Cells: the basic
unit of life
Cells
Living things are made up of tiny structures
called cells.
Small in size (microscopic) – so weren’t
discovered until invention of microscopes
(mid-1600).
Constitute structures of organisms and
perform various functions.
Cell discovery
In 1665, Robert Hooke built a microscope &
looked at a thin slice of cork. Cork is found in
the bark of cork trees. The cork looked like it
was made of little boxes. Hooke named these
boxes cells.
Hooke also looked at feathers, fish scales, and
the eyes of houseflies. But he spent most of his
time looking at plants and fungi.
The cells of plants and fungi have cell walls.
This makes them easy to see.
Finding cells in other organisms
Anton van Leeuwenhoek 1673, saw small
organisms in the water. He named these
organisms animalcules, which means "little
animals” – Protists.
Leeuwenhoek also looked at animal blood. He
observed that blood cells in fish, birds, and
frogs are oval. Blood cells in humans and dogs
are round and flat.
Cell theory
• In1938, Matthias Schleiden studied cells in
plants. In 1939, Theodor Schwann studied cells
in animals. Schwann wrote the first two parts of
the cell theory.
1. All organisms are made up of one or more cells
2. The cell is the basic unit of living things.
• Rudolf Virchow 1858 added third part of the cell
theory.
3. All cells come from existing cells.
Cell size and shapes
Cells vary in shape and size
– In general, prokaryotic are smaller in size &
eukaryotic cells are larger in size.
The ratio of the cell's outer surface area to the
cell's volume is called the surface area-tovolume ratio, which can be calculated by using
the following equation:
Parts of the cell
All cells have the following parts in
common.
1. The cell membrane & Cytoplasm
2. Organelles
3. Genetic material
1. The cell membrane &
Cytoplasm
cell membrane is a protective layer that covers
the cell's surface and acts as a barrier (controls
transport (nutrients, water, wastes, etc).
Two layers of phospholipids
Inside the cell is a fluid. This fluid is called the
cytoplasm
2. Organelles
Organelles are structures that perform
specific functions within the cell & they
carry out various life processes.
Most organelles are surrounded by
membranes.
Some organelles float in the cytoplasm.
Other organelles are attached to
membranes or other organelles.
3. Genetic Material
All cells contain DNA that carries
information needed to make new
cells and new organisms
In some cells, the DNA is
enclosed inside an organelle
called the nucleus
Cells
Unicellular(Eubacteria,Archaebacteri
a) and multicellular (Most of plants &
animals).
Two kinds of cells: Prokaryotic and
Eukaryotic
Prokaryotes
Eubacteria/Bacteria





Don’t have a nucleus but do have DNA.
Don’t have membrane covered organelles.
Have ribosomes.
Have cell wall.
Cell membrane & cell wall allow material into
& out of the cell.
 They live in soil & water. They also live as
parasite in other organisms.
 Have flagellum
 e.g. bacteria on your teeth, in digestive system.
Archaebacteria
Called as Archae.
Live
in
extreme
environments.
Can be of three types:
o Heat loving
o Salt loving
o Methane loving
Prokaryotic and eukaryotic cells
Eukaryotic cells
Protists– unicellular eukaryotes
(paramecium, amoeba)
Humans – multicellular eukaryotes
Plants - multicellular eukaryotes
Multicellular
organisms
are
eukaryotic.
all
1. Cell wall
Cell wall - A rigid structure that
gives support to a cell
Plant cell wall – cellulose
Fungi cell wall – chitin
Bacterial cell wall - peptidoglycan
Animal cells don’t have cell walls
2. Cell membrane
cell membrane - A protective barrier that
encloses a cell.
It allows nutrients to enter and wastes to
exit the cell.
The cell membrane contains proteins,
lipids, and phospholipids.
The cell membrane has two layers of
phospholipids.
3. Cytoskeleton
Network of proteins
Provide support, protect cell
from collapsing
Contains three types of proteins
One protein is a hollow tube.
The other two are long, stringy
fibers
4. Nucleus
Membrane bound organelle contains DNA
DNA contains information about protein
synthesis
Covered by two membranes (inner and outer)
Only in eukaryotes (plants and animals)
The nucleus has a dark area called the
nucleolus - where a cell begins to make its
ribosomes.
Nucleus
5. Ribosome
Organelles involved in protein synthesis
Some ribosomes float freely in the
cytoplasm. Others are attached to
membrane or the cytoskeleton.
Proteins are made of amino acids - 20
different organic molecules that are used
to make proteins.
6. Endoplasmic reticulum
System of folded membranes
Transport and delivery of substances
Extended network throughout the cell
Endoplasmic reticulum is either rough ER or
smooth ER.
If the ribosomes are attached on ER - rough
ER – synthesize protein
Without ribosomes -smooth ER
The functions of smooth ER include making
lipids & detoxification of the cell.
Endoplasmic reticulum
7.Mitochondria
Power house of a cell.
Two membranes (inner and outer)
Sugars are broken down to produce
energy
Energy generated is stored in form of ATP
Mitochondria have their own DNA and
ribosomes
They can divide within a cell
Mitochondria
8. Chloroplast
Found in plants & algae cells. Absent in animal cells.
Chloroplasts contain green colored pigment known as
chlorophyll which absorbs light for photosynthesis
Chloroplasts also have two membranes
Chlorophyll is found inside the inner membrane of a
chloroplast.
During photosynthesis, plants produce sugars and
oxygen by using CO2, sunlight and water
The sugar produced is utilized by mitochondria to
produce ATP
Chloroplast
9. Golgi complex
Package and distribute proteins
Materials (lipids, proteins etc.) are delivered
from ER to Golgi complex and are processed
& modified there
The final material leaves Golgi complex
enclosed in a piece of Golgi membrane. The
membrane pinches off to form a small
bubble.
The bubble transports its contents to other
parts of the cell or out of the cell.
Golgi complex
10. Vesicle
The bubble that forms from the Golgi
complex's membrane is a vesicle.
 A vesicle is a small sac that surrounds
material to be moved into or out of a cell.
vesicles carry new protein from the ER to the
Golgi complex.
Other vesicles distribute material from the
Golgi complex to other parts of the cell.
11. Lysosomes
Lysosomes are vesicles involved
in cellular digestion
They contain digestive enzymes
Degrade foreign material or
damaged cellular material, get rid
of wastes
12. Vacuoles
Vacuoles are vesicles meant for storage
They have variety of sizes and store different
types of materials
e.g. some store digestive enzymes
Plant vacuoles are larger in size. They store
water and salts. When there is enough water,
plant vacuole swell and help in supporting plant
cells. Vacuoles with less water result in wilting.
Lysosomes and vacuoles
Summary