In this chapter 2 The Invisible Living World: Beyond Our Naked Eye, students will embark on a journey into this invisible living world. They will learn about cells, the building blocks of life, and explore the structure of plant and animal cells, the importance of microorganisms, and the ways microbes impact our environment, health, and food.
Through engaging activities and inquiry-based learning, learners discover the diversity, structure, and significance of these unseen organisms.
The Invisible Living World Worksheet
The world around us is teeming with life – not just the visible plants and animals, but also an entire universe of living organisms that are too small to be seen with the naked eye.
Our worksheet covers important concepts such as cells, cell structure, microorganisms, levels of organisation, decomposition, fermentation, Rhizobium, yeast, Lactobacillus, and microalgae.
It includes fill in the blanks, MCQs, short-answer questions, and long-answer questions to strengthen understanding and exam preparation.
Download the worksheet today and make your Science preparation easier, smarter, and more effective!
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Science Class 8 Chapter 2 Study Notes
What is a Cell?
A cell is the basic unit of life in all living organisms.
First discovered by Robert Hooke in 1665 using a microscope.
Antonie van Leeuwenhoek improved lenses and observed microorganisms.
Parts of a cell
– Cell membrane – outer lining that allows material exchange.
– Cytoplasm – jelly-like substance where life processes occur.
– Nucleus – controls cell activities.
– Cell wall – only in plant cells, provides rigidity.
– Chloroplasts – present in green plant cells; site of photosynthesis.
– Vacuole – stores water, nutrients, and waste.
Shape & Structure of Cells
Cells differ in size, shape, and function.
Muscle cells are spindle-shaped; nerve cells are long and branched.
Cell shape helps in their specific function.
Levels of Organisation
Cell → Tissue → Organ → Organ System → Organism
Organisms may be unicellular (one cell) or multicellular (many cells).
What are Microorganisms?
Tiny organisms not visible to the naked eye.
Categories:
– Bacteria (unicellular)
– Protozoa (e.g., Amoeba, Paramecium)
– Fungi (e.g., yeast – unicellular; mould – multicellular)
– Algae
Observed in pond water, soil, air, and our body.
Viruses are acellular and reproduce only inside host cells.
The Invisible Living World Extra Questions
Q1. Why is the cell considered the basic unit of life?
Ans: The cell is considered the basic unit of life because all living organisms are made up of one or more cells. A cell contains various components that perform essential life processes. In unicellular organisms, a single cell performs all necessary functions, while in multicellular organisms, different cells perform specialised functions and work together.
Q2. What are microorganisms? Name some microorganisms and state where they are found.
Ans: Microorganisms are very small living organisms that cannot be seen with the naked eye. They are also called microbes. They include bacteria, protozoa, fungi and some algae. They are found in air, water, soil, food, and even inside the bodies of plants and animals.
Q3. How do microorganisms help in cleaning the environment?
Ans: Some microorganisms, particularly bacteria and fungi, decompose plant and animal waste into simpler substances. For example, they break down fallen leaves, fruit and vegetable peels and animal waste to form nutrient-rich manure. The nutrients return to the soil and help plants grow. Thus, microorganisms help recycle waste and nutrients in nature.
Q4. How does yeast help in making bread and cakes?
Ans: Yeast is a type of fungus. Under warm conditions, yeast breaks down food and releases carbon dioxide during respiration. The carbon dioxide forms bubbles in the dough, making it soft and fluffy. This property of yeast is used in making bread, cakes and other baked foods.
Q5. What is the role of Rhizobium bacteria in leguminous plants?
Ans: Rhizobium bacteria live in the root nodules of leguminous plants such as beans, peas and lentils. They trap nitrogen from the air and make it useful for plants. This helps the plants grow better and naturally increases the nitrogen content and fertility of the soil, reducing the need for nitrogen-rich chemical fertilisers.
Q6. Why does curd form faster in warm conditions?
Ans: Curd contains bacteria such as Lactobacillus. These bacteria feed on the sugar (lactose) present in milk and ferment it to produce lactic acid. Warm conditions help these bacteria grow and multiply, so milk kept in a warm place turns into curd faster. The lactic acid produced also gives curd its sour taste.