The Cell
 Cells Were discovered by
Robert Hooke
 He observed the slices of cork from the
bark of an oak tree (dead plant cells).
 Anton Van Leewenhoek observed pond
water & saw it was full of living things.
 Observations and conclusions of
scientists from the late 17th century
to the time of scientists, Schwann,
Schleiden, and Virchow are
summarized into the Cell Theory.
Three parts of the cell theory:
1. All living things are made of one or more
cells.
2. The cell is the basic unit of structure and
function in organisms.
3. All cells come from pre-existing cells.
=
Life
Types of Cells
1.) Prokaryote-the simplest cells
 Small, simple and lack membrane-bound
organelles.
 They have no nucleus.
 DNA is found floating in the cytoplasm.
Prokaryotic cells contain:
 cell wall
 cell or plasma membrane
 Cytoplasm
 Ribosomes
Prokaryotic Cells
Examples: BACTERIA
 Flagella-Many bacteria have flagella,
which are long, threadlike structures that
protrude from the cell’s surface and
enable movement.
 Bacteria flagella rotate, propelling a
bacterium through its environment.
Types of Cells
2. Eukaryote – Large, complex and contain
membrane bound organelles such as a nucleus.
 Example: Plants, Fungi, and Animals
 Eukaryotic cells have a nucleus which is an
internal compartment that houses the cell’s
DNA.
 Other internal compartments, called
organelles, enable eukaryotic cells to function
in ways different from bacteria.
 An organelle is a structure that carries out
specific activities in the cell.
Cell Movement
 Many single-celled eukaryotes use flagella for
movement.
 Short hair like structures packed in tight rows, called
cilia protrude from the surface of some eukaryotic
cells.
 Flagella or cilia propel some cells through their
environment.
 In other cells, cilia and flagella move substances
across the cell’s surface.
 Example: Cilia on cells of the human respiratory
system sweep mucus and other debris out of the
lungs.
Cell Size
 The symbol “ ” stands for the prefix
micro.
 A micrometer (μm) is a unit of linear
measurement equal to one-millionth of a
meter, or one-thousandth of a millimeter.
 Cell size and organelle size are measured
in micrometers (μm).
 This means that they are microscopic.
Both Animal and Plant Cells Contain
These Organelles
1. Cell Membrane
 The cell membrane is primarily composed of
phospholipids. Various proteins are located
in the lipid bilayer of a cell membrane.
 A phospholipid is a lipid made of a
phosphate group (head) and two fatty acids
(tails).
 A phospholipid “head” is polar and its two
fatty acid “tails” are nonpolar. Transport
proteins aid in the movement of substances
into and out of the cell.
Both Animal and Plant Cells Contain These
Organelles
• Cell Membrane Cont.
It surrounds and protects the cell and
allows only certain substances to pass in
and out of the cell. The cell membrane
allows the cell to remain separate from
the environment.
It is a Selectively permeable membrane,
which means it keeps out some molecules
but allows others to pass through.
Both Animal and Plant Cells Contain
These Organelles
Cell Membrane Cont.
Small molecules like H2O, CO2,O2 and soluble end
products of digestion pass through easily.
Large molecules like glucose and ions do not pass
through easily.
The cell membrane regulates or controls what
comes into and out of the cell. Like gases, nutrients
and wastes. This control keeps the cell alive and
well. If it wasn’t selectively permeable everything
on the outside would come into the inside.
Both Animal and Plant Cells Contain These
Organelles
2. Cytoplasm
A fluid-like material that fills the space
between the cell membrane and the
nucleus.
Contains the organelles
 **The cytoskeleton (in the
cytoplasm) is a web of protein fibers
that holds the cell together and keeps
the cell membrane from collapsing or
folding.
Both Animal and Plant Cells Contain These
Organelles
3. Nucleus
The control center or “brain” of the cell (Most
functions of a eukaryotic cell are controlled by
the cell’s nucleus).
The nucleus directs cell activities and stores
DNA.
Both Animal and Plant Cells Contain These
Organelles
3. Nucleus (continued)
The nucleus is surrounded by a double
membrane called the nuclear envelope The
nuclear envelope is made of two bilayers that
separate the nucleus from the cytoplasm.
Substances that are made in the nucleus include
ribosomal proteins and RNA. After they are
made, both of these move into the cytoplasm
through nuclear pores.
Both Animal and Plant Cells Contain These
Organelles
4. Nucleolus
Dense structure inside
the
nucleus.
Stores RNA
that forms
ribosomes.
Both Animal and Plant Cells Contain These
Organelles
5. Ribosomes
 Tiny “dot” organelles located on the
rough ER and throughout the cytoplasm.
 They are the site of protein synthesis.
 A cell makes proteins on ribosomes. The
building of proteins from amino acids
occurs on the cell’s ribosomes.
Both Animal and Plant Cells Contain These
Organelles
5. Ribosomes (continued)
 Some ribosomes float freely in the
cytoplasm, while others are attached to
the endoplasmic reticulum.
Both Animal And Plant Cells Have These
Organelles
6. Endoplasmic Reticulum
 Materials can be moved around within a cell by using
the endoplasmic reticulum.
 The rough ER helps transport the proteins that are
made by its attached ribosomes. As each protein is
made, it crosses the ER membrane and enters the ER.
Both Animal And Plant Cells Have These
Organelles
6. Endoplasmic Reticulum (continued)
 The portion of the ER that contains the completed
protein then pinches off to form a vesicle.
 A vesicle is a small, membrane-bound sac that
transports substances in cells.
 By enclosing certain proteins inside vesicles, the
eukaryotic cell keeps these proteins separate from
proteins that are produced by free ribosomes in the
cytoplasm.
 Proteins must enter the endoplasmic reticulum to be
transported to other parts of the cell.
Both Animal And Plant Cells Have These Organelles
6. Endoplasmic Reticulum Cont.
 A network of tunnels, channels or canals that transports
proteins and other substances throughout the cell. The
canals of the ER connect the cell membrane with the
nuclear membrane.
Both Animal And Plant Cells Have These Organelles
Two Types of ER:
1. Rough ER
Has ribosomes on the membrane and helps
transport the proteins that are made by its
attached ribosomes.
A vesicle is a small, membrane-bound sac that
transports substances in cells. By enclosing certain
proteins inside the vesicles, the eukaryotic cell
keeps these proteins separate from proteins that
are produced by free ribosomes in the cytoplasm.
2. Smooth ER
It lacks ribosomes (appearing smooth) and
produces certain lipids.
Both Animal And Plant Cells Have These
Organelles
7.
Golgi Apparatus
 Vesicles that contain newly made proteins move through
the cytoplasm from the ER to an organelle called the golgi
apparatus.
 It is stacks of flattened membranes with vesicles that
packages and assembles many cell products. The Golgi
Apparatus serves as the packaging and distribution center.
It receives, chemically modifies, and repackages proteins
into forms the cell can use, expel, or keep stored. The
modified proteins are then enclosed in new vesicles that
bud from the surface of the golgi apparatus. Some of these
vesicles include lysosomes.
Both Animal And Plant Cells Have These
Organelles
• 8. Lysosomes
– Small spherical organelles that contain
digestive enzymes.
– They take care of
foreign particles
entering the cell and
“digest” worn out cell
parts.
Both Animal And Plant Cells Have These
Organelles
9. Mitochondria
They are called the “powerhouse” of the cell
because it produces energy (ATP).
They are the site of aerobic cellular respiration.
A cell that requires a lot of energy, like a muscle
cell, would contain large numbers of
mitochondria.
Both Animal And Plant Cells Have These
Organelles
10. Vacuole
 Small, fluid-filled structures that store materials like food,
enzymes, and other materials needed by the cell.
 Plant Cell have a single large vacuole.**
Found In Animal cells Only
1. Centrioles
 Tiny, cylindrical structures that are found in pairs near
the nucleus.
 They are involved in cell division.
Found In Plant Cells Only
1.
Chloroplasts
 Small green pigmented structures that contain chlorophyll.
 It is the site of photosynthesis.
Found in Plant Cells Only
2. Cell Wall
The cell wall consists of a mixture of proteins
and carbohydrates, including the polysaccharide
cellulose. A polysaccharide is also known as a
sugar.
Structure found outside of the cell membrane in
plants that provides strength and rigidity, but
does not affect passages of materials in and out
of the cell