement through a plant and its evaporation from aerial parts, such as from leaves but also from stems and flowers (termed as necessary evil as inevitable to the process of photosynthesis) • It occurs chiefly at the leaves while their stomata are open for the passage of CO2 and O2 during photosynthesis. • Basically of 3 types: i) Cuticular – Accounts for 10% of water loss through transpiration ii) Lenticular– Accounts for 1% water loss through transpiration iii) Stomatal - Accounts for 80-90% water loss through transpiration • There is a difference in distribution of stomata in monocots and dicots. • Monocots(equal no. of stomata on both adaxial and abaxial surfaces) • Dicots(More no. of stomata on abaxial surface(lower).

5. Uses of Transpiration • Provides a cooling effect to the plant • Enables mass flow of nutrients and minerals along with water to shoots and leaves from roots

6. Factors affecting the rate of transpiration • No. of leaves • No. of stomata • Temperature • Humidity • Intensity of sunlight • Wind • Water supply to the plant

7. Measurement of the rate of transpiration • Equipment used: Potometer(we would be using Ganong’s potometer) • A potometer( transpirometer) is a device used for measuring the rate of water uptake of a leafy shoot.

8. Points to remember… • Ganong’spotometer only measures the rate of water uptake ,it cannot give an idea of actual transpiration rate • Alterations to light intensity, wind and humidity should be avoided • Immediately after the twig it cut, immerse it under water to prevent entry of air to xylem vessels • Twig may not be active for long time. • Correct sealing by wax should be done to avoid any leakage.

9. Calculations