Problem 110 - Objective Biology for NEET

Question

Guard cells are found in (a) Stomata (b) Root tips (c) Ovary (d) Lenticels

Step-by-Step Solution

Answer

Guard cells are found in stomata.

Step 1: Understanding the Terms

Firstly, understand what guard cells are: Guard cells are specialized plant cells in the epidermis of leaves, stems and other organs that are used to control gas exchange. They are produced in pairs with a gap between them that forms a stomatal pore

Step 2: Recall the Concept

Remember that guard cells are always associated with stomata, which are tiny openings or pores in plant tissue that allow for gas exchange.

Step 3: Select the Correct Option

Based on the above knowledge, one can conclude that guard cells are found in stomata.

Key Concepts

Stomata

Imagine tiny mouths on a plant's surface that open and close to breathe in carbon dioxide and release oxygen; these are known as stomata. Located predominantly on the underside of leaves, stomata play a vital role in a plant’s life, allowing it to perform photosynthesis—a process that converts carbon dioxide and sunlight into sugars the plant uses for energy.

Each stoma consists of two kidney-shaped guard cells that swell or shrink to open or close the pore. This mechanism is akin to inflating a balloon to open up space or deflating it to close a gap. When guard cells absorb water, they curve outward, opening the stoma to facilitate gas exchange. Conversely, when they lose water, the guard cells become flaccid and the stoma closes, conserving water within the plant. It's a delicate balance between the need for carbon dioxide and the prevention of water loss, especially in arid conditions.

Gas Exchange in Plants

Plants are master chemists, especially when it comes to exchanging gases with their environment. They take in carbon dioxide (CO2) and release oxygen (O2) during the daytime photosynthesis process while at night, they primarily respire, taking in oxygen and releasing carbon dioxide. This exchange is critical for the plant to make food and grow.

The opening and closing of stomata are the gatekeepers of this process. Guard cells react to environmental cues like light, carbon dioxide concentration, and internal water pressure, adjusting the size of the stomatal pores accordingly. When a plant needs to conserve water, the guard cells close, reducing water loss through a process called transpiration. Simultaneously, this limits the plant's ability to take in carbon dioxide, creating a trade-off between obtaining essential gases and preserving water. It's a complex dance that every plant must manage to survive and thrive.

Plant Epidermis Structure

The plant epidermis is the outermost layer of cells covering leaves, flowers, roots, and stems, serving as a protective barrier much like our own skin. It's composed of multiple cell types, including the guard cells discussed earlier. However, not all epidermal cells are the same; some are flat and pavement-like, providing a protective layer, while others, known as trichomes, can appear hair-like and protect the plant from herbivores.

The epidermis also houses specialized cells like the aforementioned stomata for gas exchange. It is a waterproof barrier thanks to a waxy cuticle, which helps in reducing water loss. Remarkably, this structure has evolved to be selectively permeable, letting in as much light as possible for photosynthesis while defending against excessive water loss and disease-causing pathogens. Every component of the epidermis, whether stomata for gas exchange or trichomes for defense, plays a crucial role in the survival of the plant.