Experiment No 9 i Preparation of temporary mount

Experiment No. 9 (i) Preparation of temporary mount of leaf epidermis to study the structure of stomata (i) Measurement of transpiration rate using Ganong’s potometer

Temporary mount of stomata Stomata • This is not the exact image. • The dark dots represent stomatal pore surrounded by two bean shaped guard cells. 1. Peel can be taken from either surface as Aloe vera is a monocot( equal distribution of stomata) 2. Place a drop of water on the epidermal peel kept on the slide and visualize under the microscope

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

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 CO 2 and O 2 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 q There is a difference in distribution of stomata in monocots and dicots. q Monocots(equal no. of stomata on both adaxial and abaxial surfaces) q Dicots(More no. of stomata on abaxial surface(lower).

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

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

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.

Points to remember… • Ganong’s potometer 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.

Calculations •