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Notes on Viruses and Bacteria (Grade 11 Science - Canada)

Viruses: General Notes

• Viruses are non-living infectious agents made up of genetic material (DNA or RNA) enclosed in a protein coat (capsid).

• They cannot reproduce on their own and must infect a host cell to replicate.

• Viruses are much smaller than bacteria and can only be seen using an electron microscope.

• Some viruses have an outer lipid envelope, which helps them infect host cells (e.g., influenza virus).

• They can mutate rapidly, making it difficult to develop long-lasting treatments or vaccines (e.g., flu viruses change yearly).

Introduction to Viruses

• Viruses are obligate intracellular parasites, meaning they rely entirely on a host cell for replication.

• They do not have organelles, cytoplasm, or cell membranes, so they don’t carry out metabolism or other life functions.

• Viral Replication Cycle:

  1. Attachment – The virus attaches to a specific receptor on the host cell.

  2. Penetration/Entry – The viral DNA or RNA enters the host cell.

  3. Replication – The host cell’s machinery replicates the viral genetic material.

  4. Assembly – New virus particles are put together inside the host cell.

  5. Release – The new viruses burst out (lysis) or exit through budding, ready to infect more cells.

Two Types of Viral Cycles:

• Lytic Cycle: The virus immediately takes over the host, rapidly producing new viruses and causing the host cell to burst.

• Lysogenic Cycle: The viral DNA integrates into the host genome and stays dormant before becoming active.

Vaccines & Prevention

• Vaccines expose the immune system to a harmless form of the virus, helping build immunity (e.g., HPV, measles, flu vaccines).

• Antibiotics DO NOT work on viruses because viruses are not cells.

• Antiviral drugs (e.g., Tamiflu for influenza) slow down viral replication but do not cure viral infections.

Introduction to Monerans (Bacteria)

• Monerans are unicellular prokaryotic organisms that lack a nucleus and membrane-bound organelles.

• The kingdom Monera used to include all bacteria, but modern classification splits them into:

  1. Eubacteria – “True bacteria,” found everywhere (e.g., E. coli, Streptococcus).

  2. Archaebacteria – Found in extreme environments like hot springs and deep-sea vents (e.g., methanogens).

• Bacteria reproduce rapidly, adapt easily, and play essential roles in the ecosystem.

Bacterial Cell Structure:

• Cell Wall – Provides structure and protection.

• Plasma Membrane – Controls what enters and exits the cell.

• Cytoplasm – Contains enzymes and ribosomes.

• DNA (Nucleoid Region) – Bacterial genetic material is a single, circular chromosome.

• Flagella – Tail-like structure used for movement.

• Pili – Hair-like structures used for attachment and DNA exchange.

Reproduction in Bacteria

Bacteria reproduce in two main ways:

1. Asexual Reproduction (Binary Fission)

• The most common method.

• A single bacterium divides into two identical daughter cells.

• Steps in Binary Fission:

  1. The bacterial DNA replicates.

  2. The cell elongates, and the DNA moves to opposite ends.

  3. A new cell wall forms, splitting the bacterium into two identical cells.

• This allows bacteria to multiply very quickly (e.g., E. coli can divide every 20 minutes under ideal conditions).

2. Genetic Variation Methods in Bacteria

• Since bacteria reproduce asexually, they have alternative ways to increase genetic diversity:

  1. Conjugation – Two bacteria connect using a pilus and transfer genetic material.

  2. Transformation – Bacteria pick up free DNA fragments from the environment.

  3. Transduction – Viruses (bacteriophages) transfer DNA from one bacterium to another.

These processes help bacteria develop resistance to antibiotics over time.

Importance of Bacteria

Bacteria are essential to ecosystems, medicine, and industry. Some key roles include:

Beneficial Bacteria

Decomposers – Break down organic matter and recycle nutrients (e.g., soil bacteria).
Nitrogen Fixation – Convert nitrogen gas into usable forms for plants (e.g., Rhizobium).
Digestion Aid – Help break down food in human intestines (e.g., gut microbiota like Lactobacillus).
Food Production – Used to make cheese, yogurt, and vinegar.
Bioremediation – Help clean up oil spills and wastewater.

Harmful Bacteria (Pathogens)

Cause Diseases – Some bacteria cause infections like pneumonia, tuberculosis, and food poisoning (e.g., Salmonella, Streptococcus).
Produce Toxins – Some bacteria release harmful substances (e.g., botulism from Clostridium botulinum).

Controlling Bacterial Growth

• Antibiotics target bacterial cell walls, protein synthesis, or DNA replication.

• Antibiotic resistance is a major issue, caused by overuse of antibiotics.

• Sterilization & Disinfectants kill bacteria on surfaces.

• Pasteurization (heating liquids) helps kill harmful bacteria in milk and juice.

Summary

Viruses are non-living and need a host to replicate; antibiotics don’t work on them.
Bacteria are unicellular prokaryotes that reproduce rapidly through binary fission.
Bacteria can be beneficial or harmful, playing key roles in ecosystems and human health.
Antibiotic resistance is a growing concern due to bacterial evolution.