Question

What is a thick, tough, layer of glycocalyx known as? (a) Slime layer (b) Capsule (c) Cell wall (d) Cell envelope

Short answer

The thick, tough, layer of glycocalyx is known as the Capsule.

Step-by-step solution

- Understand key terms

Get familiar with biological terms, such as glycocalyx, slime layer, capsule, cell wall, and cell envelope. The glycocalyx is a glycoprotein-polysaccharide covering that surrounds the cell membranes of some bacteria, epithelia and other cells. The thick, tough layer of glycocalyx, which is less easily detached than a slime layer and can protect the bacteria against phagocytosis and from drying out, is known as a capsule.

- Match with the answers

After understanding the key terms, match the correct definition for a thick, tough layer of glycocalyx. From the options provided, the right answer is the Capsule

Key concepts

Capsule

The capsule is a distinctive feature of many bacterial cells. It envelops the cell's surface, acting as a protective barrier. This polysaccharide layer is often associated with pathogenic bacteria, playing a critical role in their ability to evade a host's immune system. The capsule's thick, mucous-like consistency aids in preventing desiccation (drying out) and shields the cell from attacks by phagocytic cells, which are key defenders in the body's immune response.

Moreover, the capsule can enhance a bacterium's virulence by facilitating adherence to surfaces, including tissues in the host organism. This attribute allows the bacteria to form biofilms, complex communities that are difficult to eradicate due to their resilience against antibiotics and natural host defenses. In a textbook exercise, identifying the capsule out of given options highlights its significance in bacterial structure and function, compelling students to learn how it differs from other components like the slime layer, which is more loosely attached and not as structured as the capsule.

Cell Wall

The cell wall is another critical component of a bacterial cell structure. Unlike the capsule, the cell wall is a rigid structure providing physical support and determining the cell's shape. Primarily composed of peptidoglycan, a network of sugar and amino acid polymers, bacterial cell walls differ significantly in Gram-positive and Gram-negative bacteria, which can be distinguished by their varying layers of peptidoglycan and outer membranes when stained during a Gram test.

Gram-Positive vs. Gram-Negative Bacteria

In Gram-positive bacteria, the cell wall is thick with multiple peptidoglycan layers, while Gram-negative bacteria have a thinner peptidoglycan layer but an additional outer membrane. This structure acts as a protective shield, preventing the cell from bursting due to osmotic pressure differences between the inner and outer cellular environments. Understanding the composition and function of the cell wall is key for students, as it is targeted by certain antibiotics and plays a role in the effectiveness of treatment against bacterial infections.

Bacterial Cell Structure

Bacterial cell structure is complex and involves several key elements aside from the capsule and cell wall. It includes features such as the cytoplasmic membrane, genetic material (DNA), ribosomes, and in some bacteria, additional structures like flagella or pili that aid in motility and attachment.

Each component plays an essential role in the survival and function of the bacterial cell. The cytoplasmic membrane controls the influx and efflux of substances, including nutrients and waste products. The genetic material, usually a single circular DNA molecule, directs all of the cell's functions and carries the genetic information necessary for reproduction. Ribosomes are the sites of protein synthesis, crucial for the growth and repair of the cell.

External Structures

Furthermore, bacteria may have external structures like flagella, which propel the cell through its environment, and pili (or fimbriae), hair-like projections that aid in adhesion to surfaces and in some cases, genetic material exchange.