Plant Physiology: Transpiration Quiz

Plant Physiology: Transpiration

• Transpiration is the loss of water from plants in the form of vapor.
• It occurs in two phases: evaporation and diffusion.
• Evaporation of water happens within mesophyll cells, which border intercellular spaces.
• Diffusion is the movement of water vapor due to high temperatures.
• 90% of the water absorbed by plant roots is used in transpiration.
• The remaining 10% is used in chemical reactions and plant tissue processes.

Importance of Transpiration

• Transpiration controls water movement in plants, which depends on this process.
• It supplies water for photosynthesis
• It transports minerals from roots for biosynthesis within leaves
• Evaporation of water through transpiration cools the plant

Evaporating Surfaces

• Key areas for water loss include mesophyll cells that border intercellular air spaces.
• Surfaces of epidermal cells are also evaporating sites.
• Guard cells which form the stomata apparatus are also sites of water evaporation.

Leaf Structure

• A leaf's structure includes the cuticle, upper epidermis, palisade mesophyll, bundle sheath, xylem, phloem, lower epidermis, spongy mesophyll, guard cells, and stomata.
• Diagram shows these locations in the leaf.

General Mechanism of Water Movement

• Plants have a vascular system that connects roots to shoots.
• Water loss occurs through transpiration.
• Stomata control the balance between water absorption and transpiration.

General Mechanism of Water Movement (Continued)

• Water loss occurs from leaves when the stomata are open.
• This process is known as transpiration.
• Transpiration creates a pressure gradient leading to the movement of water into cells.
• Water can be lost through the cuticle, lenticels, and stomata structures.

Cuticular Transpiration

• The cuticle is a layer of wax covering the epidermis of leaves and herbaceous stems.
• It is designed to regulate transpiration.
• Some water loss can still happen through the cuticle.
• This accounts for approximately 20% of the total water loss in a plant.

Lenticular Transpiration

• Water vapor loss occurs via lenticels in woody stems and fruits.
• It accounts for 1-5% of total water loss in a plant.

Stomatal Transpiration

• Stomata are small pores on the epidermis of green leaves.
• Opening and closing of stomata are controlled by guard cells.
• Stomatal activity is responsible for most water loss (80-90%).

Stomatal Transpiration (Continued)

• Transpiration rates are linked to photosynthesis rates.
• To absorb carbon dioxide during photosynthesis plants must open stomata.
• This exposes the plant to water loss through stomata.

Control of Water Movement

• Stomata opening initiates evaporation and water loss, causing an increase in water flow.
• A feedback mechanism is a part of water movement control; the mechanisms includes root absorption, root temperature, and root aeration influencing transpiration rates.

Mechanism of Stomatal Action

• Each stoma is flanked by two guard cells capable of changing shape and size.
• Guard cells regulate the gap size between them.
• When guard cells intake water, they become turgid and swell, widening the gap between them.
• If the plant loses water, the guard cells become flaccid, causing the gap to shrink, preventing water loss.

Mechanism of Transpiration (Continued)

• Turgor pressure within mesophyll cells of leaves pushes water outwards through the cell walls.
• Water collects in intercellular spaces and diffuses out into the surrounding atmosphere.
• Closing stomata responds to a lack of soil water and reduces transpiration while limiting photosynthesis.

How Much Water Do Plants Transpire?

• During a growing season, leaves transpire significantly more water than their weight.
• An acre of corn can lose 3,000-4,000 gallons, and a large oak tree, 40,000 gallons of water daily/annually.

Factors Affecting Transpiration

• Temperature: Higher temperatures increase transpiration rates, especially during the growing season, and high temps can cause stomatal closure.
• Relative Humidity: Rising humidity is associated with lower transpiration rates. It is easier for water to evaporate into drier air.
• Wind/Air Movement: Increased air movement leads to higher transpiration rates, as saturated air is replaced by dryer surrounding air.
• Soil Moisture Availability: Plants cannot lose water rapidly if transpiration rates outpace their ability to replace the lost water from the soil..
• Type of Plant: Different plants have varying transpiration rates. Plants in arid regions conserve water by transpiring less.

Test your knowledge on transpiration, the vital process of water loss in plants. This quiz covers the mechanisms, importance, and key surface areas involved in transpiration. Understand how plants manage water movement and its role in photosynthesis and cooling.