Problem 115 - Objective Biology for NEET

Question

Guard cells are surrounded by (a) Epidermal hairs (b) Mesophyll cells (c) Palisade cells (d) Subsidiary cells

Step-by-Step Solution

Answer

The correct answer is (d) Subsidiary cells.

Step 1: Understand the keyword

The keyword in this question is 'Guard cells'. Guard cells are specialized cells in the epidermis of leaves, stems and other organs that are used to control gas exchange. They are produced alongside pore, termed a stoma, through which this exchange occurs.

Step 2: Matching associated cell type

From the acquired knowledge, look at the options and match which of them is known to be the neighbor of the 'Guard cells'.

Step 3: Select the correct answer

Among the options given, (d) Subsidiary cells are surrounding the guard cells. Subsidiary cells (also known as accessory cells) are epithelial cells located near the guard cells that help in the opening and closure of pore of the guard cells of the plants.

Key Concepts

Subsidiary Cells

Subsidiary cells, also known as accessory cells, play an essential role in plant physiology. They are found adjacent to guard cells and form part of the epidermis. These cells assist the guard cells in regulating the opening and closing of stomata.

Unlike guard cells, subsidiary cells do not directly control the pore size. However, they provide mechanical support and help maintain the shape that allows guard cells to function effectively.

• They mitigate stress on guard cells during the opening and closing process.
• They contribute to the hydraulic functioning of guard cells through osmotic pressure regulation.

In summary, while subsidiary cells do not partake directly in gas exchange, they enable guard cells to adopt their physiological roles efficiently.

Stomata

Stomata are tiny pores found mainly on the surface of leaves but also on stems and other plant organs. They play a vital role in photosynthesis by facilitating gas exchange. Each stoma has two specialized guard cells that surround it. These cells adjust the size of the stoma according to environmental conditions.

The opening and closing mechanism of stomata is triggered by external factors such as light, carbon dioxide levels, and internal factors like water pressure within guard cells.

• When guard cells are filled with water, they swell and bend away from each other, opening the stoma.
• Conversely, when they lose water, they come back together, closing the stoma.

Through this dynamic process, plants manage the exchange of gases efficiently, balancing carbon dioxide intake and oxygen release.

Gas Exchange

Gas exchange in plants primarily occurs through the stomata. This process involves the movement of gases like carbon dioxide, oxygen, and water vapor in and out of the plant. It's crucial for photosynthesis, which requires carbon dioxide, and for respiration, which uses and produces oxygen.

During daylight, stomata usually open to allow carbon dioxide in for photosynthesis. This is when the plant can maximize its food production.

• Oxygen, a byproduct of photosynthesis, exits through the same pathway.
• Water vapor is also lost in a process called transpiration.

At night, stomata often close to conserve water and maintain the plant's internal moisture balance. Therefore, gas exchange through stomata is not only vital for photosynthesis, but also for maintaining water balance.

Epidermis

The epidermis is the outermost layer of cells in plant organs, including leaves, stems, and roots. It serves as a protective barrier, safeguarding against mechanical injury, pathogens, and water loss. This layer often consists of a single cell layer thick, but can sometimes be multi-layered.

The epidermis includes several cell types such as guard cells and subsidiary cells, as well as structures like stomata and epidermal hairs.

• Guard cells within the epidermis regulate gas exchange and water loss.
• Epidermal hairs can reduce wind speed and water loss, further protecting the plant.

Overall, the epidermis is crucial in maintaining the internal conditions of the plant, acting as a first line of defense while accommodating the functions of the stomata.

Plant Physiology

Plant physiology is the study of how plants function and how they interact with their environment. It encompasses all aspects of the plant’s life, from molecular processes to the functioning of entire ecosystems.

A critical component of plant physiology is the understanding of how different plant structures, like stomata, contribute to essential functions such as transport and exchange processes.

• Guard cells and stomata are vital for photosynthesis by regulating gas exchange.
• Subsidiary cells help optimize the functioning of guard cells.
• The epidermis protects plant organs and aids in water retention.

Together, these components allow plants to perform necessary life processes efficiently, adapting to varying environmental conditions. By understanding plant physiology, we can improve agricultural practices, promote sustainability, and better comprehend plant-environment interactions.