Cell: The Building Block of Life — Class 9 MCQs with Answers

Cell: The Building Block of Life — important questions & MCQs with answers (Class 9 Science)

6 solved questions from this chapter's difficulty levels, each with its answer and explanation. Tap an option to check yourself.

0 of 6 answered

1. Q1 of 6Easy

   Cells were first discovered by:

   ASchwannBAnton van LeeuwenhoekCSchleidenDRobert Hooke
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   Answer: Robert Hooke

   Explanation: Robert Hooke examined cork under a compound microscope in 1665 and named the box-like compartments he saw 'cells' — the first recorded cell observation, distinct from Leeuwenhoek's later discovery of live cells in pond water.

2. Q2 of 6Easy

   Which organelle is called the "powerhouse of the cell"?

   AMitochondrionBRibosomeCNucleusDLysosome
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   Answer: Mitochondrion

   Explanation: Mitochondria carry out aerobic respiration, breaking down glucose to release energy stored as ATP, earning them the nickname 'powerhouse of the cell' — unlike ribosomes, which build proteins rather than energy.

3. Q3 of 6Medium

   Prokaryotic cells lack:

   ACell membraneBCytoplasmCNuclear membraneDDNA
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   Answer: Nuclear membrane

   Explanation: Prokaryotes such as bacteria keep their DNA loose in the cytoplasm rather than enclosed in a membrane-bound nucleus, even though they still possess a cell membrane, cytoplasm, and DNA.

4. Q4 of 6Medium

   Assertion (A): Mitochondria are called the powerhouses of the cell. Reason (R): In mitochondria, glucose is broken down during cellular respiration to release energy, which is stored as ATP.

   ABoth A and R are true and R is the correct explanation of ABBoth A and R are true but R is not the correct explanation of ACA is true but R is falseDA is false but R is true
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   Answer: Both A and R are true and R is the correct explanation of A

   Explanation: Both statements are true. Mitochondria get this name because they release the energy, stored as ATP, that most cell activities use, so R explains A.

5. Q5 of 6Hard

   When a cell is placed in a hypertonic solution, it will:

   ASwell upBBurstCShrinkDStay the same
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   Answer: Shrink

   Explanation: In a hypertonic solution the surrounding fluid has a higher solute concentration than the cell's cytoplasm, so water leaves the cell by osmosis and it shrinks — the opposite of swelling, which happens in a hypotonic solution.

6. Q6 of 6Hard

   Assertion (A): Mitochondria and plastids can make some of their own proteins. Reason (R): Mitochondria and plastids do not have their own ribosomes.

   ABoth A and R are true and R is the correct explanation of ABBoth A and R are true but R is not the correct explanation of ACA is true but R is falseDA is false but R is true
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   Answer: A is true but R is false

   Explanation: A is true. R is false: mitochondria and plastids have their own DNA and ribosomes, which is why they can make some of their own proteins.

Cell: The Building Block of Life notes: key concepts (Class 9 Science)

Every living thing is built from cells, and a cell is a working compartment with specialised organelles. This chapter compares prokaryotic and eukaryotic cells, walks through the organelles and their jobs, and explains how substances cross the plasma membrane.

Cell

The basic structural and functional unit of all living organisms; every organism is either one cell or many working together.

Discovery of the cell

Robert Hooke first saw and named cells in cork in 1665; Leeuwenhoek later observed the first living cells.

Cell theory

All living organisms are made of cells, the cell is the basic unit of life, and every cell arises from a pre-existing cell.

Prokaryotic cell

A cell without a true nucleus or membrane-bound organelles, its genetic material lying free in the cytoplasm, as in bacteria.

Eukaryotic cell

A cell with a true membrane-bound nucleus and specialised organelles, found in protists, fungi, plants and animals.

Plasma membrane

The selectively permeable boundary that controls what enters and leaves the cell; it is flexible, which allows engulfing of material.

Diffusion and osmosis

Diffusion is the movement of a substance from higher to lower concentration; osmosis is the same movement for WATER across a semi-permeable membrane.

Hypotonic, isotonic and hypertonic

A cell swells in a hypotonic solution, stays unchanged in an isotonic one and shrinks in a hypertonic one.

Cell wall

A rigid outer layer of cellulose found only in plant cells, giving shape and allowing the cell to withstand dilute surroundings without bursting.

Nucleus

The control centre containing chromosomes made of DNA and protein, directing all the cell's activities and carrying hereditary information.

Endoplasmic reticulum

A network of membranes; the rough type bears ribosomes and makes proteins, while the smooth type makes lipids and detoxifies.

Golgi apparatus

Stacked membrane sacs that modify, package and dispatch materials made in the endoplasmic reticulum.

Mitochondria

The powerhouse of the cell, releasing energy as ATP during respiration; it has its own DNA and ribosomes.

Plastids

Found only in plant cells: chloroplasts carry chlorophyll for photosynthesis, while leucoplasts store starch, oils and proteins.

Lysosomes

Sacs of digestive enzymes that break down worn-out organelles and foreign material; called suicide bags because they can digest their own cell.

Vacuole

A storage sac; in plant cells one large central vacuole provides turgidity and stores cell sap, while animal cells have only small ones.