Problem 54 - Objective Biology for NEET

Question

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

Step-by-Step Solution

Answer

The structure externally adjacent to the glycocalyx layer in prokaryotic cell like bacteria is the cell wall. Thus, the correct answer is (a) Cell wall.

Step 1: Understand the bacterial cell structure

In prokaryotic cells, like bacteria, starting from the inside, the structure is: cytoplasm and DNA (not enclosed by a nucleus), surrounded by a plasma membrane (also known as cell membrane).

Step 2: Locate glycocalyx

The glycocalyx is a structure external to the plasma membrane. It is a capsule made up of sugary molecules which provides protection to the cell. Organisms can also use it to stick to surfaces.

Step 3: Determine what is external to the glycocalyx

Moving outward from the glycocalyx, the next layer is the cell wall in the bacterial cell structure. It provides shape to the cell and offers added protection.

Key Concepts

Glycocalyx

The glycocalyx is a crucial outermost layer found in many prokaryotic cells, particularly bacteria. It's a protective coating made of polysaccharides, peptides, or a complex mixture of both. The glycocalyx can appear in two main forms: a well-structured capsule or a more loosely attached slime layer.

• The capsule form is rigid, providing enhanced protection against environmental threats and helping the cell evade the host's immune system.
• The slime layer is more diffuse and allows bacteria to adhere to surfaces, facilitating the formation of biofilms, which are communities of bacteria that can be very difficult to remove.

Understanding the glycocalyx is essential because it plays a significant role in bacterial survival and pathogenicity. By offering a mechanism for attachment and defense, the glycocalyx ensures the bacteria remain effective in varying environments.

Bacterial Cell Wall

The bacterial cell wall is a stiff yet flexible structure that lies just outside the glycocalyx. It is vital for maintaining the bacterial cell's shape and ensuring protection against environmental stresses. Bacterial cell walls are primarily composed of peptidoglycan, a strong polymer made of sugars and amino acids.
The cell wall's composition and thickness can vary significantly among bacteria, leading to different classifications:

• Gram-positive bacteria: These have thick cell walls rich in peptidoglycan, which retains the purple color during Gram staining, a laboratory technique used to identify bacterial types.
• Gram-negative bacteria: These possess a thinner peptidoglycan layer and an additional outer membrane, causing them to lose the purple stain and appear red or pink after Gram staining. The outer membrane also includes lipopolysaccharides, which can be harmful to hosts.

This structural integrity provided by the cell wall not only preserves the bacteria's form but also acts as a barrier to protect against physical damage and osmotic pressure changes.

Plasma Membrane

The plasma membrane is an essential component of all cells, including prokaryotic bacteria. It is located just beneath the cell wall and serves as a critical boundary separating the cell's interior from its external environment. Made up of a phospholipid bilayer, the plasma membrane is embedded with proteins that contribute to its function.

• It regulates the entry and exit of substances, allowing nutrients in and waste products out, maintaining homeostasis.
• Integral proteins within the membrane facilitate various processes like nutrient transport, respiration, and signal transduction.

In prokaryotic cells, the plasma membrane is involved in additional special functions such as hosting enzymes for respiration and photosynthesis due to the lack of specialized organelles. Understanding the plasma membrane is fundamental because it ensures the survival of bacteria by controlling the cell’s interaction with its environment.