Chapter-2. The Invisible Living 2 World: Beyond Our Naked Eye Science Curiosity class 8 in english Medium CBSE Notes

Chapter 2: The Invisible Living World – Definitions & Important Points

Definitions

• Cell: The smallest unit of life that can perform all basic life functions.
• Microorganisms: Tiny living organisms that cannot be seen with the naked eye.
• Cell Membrane: The outer covering of the cell that controls the movement of substances in and out.
• Cytoplasm: Jelly-like substance inside the cell where most life processes occur.
• Nucleus: The control center of the cell that regulates all activities.
• Tissue: A group of similar cells performing the same function.
• Organ: A structure made of different tissues working together.
• Organ System: A group of organs working together to perform a function.
• Unicellular Organism: An organism made of a single cell.
• Multicellular Organism: An organism made of many cells.
• Fermentation: A process in which microorganisms convert substances into simpler products.
• Nitrogen Fixation: The process of converting atmospheric nitrogen into a usable form for plants.
• Decomposition: The breakdown of dead plants and animals into simpler substances by microorganisms.
• Biogas: A fuel produced by microorganisms from organic waste.
• Microalgae: Microscopic plant-like organisms that perform photosynthesis.

Important Points

• Cells are the basic building blocks of all living organisms.
• Microscopes help us observe the invisible world of microorganisms.
• Cells have different shapes and sizes depending on their function.
• Living organisms are organized as: Cell → Tissue → Organ → Organ System → Organism.
• Microorganisms are found everywhere – in air, water, soil, and inside living bodies.
• Microorganisms can be useful or harmful.
• Useful microorganisms help in food production, decomposition, and nitrogen fixation.
• Harmful microorganisms can cause diseases.
• Yeast is used in making bread and cakes through fermentation.
• Lactobacillus helps in the formation of curd.
• Rhizobium bacteria help in nitrogen fixation and improve soil fertility.
• Microorganisms help clean the environment by breaking down waste.
• Biogas is a renewable source of energy produced by microorganisms.
• Microalgae produce oxygen and support aquatic life.
• Cells work together in multicellular organisms to perform different functions.

Quick Revision Points

• Cell = Basic unit of life
• Microorganisms = Invisible living organisms
• Fermentation = Food production process
• Rhizobium = Nitrogen fixation
• Decomposition = Waste breakdown
• Biogas = Renewable energy

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