8.3

Transpiration

12 flashcards to master Transpiration

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Definition Flip

What is transpiration?

Answer Flip

Transpiration is the process by which plants lose water in the form of water vapor from their leaves. This primarily occurs through the stomata, small pores on the leaf surface.

Example: A sunflower plant transpiring on a hot day.
Key Concept Flip

Describe the pathway of water vapor during transpiration.

Answer Flip

Water evaporates from the moist surfaces of mesophyll cells into the air spaces within the leaf. Then, the water vapor diffuses out of the leaf through the stomata into the surrounding air.

Example: Water moving from spongy mesophyll cells, through air spaces, and out of stomata in a spinach leaf.
Key Concept Flip

How does temperature affect the rate of transpiration?

Answer Flip

An increase in temperature increases the rate of transpiration. Higher temperatures cause water molecules to evaporate more quickly from the mesophyll cell surfaces.

Example: A desert plant will transpire more when temperatures increase above 40 degree C.
Key Concept Flip

How does wind speed affect the rate of transpiration?

Answer Flip

An increase in wind speed increases the rate of transpiration. Wind removes water vapor from around the leaf, maintaining a steeper concentration gradient.

Example: A tree in a windy area will transpire more than a tree in a sheltered area.
Key Concept Flip

Explain the relationship between leaf structure and water vapor loss.

Answer Flip

The large internal surface area of mesophyll cells and the size and number of stomata significantly influence water vapor loss. A larger surface area allows for more evaporation, and more stomata provide more exit points for water vapor.

Example: Plants with many stomata lose water quicker than plants with few stomata.
Key Concept Flip

Describe the 'transpiration pull' mechanism.

Answer Flip

As water molecules evaporate from the leaf (transpiration), it creates a 'pull' that draws water up the xylem from the roots. Water molecules are cohesive (held together) and adhesive (stick to xylem walls), forming a continuous column.

Example: Like sucking on a straw, water moves up a tall tree against gravity.
Key Concept Flip

Explain the effect of humidity on the rate of transpiration.

Answer Flip

Increased humidity *decreases* the rate of transpiration. High humidity reduces the water vapor concentration gradient between the leaf and the air, slowing down diffusion.

Example: Transpiration is lower on a humid, rainy day than on a dry, sunny day.
Definition Flip

What is wilting, and why does it occur?

Answer Flip

Wilting is the drooping of leaves and stems due to a lack of water in plant cells. It occurs when the rate of transpiration exceeds the rate of water uptake by the roots, leading to a loss of turgor pressure.

Example: A tomato plant wilting on a hot, dry day due to excessive water loss.
Key Concept Flip

How do plants control water loss through stomata?

Answer Flip

Plants control water loss by opening and closing stomata. Guard cells surrounding each stoma regulate its aperture in response to environmental factors like light intensity and water availability.

Example: Stomata typically close at night to conserve water when photosynthesis isn't occurring.
Key Concept Flip

Explain how water's cohesive properties contribute to transpiration.

Answer Flip

Cohesion, the attraction between water molecules, allows water to be drawn up the xylem as a continuous column. As water evaporates from the leaves, the cohesive forces pull more water up from the roots.

Example: This cohesion allows giant redwood trees to transport water from their roots to heights of over 100 meters.
Key Concept Flip

Describe how a potometer measures transpiration rate.

Answer Flip

A potometer is a device that measures the rate of water uptake by a plant shoot, which is assumed to be directly related to transpiration rate. The potometer measures how fast a bubble moves along a scale as water is absorbed by the plant.

Example: Using a potometer to compare transpiration rates of two different plant species.
Key Concept Flip

Explain the role of stomata in regulating transpiration and gas exchange.

Answer Flip

Stomata are pores on the leaf surface that facilitate both transpiration (water vapor loss) and gas exchange (carbon dioxide uptake for photosynthesis and oxygen release). The opening and closing of stomata represents a trade-off between these processes.

Example: When stomata are open, CO2 is exchanged, but the plant risks losing water through transpiration.

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8.2 Water uptake 8.4 Translocation

Key Questions: Transpiration

What is transpiration?

Transpiration is the process by which plants lose water in the form of water vapor from their leaves. This primarily occurs through the stomata, small pores on the leaf surface.

Example: A sunflower plant transpiring on a hot day.
What is wilting, and why does it occur?

Wilting is the drooping of leaves and stems due to a lack of water in plant cells. It occurs when the rate of transpiration exceeds the rate of water uptake by the roots, leading to a loss of turgor pressure.

Example: A tomato plant wilting on a hot, dry day due to excessive water loss.

About Transpiration (8.3)

These 12 flashcards cover everything you need to know about Transpiration for your Cambridge IGCSE Biology (0610) exam. Each card is designed based on the official syllabus requirements.

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