Question

What structural features of guard cells underlie their ability to form an open pore in plant epidermal surfaces? a. thickened inner cell walls and radially oriented microfibrils b. thickened outer cell walls and radially oriented microfibrils c. thickened inner cell walls and longitudinal microfibrils d. thickened outer cell walls and longitudinal microfibrils e. uniform thickness of cell walls and randomly arranged microfibrils

Short answer

The correct answer is a. Thickened inner cell walls and radially oriented microfibrils.

Step-by-step solution

Understanding the structure of 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 in pairs with a gap in between that forms a stomatal pore.

Features of Guard Cells

Guard cells are the only epidermal cells that can make new cells once the epidermis is formed. These evolutionary exceptional cells have distinct internal structures, which includes unevenly thickened cell walls. The cell wall towards the stomatal pore is thicker than the one away from it. This is because these differences in wall thickness allow the cells to change shape, creating an open or closed stomatal pore.

Identifying the accurate features

Going through the options given, the right answer is the one that matches the features already identified. That is, guard cells have thickened inner cell walls and radially oriented microfibrils. This structural feature allows them to swell or shrink according to osmotic forces, controlling the pore's opening or closing.

Choosing the Correct Option

By matching the characteristic features of guard cells with the options given, the one that fits best is 'thickened inner cell walls and radially oriented microfibrils.'

Key concepts

Stomatal Pore

Plants have evolved a very intricate and delicate system to manage gas exchange, and at the heart of this system is the stomatal pore. Imagine it as a tiny mouth on the plant’s surface, and like our own mouths, it needs to open to breathe in carbon dioxide (CO2) and release oxygen (O2) as part of photosynthesis. However, it also has to close to stop the plant from losing too much water.

The stomatal pore is not just a hole but a sophisticated valve controlled by guard cells. These guard cells can change shape, opening or closing the pore in response to environmental conditions. For instance, in bright light or when high levels of CO2 are present, the guard cells swell, pulling the pore open to facilitate gas exchange. Conversely, during drought or at night, they deflate, closing the pore to conserve water. Understanding this mechanism helps us comprehend the significance of guard cells’ features, such as their thickened inner walls and radial microfibrill arrangement, which are crucial for the opening and closing of the stomatal pore.

Epidermal Cell Structure

Building Blocks of Plant Skin

Epidermal cell structures in plants are analogous to building blocks, with each block serving a specific structural function. The epidermis acts as the plant's protective skin, shielding it from physical damage and disease while also managing interactions with its environment. Guard cells are a specialized type of epidermal cell with unique features that distinguish them from the rest.

Notably, they have thicker inner walls towards the stomatal pore, which enables them to control the aperture through changes in shape. In contrast, standard epidermal cells are more static, with their primary function being to protect the plant, like bricks in a wall. By studying these unique differences, students can better understand how structure and function are intimately interlinked within plant cells.

Plant Gas Exchange

Plants rely on a continuous exchange of gases with the environment to survive and thrive.

Essential Gas Exchange

During photosynthesis, plants take in CO2 and release O2 – a gas exchange critical for the plant's growth and the environment. The exchange occurs mainly through the stomatal pores. Guard cells play a pivotal role by regulating these openings depending on factors such as light, CO2 concentration, and the plant's water status.

An open stomatal pore signifies a plant actively engaging in gas exchange, whereas a closed pore indicates conservation of water resources, demonstrating the delicate balance plants maintain to facilitate their life processes. Understanding this balance helps students grasp the importance of guard cells and stomatal pores as key components in the wider context of plant biology and the Earth’s ecosystems.