General Science Notes Chapter 1 Living World and Classification of Microbes Class 8 Maharashtra Board

Notes For All Chapters – General Science Class 8

What is Classification?

• The world has millions of living organisms, including plants, animals, and microbes.
• Scientists classify them into groups based on their similarities and differences.
• Biological Classification is the process of dividing organisms into groups and subgroups.

Need for Classification

There are 87 million species of living organisms.

Classification helps in:

• Easy study of organisms.
• Understanding relationships between different species.
• Identifying new organisms easily.

History of Classification

Five Kingdom Classification by Whittaker

Whittaker classified all living organisms into five kingdoms based on:

1. Cell Structure – Prokaryotic or Eukaryotic
2. Body Complexity – Unicellular or Multicellular
3. Mode of Nutrition – Autotrophic, Heterotrophic, or Saprophytic
4. Reproduction – Sexual or Asexual
5. Life Role – Producers, Consumers, or Decomposers

Kingdom Monera (Bacteria & Blue-Green Algae)

• Cell Type: Prokaryotic
• Structure: Unicellular, no true nucleus.
• Nutrition: Some bacteria make their food (autotrophic), others depend on food (heterotrophic).
• Examples: Lactobacillus (curd bacteria), Salmonella (causes food poisoning).

Kingdom Protista (Amoeba, Paramecium, Euglena)

• Cell Type: Eukaryotic
• Structure: Mostly unicellular, well-defined nucleus.
• Nutrition: Some perform photosynthesis (autotrophic), others eat small organisms (heterotrophic).
• Examples: Amoeba (moves with pseudopodia), Paramecium (moves with cilia).

Kingdom Fungi (Yeast, Mushroom, Mold)

• Cell Type: Eukaryotic
• Structure: Multicellular, thread-like structure.
• Nutrition: Saprophytic (absorbs nutrients from dead matter).
• Examples:
  • Yeast (used in bread-making).
  • Mushroom (a type of edible fungus).
  • Penicillium (used to make antibiotics).

Kingdom Plantae (Plants, Algae, Trees)

• Cell Type: Eukaryotic
• Structure: Multicellular, has cell walls and chloroplasts.
• Nutrition: Autotrophic (makes food by photosynthesis).
• Examples: Rose plant, Mango tree, Algae (like Chlorella).

Kingdom Animalia (Humans, Birds, Fish, Insects)

• Cell Type: Eukaryotic
• Structure: Multicellular, no cell wall.
• Nutrition: Heterotrophic (depends on plants or animals for food).
• Examples: Humans, Lions, Birds, Fish, Insects.

Microorganisms (Microbes)

Microorganisms are very small living organisms, some can be useful, while others can be harmful.

Types of Microorganisms:

1. Bacteria – Unicellular, found in air, water, soil (e.g., Lactobacillus, Salmonella).
2. Protozoa – Unicellular, found in water (e.g., Amoeba, Plasmodium).
3. Fungi – Multicellular, decomposers (e.g., Yeast, Mushroom).
4. Algae – Unicellular/multicellular, performs photosynthesis (e.g., Chlorella).
5. Viruses – Cannot live alone, needs a host to reproduce (e.g., COVID-19, Polio virus).

Importance of Microorganisms

Viruses – Organisms at the Edge of Living and Non-living

• Viruses are very small and can be seen only under an electron microscope.
• They are not living outside a host but act like living organisms inside a host.
• Structure: A protein coat surrounding DNA or RNA.
• Examples: Polio virus, Influenza virus, HIV.

Role of Microbes in Daily Life

Uses of Microbes:

✔ Food production: Lactobacillus helps make curd.
✔ Medicine: Penicillium is used for making antibiotics.
✔ Agriculture: Rhizobium bacteria help in nitrogen fixation.

Harmful Effects of Microbes:

❌ Diseases: Some bacteria and viruses cause diseases.
❌ Food spoilage: Bacteria cause food to rot.