This MCQ module is based on: Discovery of the Cell and the Origin of Life
TOPIC 3 OF 50
Discovery of the Cell and the Origin of Life
🎓 Class 9
Science
CBSE
Theory
Ch 2 — Cell: The Building Block of Life
⏱ ~10 min
🌐 Language: [gtranslate]
🧠 AI-Powered MCQ Assessment
▲
📝 Worksheet / Assessment
▲
This assessment will be based on: Discovery of the Cell and the Origin of Life
Upload images, PDFs, or Word documents to include their content in assessment generation.
Discovery of the Cell and the Origin of Life
Class 9 Science · Chapter 2 · Part 1 — Origin of Life & Discovery of Cells
2.1 Where Did Life Begin?
Long before microscopes existed, humans wondered how the first living thing came into being on Earth. Scientific evidence today suggests that life almost certainly began in water, billions of years ago, when early Earth was a stormy, hot planet with steaming oceans and active volcanoes.
Why water? Water dissolves a huge variety of substances. In oceans of the early Earth, simple chemicals could mix freely, react, and slowly form the very first complex molecules — the molecules of life.
Hot springs and the first cells
Some scientists believe life may have started near hot springs and underwater volcanic vents. These places are extremely hot, sometimes acidic, and packed with mineral-rich water. Surprisingly, even today, certain microorganisms called thermophiles happily live in such boiling, harsh conditions.
Puga Valley, Ladakh: India's famous geothermal hot-spring region in the Himalayas. Scientists from the Birbal Sahni Institute of Palaeosciences (Lucknow) have studied microbes living in these hot springs to understand what early life on Earth might have looked like.
Activity 2.1 — Could life survive in boiling water?L3 Apply
Predict:
If you placed a normal pond microbe in water at 80°C, would it survive? What about a thermophile?
Procedure (think experiment):
- Imagine two test tubes: tube A with pond water, tube B with hot-spring water from Puga Valley.
- Heat both to 80°C and hold the temperature for 30 minutes.
- Observe under a microscope after cooling.
Reasoning: Pond microbes have proteins that denature (unfold) above ~45°C, so they die. Thermophiles have specially shaped, heat-stable proteins and lipid membranes that stay intact even at 80°C. This shows why scientists believe life could have begun in such hot environments — the very first cells may have looked like today's thermophiles.
2.2 What Is a Cell?
Every living thing — from the smallest bacterium to the tallest banyan tree to a human being — is built out of tiny units called cells. The cell is the smallest unit that can carry out all the activities we associate with life: it can take in food, breathe, grow, respond, reproduce and finally die.
Definition: A cell is the basic structural and functional unit of all living organisms. It is the smallest part of a body that is itself "alive."
Some organisms, like the amoeba and bacteria, are unicellular — their entire body is just one cell. Other organisms, like plants, animals and humans, are multicellular, made up of trillions of cells working together.
2.3 Discovery of the Cell
Robert Hooke and the first sighting (1665)
The story of cells begins in 1665, when an English scientist named Robert Hooke looked at a thin slice of cork (the bark of an oak tree) through his self-made microscope. He saw tiny, hollow, box-like compartments arranged like the rooms of a monastery. He called these compartments cellulae — Latin for "small rooms" — and from this came the word cell.
🔬 Hooke's Discovery — Predict, then click each side L2 Understand
Before reading further, predict: which side of this diagram shows the tool Hooke used, and which side shows what he actually saw and named "cells"? Click each side to check.
Click the microscope or the cork pattern above to reveal the role each played in the birth of cell biology.
Note: What Hooke actually saw were only the dead, empty cell walls of cork — the living material had long disappeared. Even so, this was the very first sighting of cells in history.
Leeuwenhoek and the first living cells
A few years later, the Dutch lens-maker Antonie van Leeuwenhoek built much sharper microscopes (magnifying up to 270x) and, in 1674, became the first person ever to see living cells — wriggling protozoa and bacteria — in a drop of pond water. He called them "animalcules."
Robert Brown and the nucleus (1831)
In 1831, Scottish botanist Robert Brown noticed a dense, dark spot inside plant cells. He named it the nucleus. Soon scientists realised that this little structure controls almost everything the cell does.
2.4 Evolution of the Microscope
1590
Janssen brothers (Netherlands) build the first compound microscope.
1665
Robert Hooke discovers and names "cells" while studying cork.
1674
Leeuwenhoek observes the first living single-celled organisms.
1831
Robert Brown identifies the nucleus inside the cell.
1838–39
Schleiden and Schwann formulate the Cell Theory.
1855
Rudolf Virchow: "All cells arise from pre-existing cells."
1931
Ernst Ruska invents the electron microscope — reveals organelles.
2.5 The Cell Theory
By the late 1830s, two German scientists put together a great unifying idea about all living things — the Cell Theory.
Cell Theory (Schleiden, Schwann & Virchow):
- All living organisms are made of one or more cells.
- The cell is the basic structural and functional unit of life.
- All cells arise from pre-existing cells (added by Virchow, 1855).
Matthias Schleiden (1838) studied many plants and concluded that every plant body is made of cells. The next year, Theodor Schwann (1839) reached the same conclusion for animals. But neither could explain how new cells were formed. Rudolf Virchow (1855) finally proposed that every cell comes from the division of an older, pre-existing cell — completing the cell theory we use today.
Why it matters: The cell theory transformed biology. Diseases, growth, reproduction and inheritance could all now be explained at the level of the cell.
Activity 2.2 — Build your own cell-theory posterL6 Create
Task: On chart paper, draw a three-section flowchart showing the contributions of Schleiden, Schwann and Virchow. Add the year of each discovery and a one-line statement.
Hint — what was the missing piece before Virchow? Show this clearly using a "before/after" arrow.
Before Virchow: scientists thought cells could appear out of "non-living material" (spontaneous generation). After 1855, Virchow's principle Omnis cellula e cellula ("every cell from a cell") replaced this idea — meaning every new cell must come from an existing one through cell division.
Competency-Based Questions
Scenario: A team from the Birbal Sahni Institute collected water samples from a hot spring in Puga Valley (Ladakh) at 78°C. Under a microscope, they found single-celled microbes still alive and dividing. The team also examined a cork slice from a tree trunk in their lab and noticed empty box-like structures.
Q1. The empty box-like structures observed in cork were first reported by L1
Ans: (c) Robert Hooke — In 1665, Hooke saw and named "cellulae" while examining cork bark under his microscope.
Q2. Why are the microbes from Puga Valley able to survive at 78°C while ordinary pond microbes cannot? L4
Puga Valley microbes are thermophiles — their proteins and membrane lipids are heat-stable and do not denature at high temperatures. Ordinary pond microbes have proteins that lose shape (denature) above ~45°C, so their cells stop functioning and die.
Q3. State true or false: The cells Robert Hooke saw in cork were alive and dividing. L2
False. Hooke saw only the dead, empty cell walls of cork tissue. Living cells were first observed by Leeuwenhoek in 1674.
Q4. The dark, dense structure inside a cell that controls its activities was named the nucleus by ____________. L1
Robert Brown (1831).
Q5. Explain Virchow's contribution and why it completed the cell theory. L3
Schleiden and Schwann had stated that all plants and animals are made of cells, but they could not explain where new cells came from. Virchow (1855) proposed Omnis cellula e cellula — every cell arises from a pre-existing cell by division. This rejected the idea of spontaneous generation and completed the modern cell theory.
Assertion–Reason Questions
Choose: (A) Both A and R are true and R is the correct explanation of A. (B) Both A and R are true but R is not the correct explanation of A. (C) A is true, R is false. (D) A is false, R is true.
A: Life is believed to have originated in water.
R: Water dissolves a wide variety of substances, allowing complex molecules to form.
(A) — Both true, and R correctly explains A.
A: Robert Hooke discovered the cell.
R: Hooke observed living protozoa swimming in pond water.
(C) — A is true, but R is false. It was Leeuwenhoek who saw living "animalcules"; Hooke saw only the empty walls of cork.
A: Schleiden and Schwann formulated the original cell theory.
R: They proved that all new cells arise from pre-existing cells.
(C) — A is true, but R is false. The principle that all cells come from pre-existing cells was added later by Rudolf Virchow (1855).
AI Tutor
Science Class 9 — Exploration
Ready