Comprehensive notes, detailed HIV structure, Gram staining mechanism, and exercises for Chapter 2 Bacteria and Viruses, 11th Class Biology (Federal Board 2025).
Discovery: Bacteria were first observed by Antonie van Leeuwenhoek in 1673 using a simple self-made microscope. He described them as 'animalcules'. The term 'bacterium' was later coined by Ehrenberg.
Occurrence: They are omnipresent, found in air, water, soil, and inside other organisms. They can survive in extreme environments like hot springs (thermophiles) and acidic environments (acidophiles).
Composition: Made primarily of Peptidoglycan (murein). Based on Hans Christian Gram's staining technique, bacteria are divided into:
Definition: Viruses are non-cellular, obligate intracellular parasites. They contain a genome (DNA or RNA) and protein coat but lack metabolic machinery.
Structure:
Viruses that infect bacteria are called Bacteriophages (e.g., T4 phage).
HIV (Human Immunodeficiency Virus): Causes AIDS. It is a Retrovirus (RNA virus).
Structure:
Life Cycle: Attachment (to CD4 receptors on T-cells) → Fusion → Reverse Transcription (RNA to DNA) → Integration (Viral DNA enters host nucleus) → Transcription & Translation → Assembly → Budding.