Transpiration Process and Experiments

Transpiration

• Transpiration is the process of water loss in the form of water vapor from aerial plant parts.

Demonstration of Transpiration: Experiment 1

• Drops of water form on the inside of a plastic bag placed over a plant.
• No water collects on a plastic bag over an empty space.
• Water vapor from the plant saturates the plastic bag and condenses.

Demonstration of Transpiration: Experiment 2

• Experiment setups A and B showed water vapor condensation on the inner walls of bell jars.
• Cobalt chloride paper turned pink in setups A & B, indicating water vapor presence.
• No condensation or color change in setup C.
• The color change (pink) of cobalt chloride paper shows transpiration.

Kinds of Transpiration

• Stomatal Transpiration: Water vapor escapes through stomata (pores) in leaves.
• Cuticular Transpiration: Water loss occurs directly from the leaf's surface.
• Lenticular Transpiration: Water loss takes place through lenticels (pores) in stems.

Stomata

• Stomata are pores surrounded by guard cells.
• Stomata number can range from 1,000 to 10,000 per cm².

Mechanism of Stomatal Transpiration

• Water vapor saturates air spaces within spongy mesophyll.
• Water vapor diffuses into interconnected intercellular spaces and to the sub-stomatal space.
• Water then evaporates and diffuses out through stomata.
• Guard cells regulate stomatal opening and closing.

Experiment: Leaf Surface Transpiration

• Cobalt chloride paper on the lower leaf surface turns pink faster than the upper surface.
• This suggests more transpiration from the leaf's lower surface, attributed to more stomata.

Rate of Transpiration: Potometer Method

• A potometer measures water uptake (closely related to transpiration rate).
• Air bubbles move in a capillary tube as water is drawn.
• Factors affecting transpiration rate include light intensity, temperature, wind speed, humidity, CO2 levels, and atmospheric pressure.

Factors Affecting Transpiration Rate

• Light Intensity: Higher light intensity increases transpiration rate.
• Temperature: Higher temperature increases transpiration rate.
• Wind Velocity: Increased wind speeds increase transpiration.
• Humidity: Low humidity increases transpiration rate.
• Carbon Dioxide: Increased CO2 levels decrease transpiration rate.
• Atmospheric Pressure: Lower atmospheric pressure increases transpiration rate.

Adaptations in Plants to Control Transpiration

• Plants in dry climates have adaptations:
  • Rolled or folded leaves
  • Spines (instead of leaves)
  • Reduced stomata
  • Thick waxy cuticles

Significance of Transpiration

• Transpiration cools leaves.
• Creates a suction force pulling water up through the plant
• Promotes water uptake and nutrient absorption by roots, affecting plant growth.

Differences between Transpiration and Evaporation

• Transpiration: Water loss in vapor form from plants via stomata and lenticels.
• Evaporation: Water loss from any surface to the atmosphere as water vapor.

Guttation and Bleeding

• Guttation: Water loss as liquid from hydathodes in plants, most often at night following high humidity.
• Bleeding: Water loss from a cut plant stem, i.e., in form of sap.

Differences between Transpiration and Guttation

• Transpiration: Loss is water vapor.
• Guttation: Loss is liquid water.

Explore the fascinating process of transpiration, where plants lose water in the form of vapor. This quiz covers two experiments demonstrating transpiration and its different types, including stomatal, cuticular, and lenticular transpiration. Test your knowledge about how plants manage water loss!