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Unit 3 : Cells
Cell Structure
And Function
All
Living
Things
Are
Made
Up
of
Cells
“The Cell Theory”
1. All living things are composed of cells.
2. Cells are the basic units of structure and
function in living things.
3. New cells are produced from existing
cells.
Cell Size
• Typical cells range in size from 5 to 50
micrometers in diameter.
• Cell shapes are directly related to its
function.
Basic Cell Structures
• Cell Membrane
• Cell Wall
• Nucleus
• Cytoplasm
Cell Structures (cont)
• Cell Membrane – thin flexible barrier
around a cell.
• Cell Wall – rigid layer surrounding the cell
membrane in some cells.
• Nucleus – Control center of the cell
• Cytoplasm – material inside the cell
membrane (excluding the nucleus).
Prokaryotes vs. Eukaryotes
Major Differences
Prokaryotes
Eukaryotes
(Pro = No)
(Eu = True)
• Smaller cells
• NO Nucleus
• Lack organelles except
cell membrane.
• Bacteria are prokaryotes
• DNA is in the cytoplasm
• Larger cells (by
comparison)
• Have a nucleus
• Plants, animals, and
fungi are eukaryotes.
• Have specialized
organelles
• DNA is in the nucleus
Section 7-2
Cell Structures
Cell Wall :
The Support System
• Cell walls are found in many plants, algae, fungi,
and prokaryotes.
• The cell wall lies outside the cell membrane
• Function: To provide support and protection for
the cell.
• Made mostly of a hard starch known as cellulose.
The Nucleus:
AKA
“The Control Center”
Nucleus (cont.)
Function: Controls most cell
processes.
* Contains DNA that controls
the building of proteins.
Nucleolus
Nucleolus
What is it?
Small dense area within the nucleus that
functions as a “protein factory”
Nuclear Envelope
• Porous membrane that surrounds the
nucleus.
• Function: Allows materials to move into
and out of the nucleus.
Cytoskeleton
• Function: Gives the cell
support and movement.
• Made up of protein filaments.
Movement in the cell
Microtubules
Microfilaments
• Hollow protein tubes
that organelles slide
along.
• Similar to “tracks”
• Form centrioles in
animal cells during
mitosis.
• Also form cilia and
flagella on the outside
of cells to enable cells
to move.
• Smaller tubes that
form a tough and
flexible framework to
support the cell.
Play Video:
actin_cytoskeleton
Organelles in the Cytoplasm
AKA “little organs”
Ribosomes
• The protein factories of the cell
• Made up of RNA (ribonucleic acid) and
proteins
Endoplasmic Reticulum
• An “intracellular highway”
• Function: Area where cell membrane parts
are assembled and some proteins are
modified.
• Two different types of endoplasmic
reticulum (ER) ……..
ER Continued
Rough ER
• Embedded with
ribosomes that build
proteins to be released
from the cell.
• Called “rough”
because the ribosomes
resemble bumps on
the surface.
Smooth ER
• Does not have
ribosomes, but may
build lipids, regulate
enzymes in muscle
cells, and break down
toxic substances in the
liver.
Golgi Apparatus
“Shipping is our business”
Golgi Apparatus
• Function: The shipping, packaging, and
secreting organelle of the cell.
• Shaped like stacks of flattened sacks.
• Packages proteins made in the rough ER
into small packages called vesicles.
Vacuoles
Vacuoles
• Sometimes called the “waste dumps of the
cell”.
• Contain fluid filled sacs that store water,
salts, and enzymes.
• Vacuoles are commonly found in plant
cells and some protozoans.
• Vacuoles can be very large and take up as
much as 90% of a cell’s volume.
Lysosomes
Lysosome
“Enzyme Sacs”
•
•
•
•
•
Functions
Break down food particles in the cell
Digests worn out organelles in the cell
Also digests ingested bacteria and other debris.
Shapes the appendages in early development.
(Selective destruction)
Common in animals, fungi, and algae cells.
Lysosome Animations
Chloroplasts
“The Sugar Factory”
Chloroplasts
• Site of photosynthesis
in plant cells, algae,
and some bacteria.
• Contains the green
pigment, chlorophyll.
Mitochondria
AKA
“The Powerhouse”
Mitochondria
• Uses food to produce
the high energy
molecule ATP.
• The site of cellular
respiration.
• Found in all
eukaryotic cells.
Mitochondria History
• Mitochondria contain its
own DNA.
• This means that it might
have originated as an
ancient bacteria.
• Your mitochondria cells
are inherited from your
mother. They come from
her egg cells.
Comparing Plant vs. Animal Cells
Plant Cells vs. Animal Cells
• Plant cells have cell walls, chloroplasts,
and vacuoles which are NOT found in animal
cells. (Some animal cells may contain small
vacuoles.)
• Plant cells rarely have lysosomes, but animal
cells do.
• All other organelles are common to both.
Movement Through the Membrane
The Role of the Cell Membrane
• Cell membrane regulates what enters and leaves
the cell.
• Provides protection and support to the cell.
• The cell membrane’s structure is known as a
“lipid bilayer”.
• Cell membrane has a double layer of lipids which
protect the cell.
• Embedded with protein molecules that form
channels or pumps to move materials across the
cell membrane.
Lipid Bilayer
Hydrophilic Head,
Hydrophobic Tail
How do molecules move across
the cell membrane?
• Diffusion – The movement of molecules from an
area where they are in high concentration to an
area where they are less concentrated.
• Many substances move constantly from high to
low concentration. This can be in or out of the
cell.
• This movement continues until the concentration
on both sides is equal. (AKA equilibrium.)
Permeability in Cell Membranes
• If a membrane allows a substance to cross,
it is said to be permeable to that substance.
• Most membranes are selectively
permeable, which means that some
substances can pass, but not others.
Osmosis
• Osmosis – the diffusion
of water through a
selectively permeable
membrane.
Tonicity of Solutions
• Osmosis (and diffusion)- solutions flow from
areas of HIGH concentration to LOW
concentration.
• Hypotonic solution- has a high concentration of
water and a low concentration of sugar. (or salt)
• Hypertonic solution – has a low water
concentration and a high sugar concentration.
• Water moves from hypertonic to hypotonic
solutions to reach equilibrium.
• Equal solutions are said to be isotonic.
(Iso = same or equal)
Homeostasis
(Hypotonic Solutions)
• An internal balance
• Cells placed in a hypotonic solution like
pure water –will swell.
• In plant cells , the swelling is limited by the
cell wall but the cell does build up turgor
pressure.
• Animal cells may swell and even burst,
which is called cytolysis.
Homeostasis
(in Hypertonic Solutions)
• Cells placed in hypertonic solutions full of
salt will collapse.
• Plant cells will wilt in hypertonic solutions.
This is called plasmolysis. (Usually
temporary, but can lead to the death of the
cell.
• Animal cells will also shrink in hypertonic
solutions.
Tonicity of Fresh vs. Saltwater
Environments
• Freshwater environments
are naturally hypotonic .
• Some aquatic organisms
have organelles called
contractile vacuoles that
pump out excess water.
• Freshwater fish maintain
homeostasis by frequent
urination.
• Saltwater environments
are naturally hypertonic.
• Saltwater fish maintain
homeostasis by excreting
salt in their urine and from
their gills as well.
Passive Transport
• Does not require cell energy to move
materials across the cell membrane. 3 types
• 1. Occurs by diffusion of small molecules
like salt (NaCl)
• 2. Occurs by osmosis (diffusion of water)
• 3. Occurs by facilitated diffusion which
moves the sugar glucose across the
membrane through protein channels.
Active Transport
• Active Transport does require energy to
move materials across a cell membrane
from low concentration to high
concentration. (Normally goes from high to
low.)
Active Transport Types
• Sodium-Potassium pump uses cell energy to
move Na+ ions outside the cell and put K+
ions inside the cell.
• Endocytosis- uses cell energy to transport
large molecules into a vesicle on the cell
membrane. There are two types:
Endocytosis Types
• Phagocytosis – “cell
eating” – moves large
particles or whole cells
into the cell
membrane.
• Used by white blood
cells called phagocytes
to eat bacteria.
Endocytosis Types
• Pinocytosis “cell
drinking” transports
fluids or solutes across
the cell membrane.
Exocytosis
(Exo = out)
• Exocytosis (Opposite of
endo) The vesicles form on
the inside of the membrane
and pooch outwards – then
rupture and release the
contents.
• Used to release packaged
molecules like proteins.
• Also used by the nervous
system to release
neurotransmitters.
7-4 Diversity of Cellular Life
A. Unicellular Organisms
• Are single-celled organisms that maintain
all life functions.
• Made up of both prokaryotes and
eukaryotes.
• This is the most dominant life form on
Earth.
• Examples are: yeast, bacteria, and some
algae.
B. Colonial Organisms
• Consist of groups of
unicellular organisms
clustered together.
• Ex. volvox aureus (type of
algae)
• Each cell is held to other
cells using cytoplasmic
strands.
• They are still singlecelled organisms
working together.
C. Multicellular Organisms
• Have cells that are more complex and also
more dependant on other cells.
• These cells also exhibit a division of labor.
Ex: movement, coverings.
• Examples of multicellular organisms
include: humans, other mammals, reptiles,
etc.
D. Levels of organization within
a multicellular organism
1. Cell – Functional unit but depends on other
cells.
2. Tissue – composed of groups of cells alike in
their structure and function. There are 4 types in
humans.
a. Nervous
b. Epithelial (covers and lines the body and
organs. Ex. skin
c. Muscle
d. Connective – bones, blood, cartilage, lymph
D. Levels of organization within
a multicellular organism
3. Organs – made up of groups of tissues
working together to perform one major task.
a. The stomach is an organ made up of
epithelial, muscle, nervous, and connective
tissues.
b. Examples of organs are: heart, lungs,
skin, pancreas, etc.
D. Levels of organization within
a multicellular organism
• Organ systems – consist of groups of organs that
work together to perform a specific function for
the organism.
a. There are 11 major organ systems in humans.
b. Examples of organ systems are: muscular
system, skeletal system, circulatory system, etc.
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