CHAPTER - 5

THE FUNDAMENTAL UNIT OF LIFE

Q. Can you name some living
things?

Q. How are they different?

Q. Why are they different?

Q. What does this picture depict?
Any living thing (plant or animal) is when
seen under microscope shows that it is
made up of many, small units called
cells. Cells are very small and cannot be
seen by naked eyes.

Cell: Cell is a Latin word for ‘a little

room’. Cell is the smallest, structural
and functional unit of life.
Discovery

Cork cell
• Discovered by Robert Hook in non- living cell.

• Cork cells of bark of oak tree was observed

under a self constructed microscope.

• Small honey comb like small rooms ware

observed.

• Small room means cell.

 DISCOVERY
❑ * Non- living Cell: Robert Hooke (1665).

❑ * Free living cells in pond water (Bacteria): Anton Van

Leeuwenhoek (1671).

❑ * Nucleus: Robert Brown (1831).

❑ * Protoplasm: Purkinje (1839).

❑ * Cell theory: Schleiden (1838) and Schwann (1839) in

plants and animals respectively.

❑ * All cell arises from pre existing cell: Virchow (1855)

 HOMEWORK-1
Simple HOTS

Q. The cell theory, jointly given by Schleiden and Q. Assertion- Robert Brown discovered nucleus.
Schwann did not explain Reason- Nucleoplasm and cytoplasm of a living
cell together form the protoplasm
A) all living organism are composed of cells and
A) Both A and R are true and R is correct
their products explanation of the A
B) cell is the structural and function unit of living B) Both A and R are true, but R is not the correct
organisms. explanation of the A
C) Formation of new cells C) A is true, but R is false
D) None of the above D) A is false, but R is true

Q.Shilpa is telling her 10 years old sister that cells

Q. Which scientist coined the term cell? Explain were discovered by Robert Hook in 1665. Based
the discovery.(3) on his observation, cell theory was developed.(2)
You do not have a microscope and hence, not
able to show that structure of a cell to her sister.
Her sister is too small to understand this and
asked Shilpa to show her a cell.
(i) What will Shilpa show to her sister which
can give her an idea of a cell?
(ii) What is the life of a cell?
Match the following columns.

Column I Column II
A. Robert Hooke 1. Discovery of
nucleus
B. Schleiden and 2. Protoplasm
Schwann
C. Robert Brown 3. Cell theory
D. Purkinje 4. Discovered cel

Codes
A) A-3,  B-4,  C-1,  D-2
B) A-1,  B-2,  C-3,  D-4
C) A-2,  B-4,  C-1,  D-3
D) A-4,  B-3,  C-1,  D-2
 Why is cell called the structural
and functional unit of life?
functional unit - A cell is capable of carrying out
all life processes, such as nutrition, excretion,
respiration, etc. Hence it is called as the functional
unit of life.

Structural unit - The cell is the smallest unit of life

and all the living beings are made up of cells. Hence a
cell is called the structural unit of life.
 Things to remember

Smallest cell: PPLO ( Pleuro Pneumonia Like

organism ). It is called mycoplasma

Largest cell: Ostrich egg.

Smallest cell in our body: Red blood cell.

Largest cell in our body: Nerve cell (neuron).

 SMALLEST CELL LARGEST CELL

SMALLEST CELL IN OUR BODY LARGEST CELL IN OUR BODY

Q. Can you name the organism shown in
first and second picture?

Q. What is similar in both the pictures?

Q. What difference do you observe in
both the pictures?
On the basis of number of cells an individual is made,
are divided into two categories 
Unicellular Organisms Multicellular Organisms
Multicellular organisms are
Unicellular organisms are
composed of more than one
composed of a single cell
cell
Simple body organization Complex body organization
A single cell carries out all Multiple cells perform
necessary life processes different functions
The total cell body is exposed Only the outer cells are
to the environment exposed to the environment
Injury to a cell does not cause
Injury to the cell leads to the
the death of the multicellular
death of the organism
organism
Includes both eukaryotes and
Includes only eukaryotes
prokaryotes
A lifespan of a unicellular Multicellular organisms have a
organism is usually short comparatively longer lifespan
UNICELLULAR ORGANISMS
MULTICELLULAR ORGANISM
ANIMALS
 HOMEWORK-2
Simple HOTS

The only cell organelle seen in prokaryotic Q. The undefined nuclear region of
cell is                                              prokaryotes are also known as   
A) mitochondria      A) nucleus             
B) ribosomes B) nucleolus
C) plastids            C) nucleic acid       
D) lysosomes D) nucleoid

Q. Differentiate unicellular and Q. Describe complexity in structure of

multicellular organisms with the help of organisms.(5)
well- labelled diagram.(5)
STRUCTURAL ORGANIZATION OF
A CELL

Cell membrane
cell

cytoplasm organelles

nucleus
Basic structural organization of
cell
❖ I) Plasma membrane/cell membrane:
✔ * Discover by C.Nageli and C. Cramer in 1855.

✔ * It is the outermost covering of cell except plant cell that

separates the contents of the cell from its external environment.

✔ * It allows the entry and exist of some materials ( ions and

molecules ) in and out of the cell.

✔ * It also prevents the movement of some other materials.

✔ * It is a very thin, elastic, living and selective permeable

membrane.

✔ * It is made up of lipid and proteins.

✔ * It encloses nucleus and cytoplasm.

✔ *It helps in protection of cellular component.

PLASMA MEMBRANE
How does the movement of substance takes
place into the cell? How do substances
move out of the cell?

Diffusion
movement
of
substance
Osmosis
Diffusion - is defined as the movement of individual
molecules of a substance through a
semipermeable barrier from an area of higher
concentration to an area of lower concentration.
Significance of diffusion:
Gaseous exchange between the leaves and air takes
place.
Transport of food through phloem takes place.
Loss of water from the plants is based on the principle of
diffusion.
Movement of ions and solutes from one cell to another
cell takes place through diffusion.
Osmosis - is the movement of water molecules from a solution
with a high concentration of water molecules to a solution
with a lower concentration of water molecules, through a
cell's partially permeable membrane.

Significance of osmosis:
❑ * Absorption of water by roots and root hairs.
❑ * Water moves from one cell to another cell.
❑ * It controls the amount of water within the cell.
❑ * It controls various physiological activities :
❖ 1) Opening and closing of stomata.
❖ 2) Splitting of fruits due to over irrigation.
❖ 3) Dehiscence of fruits and seeds for dispersal.
 HOMEWORK-3
Simple HOTS

Q. Which one of the following Q. The process by which water moves

statements is correct? through a semipermeable membrane
from a region of high concentration to
Statement 1: The cell is the basic, a region of lower concentration is
structural and functional unit of living called
organisms. A) diffusion        
Statement 2: The tissue is the basic,
B) osmosis
structural and functional unit of living
C) evaporation     
organisms.
  D) All of these
A) Statement 1
B) Statement 2 Q. Why is plasma membrane called a
C) Both statements are correct selectively permeable membrane?
D) Both statements are incorrect. How do the substances like  and water
move in and out of cell? (3)
Q. Differentiate between diffusion and
osmosis.(3)
 HYPOTONIC, ISOTONIC AND
HYPERTONIC SOLUTION
❑ Hypotonic solution: If the medium surrounding the cell
has a higher water concentration than the cell. Such a
solution is called hypotonic solution. In this case the
cell is likely to swell up.
❑ Hypertonic solution: If the medium surrounding the cell
has a lower concentration of water than the cell. Such
a solution is called a hypertonic solution. In this case
the cell will shrink.
Isotonic solution: If the medium surrounding the
cell has exactly the same water concentration as the
cell, there will be no net movement of water across
the cell membrane. Such a solution is called isotonic
solution. The cell will stay the same size.
Endocytosis:
The flexibility of the cell membrane also enables the
cell to engulf in food and other materials from its
external environment. Such a process is known as
endocytosis. Amoeba acquires its food through this
process.

Types of endocytosis:

⮚ Phagocytosis: Cell takes in solid food material through

plasma membrane.

⮚ Pinocytosis: Cell takes in fluid matter through plasma

membrane.
⮚ Exocytosis: It is the process of exudation of
secretions or the waste materials out of the cell
through plasma membrane. It is opposite of
endocytosis.
 HOMEWORK-4
Simple HOTS

Q. If you are provided with some Q. Assertion - Cells having cell wall
vegetables to cook you generally add withstand very dilute (hypotonic)
salt into during cooking process. After external media without bursting.
adding salt vegetables release water.   Reason - The cell wall exerts an equal
Which   mechanism   is responsible for pressure against the swollen cell.
this?  (1)
Q.   If cells of onion peel and RBCs are
separately kept in hypotonic solution.
Q.   A plant cell is placed in a hypotonic What among the following will take
solution. What will happen? Will the place? Explain the reason for your
cell burst? Why or why not? (3) answer.
(i) Both the cell will swell
(ii) RBC will burst easily, while cells of
onion peel resist the bursting to some
extent.
(iii) and (b) both are correct
(iv) RBC and onion peel cell will
behave similarly.(4)
Cell wall:
• In plant cells, there is another rigid outer covering called cell
wall.
• It lies out side the plasma membrane.
• In plant cell , cell wall is mainly composed of cellulose. Cell wall
is non-living.
Function of cell wall:

❖ * It gives a shape to the cell.

❖ * It helps in giving rigidity to the cell.
❖ * It gives mechanical strength.
❖ * It also support the internal structure of the cell.
❖ * It protects the cell from osmotic bursting.
❖ * It helps in the expansion of cells.
Plasmolysis: When a living plant cell looses
water through osmosis then there is
shrinkage or contraction of the contents
of the cell away from the cell wall. This
phenomenon is called plasmolysis.
Protoplasm: All living components of a cell
is protoplasm. It is clear colourless or
slightly translucent, jelly like, viscous
semi fluid substance. It can be
distinguished into a centrally located
nucleus and cytoplasm.
PLASMOLYSIS
PLASMOLYSIS
 HOMEWORK-5
Simple HOTS

Q. Plasmolysis in a plant cell is defined Q. The cell wall of which out of these is
as not made up of cellulose?        
A) breakdown (lysis) of plasma A) Bacteria
membrane in hypotonic medium B) Hydrilla
B) shrinkage of cell content in C) Mango tree        
hypertonic medium D) Lactus
C) shrinkage of nucleoplasm

Q. What will happen if a plant cell is kept

Q. What do you mean by plasmolysis? in hypertonic solution?(2)
Explain the process.(3)

Q. What do you mean by

plasmodesmata?(1)
❖ Nucleus:
✔ * It is the largest and most prominent structure of the
cell.
✔ * Generally one nucleus is present in each cell.
✔ * Generally present in the center of younger cell but it is
pushed towards the periphery in the mature cell.
✔ * It governs the cell that is why it is called controlling
center of the cell ( governor of the cell ).
✔ * It is bounded by double layer membrane.
✔ The membrane have pore called nuclear pore.

❖ Important parts of nucleus:

▪ Nuclear membrane.
▪ Nucleoplasm.
▪ Chromatin network.
▪ Nucleolus.
❑ Nuclear membrane:
❖ * It is double layer membrane that separates
nucleoplasm from cytoplasm.
❖ * It has number of pores which helps in exchange of
materials between nucleus and cytoplasm.
❖ * It disappears during cell division.
❑ Nucleoplasm:
❖ * The fluid which is present inside the nucleus is
called nucleoplasm/ karyolymph.
❖ * It is a gel like dense substance present within the
nucleus.
❖ * In this chromatin material and nucleolus are
present.
❑ Chromatin net work or chromatin material:
❖ * It is the entangled mass of thread like structures.
❖ * During cell division, it is organized to form
chromosomes. Chromosomes are made up of DNA
(deoxyribonucleic acid) and proteins.
❖ * DNA is the master molecule and it controls all the
activities of the cell. Functional segment of DNA are
called genes. Genes control the characters.
❖ * On one chromosome many genes are present. *
Chromosome are considered as ‘heredity vehicle’ as it
transfers the characters from parent to offspring.
❑ Nucleolus:
❖ * Spherical or oval body present within the nucleus.
❖ * It is generally bigger in size in those cells which are
actively concerned with protein synthesis.
❖ * It is more prominent in non-dividing cells.
❖ * It contains large amount of RNA and protein, also a
small amount of DNA.
Function of nucleus:
⮚ * It helps in maintenance of cell.
⮚ * It helps in cell division.
⮚ * It is needed for inheritance of character from parent to
offspring.
⮚ * It controls various cytoplasmic activities.
 HOMEWORK-6
Simple HOTS

Q. When the cell is about to divide, the Q. The layer which separates the
chromatin material gets organised into protoplasm and the outer environment
A) DNA            is called:
B) nucleoid A)  Nuclear Membrane
C) genes                                         B)  Plasma membrane
D) chromosomes C)  Leucoplast
D)  Cell Wall

Q.  Why is nucleus called controller of Q. How are chromatin, chromatid and

the cell? (2) chromosomes related to each other?
(3)
❑Cytoplasm:
❖ * The fluid which is present inside the cell but outside the
nucleus is called cytoplasm.
❖ * It is a larger region of each cell enclosed by a cell
membrane.
❖ * It is transparent, semi solid ground substances in which
various cell organelles are present.
❖ * Water is the main component of cytoplasm which contains
fats, proteins, carbohydrates and various organic
substances.
❖ * It helps in exchange of materials between cell
organelles.
❖ * It acts as a site of chemicals reactions like glycolysis.
❖ Cytoplasm takes very little stain.
Prokaryotic cell Eukaryotic cell
 CHARACTER PROKARYOTIC CELL EUKARYOTIC CELL
Size Generally small (1-10 Generally large ( 5-100
micro meter). micro meter).
Nuclear region Not well defined and Well defined and
not surrounded by a surrounded by a nuclear
nuclear membrane & membrane.
known as nucleoid.
Chromosomes Single and circular. More than one and
linear.
Membrane bound Absent. Present.
organelles
Cell division By simple fission By mitosis and meiosis.
(amitosis).
Nucleus Lack true nucleus. True nucleus present.
Ribosome Smaller in size and Bigger in size and
randomly scattered in attached to the
cytoplasm. endoplasmic reticulum or
freely present in
cytoplasm.
 HOMEWORK-7
Simple HOTS

Q. Assertion - Prokaryotic cells are Q. Which one of the following has

primitive and larger than eukaryotic irregular and variable shapes?
cells. A)  Algae
Reason - Prokaryotic cells lack B)  Ameoba
cytoplasmic organelles. C)  Paramecium
A) Both A and R are true and R is D)  Euglena
correct explanation of the A
B) Both A and R are true, but R is not Q. What is a nucleoid? How is
the correct explanation of the A bacterial cell different from onion
C) A is true, but R is false peel? (5)
D) A is false, but R is true

Q. Which is true about genetic material

of a prokaryotic cells?
A) It contains only nucleic acids
B) It has poorly defined regions
C) Not enveloped by nuclear
membrane
D) AII of the above
 CELL ORGANELLES

The membrane bound structures present

in the cytoplasm are called cell
organelles ( mitochondria, chloroplast,
nucleus, endoplasmic reticulum etc.).
The structures which are not bounded by
membranes are called cell inclusions
(ribosome, centriole ).
 ENDOPLASMIC
RETICULUM
❑ It consists of an irregular network of channels
which are bounded by membrane and are
interconnected with each other.
❑ They are seen with the help of electron
microscope only.
❑ If ribosomes are seen attached to their
surface, then they are called rough
endoplasmic reticulum (R.E.R).
❑ If ribosomes are not present on endoplasmic
reticulum, they are called smooth endoplasmic
reticulum (S.E.R).
❑ FUNCTION OF ENDOPLASMIC RETICULUM:
❖ Ribosomes present are the sites of protein
synthesis.
❖ The S.E.R helps in the manufacture of fat
molecules or lipids.
❖ It helps in the intracellular transport of
substances (proteins).
❖ It helps in the synthesis of steroid hormones
(which detoxifying many poisons and drugs).
❖ It acts as skeleton system of the cell.
Membrane biogenesis:
The S.E.R helps in the manufacture
of fat molecules or lipids,
important for cell function. Some
of these proteins and lipids help in
building the cell membrane. This
process is known as membrane
biogenesis.
 HOMEWORK-8
Simple HOTS

Q. SER plays a role in detoxifying Q. Which cell organelle plays a crucial

many poisons and drugs in role in detoxifying many poisons and
A) stomach cells    drugs in a cell?        (NCERT
B) pancreas cells Exemplar)
C) liver cells        A) Golgi apparatus
D) brain cells B) Lysosomes
C) Smooth endoplasmic reticulum
Q. Differentiate between rough D) Vacuoles
endoplasmic reticulum (RER) and
smooth endoplasmic reticulum (SER). Q. Which one of the following cell
(3) organelles plays the most important
role in the synthesis of proteins?
Q. How endoplasmic reticulum is A) Ribosomes                    
important for membrane B) Plastids
biosynthesis?   (2) C) Mitochondria                 
D) Vacuoles
GOLGI APPARATUS / GOLGI BODIES
❑ Discovered by Camillo Golgi.
❑ They are the membrane bound
(single layer) structures that
occur in the form of tubules,
vesicles or cisternae.
❑ They are usually seen aggregated
towards the nucleus.
❑ In plants they occur as
unorganized and unconnected
channels like structures called
dictyosomes.
FUNCTION OF GOLGI BODIES:
❑ Helps in the synthesis of some polysaccharides
from simple sugar.
❑ Helps in formation of glycoprotein.
❑ It is involved in the transformation.
❑ Primary lysosomes are formed from
golgibodies by budding.
❑ They are responsible for secretion and
transport in the cell.
 HOMEWORK-9
Simple HOTS

Q. The cell organelle involved in Q. Assertion Golgi bodies store, modify

forming complex sugars from simple and pack products in vesicles.
sugars are           Reason They are involved in the
A) endoplasmic reticulum                 formation of lysosomes.
B) ribosomes A) Both A and R are true and R is
C) plastids                                      correct explanation of the A
D) Golgi apparatus B) Both A and R are true, but R is not
the correct explanation of the A
Q. Why is the Golgi apparatus called C) A is true, but R is false
the secretary organelle of the cell? (2) D) A is false, but R is true

Q. What will happen if Golgi bodies are

removed from a cell? (2)
 LYSOSOMES
❑ They are small sized enzyme containing
vesicles which are bounded by single
membrane.
❑ During the disturbance in cellular
metabolism, for example when the cell
gets damaged, lysosome may burst and
the enzymes digest their own cell.
Therefore lysosomes are also called
suicide bags of the cell.
❑ Enzymes present in lysosomes are made
by R.E.R.
❑ They also destroy the foreign materials
 FUNCTION OF LYSOSOMES:
❑They helps in the digestion of food
within the cell ( intracellular digestion ).
❑They protect the body from bacteria
and other harmful organisms.
❑They help in the removal of old worn out
cell organelles.
 HOMEWORK-10
Simple HOTS

Q. Which one of the following cell Q. Lysosome arises from        

organelles is known as suicidal bag? A) endoplasmic reticulum
A) Ribosome                       B) Golgi apparatus
B) Lysosome C) nucleus
C) Golgi apparatus  D) mitochondria
D) Mitochondria

Q. Which cell has most lysosomes? What

Q. Why are Lysosomes Considered as happens when a lysosomes break? (3)
the “Garbage Trucks” / “suicidal bag”
of Cells?(2)
 MITOCHONDRIA

❑ They are small bodies that occur

in large numbers.
❑ A mitochondrion consists of:
⮚ An outer membrane.
⮚ An inner membrane.
⮚ Inner membrane folded inwards to
form the cristae.
⮚ The cristae lie in a ground
structure called matrix.
❑ They have their own DNA and
MITOCHONDRIA
FUNCTION OF MITOCHONDRIA:
Mitochondria have enzymes
necessary for the oxidation of
glucose thus releasing energy in
the form of ATP. They are
therefore called power house of
the cell.
 HOMEWORK-11
Simple HOTS

Q. Organelle other than nucleus, Q. (3)

containing DNA is                   
A) endoplasmic reticulum
B) Golgi apparatus
C) mitochondria
D) lysosome

Q. Which molecules in a cell are

known as the energy currency of the
cell? (1)

Q. Give scientific reason for the

following (i) Inner membrane of
mitochondria is deeply folded. (ii)
Mitochondria are able to make some of
their proteins.(2)
 PLASTIDS
❑ Only present in plant cell.
❑ It is of two types: chromoplast
(coloured plastid) and leucoplast (white
or colourless).
❑ It is a lamellated structure which is
bounded by double membrane.
❑ Plastids containing the pigment
chlorophyll (green pigment) are called
chloroplast.
❑ Chloroplast is important for
photosynthesis.
❑ Leucoplast stores starch, oil, protein
granules.
FUNCTION OF PLASTIDS:
❑Chloroplast is called kitchen of the cell
as food is synthesized by the process of
photosynthesis.
❑Chromoplast gives various colours to
different parts of the plant (petals of
flower).
❑Leucoplast stores food.
 HOMEWORK-12
Simple HOTS

Q. Chloroplasts found in plant cells Q. Match the following columns-

A) are colourless plastids Column I   Column II
B) do not contained DNA
C) are involved in storing of starch, oils and A. Chromopla 1. Colourless
proteins sts plastids
D) contain various yellow or orange pigments B. Leucoplasts 2. Yellow or
orange
Q. There would be no plant life if chloroplasts did pigments
not exist. Justify.(3)
C. Chloroplast 3. Coloured
Codes s plastids
A) A-3,  B-1,  C-2
B) A-1,  B-2,  C-3
C) A-2,  B-3,  C-1
D) A-1,  B-3,  C-2

Q. Assertion Leucoplast are the colourless

plastids.
Reason They play a role in photosynthesis.
A) Both A and R are true and R is correct
explanation of the A
B) Both A and R are true, but R is not the correct
explanation of the A
C) A is true, but R is false
D) A is false, but R is true
 VACUOLE
❑ Vacuoles are sac like structure meant for storage of
solid and liquid material.
❑ Vacuoles are small sized in animal cells while large
sized in plant cell.
❑ In plant cells vacuoles are full of cell sap that
contains amino acids, water, protein, organic acid,
sugar etc. This cell sap provide turgidity and rigidity
to the cell.
❑ In unicellular organism like amoeba the vacuole having
food is called food vacuole.
❑ The outer membrane of vacuole is called tonoplast.
❑ It is osmoregulatory in function.
 HOMEWORK-13
Simple HOTS

Q. Vacuoles are ...(A)... sized in Q. Assertion The central vacuole of

animals cells, while plant cells have some plants cells may occupy 50-90%
very ...(B)... vacuoles. of the cell volume.
A) (A)-large, (B)-small Reason They provide energy to the
B) (A)-small, (B)-large plant cell.
C) (A)-small, (B)-small                     A) Both A and R are true and R is
D) (A)-large, (B)-large correct explanation of the A
B) Both A and R are true, but R is not
Q. In plant cells, vacuoles are involved the correct explanation of the A
in C) A is true, but R is
A) storage of substances false                          
B) transport of substances D) A is false, but R is true
C) expelling excess water
D) expelling waste
Q. Why do plant cell possess large
Q. What is cell sap? Give its sized vacuoles?  (2)
composition.(2)
Difference between plant cell and animal cell

Plant cell Animal cell

Q. Name the following organelles (i) Power house of the cell (ii) Kitchen of the cell (iii) Suicidal bags of the
cell (iv) Controlling centre of the cell (v) Export firms (vi) Internal transport system.
Q. Why is mitochondria called power house of cell? Give three similarities and one difference between
mitochondria and plastid.
Q. Which of the following is true about animal cell?
A) Animal cells are generally smaller in size as compared to plant cells.
B) Cell wall is absent.
C) Cell wall is present.
D) Both [a] and [b]

Q. Which of the following differentiate plant cells from animal cell?

A) Large vacuoles, plastid and cell wall
B) Cell wall, plastid and centriole
C) Cell wall, plastid and mitochondria
D) Cell membrane, plastids and cell wall

On       
All the living organisms are made up of cells. It is a fundamental, structure and functional
unit of life. The given diagram shows the plant cell.

\ the basis of given diagram, answer the Which

A) Large vacuoles, plastid and cell wall

B) Cell wall, plastid and centriole
of the
following following differentiate plant cells from animal cell?
question

C) Cell wall, plastid and mitochondria

D) Cell membrane, plastids and cell wall
THANKS