New NCERT Curiosity · Class 8 Science · Term I · Chapter 2: The Invisible Living World: Beyond Our Naked Eye
This chapter takes us into the world we cannot see with the naked eye. It explains the cell as the basic unit of life, compares plant and animal cells, and introduces microorganisms — where they live and how many of them help us in food, farming and cleaning the environment.
From the Class 8 Science Short Notes, made as per the new NCERT book Curiosity · Pages 4–11 of the book.
Key points
- A curved piece of glass shaped like a lentil seed makes small things look bigger; it is called a lens. Lenses led to microscopes.
- Robert Hooke (1665) saw small compartments in a thin slice of cork and called each one a cell.
- All living beings are made of cells. The cell is the basic unit of life, like a brick in a wall.
- Main cell parts are the cell membrane, cytoplasm and nucleus. Plant cells also have a cell wall, chloroplasts and a large vacuole.
- The shape of a cell suits its job — muscle cells are spindle-shaped, nerve cells are long and branched, cheek cells are thin and flat.
- Levels of organisation: cell → tissue → organ → organ system → organism.
- Microorganisms are too small to see with the naked eye. Some are unicellular (bacteria, Amoeba); some fungi and algae are multicellular.
- Microbes are found everywhere — in water, soil, air and even inside our body.
- Decomposers like fungi and bacteria break down waste into nutrient-rich manure; some bacteria without oxygen make biogas.
- Yeast makes dough fluffy with carbon dioxide; Lactobacillus turns milk into curd; Rhizobium traps nitrogen in root nodules of legumes.
- Microalgae make their own food using sunlight and produce more than half of Earth's oxygen.
- Bacteria have no well-defined nucleus; they have a nucleoid instead.
Key terms
- Cell: The basic unit of life; all living beings are made up of cells.
- Nucleus: The round structure in the middle of the cell that controls all its activities and regulates growth.
- Cell membrane: The thin, porous outer layer that encloses the cytoplasm and nucleus and lets materials in and waste out.
- Tissue: A group of similar cells.
- Microorganisms (microbes): Living beings so small that they cannot be seen with the naked eye.
- Decomposition: Breaking down of complex substances like dead plants, animals and dung into simpler, nutrient-rich substances by microorganisms.
- Biogas: Gas, mainly carbon dioxide and a high proportion of methane, released when some bacteria decompose waste without oxygen.
- Nucleoid: The region in bacteria that takes the place of a well-defined nucleus; bacteria have no nuclear membrane.
Diagrams to learn
- An animal cell and a plant cell (Fig 2.1)
- Table comparing plant cell and animal cell
- Table of microorganisms seen in pond water and soil
- Table of useful microbes and their work
- Table comparing plant, animal and bacterial cells
- A cell is not just a simple bag of liquid — it is a complex structure with many parts, each with a special job.
- Viruses are microscopic but acellular; they multiply only inside a living cell.
- Not all microbes are harmful — many help us with manure, curd, bread, nitrogen for crops and oxygen.
- A stain increases contrast so cell parts are seen clearly; glycerin keeps the cells from drying.
A real page from the book
Get the full chapter in the book
This page is a summary. The Class 8 Science Short Notes has the complete chapter in colour, with every diagram and worked example.
Frequently asked questions
What is the difference between a plant cell and an animal cell?
Plant cells have a cell wall, chloroplasts in green parts and one large vacuole. Animal cells have no cell wall or chloroplasts, and their vacuoles are absent or small. Both have a cell membrane, cytoplasm and nucleus.
How are microorganisms useful to us?
Yeast makes bread and cakes fluffy, Lactobacillus sets curd, and Rhizobium traps nitrogen for legume plants. Decomposers turn waste into manure, and some bacteria make biogas from waste.
Who is called the Father of Microbiology?
Antonie van Leeuwenhoek, a Dutch scientist of the 1660s. He made better lenses and microscopes and was the first to clearly see and describe bacteria and blood cells.
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