Class 8 Science · Original EZT practice
The Invisible Living World (Class 8): original worked practice
The invisible world becomes understandable when each claim names its evidence: a cork cell drawing, a living microbe seen through a lens, a cell structure, or a written observation about growth conditions.
6 original worked examples, 6 fresh self-check questions and 4 mixed questions, with explained answers. These are not copied textbook exercises, an official chapter index or a full answer key. No affiliation with NCERT is claimed.
Official sources for topic and edition context, checked 17 October 2026:
Choose, solve, check, then try a fresh question.
Before calculating, read the method prompt and name the condition that makes it useful. Write your own attempt. Open the steps only when you need them, and use the check to catch a wrong sign, unit or interpretation. Finish with the fresh question before reading its answer.
Describe a cell without overclaiming
Choose the method: Separate the typical cell model from exceptions and from cells that cooperate inside a multicellular body.
EZT practice question
A student writes: every cell has a membrane, a nucleus and chloroplasts, and every cell can live as a complete organism. Identify the correct part and three overclaims.
Show the worked solution
- A cell membrane is a typical boundary, and many cells also have cytoplasm and a nucleus.
- Some specialised cells lack a nucleus, bacteria have a nucleoid rather than a well-defined nucleus, and only some plant plastids are green chloroplasts.
- Cells in a multicellular organism carry specialised functions but cooperate; they are not all autonomous organisms.
Answer: The membrane claim is typical; the universal nucleus, chloroplast and independent-life claims are overclaims.
Check: The textbook summary calls the cell a basic unit of life while also noting bacterial nucleoids and specialised cooperation.
Watch for this: Do not turn a simplified diagram into a rule for every cell type.
Now try it yourself
Why is it safer to say a cheek cell has a membrane, cytoplasm and nucleus than to say every living cell has all three?
Check your answer
Because cell structures vary across organisms and specialised cells.
Bacteria lack a well-defined nucleus, and some specialised cells lose or modify familiar parts.
Match plant and animal cell parts to their jobs
Choose the method: Name the structure first, then the function it supports in that cell type.
EZT practice question
In written diagrams of an onion cell and a cheek cell, which extra outer structure does the onion cell have, and what job does it do?
Show the worked solution
- Both diagrams include a cell membrane, cytoplasm and nucleus.
- The onion cell also has a cell wall, which provides rigidity and strength.
Answer: The onion cell has a cell wall for rigidity and strength.
Check: The plant-cell diagram also includes plastids and a large vacuole, unlike the usual animal-cell diagram.
Watch for this: Do not say every plant cell is green or photosynthetic; non-green parts can have plastids used for storage.
Now try it yourself
Which plant-cell feature often stores substances and helps maintain shape, and is usually large compared with an animal-cell vacuole?
Check your answer
The large vacuole
Plant cells commonly have a large vacuole; animal-cell vacuoles are usually small or absent.
Keep Hooke and Leeuwenhoek distinct
Choose the method: Attach each name to the observation and decade the source actually gives.
EZT practice question
Why is Robert Hooke credited with naming the cell, while Antonie van Leeuwenhoek is linked with clearly seeing tiny living things?
Show the worked solution
- In 1665 Hooke published drawings of empty compartments in thin cork and called each space a cell.
- In the 1660s Leeuwenhoek made more useful lenses and clearly saw and described tiny living things such as bacteria and blood cells.
Answer: Hooke named cork compartments; Leeuwenhoek observed living microscopic organisms more clearly.
Check: The source distinguishes cork cells in Micrographia from Leeuwenhoek's living microscopic observations.
Watch for this: Do not merge the two events into one claim that Hooke first saw bacteria.
Now try it yourself
A caption says Hooke first described bacteria in cork. What is wrong?
Check your answer
It combines the wrong observer and specimen.
Hooke drew empty cork compartments; Leeuwenhoek is the one linked to bacteria and other tiny living things.
Classify microbes and mark the virus exception
Choose the method: Decide whether the example is unicellular, multicellular or acellular before calling it an organism.
EZT practice question
Classify bacteria, Amoeba, mould and a virus by cell organisation, and identify the exception to a cellular microorganism.
Show the worked solution
- Bacteria and Amoeba are unicellular.
- Mould is a multicellular fungus.
- A virus is microscopic and acellular; it multiplies only inside a living cell, so it should not be treated as simply another cellular organism.
Answer: Bacteria and Amoeba: unicellular; mould: multicellular; virus: acellular exception.
Check: The chapter lists bacteria and protozoa as unicellular, fungi as unicellular or multicellular, and viruses as acellular.
Watch for this: Do not use one cell rule for every microscopic entity.
Now try it yourself
Can a fungus be unicellular? Give the chapter's example.
Check your answer
Yes; yeast is a unicellular fungus.
The chapter contrasts yeast with mould, which is multicellular.
Explain decomposition with conditions, not magic
Choose the method: Name the microbes' role and the environmental condition that makes the written result possible.
EZT practice question
A school record says plant waste became nutrient-rich manure under suitable temperature and moisture. What role did microorganisms play, and why does the condition matter?
Show the worked solution
- Bacteria and fungi broke complex plant waste into simpler, nutrient-rich substances.
- Manure formation occurs at an optimal temperature and appropriate moisture level; simply saying hotter or wetter is not enough.
Answer: Decomposer microbes broke down the waste, and suitable temperature and moisture supported their activity.
Check: The nutrients return to soil and can help plants grow, completing the recycling claim.
Watch for this: Do not say microbes always grow fastest whenever conditions become warmer and wetter; extreme conditions can inhibit them.
Now try it yourself
Why is a hot, waterlogged heap not automatically the fastest place for decomposition?
Check your answer
Because microbial activity needs suitable, not extreme, conditions.
The chapter names optimal temperature and appropriate moisture, not a universal hottest-and-wettest rule.
Distinguish yeast and curd bacteria by product
Choose the method: Use the organism, input and written product instead of giving a kitchen procedure.
EZT practice question
In written classroom records, yeast makes dough rise while Lactobacillus helps milk form curd. Explain the different products.
Show the worked solution
- Yeast is a fungus that respires sugar and releases carbon dioxide, whose bubbles make dough soft and fluffy.
- Lactobacillus is a bacterium that ferments lactose and produces lactic acid, which makes curd sour.
- Both records use warm conditions, but the organism and product are different.
Answer: Yeast releases carbon dioxide; Lactobacillus produces lactic acid.
Check: The textbook identifies yeast as a fungus used in bread and Lactobacillus as one bacterium involved in curd formation.
Watch for this: Do not turn this into instructions to prepare or taste food; use the written record and follow adult-supervised school safety rules separately.
Now try it yourself
Why can high salt or sugar in a preserve slow microbial growth without proving the food is sterile?
Check your answer
It limits growth conditions but does not show that every microbe is absent.
The chapter says high concentrations of salt or sugar do not allow these organisms to grow; it does not claim sterility or universal safety.
Try a mixed set
Choose a method or explanation before opening each answer.
1. Does a pond-water observation prove that every pond contains the same number of microbes?
Show answer and reason
No.
It is evidence about the observed sample and conditions, not a universal population count.
2. Why are viruses treated differently from bacteria in this chapter?
Show answer and reason
Viruses are acellular and reproduce only inside host cells.
Bacteria are unicellular organisms; viruses do not fit that cellular organisation.
3. Can excessive heat or moisture support every microbe's growth?
Show answer and reason
No.
The chapter uses optimal temperature and appropriate moisture. Extreme conditions can inhibit growth, and different microbes live in different environments.
4. A microscope makes a microbe visible at 100 to 400 times magnification. Does visibility alone identify its species?
Show answer and reason
No.
Visibility shows shape or movement, but reliable identification can require more detail, comparison and controlled observation.
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Questions about this practice page
- What is the smallest unit of life?
- The cell is called a basic unit of life. That does not mean every specialised cell has an identical structure or can live independently.
- Who first saw microorganisms?
- The chapter links Antonie van Leeuwenhoek in the 1660s with clearly seeing and describing tiny living things such as bacteria and blood cells. Robert Hooke's earlier 1665 cork observation named cells.
- Are all microorganisms harmful?
- No. Bacteria and fungi can decompose waste, yeast is used in bread-making, and Lactobacillus helps form curd. Some microbes cause disease, but that is not every microbe.
- Are viruses microorganisms in the same way as bacteria?
- No. Viruses are microscopic and acellular, and they reproduce only inside living host cells. Bacteria are unicellular organisms.
- Are these the NCERT Curiosity exercise questions?
- No. These are original EZT written practice questions on this chapter's ideas. They do not replace the textbook, its activities or school safety instructions.