Question

Transpiration is affected by (a) Humidity (b) Wind speed (c) Light and temperature (d) All of these

Short answer

The correct choice is (d) All of these. It means that transpiration is affected by humidity, wind speed, light, and temperature.

Step-by-step solution

Understanding Humidity

Humidity is the amount of water vapor in the air. In high humidity, the rate of transpiration decreases. This is because the moisture level in the air is high which decreases the concentration gradient of water between the leaf and the surrounding. As the gradient decrease, the water loss from the plant reduces, thus lowering the transpiration rate.

Understanding Wind Speed

Wind speed also affects the rate of transpiration. When wind movement around a given plant increases, it speeds up the rate of evaporation which increases water loss from the plant's surface thus increasing the rate of transpiration. However, at very high wind speeds, the rate of transpiration significantly decreases because stomata are closed to prevent excessive water loss.

Understanding Light and Temperature

Light is also a factor that affects the rate of transpiration. Higher light levels can increase the temperature, which can increase the rate of evaporation of water from the plant, thus increasing the rate of transpiration. Moreover, more stomata are triggered to open under light conditions to facilitate photosynthesis, leading to increased water loss. Temperature is a vital factor as well. As the temperature increases, the rate of evaporation of water from the leaf's surface also increases, which in return increases the rate of transpiration.

Determining the Correct Choice

Considering the above explanations of each factor's impact on the transpiration process, it could be concluded that all the mentioned factors, namely humidity, wind speed, light, and temperature, affect the rate of transpiration. This means that the correct choice is (d) All of these.

Key concepts

Humidity Effects on Transpiration

Humidity plays a crucial role in the natural process of transpiration in plants. Imagine the air around us as a sponge that soaks up water vapor; when it's already damp, it can't hold much more. This is what happens with humidity: the higher the humidity, the more water the air contains, which means there's less of a 'thirst' for the moisture from the leaves of plants.

As humidity rises, the concentration gradient between the moisture inside the plant and the air outside decreases. Think of it as a gentle slope versus a steep hill; water can easily travel down a steep hill, but on a gentle slope, the journey slows. This results in a decreased rate of transpiration when the air is humidity-saturated. In contrast, when humidity is low, the air is like a dry sponge, eager to absorb moisture, which increases the rate of water loss from plants.

Wind Speed and Transpiration

Feel the breeze on a windy day and how it quickly dries sweat from your skin. Something similar happens with plants. Wind passing over leaves works like a charm to whisk away moisture, speeding up transpiration. It's the plant's version of evaporation accelerated by a fan.

With gentle winds, plants might breathe a sigh of relief, as these breezes help carry away the humid air. This clears the space for more moisture to escape from the leaves. However, it's not all breezy; extremely high winds can stress plants. They respond by shutting down their tiny pores called stomata, turning off the taps to prevent too much water loss. This complex relationship means wind speed has a direct yet variable impact on how fast or slow plants lose water.

Light Impact on Transpiration

Light serves as a wakeup call for plants to start their day. When sunlight kisses the leaves of a plant, it's not just providing energy for photosynthesis; it's also turning up the dial on transpiration. During daylight, plants open their stomata—the tiny windows on their leaves—welcoming carbon dioxide for photosynthesis and inadvertently letting water vapor slip away.

More light means more photosynthetic activity and increased warmth, which collectively encourages the plant to release more water. While shaded or dark conditions slow down this process, a bright day could mean a busy one for water transport in plants. This balancing act is a crucial component of their day-to-day functioning.

Temperature Effects on Transpiration

Temperature is one of the main drivers of a plant's transpiration rate. When the thermostat goes up, it's like turning on the heat under a pot of water; the evaporation rate climbs. In the world of plants, warm air hugs the leaf surface, teasing water molecules away faster, increasing the rate of transpiration.

The warm air not only holds more water but also makes the water inside the plant eager to escape to the cooler surrounding environment. This game of hot and cold results in plants often losing more water on a hot day compared to when it's cool. Temperature, just like the three other factors, significantly influences the ebb and flow of water from leaves to air.