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A quick map of how the big ideas of this chapter connect together.
The Invisible Living World
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The Cell
the basic unit of life
Parts of a cell
membrane, cytoplasm, nucleus
Levels of organisation
cell to tissue to organ to body
Types of cells
plant, animal, fungal, bacterial
Microorganisms
too small to see
Four groups
protozoa, algae, fungi, bacteria
Connected to microbes
how microbes help us
Cleaning the environment
decomposition and manure
Microbes and food
yeast, curd, Rhizobium
Microalgae
make oxygen and food
Why does the invisible living world matter?
All living things are made of cells
The cell is the basic unit of life
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Cells group together
Forming tissues, organs, and a body
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Some living things are single-celled
These tiny microbes are everywhere
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Microbes act on waste and food
Making manure, curd, and oxygen
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The invisible living world supports life on Earth
📸 Snapshots
- Microorganisms are small-sized organisms and are not visible to the unaided eye.
- They can live in all kinds of environments, and even in the bodies of plants and animals.
- They are either unicellular or multicellular. Bacteria and protozoans are unicellular; fungi can be unicellular or multicellular, while plants and animals are multicellular.
- The cell is a basic unit of life.
- The body of all living organisms is made up of cells. A cell contains various components which help the organisms perform their functions and survive.
- A typical cell is bounded by a cell membrane, filled with cytoplasm and contains a nucleus. Plant, fungal, and bacterial cells have an extra covering, called a cell wall, around the cell membrane. Bacteria lack a well-defined nucleus.
- Cells differ in shape and size. Their shape is related to the function performed by them.
- Bacteria, fungi, and protozoa are different kinds of microorganisms.
- Viruses are also small in size, but they are different from other microorganisms since they reproduce only inside the host organism.
- Microorganisms can be beneficial or harmful to us.
- Some microorganisms decompose the plant and animal waste into simple substances and clean up the environment.
- Some microorganisms reside in the root nodules of legumes, such as peas, beans, and lentils. They trap nitrogen from the air and increase the soil fertility.
- Yeasts are fungi which are used in the process of making breads, cakes, pastries, idlis, dosas, and bhaturas.
- Lactobacillus is used in the curd formation at home and fermentation process in food industry.
🤔 Probe and ponder
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Have you ever wondered what you might see if the invisible world around you became visible?
View answer
AnswerWe would see a crowd of microorganisms everywhere — bacteria, protozoa, algae and fungi in water, soil, air, on our food and even inside our body. A single drop of pond water would look like a busy world of tiny living things. -
How do you think your observation of this hidden world might change the way you think about size, complexity, or even what counts as ‘living’?
View answer
AnswerWe would learn that being alive has nothing to do with being big. A single-celled microbe grows, feeds, and multiplies just as a tree or an animal does — so even one tiny cell can be a complete living organism. -
Have you thought how these tiny living beings interact with each other?
View answer
AnswerThey interact constantly. Some decompose dead matter and return nutrients to the soil, some live in the root nodules of legumes and fix nitrogen for the plant, some help us make curd and bread, and some cause disease or spoil our food.
The Invisible Living World
Class 8 — Chapter 2
2.1
The Cell
membrane, cytoplasm, nucleus; plant vs animal cell
2.2
Levels of Organisation
cell, tissue, organ, organ system, organism
2.3
Microorganisms
protozoa, algae, fungi, bacteria; microscope
2.4
Connected to Microbes
decomposition, manure, biogas; food and microbes
2.4.2–3
Food & Microalgae
yeast, Lactobacillus, Rhizobium, Spirulina
2.5
Basic Unit of Life
cell carries out life; bacteria have a nucleoid
Key Terms
- Cell
- The basic building block of all living things.
- Cell membrane
- The outer layer that controls what enters and leaves the cell.
- Cytoplasm
- The jelly-like material inside the cell where most life processes happen.
- Nucleus
- The round central part that controls the cell's activities and growth.
- Cell wall
- An extra strong outer layer found in plant, fungal, and bacterial cells.
- Tissue
- A group of similar cells working together.
- Organ
- Different tissues organised to do a major job.
- Organ system
- Several organs working together for a major function.
- Multicellular organism
- A living being made up of many cells.
- Microorganism
- A living thing too small to be seen with the naked eye.
- Decomposition
- Breaking down of dead matter by microbes into nutrient-rich substances.
- Manure
- Nutrient-rich material formed when microbes break down waste.
- Yeast
- A unicellular fungus that releases carbon dioxide, used to make dough rise.
- Fermentation
- The breakdown of sugar by microbes, used in making curd, idli, and dosa.
- Legumes
- Plants whose seeds grow in pods, such as peas, beans, and lentils.
- Rhizobium
- Bacteria in legume root nodules that trap nitrogen from the air.
- Microalgae
- Microscopic plant-like organisms that make food and release oxygen.
- Nucleoid
- The region in a bacterial cell holding genetic material, with no membrane.
