Problem 53 - Objective Biology for NEET

Question

What is external to the plasma membrane in a prokaryotic cell like bacteria? (a) Glycocalyx layer (b) Cell wall (c) Both (a) and (b) (d) None of these

Step-by-Step Solution

Answer

The correct answer is (c): Both the glycocalyx layer and the cell wall are located externally to the plasma membrane in a prokaryotic cell like bacteria.

Step 1: Understanding the Cell Structure

Looking at the typical structure of a prokaryotic cell, it is known that these cells, including bacterial cells, are surrounded by a plasma membrane. External to this plasma membrane, two structures can be found: the cell wall and the glycocalyx.

Step 2: Analyzing the Options

Option (a): The glycocalyx layer is a layer located outside of the cell wall in bacteria, thus it is external to the plasma membrane. Option (b): The cell wall is located directly outside of the plasma membrane in bacteria, thus it is also external to the plasma membrane.

Step 3: Choosing the Correct Option

Considering both the glycocalyx layer and the cell wall are located externally to the plasma membrane in a bacterial cell, the answer would be option (c): Both (a) and (b).

Key Concepts

Glycocalyx Layer

The glycocalyx layer is an essential feature of prokaryotic cells like bacteria. It is a viscous, gel-like coating that envelopes the cell, lying outside the cell wall. This layer is primarily composed of polysaccharides, proteins, or both, forming a capsule or a slime layer depending on its structure and thickness.

The glycocalyx serves multiple functions. It offers protection to the cell against dehydration and loss of nutrients. Additionally, it plays a critical role in the adherence of cells to surfaces, which is crucial in the formation of biofilms. This can be particularly important in pathogenic bacteria that form biofilms on medical devices or host tissues. Moreover, the glycocalyx can also protect against phagocytosis by host immune cells, contributing to a bacterium's virulence.

Importance in Identification and Immune Evasion

Importantly, the glycocalyx can vary among species and even among strains of the same species. This variation is used in laboratory settings to identify different bacteria. Furthermore, since it helps in evading the host's immune system, understanding the glycocalyx layer can be key in developing treatments and preventative measures against bacterial infections.

Cell Wall

The cell wall in prokaryotic cells acts as a protective structural layer that is situated just outside the plasma membrane. For bacterial cells, the composition of the cell wall includes peptidoglycan, a complex polymer of sugars and amino acids, which provides strength and rigidity to the cell, maintaining its shape and preventing it from bursting in hypotonic environments.

There are two primary types of cell walls in bacteria, classified based on their staining characteristics in the Gram stain test: Gram-positive and Gram-negative. Gram-positive bacteria have a thick peptidoglycan layer and stain purple, while Gram-negative bacteria have a thinner peptidoglycan layer, surrounded by an outer membrane, and they stain pink or red.

Role in Antibiotic Susceptibility

The structure of the cell wall is crucial for the effectiveness of certain antibiotics. For instance, penicillin targets the synthesis of peptidoglycan, which is more effective against Gram-positive bacteria due to their thicker peptidoglycan layer. Thus, the cell wall is not only important for the structural integrity and survival of bacteria but also for medical treatments targeting bacterial infections.

Plasma Membrane

Encapsulating the cytoplasm, the plasma membrane is a fundamental component of all cells, including prokaryotes. It's a selectively permeable barrier, allowing for the control of substances entering and exiting the cell. Composed primarily of phospholipid bilayers with embedded proteins, the plasma membrane's fluid mosaic model describes its dynamic nature.

The plasma membrane is involved in a variety of cellular processes. These include transport of nutrients, waste removal, cell communication, and energy conversion in processes like photosynthesis and respiration for some bacteria.

Interaction with the Environment

Moreover, the plasma membrane is essential in sensing and responding to environmental changes, aiding in protection against harmful conditions. It's also where the concentration gradients are maintained, which are vital for processes such as the generation of ATP in cellular respiration. This dynamic interface between the cell and its environment is fundamental to cellular function and survival.