Problem 166 - Objective Biology for NEET

Question

Assertion: Bacterial cell walls are not like the plant cell. Reason: Bacterial cell wall is not made up of cellulose.

Step-by-Step Solution

Answer

Yes, the assertion is true and the reason provided is valid. Bacterial cell walls are not like plant cell walls due to their makeup, bacterial cell walls are typically composed of peptidoglycan and not cellulose as in plant cell walls.

Step 1 Understanding the Difference

Differentiate between the bacterial and plant cell walls. It is known that plant cell walls are composed mainly of cellulose, a type of complex glucose structure. Contrastingly, bacterial cell walls do not contain cellulose, but are composed of peptidoglycan - a protein-sugar (polysaccharide) molecule.

Step 2 Verifying Details

Verify the composition of the bacterial cell wall. Bacterial cell wall comprises of either one of the two types of molecules: gram-positive bacteria have a thick layer of peptidoglycan, whereas gram-negative bacteria have a thin layer sandwiched between an inner and outer membrane.

Step 3 Validating the Statement

Since bacterial cell walls are made up of peptidoglycan and not cellulose, it can be confirmed that the initial assertion that bacterial cell walls are not like plant cell walls is valid and true. Similarly, it proves that the reason, bacterial cell wall is not made up of cellulose, provided in the exercise is valid and factual.

Key Concepts

Plant Cell Walls

Plant cell walls play a crucial role in maintaining the structure and integrity of plant cells. They are composed mainly of cellulose, a robust carbohydrate that gives plants their rigidity and ability to stand upright. Because of cellulose, plant cells form a rigid wall that can resist turgor pressure. Turgor pressure is the force exerted by the fluid inside the cell against the cell wall.

Some key functions of plant cell walls include:

• Providing structural support and shape to the plant.
• Protecting cells against mechanical stress and pathogen attacks.
• Facilitating communication between cells through plasmodesmata, which are tiny channels that pierce the cell walls.

Unlike animal cells, plant cells do not have a skeletal structure to support them. Therefore, the plant cell wall is fundamental in allowing plants to grow and develop properly in their natural environment.

Peptidoglycan

Peptidoglycan is the essential structural component of bacterial cell walls. It is a polymer consisting of sugars and amino acids that forms a mesh-like layer outside the plasma membrane of most bacteria, providing strength and rigidity. Unlike plant cells, which use cellulose, bacterial cell walls rely on peptidoglycan for structural integrity.

Bacteria can be broadly classified into gram-positive and gram-negative based on their cell wall structure:

• **Gram-positive bacteria** have thick layers of peptidoglycan which allow them to retain the violet stain used in Gram staining technique. This makes these bacteria appear purple under a microscope.
• **Gram-negative bacteria** have a much thinner layer of peptidoglycan, which is sandwiched between an inner and an outer membrane. These bacteria do not retain the violet stain, appearing pink when observed.

This difference in structure is crucial for various industrial and medical applications, including determining the type of antibiotics that will be effective against a particular bacterial infection.

Cellulose

Cellulose, a key component of plant cell walls, is a polysaccharide composed of glucose units linked together. It provides significant strength and rigidity to plant structures, allowing them to withstand various environmental pressures.

Here are some important attributes and roles of cellulose:

• **Abundance**: It is the most abundant organic polymer on Earth, forming approximately 33% of all plant matter.
• **Industrial importance**: Due to its strength and biodegradability, cellulose is vital in industries, including paper, textiles, and biofuels.
• **Digestibility**: Most animals cannot digest cellulose because they lack the necessary enzymes. However, some organisms, like ruminants and termites, can break it down with the help of specific micro-organisms in their gut.

Its insolubility in water and ability to form long chains contribute to its function in maintaining cell wall structure and enabling plant growth.