The Invisible Living World: Beyond Our Naked Eye | Class 8 Science Notes
By ConceptScroll Team · Published on 17 July 2026 · 5 min read
The Invisible Living World: Beyond Our Naked Eye – this guide gives you a concise, exam-ready overview of The Invisible Living World: Beyond Our Naked Eye from Class 8 Science, written by ConceptScroll editors and reviewed against the latest NCERT textbook.
What Is a Cell?
All living organisms are made up of cells, which are the fundamental units of life. Cells vary in shape, size, and structure depending on their function and the organism they belong to. To understand cells better, we can observe them under a microscope. For example, the onion peel contains cells that can be stained and viewed to reveal their structure. The onion peel cells are rectangular and closely packed without spaces. Similarly, human cheek cells can be observed by scraping the inside of the mouth, staining, and viewing under a microscope. These cells are polygon-shaped and form the inner lining of the mouth. Cells have three main parts: the cell membrane, cytoplasm, and nucleus. The cell membrane encloses the cell and controls the entry and exit of substances. Cytoplasm is a jelly-like substance where most life processes occur. The nucleus regulates cell activities and growth. Plant cells, like onion cells, have an additional cell wall that provides rigidity and strength. Plant cells also contain plastids such as chloroplasts, which contain chlorophyll and help in photosynthesis. They have a large vacuole that stores substances and maintains cell shape. Animal cells may have small or no vacuoles. Different cells have different shapes related to their functions, such as muscle cells being spindle-shaped and nerve cells being long with branches. Cells group to form tissues, organs, organ systems, and ultimately an organism.
📊 Diagram: Figure 2.3 shows (a) onion bulb, (b) onion peel, (c) microscopic view of onion peel cells showing rectangular cells, and (d) microscopic view of human cheek cells showing polygon-shaped cells.
🧪 Activity: Activity 2.2: Preparing onion peel slide stained with safranin to observe cells under microscope. Activity 2.3: Collecting and staining human cheek cells with methylene blue for microscopic observation.
🔗 Connection: This section leads to understanding the diversity of cell shapes and their relation to function, and then to levels of organization in living organisms.
Frequently asked questions
1. Various parts of a cell are given below. Write them in the appropriate places in the following diagram. Nucleus Cytoplasm Chloroplast Cell wall Cell membrane Nucleoid
The student should label the parts of the cell diagram as follows:
- Nucleus: The control center of the cell, usually a large spherical structure.
- Cytoplasm: The jelly-like substance filling the cell.
- Chloroplast: Green structures present in plant cells responsible for photosynthesis.
- Cell wall: The rigid outer layer surrounding plant, fungal, and bacterial cells.
- Cell membrane: The thin layer just inside the cell wall that controls entry and exit of substances.
- Nucleoid: The region in
2. Aanandi took two test tubes and marked them A and B. She put two spoonfuls of sugar solution in each of the test tubes. In test tube B, she added a spoonful of yeast. Then she attached two incompletely inflated balloons to the mouth of each test tube. She kept the set-up in a warm place, away from sunlight. (i) What do you predict will happen after 3–4 hours? She observed that the balloon attached to test tube B was inflated. What can be a possible explanation for this? (a) Water evaporated in test tube B and filled the balloon with the water vapour. (b) The warm atmosphere expanded the air inside the test tube B, which inflated the balloon. (c) Yeast produced a gas inside the test tube B which inflated the balloon. (d) Sugar reacted with warm air, which produced gas, eventually inflating the balloon. (ii) She took another test tube, 1/4 filled with lime water. She removed the balloon from test tube B in such a manner that the gas inside the balloon did not escape. She attached the balloon to the test tube with lime water and shook it well. What do you think she wants to find out?
(i) The correct answer is (c) Yeast produced a gas inside the test tube B which inflated the balloon. Explanation: Yeast ferments sugar and produces carbon dioxide gas, which inflates the balloon.
(ii) Aanandi wants to test whether the gas produced is carbon dioxide. When the gas from the balloon is shaken with lime water, if the lime water turns milky, it confirms the presence of carbon dioxide.
3. A farmer was planting wheat crops in his field. He added nitrogen-rich fertiliser to the soil to get a good yield of crops. In the neighbouring field, another farmer was growing bean crops, but she preferred not to add nitrogen fertiliser to get healthy crops. Can you think of the reasons?
Beans are legumes and have nitrogen-fixing bacteria (Rhizobium) in their root nodules that convert atmospheric nitrogen into a form usable by plants. Therefore, they do not require additional nitrogen fertiliser. Wheat crops do not have this ability and need nitrogen fertiliser to improve soil fertility and yield.
4. Snehal dug two pits, A and B, in her garden. In pit A, she put fruit and vegetable peels and mixed it with dried leaves. In pit B, she dumped the same kind of waste without mixing it with dried leaves. She covered both the pits with soil and observed after 3 weeks. What is she trying to test?
Snehal is testing the effect of mixing dried leaves with fruit and vegetable waste on the decomposition process. Mixing dried leaves provides carbon and aeration, which helps microorganisms decompose the waste faster. Pit A is expected to show faster decomposition than pit B.
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