Problem 121 - Objective Biology for NEET

Question

Assertion: \(\mathrm{K}^{+}\) is useful for transpiration process. Reason: \(\mathrm{K}^{+}\) ion help in opening and closing of stomata.

Step-by-Step Solution

Answer

The assertion that \( \mathrm{K}^{+} \) is useful for transpiration process is correct, as it leads to the opening and closing of the stomata in plants, which in turn is a crucial part of the transpiration process. Similarly, the reason provided is also correct, as \( \mathrm{K}^{+} \) ions indeed help in the opening and closing of stomata.

Step 1: Understanding Transpiration Process

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. Water is necessary for plants but only a small amount of water taken up by the roots is used for growth and metabolism. The remaining 97–99.5% is lost by transpiration and guttation.

Step 2: Role of Stomata in Transpiration Process

Stomata are tiny openings or pores in plant tissue that allow for gas exchange. The stomata are bordered by guard cells that open and close the pore. Carbon dioxide, a key reactant in photosynthesis, is taken in from the atmosphere through these stomata. Similarly, excess water is also released into the atmosphere via the stomata. This process is known as transpiration.

Step 3: Role of Potassium Ions in Stomatal Movement

Stomatal opening is triggered by the accumulation of potassium ions in the guard cells. Conversely, when potassium ions leave the guard cells, the water potential increases, leading to the exit of water from the guard cells, causing stomatal closure. Hence, potassium ions play a role in the opening and closing of stomata, affecting transpiration process.

Key Concepts

Stomata

Stomata are small openings located on the leaves of plants, serving as channels for gas exchange. These pores are crucial for the plant’s metabolic processes because they allow carbon dioxide to enter and oxygen to exit. This exchange is vital for photosynthesis, the process by which plants convert light into energy.

During this process, water vapor is also released into the atmosphere through the stomata, which is a part of transpiration. This release of water helps in cooling the plant and maintaining the flow of nutrients from the roots. Stomatal regulation is essential because it balances water retention with the need for carbon dioxide for photosynthesis.

Potassium Ions

Potassium ions ( K^+ ) are essential elements in plant physiology especially in controlling the opening and closing of stomata. The movement of these ions into and out of the guard cells surrounding each stoma regulates their aperture.

When potassium ions accumulate in the guard cells, they cause an osmotic uptake of water due to the lower internal water potential. This water influx makes the guard cells turgid and results in the stomata opening. Conversely, when potassium ions exit the guard cells, the loss of osmotic pressure causes water to leave as well, leading to the closing of stomata.

Guard Cells

Guard cells are specialized cells that flank each stomatal pore and are responsible for controlling its opening and closing. These cells are unique in their ability to change shape, which regulates the size of the stomatal opening.

When guard cells take up water, facilitated by potassium ion influx, they swell and curve, pulling the stomata open. When they lose water, they become flaccid, causing the stomata to close. This dynamic activity is crucial for optimizing photosynthesis and minimizing water loss, effectively balancing the plant's need for gas exchange with the conservation of water.

The ability of guard cells to regulate stomatal apertures is influenced by environmental cues such as light, carbon dioxide concentration, and internal water status, making them integral to the plant's environmental responsiveness.

Plant Physiology

Plant physiology encompasses the various biological and chemical processes that occur within plants. Central to these processes is the management of water and nutrient transport, which involves transpiration as facilitated by stomatal function. Transpiration not only aids in cooling the plant but also plays a role in the movement of minerals and nutrients from the soil into the plant.

Understanding plant physiological processes, such as transpiration and photosynthesis, provides insights into how plants grow, reproduce, and survive in different environments. The role of potassium ions, guard cells, and stomata in these processes reflects the complexity and efficiency of plant responses to environmental changes and internal signaling, ensuring plant health and productivity.