Worksheet Solutions-1: The Invisible Living World: Beyond Our Naked Eye | Worksheets with Solutions for Class 8 PDF Download

Multiple Choice Questions (MCQs)

Instruction: Select the correct option for each question.

Q1. Who first used the term “cell” after observing thin slices of cork?
a) Antonie van Leeuwenhoek
b) Robert Hooke
c) Louis Pasteur
d) Ananda Mohan Chakrabarty
Ans:  b) Robert Hooke

In 1665, Robert Hooke observed cork under a microscope and named the tiny compartments “cells.”

Q2. Which tool allows us to view objects too small to be seen with the naked eye?
a) Telescope
b) Periscope
c) Microscope
d) Binoculars
Ans: c) Microscope

Microscopes magnify tiny objects, revealing details invisible to unaided eyes.

Q3. A round-bottom flask filled with water can act as:
a) A lens/magnifier
b) A telescope
c) A prism
d) A mirror
Ans: a) A lens/magnifier

The curved water-filled flask bends light like a lens, making objects appear larger.

Q4. Which cell structure is present in plant cells but absent in animal cells?
a) Nucleus
b) Cell membrane
c) Cell wall
d) Cytoplasm
Ans: c) Cell wall

Plant cells have a rigid cell wall; animal cells do not.

Q5. Which statement is true about cheek cells?
a) They are rectangular and have a cell wall.
b) They have a large central vacuole. 
c) They contain chloroplasts.
d) They are polygon-shaped and lack a cell wall.
Ans: d) They are polygon-shaped and lack a cell wall.

Cheek cells are animal cells—irregular, flat, with no cell wall.

Fill in the Blanks

Q1. The jelly-like substance inside a cell where life processes occur is the ______.
Ans: cytoplasm

Cytoplasm contains nutrients and is the site of many cell activities.

Q2. The thin, flexible boundary of a cell that controls entry and exit is the ______ ______.
Ans: cell membrane

The cell membrane is porous and selectively allows substances in and out.

Q3. In onion peel cells, staining with ______ helps make the cells visible.
Ans: safranin

Red safranin stain highlights cell parts under a microscope.

Q4. Cheek cells are commonly stained with ______ ______.
Ans: methylene blue

Methylene blue makes the nucleus and cell boundaries more visible.
Cheek Cells

Q5. The bacteria that fix nitrogen in legume root nodules are called ______.
Answer: Rhizobium

Rhizobium converts atmospheric nitrogen into usable forms for plants.

True/False Questions

Q1. The nucleus controls all cell activities like growth and division.
Ans: True

The nucleus is called the control center of the cell because it regulates all activities, including growth and division.

Q2. Spirulina is a fungus used in bread making.
Ans: False

Spirulina is not a fungus; it is a protein-rich microalga widely used as a superfood.

Q3. Lactobacillus is the microorganism responsible for converting milk into curd.
Ans: True

Lactobacillus ferments milk sugar (lactose) into lactic acid, which causes milk to set into curd.

Q4. The process by which yeast releases carbon dioxide to make dough rise is called fermentation.
Ans: True

Yeast ferments sugars and releases carbon dioxide, which makes the dough fluffy and rise.

Q5. In bacteria, the genetic material is enclosed in a well-defined nucleus.
Ans: False

Bacteria do not have a true nucleus; their DNA is present in a region called the nucleoid.

Very Short Answer Questions 

Instruction: Answer the following questions in one line.

Q1. Who is known as the Father of Microbiology?
Ans: Antonie van Leeuwenhoek.

Q2. What do chloroplasts contain that enables photosynthesis?
Ans: Chlorophyll.

Q3. Name the large storage cavity commonly found in plant cells.
Ans: Vacuole.

Q4. What shape are muscle cells typically described as?
Ans: Spindle-shaped (tapered at both ends).

Q5. Which organisms decompose waste to form manure?
Ans: Bacteria and fungi (microbes).

Short Answer Questions

Q1. Why are some microorganisms invisible to the naked eye?
Ans: They are extremely small—often single-celled—and fall below the resolution limit of human vision. Microscopes are needed to magnify them for observation.

Q2. How does high salt or sugar preserve pickles and murabbas?
Ans: High salt/sugar creates conditions that draw water out of microbial cells (osmotic effect), preventing their growth and spoilage.

Q3. How do nerve cells (neurons) suit their function?
Ans: Neurons are long and branched, allowing rapid transmission of messages over distances in the body.

Q4. Why is warm milk preferred for curd formation?
Ans: Warm conditions help Lactobacillus multiply and convert lactose into lactic acid faster, thickening the milk.

Q5. What role do microalgae play in Earth’s oxygen supply?
Ans: Microalgae perform photosynthesis and release a major share of Earth’s oxygen, supporting life and aquatic food chains.

Match the Following 

Instruction: Match Column A with the correct option in Column B.

Ans:

1. Yeast — b) Fermentation and rising of dough
   Explanation: Yeast ferments sugars, releasing CO2 that makes dough rise.

2. Robert Hooke — e) Coined the term “cell”
   Explanation: He named the cork compartments “cells” after observing them.

3. Rhizobium — c) Nitrogen fixation in legume roots
   Explanation: Rhizobium in root nodules converts atmospheric nitrogen into plant-usable forms.

4. Methane — d) Main component of biogas
   Explanation: Anaerobic microbial action produces methane, a fuel.

5. Chloroplast — a) Photosynthesis in plant cells
   Explanation: Chloroplasts contain chlorophyll and perform photosynthesis.