Question

Transpiration increases with an increase in (a) Humidity (b) Temperature (c) Minerals (d) Soil moisture

Short answer

Transpiration is directly increased with an increase in (b) Temperature.

Step-by-step solution

Analyze the relationship between transpiration and humidity

Humidity refers to the amount of water vapor in the atmosphere. In areas of high humidity, the concentration of water vapor in the air outside the leaf is close to that in the intercellular spaces, hence the rate of transpiration decreases. Therefore, humidity has an inverse relationship with transpiration.

Analyze the relationship between transpiration and temperature

Temperature affects the rate of evaporation and diffusing capacity of the air. Higher temperatures increase the rate of evaporation from the leaf surfaces and the diffusing capacity of the air, thereby increasing transpiration rates. Therefore, temperature has a direct relationship with transpiration.

Analyze the relationship between transpiration and minerals

Minerals in the soil do not directly affect the process of transpiration. However, they are important for overall plant health and growth. Without the proper minerals, a plant might not function properly, which could indirectly affect how well or how much it transpires.

Analyze the relationship between transpiration and soil moisture

Similar to minerals, soil moisture also indirectly affects transpiration. If a plant has an abundant supply of water from the soil, it will be able to maintain its normal transpiration rates. But if the soil is dry, the plant might close its stomata (pores) to prevent water loss, thereby reducing transpiration. The relation here depends on various factors and cannot be straightforward.

Key concepts

Environmental Factors Affecting Transpiration

Transpiration is the process by which moisture is carried through plants from roots to small pores on the underside of leaves where it changes to vapor and is released to the atmosphere. This process is significantly influenced by environmental elements such as light intensity, air movement, temperature, and humidity.

Plants situated in areas with high light intensity and moving air will typically experience higher transpiration rates. This is because light stimulates the opening of stomata, through which transpiration occurs, and wind can remove the humid air layer surrounding the leaf, promoting more water to evaporate.

• Light intensity increases stomatal opening, promoting transpiration.
• Wind removes the humid air layer, enhancing water vapor loss.

Relationship Between Transpiration and Humidity

Transpiration is inherently linked to the humidity or moisture content in the air. Simply put, when humidity is high, the air is already saturated with water vapor, making it difficult for plants to release more into the atmosphere. This results in a decrease in transpiration rates. Conversely, dryer conditions lead to a steeper vapor pressure gradient between the leaves and the air, which accelerates the rate of transpiration.

It's like trying to add more people into a crowded room; the fuller it is, the harder it is to squeeze more people in. Similarly, plants struggle to release water vapor into already moist air.

• High humidity reduces vapor pressure gradient, decelerating transpiration.
• Low humidity increases vapor pressure gradient, accelerating transpiration.

Impact of Temperature on Transpiration

Temperature plays a dual role in controlling transpiration by influencing both the rate of evaporation from the leaf surface and the capacity of the air to hold water vapor. With rising temperatures, water molecules move faster, and the evaporation rate increases. This, combined with the greater ability of warmer air to hold more vapor, pushes the plant to release more water into the air.

Think of it like heating a pot of water; as it gets hotter, it boils more vigorously. In a similar manner, as the temperature around a plant increases, the 'boiling off' of water from the leaf surface speeds up.

• Rising temperatures cause faster water molecule movement, enhancing evaporation.
• Warmer air can hold more water vapor, stimulating increased transpiration.

Soil Moisture Influence on Transpiration

The availability of water in the soil is crucial for maintaining transpiration in plants. When the soil is adequately moist, water uptake by the roots is unhindered, and the plant can continue transpiring normally. However, under dry soil conditions, plants may close their stomata to conserve water, thus slowing down transpiration. The relationship is more complex because plants can adapt to periodic dry conditions by developing deeper roots or being more conservative with water usage.

It's akin to a well-supplied water tank in a building; as long as there's enough water in the tank, the building's water system functions properly, but if the tank runs low, water usage is restricted to conserve supply.

• Adequate soil moisture ensures continuous water supply for transpiration.
• Dry soil conditions can trigger protective measures in plants, reducing transpiration.