Question

Differentiate between active absorption and passive absorption.

Answer 1

Absorption is a process that helps planTs to suck up the water and nutrients from the soil. The slow transpiring plants prefer active absorption. In addition, passive absorption is preferred by slow transpiring plants. One of the types requires ATP, while the other doesn't.

Complete answer: Absorption is a process of acquiring water and nutrients from the soil by plants. Absorption occurs by active or passive assimilation in cells and across tissues. The plants prefer the type of absorption based on their needs for water and nutrients.
Active absorption involves the absorption of water by roots. In this process, it is absorbed with the help of ATP, while in passive absorption, ATP molecules are not involved. The force for absorption is created in mesophyll cells. The mesophyll cell makes up a layer on plant leaves. The forces generated in active absorption are osmotic and nonosmotic. But in passive absorption, the force is generated by absorption pull due to transpiration from leaves. The DPD or diffusion pressure deficit which is a measure of the thirst of a cell affects the water absorption rate in active absorption. On the other hand, the tension created in the xylem sap created by transpiration pull affects or changes the rate of absorption in the passive type. The water moves through the symplast in active absorption and in passive absorption, the water moves through apoplast mainly. The symplast is the inner side of the plasma membrane where the diffusion of water occurs. The apoplast is just the opposite of the symplast. It is the space outside the plasma membrane. The materials freely diffuse in this space. The rate of water decreases in active absorption if any metabolic inhibitor is applied. But in passive absorption, the metabolic inhibitors have no such effects. The rate of flow of water is slow in active absorption as compared to passive because active absorption occurs in well-watered plants as they need less water transport. Also, passive transport is much faster than active because this type of absorption is needed in water-scarce plants.

Note: Both types of absorption are affected by the level of humidity and temperature present in the surrounding environment of the plant. The rate of absorption is more dependent on these factors. Both active absorption and passive absorption plays an important role in maintaining the physiology of plants.