Problem 52 - Objective Biology for NEET

Question

Select the incorrect statement: (a) Glycocalyx differs in composition and thickness among different bacteria. (b) All organism are made of cells or aggregates of cells. (c) ER helps in synthesis of proteins, lipoproteins and glycogen. (d) Cells of all living organisms have nuclues

Step-by-Step Solution

Answer

The incorrect statement is (d) Cells of all living organisms have nucleus.

Step 1: Evaluate Statement A

Glycocalyx refers to the outer covering of many cells, especially bacteria, and it indeed varies in composition and thickness among different bacteria. So this statement is correct.

Step 2: Evaluate Statement B

The statement that all organisms are made of cells or aggregates of cells is basic cell theory and is also correct.

Step 3: Evaluate Statement C

ER, or the endoplasmic reticulum, is part of a cell and is involved in the synthesis of proteins, lipoproteins and glycogen. So this statement is also correct.

Step 4: Evaluate Statement D

Not all cells of all living organisms have a nucleus. Prokaryotic cells, for example, do not have a nucleus. Thus, this statement is incorrect.

Key Concepts

Cell Theory

Cell theory is a fundamental principle in biology. It states that all living organisms are made up of cells, which are the basic unit of life.
This concept is crucial as it underscores the belief that cells are the building blocks for all life forms. Each cell operates as a self-contained unit of life, carrying out necessary processes.
Cell theory also asserts that new cells arise from pre-existing cells, supported by cellular division methods like mitosis and meiosis.
Therefore:

• All living things are constructed of one or more cells.
• The cell is the smallest unit of life, performing essential functions such as metabolism and replication.
• Cells only arise from the division of pre-existing cells.

Understanding the cell theory reinforces the idea that despite the diversity of organisms, a shared characteristic is their cellular composition.
It encourages further exploration into how cells function and interact within an organism.

Glycocalyx in Bacteria

Glycocalyx is an outer covering that protects many bacterial cells. It is a gelatinous layer composed of carbohydrates.
Depending on its consistency, it can be classified as a capsule if it is organized and firm, or as a slime layer if it is more disorganized and loose.
The glycocalyx serves various functions:

• Protection against phagocytosis by host immune cells.
• Aiding in the adherence to surfaces and formation of biofilms, which protects the bacteria from environmental harm.
• Retaining moisture to prevent desiccation.

The composition and thickness of the glycocalyx can greatly vary among different bacterial species. This variability allows bacteria to adapt to diverse environments effectively.
It is an excellent example of how microorganisms can evolve structural adaptations to overcome challenges.

Endoplasmic Reticulum (ER) Functions

The endoplasmic reticulum (ER) is a network of membranes found within eukaryotic cells, playing a pivotal role in biochemical processes.
It exists in two forms: rough ER, which is studded with ribosomes, and smooth ER, which is not.
Each form of ER has distinct functions:

• Rough ER: Primarily involved in the synthesis and packaging of proteins. The ribosomes on its surface translate RNA into polypeptide chains, which are then folded and modified within the ER.
• Smooth ER: Involved in lipid synthesis, metabolism of carbohydrates, detoxification of drugs and poisons, and storage of calcium ions.

Another important function of the ER is its role in the construction of cellular membranes. It synthesizes the phospholipids and cholesterol that form the cell's lipid bilayer.
The ER is crucial for the maintenance of cellular function, and its disruption can lead to various diseases.

Prokaryotic vs Eukaryotic Cells

Understanding the differences between prokaryotic and eukaryotic cells is essential for distinguishing the diversity of life forms.
The primary distinction is the presence of a nucleus:

• Prokaryotic Cells: Simple, generally smaller cells that lack a true nucleus. Their genetic material is free-floating within the cell in a region called the nucleoid.
• Eukaryotic Cells: More complex and larger, they possess a true nucleus enclosed within a nuclear membrane. This separation of DNA from the rest of the cell allows for more complex regulation and expression of genes.

In addition:

• Prokaryotes, like bacteria, often lack organelles such as mitochondria and chloroplasts.
• Eukaryotes, like animals and plants, have complex organelles that perform specialized tasks.

Recognizing these differences helps in understanding organism complexity and evolutionary biology.
It highlights the evolutionary advantages of compartmentalization in cells, enhancing efficiency in biochemical processes.