Chapter 5: The Fundamental Unit of Life

Easy & Expanded Notes

1. Discovery of Cell

Cell was discovered by Robert Hooke in 1665 while observing cork.
Anton van Leeuwenhoek observed living cells.
“Cell” means small room in Latin.

2. Cell Theory

Proposed by Schleiden and Schwann:
1. All organisms are made up of cells.
2. Cell is the structural and functional unit of life.
Rudolf Virchow added: All cells arise from pre-existing cells.

3. Types of Organisms

Unicellular: Organism made of a single cell (e.g., Amoeba).
Multicellular: Organism made of many cells (e.g., Humans).

4. Cell Size & Shape

Nerve Cell: Long and branched
RBC: Round, biconcave
Smallest Cell: Mycoplasma
Largest Cell: Ostrich egg

5. Cell Structure

a) Plasma Membrane

Outer covering of the cell
Semi-permeable: Allows selective materials in or out
Made of proteins and lipids

b) Cell Wall (only in plant cells)

Thick outer layer made of cellulose
Provides shape and protection

c) Cytoplasm

Jelly-like fluid that holds organelles
Site for chemical reactions

d) Nucleus

Control centre of the cell
Contains genetic material (chromosomes)
Parts: nuclear membrane, nucleolus, nucleoplasm, chromosomes

6. Cell Organelles

Organelle	Function
Mitochondria	Produces energy (ATP), called powerhouse
ER	RER – protein synthesis, SER – fat synthesis
Golgi Body	Packaging of proteins and forming lysosomes
Lysosomes	Digestive bag of cell, “suicidal bag”
Plastids	Only in plants – chloroplast for photosynthesis
Vacuoles	Storage of food, water (large in plants)

7. Prokaryotic vs Eukaryotic Cells

Feature	Prokaryotic Cells	Eukaryotic Cells
Nucleus	Absent (no true nucleus)	Present (with membrane)
Size	Small	Large
Examples	Bacteria	Plants, Animals

8. Plant vs Animal Cell

Feature	Plant Cell	Animal Cell
Cell Wall	Present	Absent
Plastids	Present	Absent
Vacuole	Large, central	Small, many
Shape	Rectangular	Irregular/Round

MCQs

Who discovered the cell?
a) Anton van Leeuwenhoek
b) Robert Hooke
c) Robert Brown
d) Rudolf Virchow
Which cell part controls all activities?
a) Cell wall
b) Cytoplasm
c) Nucleus
d) ER
Mitochondria is known as:
a) Kitchen of cell
b) Powerhouse of cell
c) Suicidal bag
d) Control room
Which structure is semi-permeable?
a) Cell wall
b) Nucleus
c) Cell membrane
d) Vacuole
Chromosomes are made of:
a) DNA + lipids
b) DNA + proteins
c) RNA only
d) Protein only
Organelle only found in plant cells:
a) Mitochondria
b) Lysosome
c) Chloroplast
d) Golgi
ER helps in:
a) Digestion
b) Respiration
c) Transport
d) None
Lysosome is also called:
a) Control room
b) Powerhouse
c) Suicidal bag
d) Protein factory
Which cell lacks a nucleus?
a) Bacteria
b) Animal cell
c) Plant cell
d) Fungi
Which is the smallest cell?
a) RBC
b) Virus
c) Mycoplasma
d) Amoeba
Vacuole helps in:
a) Digestion
b) Energy production
c) Transport
d) Storage
The genetic material is present in:
a) Cytoplasm
b) Cell wall
c) Nucleus
d) ER
Which organelle modifies and packages proteins?
a) Mitochondria
b) Golgi Apparatus
c) Ribosome
d) Nucleolus
The control centre of the cell is:
a) Golgi body
b) Nucleus
c) Mitochondria
d) ER
Plant cells have:
a) Plastids
b) No nucleus
c) Small vacuoles
d) No cell wall

Assertion and Reason

A: Lysosomes are known as suicidal bags.
R: They burst and destroy the cell.
a) Both A and R are true, and R explains A
b) Both A and R are true, but R doesn’t explain A
c) A is true, R is false
d) A is false, R is true

A: Plasma membrane is semi-permeable.
R: It allows all substances to pass.
a) Both A and R are true, and R explains A
b) Both A and R are true, but R doesn’t explain A
c) A is true, R is false
d) A is false, R is true

A: Mitochondria are called the powerhouse of the cell.
R: They store genetic material.
a) Both A and R are true, and R explains A
b) Both A and R are true, but R doesn’t explain A
c) A is true, R is false
d) A is false, R is true

A: Plant cells have small vacuoles.
R: Vacuoles help in storage and turgidity.
a) Both A and R are true, and R explains A
b) Both A and R are true, but R doesn’t explain A
c) A is true, R is false
d) A is false, R is true

A: ER is a single membrane-bound organelle.
R: ER helps in protein and lipid synthesis.
a) Both A and R are true, and R explains A
b) Both A and R are true, but R doesn’t explain A
c) A is true, R is false
d) A is false, R is true

Case-Based Study

Passage:
A student examined onion peel and cheek cell under a microscope. Onion peel had a cell wall and large vacuole, cheek cell lacked cell wall. The student also found that mitochondria were present in both types, and nucleus controlled all functions.

Which structure is present in onion peel but not cheek cell?
a) Nucleus
b) Cell membrane
c) Mitochondria
d) Cell wall
The vacuole in plant cells is:
a) Small
b) Large and central
c) Absent
d) Same as animals
Organelle for energy:
a) Lysosome
b) Ribosome
c) Mitochondria
d) Vacuole
Nucleus function is to:
a) Store food
b) Control activities
c) Digest waste
d) Provide energy
Cheek cell is a:
a) Plant cell
b) Animal cell
c) Bacterial cell
d) Fungal cell

Reason-Based Questions Answers)

Why is the cell called the basic unit of life?
Because all life functions like growth, reproduction, and metabolism happen inside the cell.
Why is the plasma membrane called semi-permeable?
Because it allows only some substances to enter or leave the cell.
Why do plant cells have a rigid structure?
Because they have a cell wall made of cellulose that gives shape and support.
Why is mitochondria called the powerhouse of the cell?
Because it produces energy in the form of ATP for the cell.
Why are lysosomes called suicidal bags?
Because they contain enzymes that can destroy the cell if it is damaged.
Why is the nucleus important in a cell?
Because it controls all activities and has genetic material.
Why don’t animal cells have a cell wall?
Because animal cells need flexibility for movement.
Why is ER important for the cell?
Because it helps in making proteins and fats and also in transport.
Why do plant cells have large vacuoles?
Because they store water and help maintain shape.
Why are chloroplasts absent in animal cells?
Because animals do not perform photosynthesis.
Why are prokaryotic cells considered simple?
Because they do not have a true nucleus or membrane-bound organelles.
Why are chromosomes important?
Because they carry the DNA which controls heredity and function.
Why is cytoplasm needed?
Because it is the place where reactions occur and organelles float.
Why is cell wall absent in animal cells?
Because animals need flexibility in shape and movement.
Why do multicellular organisms have different types of cells?
Because different cells perform different tasks to keep the body working.

Answer Key

MCQs:
1–b, 2–c, 3–b, 4–c, 5–b, 6–c, 7–c, 8–c, 9–a, 10–c, 11–d, 12–c, 13–b, 14–b, 15–a

Assertion & Reason:
16–a, 17–c, 18–c, 19–d, 20–a

Case-Based:
21–d, 22–b, 23–c, 24–b, 25–b