Which of the following statements is true regarding the nuclear region of a prokaryotic cell?

It is undefined and contains only nucleic acids.

It is well-defined and surrounded by a nuclear membrane.

It is undefined and contains only nucleic acids.

It contains multiple chromosomes.

What is the primary function of the rough endoplasmic reticulum (RER)?

Protein synthesis and transport

Why are mitochondria considered the 'powerhouses of the cell'?

They produce ATP through cellular respiration.

Assertion (A): Lysosomes are known as 'suicide bags' of the cell. Reason (R): Lysosomes contain powerful digestive enzymes that can break down all organic material.

A and R both correct, R explains A

Assertion (A): Plant cells do not burst when placed in a hypotonic solution. Reason (R): The cell wall provides rigidity and prevents the cell from bursting.

A and R both correct, R explains A

A student performs an experiment where they place dried raisins in plain water. After a few hours, the raisins swell up. What is the scientific phenomenon responsible for this observation?

Osmosis, as water moves from a region of higher water concentration to lower water concentration through a selectively permeable membrane.

Diffusion, as water molecules move from higher to lower concentration.

Osmosis, as water moves from a region of higher water concentration to lower water concentration through a selectively permeable membrane.

Active transport, as the raisins actively absorb water.

Plasmolysis, as the raisins gain water and expand.

Observe the diagram depicting the process of plasmolysis in a plant cell. What is the most likely reason for the cell's appearance?

The cell was placed in a hypertonic solution, causing water to leave the cell.

The cell was placed in a hypotonic solution, causing it to swell.

The cell was placed in an isotonic solution, maintaining its normal shape.

The cell was placed in a hypertonic solution, causing water to leave the cell.

The cell wall has broken down, leading to cell lysis.

Which of the following statements are correct regarding the differences between prokaryotic and eukaryotic cells? Select ALL that apply.

Prokaryotic cells generally have a single chromosome, while eukaryotic cells have more than one.

Eukaryotic cells lack membrane-bound cell organelles, unlike prokaryotic cells.

The nuclear region in prokaryotic cells is well-defined and surrounded by a nuclear membrane.

Prokaryotic cells are generally smaller in size compared to eukaryotic cells.

Is this Class 9 Science Chapter 5 quiz free?

Yes, this quiz on 'The Fundamental Unit of Life' for CBSE Class 9 Science is completely free to use, with no sign-up or registration required.

How many questions are in the quiz?

The main 'Game Mode' quiz contains 40 multiple-choice questions covering various aspects of the chapter, with a mix of easy, medium, and hard difficulties.

Is this quiz based on the NCERT textbook?

Absolutely! All questions are carefully crafted based on the latest NCERT Class 9 Science textbook for Chapter 5, ensuring full alignment with your curriculum.

Can I check my answers and get explanations?

Yes, after attempting each question, you will receive instant feedback, a short explanation, and a detailed explanation to help you understand the concepts better.

What topics does this quiz cover?

This quiz covers key topics such as cell discovery, plasma membrane, cell wall, nucleus, cytoplasm, various cell organelles (ER, Golgi, mitochondria, plastids, vacuoles, lysosomes), and the differences between prokaryotic and eukaryotic cells.

Are there questions from the NCERT textbook exercises?

Yes, the 'Book Questions' section provides solved versions of the questions from the NCERT textbook exercises for Chapter 5, helping you prepare for exams.

Home › CBSE › Class 9 › Science › THE FUNDAMENTAL UNIT OF LIFE

CBSE · Class 9 · 🔬 Science · Chapter 5

THE FUNDAMENTAL UNIT OF LIFE

Cell structureCell organelles and their functionsProkaryotic and eukaryotic cellsPlasma membrane and cell wallNucleus and cytoplasm

Chapter 5, 'The Fundamental Unit of Life', introduces students to the basic structural and functional unit of all living organisms – the cell. It covers the discovery of the cell, its various components like the plasma membrane, cell wall, nucleus, and cytoplasm, along with the functions of different cell organelles such as mitochondria, ER, Golgi apparatus, lysosomes, and plastids. Understanding this chapter is crucial for building a strong foundation in biology and comprehending how life functions at its most basic level.

Cell – The Fundamental Unit of Life

Cell ki Khoj aur Cell Theory

Robert Hooke (1665): Pehli baar cork slice mein dead cells ko observe kiya, unhe 'cells' naam diya (Latin word 'cellula' se, matlab 'little room').
Leeuwenhoek (1674): Pehli baar living cells (pond water mein) ko observe kiya advanced microscope se.
Robert Brown (1831): Cell ke andar nucleus ki khoj ki.
Purkinje (1839): Cell ke fluid substance ko protoplasm naam diya.

Cell Theory

Schleiden (1838) & Schwann (1839): Propose kiya ki sabhi plants aur animals cells se bane hote hain aur cell life ki basic unit hai.
Virchow (1855): Theory ko expand kiya aur kaha "Omnis cellula e cellula", matlab saari cells pre-existing cells se hi banti hain.

Cell Theory ke Main Points:

Sabhi living organisms cells aur unke products se bane hain.
Cell life ki structural aur functional unit hai.
Sabhi cells pre-existing cells se hi arise karti hain.

Organisms ke Types (Cell ke Number ke Aadhar par)

Unicellular Organisms:
Single cell se bane hote hain.
Ek hi cell saare life functions perform karti hai (e.g., movement, food intake, respiration, excretion).
Examples: Amoeba, Paramecium, Chlamydomonas, Bacteria.
Multicellular Organisms:
Bahut saari cells se bane hote hain.
Cells specialized functions perform karti hain aur tissues, organs, organ systems banati hain.
Examples: Fungi, Plants, Animals.

Cell Shape aur Size

Cells ki shape aur size unke specific function par depend karti hai.
Kuch cells ki shape fixed hoti hai (e.g., nerve cells), kuch ki change hoti rehti hai (e.g., Amoeba, WBCs).
Sizes bhi vary karti hain: sabse choti Mycoplasma (0.1 µm) se lekar sabse badi Ostrich egg tak.
Human body mein: Nerve cells sabse lambi hoti hain.

Cell ki Structural Organisation

Har cell mein teen main components hote hain:

Plasma Membrane (Cell Membrane)
Nucleus
Cytoplasm

1. Plasma Membrane (Cell Membrane)

Location: Cell ki outermost covering (animal cells mein) ya cell wall ke andar (plant cells mein).
Composition: Lipids (phospholipids) aur Proteins se bani hoti hai. Fluid Mosaic Model iska structure explain karta hai.
Nature: Selectively Permeable Membrane (ya semi-permeable membrane) – sirf kuch substances ko cell ke andar aur bahar jaane deti hai.
Functions:
Cell ko external environment se separate karti hai.
Substances ke movement ko regulate karti hai (entry aur exit).
Cell ko definite shape deti hai (animal cells mein).
Endocytosis (Amoeba mein food intake) aur Exocytosis (waste removal) mein help karti hai.

Substances ka Movement Across Plasma Membrane

Diffusion:
Substances ka movement higher concentration se lower concentration ki taraf.
Gases (CO₂, O₂) ka movement cell mein isi process se hota hai.
Requires no energy.
Osmosis:
Water molecules ka movement ek selectively permeable membrane ke through higher water concentration se lower water concentration ki taraf.
Water potential gradient ke according hota hai.
Requires no energy.

Solutions ke Types (Osmosis ke Context mein)

Isotonic Solution:
Cell ke andar aur bahar water concentration same hoti hai.
Net movement of water nahi hota, cell ki size unchanged rehti hai.
Hypotonic Solution:
Cell ke bahar water concentration zyada hoti hai (solution dilute hota hai).
Water cell ke andar move karta hai (endosmosis), cell swell ho jaati hai aur burst bhi ho sakti hai (animal cells mein).
Plant cells mein turgid ho jaati hai (cell wall bursting se protect karti hai).
Hypertonic Solution:
Cell ke bahar water concentration kam hoti hai (solution concentrated hota hai).
Water cell se bahar move karta hai (exosmosis), cell shrink ho jaati hai.
Plant cells mein plasmolysis hoti hai (plasma membrane cell wall se alag ho jaati hai).

2. Cell Wall (Plant Cells mein)

Location: Plasma membrane ke bahar, plant cells, fungi aur bacteria mein present hoti hai.
Composition: Mainly cellulose se bani hoti hai (plants mein). Cellulose ek complex carbohydrate hai jo structural strength provide karta hai.
Nature: Fully Permeable – sabhi substances ko easily pass hone deti hai.
Functions:
Cell ko definite shape aur structural strength provide karti hai.
Cell ko mechanical stress aur infection se protect karti hai.
Hypotonic solution mein cell ko burst hone se bachati hai (turgidity maintain karti hai).
Adjacent cells ke beech communication mein help karti hai (plasmodesmata ke through).

3. Nucleus

Location: Generally cell ke center mein (animal cells) ya periphery ki taraf (mature plant cells mein bade vacuole ki wajah se).
Structure:
Nuclear Membrane (Nuclear Envelope): Double-layered covering, pores hote hain jo material exchange mein help karte hain cytoplasm aur nucleus ke beech.
Nucleoplasm: Nucleus ke andar ka fluid substance.
Chromatin Material: Thread-like structures, cell division ke time chromosomes mein condense ho jaate hain.
Chromosomes: Rod-shaped structures, DNA aur proteins se bane hote hain. Genetic information (genes) carry karte hain parents se offspring tak.
Nucleolus: Nucleus ke andar ek small spherical body, ribosome synthesis mein help karti hai.
Functions:
Cell ki saari activities ko control karta hai (cell ka 'brain').
Genetic information store karta hai aur next generation mein pass karta hai.
Cell division ko regulate karta hai.
Protein synthesis aur ribosome formation mein important role play karta hai.

Prokaryotic vs Eukaryotic Cells

4. Cytoplasm

Location: Plasma membrane ke andar ka fluid content, nucleus ko surround karta hai.
Composition: Mainly water, salts, organic molecules (proteins, carbohydrates, fats, nucleic acids) ka mixture.
Structure:
Cytosol: Cytoplasm ka fluid portion.
Cell Organelles: Cytosol mein membrane-bound structures present hote hain jo specific functions perform karte hain.
Functions:
Metabolic reactions ka site (e.g., glycolysis).
Cell organelles ko support provide karta hai.
Substances ka transport cell ke andar.

Cell Organelles

Cell ke andar ke specialized structures jo specific functions perform karte hain.

1. Endoplasmic Reticulum (ER)

Structure: Network of membrane-bound tubules aur sheets (cisternae). Plasma membrane se nucleus tak extend karta hai.
Types:
Rough Endoplasmic Reticulum (RER): Surface par ribosomes attached hote hain. Protein synthesis aur transport mein involved.
Smooth Endoplasmic Reticulum (SER): Ribosomes absent hote hain. Lipid synthesis, steroid synthesis, aur detoxification of drugs and poisons mein involved.
Functions:
Intracellular transport channel (proteins aur lipids ka).
RER: Protein synthesis aur folding.
SER: Lipid synthesis, detoxification, calcium storage.

2. Golgi Apparatus (Golgi Complex / Golgi Body)

Structure: Flattened membrane-bound sacs (cisternae) ka stack. ER ke paas located hota hai.
Functions:
ER se aaye proteins aur lipids ko modify, package, aur dispatch karta hai.
Lysosomes ka formation karta hai.
Plant cells mein cell wall material (cellulose) synthesis mein help karta hai.

3. Lysosomes

Structure: Membrane-bound sacs containing digestive enzymes.
Functions:
Waste disposal system of the cell.
Foreign material (bacteria, food particles) aur worn-out cell organelles ko digest karta hai.
"Suicide Bags" ke naam se jaana jaata hai kyunki cell damage hone par ye burst ho jaate hain aur apne hi cell ko digest kar lete hain.

4. Mitochondria

Structure: Double-membraned organelle. Outer membrane porous, inner membrane deeply folded (cristae) jo surface area increase karti hai.
Functions:
"Powerhouse of the Cell" – ATP (Adenosine Triphosphate) molecules ke form mein energy release aur store karta hai through cellular respiration.
Apna khud ka DNA aur ribosomes hote hain, isliye semi-autonomous organelle kehte hain.

5. Plastids (Plant Cells mein)

Structure: Double-membraned organelles, apna khud ka DNA aur ribosomes hote hain.
Types:
Chloroplasts:
Chlorophyll pigment present hota hai, jo photosynthesis ke liye essential hai.
Green colour provide karte hain plants ko.
Inner structure mein stroma aur thylakoids (grana) hote hain.
Chromoplasts:
Other coloured pigments (red, orange, yellow) hote hain, flowers aur fruits ko colour dete hain.
Leucoplasts:
Colourless plastids.
Mainly food storage (starch, oil, protein granules) mein involved hote hain.

6. Vacuoles

Structure: Membrane-bound sacs, fluid se bhare hote hain.
Animal Cells: Small aur temporary vacuoles hote hain.
Plant Cells: Large central vacuole (cell volume ka 50-90% occupy kar sakta hai) hota hai.
Functions:
Storage of water, nutrients, waste products.
Plant cells mein turgidity aur rigidity maintain karta hai (turgor pressure).
Amoeba mein food vacuole food digest karta hai, contractile vacuole excess water remove karta hai.

Plant Cell vs Animal Cell

Cell Division

Cell division wo process hai jismein ek parent cell divide hokar daughter cells banati hai. Ye growth, repair aur reproduction ke liye essential hai.

1. Mitosis (Equational Division)

Purpose: Growth, repair of damaged tissues, replacement of old cells, asexual reproduction.
Occurs in: Somatic cells (body cells).
Process:
Ek parent cell divide hokar do identical daughter cells banati hai.
Daughter cells mein chromosome number parent cell ke barabar hota hai (diploid to diploid).
Stages: Prophase, Metaphase, Anaphase, Telophase (followed by Cytokinesis).

2. Meiosis (Reductional Division)

Purpose: Formation of gametes (sperm aur egg cells) for sexual reproduction.
Occurs in: Reproductive cells (germ cells).
Process:
Ek parent cell divide hokar char haploid daughter cells banati hai.
Daughter cells mein chromosome number parent cell ka half ho jaata hai (diploid to haploid).
Do successive divisions involve hote hain (Meiosis I aur Meiosis II).
Significance: Genetic variation create karta hai through crossing over aur independent assortment.

Easy (15)

Who first observed living cells?
- Robert Hooke
- Anton von Leeuwenhoek (correct)
- Robert Brown
- Purkinje
Why: Anton von Leeuwenhoek was the first to observe living cells.
The outermost covering of an animal cell is called the:
- Cell wall
- Plasma membrane (correct)
- Nucleus
- Cytoplasm
Why: The plasma membrane forms the outermost boundary of an animal cell.
Which cell organelle is responsible for packaging and dispatching materials synthesized in the cell?
- Mitochondria
- Ribosomes
- Golgi apparatus (correct)
- Lysosomes
Why: The Golgi apparatus is involved in the packaging and dispatching of materials.
The jelly-like substance present inside the plasma membrane is called:
- Nucleoplasm
- Cytoplasm (correct)
- Protoplasm
- Cell sap
Why: Cytoplasm is the fluid content inside the plasma membrane.
Which of the following is absent in animal cells but present in plant cells?
- Mitochondria
- Cell wall (correct)
- Nucleus
- Cytoplasm
Why: Plant cells have a cell wall, which is absent in animal cells.
The term 'cell' was coined by:
- Schleiden
- Schwann
- Robert Hooke (correct)
- Rudolf Virchow
Why: Robert Hooke observed cork cells and coined the term 'cell'.
Which of these is a prokaryotic cell?
- Onion cell
- Human cheek cell
- Bacteria (correct)
- Amoeba
Why: Bacteria are examples of prokaryotic cells.
The movement of water molecules through a selectively permeable membrane is called:
- Diffusion
- Osmosis (correct)
- Active transport
- Endocytosis
Why: Osmosis is the specific term for water movement across a selectively permeable membrane.
True or False: All living organisms are made up of cells.
Why: The cell theory states that all living organisms are composed of cells.
True or False: The cell wall is present in both plant and animal cells.
Why: The cell wall is characteristic of plant cells, not animal cells.
True or False: Lysosomes are known as the 'powerhouses of the cell'.
Why: Mitochondria are the 'powerhouses of the cell', not lysosomes.
The cell membrane is called a _______________ membrane because it allows only certain substances to pass through.
Why: The cell membrane's selective nature earns it the name 'selectively permeable'.
The process by which a cell engulfs food particles is called _______________.
Why: Endocytosis is the process of engulfing substances by the cell membrane.
Identify the part labeled 'X' in the given diagram of an animal cell.
- Mitochondrion
- Nucleus (correct)
- Golgi apparatus
- Endoplasmic reticulum
Why: The central, usually spherical, organelle labeled 'X' is the nucleus.
Which part of the plant cell shown in the diagram provides structural strength?
- Plasma membrane
- Cytoplasm
- Cell wall (correct)
- Nucleus
Why: The cell wall, the outermost rigid layer, provides structural strength to plant cells.

Medium (15)

If a plant cell is placed in a hypotonic solution, what will happen to its cell wall?
- It will shrink.
- It will burst.
- It will remain intact. (correct)
- It will become more permeable.
Why: The rigid cell wall prevents a plant cell from bursting in a hypotonic solution.
Which of the following statements is true regarding the nuclear region of a prokaryotic cell?
- It is well-defined and surrounded by a nuclear membrane.
- It is undefined and contains only nucleic acids. (correct)
- It contains multiple chromosomes.
- It is absent.
Why: Prokaryotic cells have an undefined nuclear region called the nucleoid, without a membrane.
What is the primary function of the rough endoplasmic reticulum (RER)?
- Lipid synthesis
- Protein synthesis and transport (correct)
- Detoxification of drugs
- Energy production
Why: RER is involved in protein synthesis due to the presence of ribosomes on its surface.
Why are mitochondria considered the 'powerhouses of the cell'?
- They store waste products.
- They synthesize proteins.
- They produce ATP through cellular respiration. (correct)
- They control cell division.
Why: Mitochondria generate energy (ATP) for the cell through cellular respiration.
Match the cell organelle with its primary function.
Why: Each organelle has a specific role: mitochondria for energy, ribosomes for proteins, lysosomes for waste, and chloroplasts for food production.
Match the cell component with its characteristic.
Why: The plasma membrane is selectively permeable, cell wall is cellulose-based, nucleus holds chromosomes, and cytoplasm is the cell's fluid.
Match the cell type with its nuclear characteristics.
Why: Prokaryotes have a nucleoid, eukaryotes a true nucleus. Plant cells have large vacuoles, animal cells small ones.
Match the scientist with their contribution to cell biology.
Why: Hooke coined 'cell', Leeuwenhoek saw living cells, Brown found the nucleus, and Schleiden/Schwann formulated cell theory.
The process of shrinkage of the protoplast of a plant cell from the cell wall due to loss of water is called _______________.
Why: Plasmolysis describes the shrinkage of a plant cell's protoplast away from its wall.
Organisms whose cells lack a nuclear membrane are called _______________.
Why: Prokaryotes are defined by the absence of a nuclear membrane in their cells.
The site of protein synthesis in a cell is the _______________.
Why: Ribosomes are the cellular machinery responsible for synthesizing proteins.
Arrange the following components of a plant cell from outermost to innermost layer: Plasma membrane, Cell wall, Cytoplasm, Nucleus.
Why: The order is Cell wall, Plasma membrane, Cytoplasm, then Nucleus.
Arrange the steps of preparing an onion peel slide in the correct order: 1. Add a drop of water on a slide. 2. Place the onion peel on the water. 3. Add a drop of safranin solution. 4. Cover with a coverslip.
Why: The correct sequence is water, peel, stain, then coverslip.
Identify the organelle responsible for photosynthesis in the given plant cell diagram.
- Mitochondrion
- Chloroplast (correct)
- Vacuole
- Nucleus
Why: Chloroplasts are the organelles that carry out photosynthesis in plant cells.
Which labeled part in the prokaryotic cell diagram represents the genetic material?
- Ribosomes
- Plasma membrane
- Nucleoid (correct)
- Cell wall
Why: The nucleoid is the region containing the genetic material in a prokaryotic cell.

Hard (10)

Assertion (A): The plasma membrane is called a selectively permeable membrane. Reason (R): It allows the movement of all substances in and out of the cell freely.
Why: The plasma membrane is selectively permeable, meaning it controls, rather than freely allows, substance movement.
Assertion (A): Lysosomes are known as 'suicide bags' of the cell. Reason (R): Lysosomes contain powerful digestive enzymes that can break down all organic material.
Why: Lysosomes are 'suicide bags' because their powerful digestive enzymes can destroy the cell itself if released.
Assertion (A): Plant cells do not burst when placed in a hypotonic solution. Reason (R): The cell wall provides rigidity and prevents the cell from bursting.
Why: The rigid cell wall of plant cells prevents them from bursting in hypotonic solutions by counteracting internal pressure.
A student observes a cell under a microscope and notes the following characteristics: 1. Presence of a cell wall. 2. Absence of a nuclear membrane. 3. Presence of ribosomes. 4. Size approximately 5 µm. Based on these observations, what type of cell is the student most likely observing?
- Eukaryotic plant cell
- Eukaryotic animal cell
- Prokaryotic cell (correct)
- Fungal cell
Why: The absence of a nuclear membrane and small size are key indicators of a prokaryotic cell.
A biologist is studying a newly discovered organism. They find that its cells have a well-defined nucleus, membrane-bound organelles, and a cell wall made of cellulose. Which category does this organism most likely belong to?
- Bacteria
- Animal
- Plant (correct)
- Fungi
Why: A well-defined nucleus, membrane-bound organelles, and a cellulose cell wall are characteristic of plant cells.
A student performs an experiment where they place dried raisins in plain water. After a few hours, the raisins swell up. What is the scientific phenomenon responsible for this observation?
- Diffusion, as water molecules move from higher to lower concentration.
- Osmosis, as water moves from a region of higher water concentration to lower water concentration through a selectively permeable membrane. (correct)
- Active transport, as the raisins actively absorb water.
- Plasmolysis, as the raisins gain water and expand.
Why: The swelling of raisins in water is due to osmosis, where water moves into the raisin (lower water potential) across its membrane.
Identify the process shown in the diagram, which results in two identical daughter cells.
- Meiosis
- Mitosis (correct)
- Binary fission
- Budding
Why: The diagram shows a mother cell dividing into two identical daughter cells, which is characteristic of mitosis.
Observe the diagram depicting the process of plasmolysis in a plant cell. What is the most likely reason for the cell's appearance?
- The cell was placed in a hypotonic solution, causing it to swell.
- The cell was placed in an isotonic solution, maintaining its normal shape.
- The cell was placed in a hypertonic solution, causing water to leave the cell. (correct)
- The cell wall has broken down, leading to cell lysis.
Why: Plasmolysis occurs when a plant cell loses water in a hypertonic solution, causing its protoplast to shrink.
Which of the following statements are correct regarding the differences between prokaryotic and eukaryotic cells? Select ALL that apply.
- Prokaryotic cells generally have a single chromosome, while eukaryotic cells have more than one. (correct)
- Eukaryotic cells lack membrane-bound cell organelles, unlike prokaryotic cells.
- The nuclear region in prokaryotic cells is well-defined and surrounded by a nuclear membrane.
- Prokaryotic cells are generally smaller in size compared to eukaryotic cells. (correct)
Why: Prokaryotes have single chromosomes and are smaller, while eukaryotes have multiple chromosomes and membrane-bound organelles.
Which two of the following organelles are known to contain their own genetic material (DNA)?
- Mitochondria (correct)
- Golgi apparatus
- Chloroplasts (correct)
- Lysosomes
Why: Mitochondria and chloroplasts are unique in having their own DNA, separate from the cell's nucleus.