Chapter 7
The Cell
• Cells Were discovered by Robert Hooke.
He observed the slices of cork from the
bark of an oak tree-dead plant cells.
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
1. There are two cell types:
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
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.
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.
– 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.
Cilia
Flagella
2. 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 is
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.
– 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.
Both Animal and Plant Cells Contain These
Organelles
• Cell Membrane Cont.
– It is a Selectively permeable membrane, which
means it keeps out some molecules but allows others
to pass through.
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 of “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.
– Stores DNA which forms long strands called chromatin.
(Chromatin is made of DNA and proteins that become
chromosomes during cell division.” **Chromosomes carry
the genes (DNA and are in the nucleus of eukaryotic
cells**
– The nucelus is surrounded by a double membrane called
the nuclear envelope or membrane. The nuclear envelope
is made of two bilayers that separate the nucleus form the
cytoplasm.
– Substances that are made in the nucleus include
ribosomal proteins and RNA, which move into the
cytoplasm through nuclear pores.
Both Animal and Plant Cells Contain These
Organelles
• 4. Nucleolus
– Dense structures 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.
– 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. The portion of the
ER that contains the completed protein then pinches
off to form a vesicle. A vesicle is a small, membranebound 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.
– 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.
=
Mitochondria
Power
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
• 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
**Plant cells have a LARGE vacuole that stores
water which can occupy most of the space in
a plant cell.**