Life originated from inorganic matter but interaction of these inorganic matter lead to the formation of organic molecules which makes up the life sustaining entity called cell. In this chapter we will study about cell, how it is discovered, cell theory, parts of cell and their functions.

1. FUNDAMENTAL UNIT OF LIFE
Discovery of cell, Cell theory, Types of cell, Division of labour, Cell
shape and size, Parts of cell (Cell wall, Cell membrane and Cell
organelles), Diffusion and Osmosis, Types of solutions, Plant cell vs
Animal cell
Topics to be covered

2. WHAT ARE LIVING BEINGS MADE UP OF?
● Our earth is inhabited by different kinds of living organisms. These living organisms
are bacteria, fungi, plants and animals.
● The bodies of living organisms are made up of microscopic units called cells.
● Cells in Latin means ‘little rooms’.
● The cell is the structural and functional unit of living organisms.
BACTERIAL CELL ANIMAL CELL PLANT CELL

3. DISCOVERY OF CELL
● Cells were discovered by Robert Hooke in 1665 in a cork slice.
● Anton Von Leeuwenhoek discovered free living cells in pond water in 1674.
● Robert Brown discovered nucleus in plant cells in 1831.
● J.E. Purkinje coined the term ‘Protoplasm’ for the living fluid substance present inside the
cell.
ROBERT HOOKE
ANTON VON
LEEUWENHOEK
ROBERT BROWN PURKINJE

4. CELL THEORY
● Cell theory was presented by German biologists, J.M. Schleiden (1838) and T. Schwann
(1839). It was refined further in 1855 by German biologist, R. Virchow.
● Cell theory states that
○ All organisms are composed of cells.
○ All metabolic reactions take place in cells. Thus, cells are structural and
functional unit of life.
○ All cells arise from pre-existing cells.

5. ORGANISMS
UNICELLULAR
ORGANISMS
MULTICELLULAR
ORGANISMS
TYPES OF ORGANISMS
● Organisms consists of single cell are
called unicellular organisms.
● They exhibit independent self
replication.
● Examples: Archaebacteria, Protozoa
and yeasts.
● Organisms consists of collection of
cells that function in a coordinated
manner to perform particular tasks are
called unicellular organisms.
● They exhibit division of labour.
● Examples: Mammals, birds, insects, etc

6. EXPERIMENT 1: To make a temporary mount of onion peel
Activity :- Take an inner fleshy leaf of onion bulb. With the help of forceps, we can peel off
the skin (epidermis) and put in a petri dish. Take a glass slide, put a drop of clean water on it
and transfer the peel to the slide. Make sure peel is perfectly flat on the slide. Use brush to
transfer the peel. Put a drop of iodine solution on the peel. This is called temporary mount of
onion peel. Observe the slide under low and high power of light compound microscope.

7. CELL
PROKARYOTIC
CELL
EUKARYOTIC
CELL
TYPES OF CELLS
● Cell lacks well defined nucleus.
● It contains single chromosomes.
● Membrane bound organelles are absent.
● Cell division takes place by budding or
fission.
● Examples: Archaebacteria, bacteria and
cyanobacteria.
● Cell has membrane bound nuclei.
● It contains more than one chromosome.
● Membrane bound organelles are present.
● Cell division takes place by mitosis or
meiosis.
● Examples: Protozoa, insects, fishes,
mammals, plants, birds consists of
eukaryotic cells

8. DIVISION OF LABOUR
● There is a division of labour within multicellular organisms. For eg: different parts of
human body perform different functions.
● Stomach has special cells such as mucous cells to secrete mucus for lubricating the food,
zymogen cells to secrete proenzyme called pepsinogen, parietal or oxyntic cells to secrete
hydrochloric acid (HCl) activating pepsinogen into pepsin for digestion of protein and for
killing germs of food.
● Like the human body, the cell itself has got division of labour. Each cell has got specific
components within it called cell organelles.
● Each cell organelle performs a specific function eg: making new material in cell such as
protein synthesis by ribosomes, food synthesis by chloroplasts, clearing up the waste
materials from the cell by lysosomes, etc.

9. CELL SHAPE
● The basic shape of eukaryotic cell is
spherical but the shape is ultimately
determined by the specific function of the
cell. Thus, the shape of cell is variable or
fixed.
● Variable shape occurs in Amoeba and white
blood cells. Fixed shape of cell occurs in
most plants and animals.
● Cells may have diverse shapes such as
polyhedral (8/12/14 sides), spherical (eggs of
animals), spindle-shaped (muscle fibres),
elongated (nerve cells), branched (pigment
cells of skin), discoidal (erythrocytes) and
many more.
Nerve cell Erythrocytes
Amoeba Egg
Paramecium Muscle cell

10. CELL SIZE
● The size of different cell ranges between broad limits. The size of cells varies from the
very small cells of bacteria (0.2 to 5.0 μm) to a very large eggs of the ostrich (18 cm).
● The prokaryotic cells usually range between 1 to 10 μm. The eukaryotic cells are
typically larger (mostly ranging between 10 to 100 μm).
● Amoeba proteus is biggest among unicellular organisms (60 μm). The small cells of
multicellular organisms are those of Mycoplasma gallisepticum (0.1 μm) also called
PPLO (Pleuro Pneumonia Like Organism).
1 micrometre (μm) = 1
or 10-6 m
1000000 m
1 nanometre (nm) = 1
or 10-9 m
1000000000 m
Mycoplasma
gallisepticum
Amoeba
proteus

11. CELL VOLUME AND CELL NUMBER
● The volume of a cell is fairly constant for a particular cell type and is independent to the
size of an organism.
● The kidney or liver cells are approximately the same size in bull, horse and mouse. The
difference in total mass of the organ or organism depends on the cell number not volume.
● The number of cells in most multicellular organisms is indefinite but the number of cells
may be fixed such as rotifers and nematodes.
● In nematodes (eg: Ascaris), the number of cells is fixed at the time of hatching. Most
growth in size of a nematode results from an increase in cell size. The phenomenon of
having a constant and genetically fixed number of cells is called eutely.
● The number of cells in multicellular organisms usually is is correlated with the size of an
organism. Thus, small-sized organism has less number of cells in comparison to large-
sized organisms.
● In human beings, the number of cells is estimated to be about 100 trillion (1014) cells.

12. STRUCTURE OF CELL
PLASMA MEMBRANE AND
CELL WALL
NUCLEUSCYTOPLASM
CELL ORGANELLESCYTOSOL
Nucleus
Cytosol
Plasma Membrane
Cell Organelles
Cell Wall
PROTOPLASM

13. PLASMA MEMBRANE
● Plasma membrane is the outer covering of every cell.
● It is present in cells of plants, animals and microorganisms.
Nature and Occurence
● Plasma membrane is a living, thin, delicate, elastic and selectively permeable membrane.
● Plasma membrane allows or permits the entry and exit of some materials in and out of the
cell. This nature is called selective permeability.
● It is about 7 nm (0.7 Ao) thick.
● Chemically, membrane is made up of approx. 40% lipids, 60% proteins and 1-10% of
carbohydrates.
● In 1972, Singer and Nicolson proposed fluid mosaic model to explain the structure of the
plasma membrane.
Structure

14. PLASMA MEMBRANE
● Provide shape to the cell
● Acts as a mechanical barrier between cell contents and environment.
● Selective permeability
● Facilitates endocytosis and exocytosis.
● Acts as a passage for water flow.
● Facilitates flow of external fluids by cilia (in protozoans) or absorption of nutrients by its
microvilli.
● Facilitates flow of information and play role in recognition.
Functions

15. FLUID MOSAIC MODEL
● The fluid mosaic model was first proposed by S.J. Singer and Garth L. Nicolson in 1972
to explain the structure of the plasma membrane.
● The principal components of a plasma membrane are lipids (phospholipids and
cholesterol), Glycoproteins, Glycolipids ,some integral and peripheral proteins.
● The phospholipid molecules are amphiphilic in nature i.e. its polar head attracted towards
water while the tail repels water hence form a bilayer in which tails are inside and heads
are outside..
● Integral proteins single-pass the bilayer forming channels for the passage of certain types
of molecules. That’s why plasma membrane is selectively permeable.
● The Glycoproteins and Glycolipids forms recognition sites so that immune cells
recognize them as self cells otherwise kill the cell. The Glycoproteins and Glycolipids
together form Glycocalyx which is hydrophilic in nature and attract water enhancing
cell’s ability to absorb substances dissolved in water.

16. FLUID MOSAIC MODEL

17. DIFFUSION
● Diffusion is a process of passive transport in which molecules move from an area of higher
concentration to one of lower concentration.
● A single substance tends to move from an area of high concentration to an area of low
concentration until the concentration is equal across a space.

18. FACTORS AFFECTING DIFFUSION
● Concentration Gradient: The greater the difference in concentration, the more rapid the
diffusion.
● Mass of the Molecules: Heavier molecules move more slowly; therefore, they diffuse
more slowly. The reverse is true for lighter molecules.
● Temperature: Higher temperatures increase the energy and therefore the movement of the
molecules, increasing the rate of diffusion.
● Solvent density: As the density of a solvent increases, the rate of diffusion decreases.If the
medium is less dense, diffusion increases.
● Solubility: Nonpolar or lipid-soluble materials pass through plasma membranes more
easily than polar materials, allowing a faster rate of diffusion.
● Surface area and thickness of the plasma membrane: Increased surface area increases
the rate of diffusion, whereas a thicker membrane reduces it.
● Distance travelled: The greater the distance that a substance must travel, the slower the
rate of diffusion.

19. OSMOSIS
● Osmosis is the movement of water through a semipermeable membrane according to the
concentration gradient of water across the membrane, which is inversely proportional to
the concentration of solutes.
● It is a type of passive transport and is directed towards the direction that tends to equalize
the solute concentration across a semipermeable membrane.

20. FACTORS AFFECTING OSMOSIS
● Temperature: The rate of osmosis increase with the increase in temperature of the
system.
● Concentration gradient: As the concentration of solute molecules is essential in the
driving force of osmosis, any changes in the concentration directly affect the rate of
osmosis.
● Water potential/ Solvent potential: The water potential across a semipermeable
membrane also influences the rate of osmosis. As the water potential of a solution is more,
the water molecules can move across the membrane as the pressure exerted by the particles
is increased.
● Surface area and thickness of the membrane: With the increase in surface area, more
space will be available to the molecules for their movement which in turn will increase the
rate of osmosis
● Pressure: The pressure is an essential factor influencing the process of osmosis as it might
even change the direction of osmosis.

21. TYPES OF OSMOSIS
FORWARD OSMOSIS REVERSE OSMOSIS
Forward osmosis is a osmosis in which
separation of solute and solvent by exploiting
solution of higher concentration of solute
which extract solvent molecules from the
sample.
Reverse osmosis is a osmosis in which force
is used in separation of a solvent through a
semipermeable membrane resulting in solute
molecules on one side and solvent molecules
on the other side.

22. TYPES OF OSMOSIS
ENDOSMOSIS EXOSMOSIS
● The movement of water into the cell
which occurs when a cell is placed in a
solution having a higher concentration of
water than the cell.
● Cells swell up in size after endosmosis.
● The movement of water out of the cell
which occurs when a cell is placed in a
solution having a higher concentration of
solute than the cell.
● Cells shrink after exosmosis.

23. TYPES OF SOLUTIONS FOR OSMOSIS
HYPOTONICISOTONIC
● Medium has high water
concentration than cell.
● Solution is dilute.
● Cell will swell up.
● Medium has less water
content than cell.
● Solution is
concentrated.
● Cell will shrink
HYPERTONIC
● Medium has exactly
same concentration of
water as than of cell.
● No change in shape of
cell.

24. TYPES OF SOLUTIONS FOR OSMOSIS
HYPOTONICISOTONICHYPERTONIC

25. OSMOSIS IN NATURE
WATER INTAKE BY UNICELLULAR
FRESHWATER ORGANISMS
ABSORPTION OF WATER BY PLANTS

26. TYPES OF TRANSPORT IN NUTRITION
ACTIVE TRANSPORTPASSIVE TRANSPORT
DOES NOT REQUIRE ENERGY FOR
TRANSPORT IN AND OUT OF THE CELL
REQUIRE ENERGY FOR TRANSPORT IN
AND OUT OF THE CELL
DIFFUSION OSMOSIS SYMPORT ANTIPORT UNIPORT

27. ENDOCYTOSIS

28. CELL WALL
● Cell Wall is made up of
cellulose.
● Cell wall of plants help cell to
withstand hypotonic solution
and changes brought by it.
● Cell wall exert equal pressure
against swollen cell hence
maintain its shape and stop it
from bursting.

29. ACTIVITY 5.6- PLASMOLYSIS EXPERIMENT
OBSERVATIONS
● When cells are placed in 5%
sodium chloride solution, the
cells undergo plasmolysis.
● When cells are placed in
0.1% of sodium chloride
solution, the cells swells up
and become turgid.

30. NUCLEUS
● Most important part of cell and
controls all functional activities
of the cell.
● Discovered by Robert Brown
{1831} in the cells of orchid.
● Structure:
○ Oval in shape, near the
centre of cell.
○ Controlling centre of cell
activities.
○ Enclosed by double
membrane called nuclear
membrane.

31. NUCLEUS
● Intertwined mass of
thread like structure.
● Consists of only DNA.
● DNA is responsible for
passing characteristics
from one generation to
another.
● DNA structure is double
helical.
● DNA of chromatin
condenses to form
chromosomes.
● In humans, there are 23
pairs of chromosomes.
CHROMATIN NUCLEOLUS
● Consists of
RNA and
proteins.
● Participates in
the formation
of ribosomes.
NUCLEOPLASM
NUCLEAR
ENVELOPE
● Double layered
membrane with
pores.
● Maintains shape of
nucleus.
● The pores helps in
exchange of
materials.
● The gelatinous
substance inside
nucleus in which
chromatin is
suspended.
● Also called
karyoplasm.

32. NUCLEUS

33. NUCLEUS
● It regulates cell cycle.
● It is responsible for passing characteristics from one generations to another.
● It controls all cell activities.
● Storage of proteins and RNA {RiboNucleic Acid}
Functions

34. CELL CYCLE
Cell cycle is the series of events that take place in a cell, resulting in the duplication of DNA
and division of cytoplasm and organelles to produce daughter cells.
LONG PERIOD
{INTERPHASE}
SHORT PERIOD
{M-PHASE}
G1 PHASE S - PHASE G2 PHASE
DIVISION OF
NUCLEUS
DIVISION OF
CYTOPLASM

35. CELL CYCLE
Cell cycle is the series of events that take place in a cell, resulting in the duplication of DNA
and division of cytoplasm and organelles to produce daughter cells.

36. M-PHASE : MITOSIS
Mitosis is a process where a single
cell divides into two identical
daughter cells (cell division)
Stages of Mitosis:
Interphase
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis

37. M-PHASE : MEIOSIS
Meiosis is a process where a single
cell divides twice to produce four
cells containing half the original
amount of genetic information.
Stages of Meiosis:
Meiosis I
Meiosis II

38. CELL ORGANELLES
ENDOPLASMIC
RETICULUM RIBOSOMES MITOCHONDRIA PLASTIDS
GOLGI COMPLEX VACUOLES LYSOSOMES
CENTROSOMES CYTOSKELETON MICROTUBULES
PEROXISOMES

39. CELL ORGANELLE: ENDOPLASMIC RETICULUM
● System of membranes attached to the
nucleus but present in cytoplasm.
● Types:
○ Rough Endoplasmic Reticulum { RER }
○ Smooth Endoplasmic Reticulum { SER }
● RER possess ribosomes on its surface and
involved in protein synthesis.
● SER does not have ribosomes on its surface
and involved in detoxification.
FUNCTIONS
● Protein synthesis
● Detoxification
● Synthesis of fats, steroids and cholesterol.
● Support framework of cell

40. CELL ORGANELLE: RIBOSOMES
● Smallest organelles of the cell.
● They are dense , spherical and granular
particles. Also called RNP { Ribo Nucleo
Protein} particles.
● Made up of two subunits;
○ Large Subunit
○ Small Subunit
● Many ribosomes are attached with mRNA to
form polyribosomes.
FUNCTIONS
● They are ‘Protein Factories’ of the cell as they are involved in protein synthesis.

41. CELL ORGANELLE: MITOCHONDRIA
● They are rod-shaped double membranous
organelles.
● The outer membrane is smooth, inner
membrane fold to form cristae.
● Central cavity is filled with gel like
substances in which mitochondrial DNA,
ribosomes and other granules freely
suspended.
● They are also known as semi-autonomous
organelle as it is capable to replicate itself
FUNCTIONS
● They are called powerhouse of the cell as it involves in producing energy currency {ATP} for cells.

42. CELL ORGANELLE: PLASTIDS
● They are double membranous organelles
found in plant cells.
● They are also known as semi-autonomous
organelle as it is capable to replicate itself.
● Types:
○ Chromoplast- Coloured plastids
○ Chloroplast- Green plastids
○ Leucoplast-Colourless plastids
FUNCTIONS
● They are the ‘kitchen’ of the cell by making food with the help of photosynthesis.
● They help in pollination.

43. CELL ORGANELLE: GOLGI COMPLEX
● Absent in prokaryotic cells but present in all
eukaryotic cells.
● Made up of interncoonected cisternae; has
cis and trans face.
● Golgi Complex forms vesicles for post
processing of cellular secretions.
FUNCTIONS
● They are secretory in nature.
● Protein processing: It modifies proteins by adding or removing carbohydrates.
● Cell membrane formation by processing lipids.
● Formation of lysosomal proteins.

44. CELL ORGANELLE: VACUOLES
● Temporary storehouse for many cell components.
● They are surrounded by a membrane called tonoplast.
FUNCTIONS
● They help in maintaining osmotic pressure in a cell.
CELL ORGANELLE: LYSOSOMES
● Also called suicidal bags, scavengers, house keepers of the cell.
● They are tiny spherical sac like structures evenly distributed in the cytoplasm.
● They contain powerful digestive enzymes.
FUNCTIONS
● They remove worn out and poorly woring cellular organelles by digesting them.
● They digest foreign particles/organisms that enter into the cell.

45. CELL ORGANELLE: CENTROSOMES
● Consists of two sets cylindrical rod-like structures called centrioles.
● Each centriole is made up of microtubules.
FUNCTIONS
● Helps in cell division by forming spindles for attachment of chromosomes.