Evaporation and transpiration are both natural processes that help vapor formation through the loss of water. However, since they perform a similar function, it is often difficult to distinguish between evaporation and transpiration. Nevertheless, there are a lot of differences between these two processes.
The differences between evaporation and transpiration is discussed below -
Most of us are familiar with the concept of evaporation, whereby water is converted from its liquid state to a gaseous state. Evaporation usually takes place when solar energy heats water on surface water bodies like oceans, rivers and ponds.
Aside from water bodies, this process can also occur on other surfaces containing moisture such as soil and trees.
Evaporation is a continuous process; however, the rate of evaporation at a given time can vary based on several factors. These factors are as follows –
Temperature – High-temperature results in an increasing rate of evaporation and vice versa.
Humidity – High level of humidity means that the atmosphere already contains a significant amount of water droplets. Therefore, the rate of evaporation will be low.
The Surface Area of Water – The surface area of water is directly proportional to the rate of evaporation.
Wind – Wind helps in evaporation by carrying away water vapor, which helps in the formation of more water vapor. Hence, wind speed also affects the rate of evaporation.
The process through which plants absorb through their roots and then lose the excess water via stomata is known as transpiration.
This process is similar to perspiration in human beings, preventing plant tissues from overheating when the temperature is high. Along with water, plants also gather essential nutrients from the soil. These nutrients are then transported to different parts of a plant such as stems and leaves through transpiration.
Temperature – When the temperature is high, plants transpire more as water on the surface of leaves starts evaporating more quickly with increasing temperature.
Light – The stomata or tiny pores present in leaves detect presence and absence of light. The stomata open up widely when there is enough light, which facilitates both transpiration and photosynthesis.
Water Content in Soil – this is one of the most critical factors that affect transpiration in plants. A plant loses a large amount of water during transpiration. They make up for the loss of water by drawing water from the soil. Thus, if the soil does not contain adequate water, the stomata will close to preserve water leading to less photosynthesis.
The diagram below shows transpiration in plants –
(Image will be uploaded soon)
The main differences between evaporation and transpiration have been illustrated in the table below.
The total loss of water from the soil via evaporation and transpiration by plants is referred to as evapotranspiration. The concept of evapotranspiration is vital in relation to agriculture. It is because if evapotranspiration rates can be predicted ahead, one can ascertain how much irrigation is required for crops.
In addition to irrigation, evapotranspiration also affects soil moisture or the level of water that is in soil. The factors that determine evapotranspiration rate are – the crop type, soil type, temperature, soil moisture level, humidity and wind.
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Evaporation and Transpiration are natural processes that help to add water vapors to the environment. Now, we will learn how much water is transpired by plants.
Transpiration from plants is an invisible process. You cannot see when water transpired from the leaves. If you want to see transpiration in plants, you can put a plastic bag around the plant leaves. You can see transpired water on the inside of the bag. It is visible due to condensation. When plants are in the growing stage, the leaf will transpire more water than its weight.
At some places, the top layer of the soil where roots are found is located above the water table and is often wet. The soil above the water table is wet and when the rain comes the water infiltrates into the ground from the surface. But the water dries out without any precipitation. The water table is below the depth of plant roots, thus plants are dependent on water supplied by precipitation. If the water table is near the surface the roots can penetrate into the saturated zone below the water table and will help the plants to transpire water directly from the ground water. Thus, transpiration of groundwater results in depletion of the water table.
1. Which part of the plant evaporates water?
Leaves have tiny pores called stomata through which plants evaporate water.
2. Name the external factors that affect the transpiration process?
External factors that affect the transpiration process are humidity, sunlight, amount of light available, temperature and wind.
3. What is the difference between transpiration and respiration?
The process through which water is circulated to different parts of a plant is known as transpiration. Whereas, respiration is the process where plants convert carbon dioxide to oxygen.
4. Why is transpiration important?
Transpiration is an important process of the water cycle. It helps in adding water vapors to the air that condenses to form clouds and finally results in rain. If there will be no transpiration, there will be less water vapor in the air and this can result in drought at many places. Transpiration is also an important process for plants because it helps to prevent wilting of plants which means plants can die if there will be too much water in their leaves and roots. Thus, transpiration is an important process for both the environment and plants.
5. What are the factors that affect evaporation?
Evaporation occurs naturally, which means water is evaporated continuously from the surface of rivers, lakes, and oceans due to the heat of the sun. There are many factors that affect the rate of evaporation at a given time or place. Different factors that affect the rate of transpiration are given here:
Humidity: If there is high humidity in the air, the rate of evaporation will be slow because high humidity means more water vapors in the air.
Surface of the area of water: If the surface of the area of water is more the rate of evaporation will be more and if the surface of the area of water is less the rate of evaporation will be slow.
Wind: The speed of wind also affects the rate of evaporation. If the speed of wind is high, the rate of evaporation will be more because wind helps in carrying water vapors and leads to the formation of more water vapors.
Sunlight: If there is more sunlight the rate of evaporation will be faster because the heat of the sun is the most important factor that increases the rate of evaporation. If there is no sun, there will be less or no evaporation.
Thus, students must know the differences between evaporation and transpiration and factors affecting the two processes to understand this topic properly.