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Questions and Answers
What is the primary process by which plants lose water?
What is the primary process by which plants lose water?
Higher temperatures reduce the rate of evaporation in plants.
Higher temperatures reduce the rate of evaporation in plants.
False
What effect does wind have on water vapor concentration around stomata?
What effect does wind have on water vapor concentration around stomata?
It reduces concentration by carrying away water vapor.
Plants adapt to reduce water loss by having an impermeable ________ cuticle.
Plants adapt to reduce water loss by having an impermeable ________ cuticle.
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Match the following factors with their effects on transpiration:
Match the following factors with their effects on transpiration:
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Which of the following is NOT a significance of transpiration in plants?
Which of the following is NOT a significance of transpiration in plants?
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Submerged plants have many stomata to facilitate gas exchange.
Submerged plants have many stomata to facilitate gas exchange.
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How do guard cells respond when the plant is dehydrated?
How do guard cells respond when the plant is dehydrated?
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Study Notes
Transpiration in Plants
- Plants lose water through evaporation of water vapor
- This process is called transpiration
Transpiration Pull
- Water evaporates from the mesophyll cells into air spaces
- Water is drawn from xylem vessels, creating a pull
- Water is drawn from neighbouring cells through osmosis
- Water vapor diffuses from the air spaces into the atmosphere through the stomata
- Loss of water from mesophyll cells lowers water potential in the cells
Significance of Transpiration
- Creates transpiration pull, which transports water and dissolved minerals up the xylem
- Helps in absorption of water and dissolved minerals
- Promotes evaporation for heat loss
Factors Affecting Transpiration
Environmental Factors
- Relative Humidity: Lower humidity increases transpiration rate, while higher humidity reduces transpiration rate. A larger concentration gradient of water vapor between the air spaces and surrounding air results in a higher rate of transpiration.
- Temperature: Higher temperature increases evaporation from mesophyll cell surfaces. Increased air temperature holds more water vapor, increasing the concentration gradient between the air spaces and the atmosphere. This leads to higher transpiration rates.
- Air Movement: Windy conditions increase transpiration rate. Air movement carries water vapor away from leaf surfaces, increasing the concentration gradient.
- Light Intensity: Higher light intensity increases transpiration rate as stomata open wider, allowing more water vapor to diffuse out. Higher light intensity increases leaf temperature.
Adaptations to Reduce Water Loss
- Impermeable Waxy Cuticle: Reduces evaporation
- Guard Cells: Close stomata when dehydrated
- Upper Epidermis: Fewer stomata in the upper epidermis, as the upper surface is directly exposed to sunlight and higher temperatures.
- Density of Stomata: Land plants have fewer stomata on the upper epidermis to reduce water loss. Submerged plants, lacking a cuticle, often have no or few stomata.
Xylem
- Xylem vessels have no cytoplasm and nuclei; they form hollow tubes
- Xylem tubes have no end walls between adjacent cells
- Xylem functions for water and mineral transport, and is non-living
Phloem
- Sieve plates have pores for organic nutrient transport
- Sieve tubes contain cytoplasm but lack a nucleus; organic nutrients move along with minimal resistance
- Companion cells have large amounts of mitochondria and cytoplasm; they support the metabolic activities of sieve tubes
- Phloem transports organic nutrients (sugars, amino acids) from leaves to other parts of the plant, with minimal resistance
Water and Mineral Transport
- Water moves from xylem to leaf cells
- Water evaporates from moist surfaces of mesophyll cells into air spaces
- Water diffuses out of the stomata
- Transpiration pull draws water up the xylem vessels
- Water passes through the cortex into the xylem
- Water moves into the root hairs via osmosis
Turgidity
- Sufficient Water: Thin-walled cells (e.g., pith and cortex) become turgid due to pressure from full cells
- Not Sufficient Water: Thin-walled cells become flaccid (less rigid)
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Description
This quiz focuses on the process of transpiration in plants, detailing how water vapor is lost, the transpiration pull, and the significance of this process. It also explores various environmental factors affecting transpiration rates.
