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Cell Unit
Objectives:
• Describe cell organelles and their functions.
• Differentiate between prokaryotic and eukaryotic cells.
• Compare and contrast plant and animal cells.
• Identify scientists who were important to cell discovery and
cell theory and discuss these findings.
• Label cell structures.
Vocabulary:
cell * unicellular * multicellular * Hooke * Virchow *
Leeuwenhoek * Schleiden * Schwann * cell theory *
eukaryote * endosymbiosis * prokaryote * cell membrane
* cytoplasm * nucleus * selectively or semi-permeable *
cytoplasmic streaming * organelle * ribosome * rough &
smooth endoplasmic reticulum * Golgi apparatus *
Mitochondria * lysosomes * microtubules *
microfilaments * spindle fibers * cilia * flagella *
nucleoplasm * nucleolus * cell wall * vacuole * plastid *
chloroplast * chromoplast * leukoplast * tissues * organ *
organ system * osmosis * diffusion * hypertonic * isotonic
* hypotonic * homeostasis * concentration gradient *
equilibrium * turgor pressure * plasmolysis * cytolysis *
contractile vacuoles * passive transport * active transport
* facilitated diffusion * endocytosis * pinocytosis *
phagocytosis * exocytosis
Robert Hooke was the first to see little box shaped
structures in dead plant tissue. He called them “cells”.
Anton van Leeuwenhoek (a microscope maker) was the
first to observe living cells.
How might the appearance of dead cells differ from living cells?
Botanist, Matthias Schleiden, discovered all plants are
made of cells.
Theodor Schwann declared that all animals are made of
cells.
Rudolf Virchow found that all cells come from pre-existing
(already living) cells.
And so it became apparent that the cell is the basic unit of
life.
Cell Theory:
1.
2.
3.
All living things are made of one or more cells.
Cells are the basic unit of structure and function in
living things.
Cells are produced by existing cells. (Virchow)
Types of Cells:
Eukaryotes which contain a membrane bound nucleus and
membrane bound organelles. (Ex: plant, animals,
fungi, algae, etc.) Some scientists believe that
eukaryotic cells evolved from prokaryotic cells through
endosymbiosis.
Prokaryotes which lack a true nucleus and membrane
bound organelles. (Ex: Bacteria)
Note: bacteria, and only bacteria, are prokaryotes.
Cell Structure
Nucleus - The nucleus is considered the control center of
the cell. It directs all cell activities including cell division.
The nucleus is filled with a gel-like fluid called
nucleoplasm which contains chromatin (DNA and protein
- the hereditary information) Chromatin condenses to
form chromosomes when the cell is ready to divide. The
genetic material in the nucleus codes for all of the
proteins and other substances the body needs.
The nucleolus - is found in most cell nuclei and this is
where the assembly of ribosomes occurs before being
transported out of the nucleus to the cytoplasm.
The nuclear envelope is a double membrane made mostly
of lipids but containing pores and protein channels to
allow certain substances in and out.
Outside of the nucleus lie many organelles (“little organs” each with a specific function) surrounded by the
cytoplasm:
Cytoplasm - a protein rich, gel-like substance containing
water and mineral salts. The cytoplasm flows around
(and with) the organelles carrying nutrients, etc. to them
and taking wastes away. The movement of the
cytoplasm is called cytoplasmic streaming.
The cell membrane:
- surrounds the cytoplasm, separating it from the
environment
- gives shape to the cell
- regulates what enters or leaves the cell. Since only
certain things may pass through, the membrane is called
“semipermeable” or “selectively permeable”.
Figure 7-15 The Structure of
the Cell Membrane
Outside
of cell
Proteins
Carbohydrate
chains
Cell
membrane
Inside
of cell
(cytoplasm)
Protein
channel
Lipid bilayer
Analogy: In or Out?
• How is a window screen similar to a cell membrane? Read on to
find out.
• 1. What are some things that can pass through a window
screen?
air, fine dust, and rainwater
• 2. What are some things that cannot pass through a window
screen? Why is it important to keep these things from moving
through the screen?
Insects, leaves, and other matter that may fall from trees.
The screen keeps out annoying insects and objects that may
bring dirt into the home.
• 3. The cell is surrounded by a cell membrane, which regulates
what enters and leaves the cell. Why is it important to regulate
what moves into and out of a cell?
Materials such as oxygen and food that are needed by
the cell have to be able to get inside the cell. At the same time,
excess materials have to leave the cell.
The cytoskeleton is made of protein structures called
microtubules and microfilaments. They are the cell’s
framework, helping the cell maintain its shape. They also
help organelles move.
Microfilaments just under the cell membrane help material
move in cytoplasmic streaming.
Specialized microtubules, called spindle fibers, help the
movement of chromosomes during cell division. Other
specialized microtubules form the centrioles in animal
cells from which the spindle fibers project toward the
chromosomes.
Some microtubules form hair-like projections extending out
from the cell membrane. Cilia (short projections) and
flagella (longer projections) help certain cells move.
(Sperm move using flagella. Euglena move using cilia.
Cilia line the respiratory tract to help expel dust, mucus,
etc.)
Cell membrane
Endoplasmic
reticulum
Microtubule
Cytoskeleton
Microfilament
Ribosomes
Michondrion
Ribosomes - make protein (used in growth, repair,
hormones, enzymes, etc.) If the ribosome is free in the
cell, it will probably make a protein that will be used
within that cell. If the ribosome is bound to a folded
membrane extension coming off of the nuclear
membrane, called the endoplasmic reticulum, the protein
will probably be exported from the cell.
Endoplasmic Reticulum (ER) is a folded membrane
network:
A) Rough ER - contains ribosomes and will modify the
proteins made by the attached ribosome.
B) Smooth ER - is continuous with rough ER but has no
ribosomes. Smooth ER can store proteins from rough
ER, make lipids, help prepare proteins for transport to
Golgi apparatus, etc.
Figure 7-5 Animal Cells
Ribosome
(attached)
Nucleolus
Ribosome
(free)
Cell
Membrane
Nucleus
Nuclear
envelope
Mitochondrian
Rough
endoplasmic
reticulum
Smooth
endoplasmic
reticulum
Centrioles
Golgi apparatus
Animal Cell
Golgi Apparatus - receives proteins made by ribosomes on
the rough ER and may attach a lipid or carbohydrate to the
protein. It then packages the protein in a membrane bound
vesicle for transport out of the cell via exocytosis.
Mitochondria - These are scattered throughout the cytoplasm.
This is where cellular respiration occurs. Nutrients from
food are converted to ATP, the cellular energy currency.
They are the cell’s power plants. Mitochondria are so
important that they have their own DNA!! (This is inherited
strictly from the mother!) Cells that require more energy
(Ex: muscles, the brain), have more mitochondria.
Lysosomes - are small, spherical organelles, containing
strong enzymes that can help break down lipids, carbs.,
proteins, worn out organelles, bacteria, etc. They are like
the garbage disposal is many ways. They are also
important to embryonic development. They selectively
destroy tissue on the hand so fingers can form. (Not found
in plant cells.)
Cell wall - plant cells, fungal cell, and some bacteria have
cell walls. Plant cell walls are made of cellulose (a
tough carbohydrate) and lignin. Wood is made of old
plant cell walls. The cell wall supports and protects the
cell. It prevents plant cells from bursting from excess
pressure if too much water is taken in. Note: Animal cells
do NOT have cell walls! Too much water will cause
animal cells to burst. This is called cytolysis.
Vacuoles - are storage areas for water, certain nutrients,
toxins, etc. Plants often have a single large vacuole. The
water pressure in the vacuole can help plant cells stay
firm. If a plant becomes dehydrated, the cell membrane
may pull away from the tough, fibrous cell wall. This is
called plasmolysis. If a plant’s vacuoles are filled with
fluid and the plant stands erect, this is called turgor
pressure. (Animal cells may have SMALL vacuoles.)
Plants also have specialized organelles called plastids.
Chloroplasts contain green chlorophyll and/or other
secondary pigments that help absorb energy from
sunlight to drive photosynthesis. Carbon dioxide from
the air and water from the soil are combined to make
sugar. Oxygen and water are “waste” products.
6 CO2 + 12 H2O  C6H12O6 + 6 O2 + 6 H2O
Chromoplasts - manufacture pigments (the colors in plants)
Leukoplasts - store food, i.e. starch (Ex: potatoes)
See p. 183 for a comparison of cell types.
Venn Diagram
Animal Cells
Lysosomes
Plant Cells
Cell membrane
Ribosomes
Nucleus
Endoplasmic reticulum
Golgi apparatus

Vacuoles
Mitochondria
Cytoskeleton
Cell Wall
Chloroplasts
Cells working together for a common purpose/function
form tissues. (Ex: certain cell types work together to form
the linings covering our organs) Tissues working toward
a common function form organs. (Ex: the tissues
covering our organs may work with contractile tissues
and vascular tissues to form the heart) Organs working
toward a common function form organ systems. (Ex: In
the circulatory system, the heart works with arteries,
veins, capillaries, etc. to deliver blood.)
Cells  tissues  organs  organ systems
Improperly functioning cells can lead to illness or cancer.
Levels of Organization
Muscle cell
Smooth muscle tissue
Stomach
Digestive system
Cell Homeostasis and Transport
Homeostasis - a balance that is maintained by regulating
what gets in or out of the cell.
Diffusion - movement of molecules from an area of high
concentration to low concentration. (Ex: when a sugar
cube is put in hot tea and it breaks apart and spreads
throughout the tea, sweetening it all.)
Concentration gradient - difference in concentration of a
substance across space or across a membrane. (Ex: at
first there are more sugar molecules close to the cube
than in the rest of the tea)
Equilibrium - when molecules are evenly distributed
throughout a substance or across a membrane.
Small molecules can sometimes move freely across a cell
membrane by simple diffusion. When no ATP is needed
to move a substance, it is called passive transport.
Water can diffuse freely across. When water diffuses
across, it’s called osmosis.
But larger molecules may need special protein channels to
allow them passage through the semi-permeable cell
membrane. This is called facilitated diffusion. This is a
type of passive transport.
Some substances cannot freely enter or leave the cell or
they are being moved against the concentration gradient
(from low to high concentration) These may require
energy (ATP) and special protein gates for movement.
This is called active transport. (Ex: the sodiumpotassium pump concentrates K+ in the cell and Na+
outside)
Facilitated Diffusion
Glucose
molecules
High
Concentration
Cell
Membrane
Low
Concentration
Protein
channel
Single celled organisms often have a special organelle
known as a contractile vacuole to regulate the amount of
water or dissolved solutes within their cell. This prevents
cell death. This too involves active transport.
Some substances cannot freely enter or leave the cell.
These may require energy (ATP) and special protein
gates for movement. This is called active transport.
If the solution surrounding a cell has more dissolved
substances in it than the cell’s interior, the solution is
hypertonic and water will try to leave the cell. In plant
cells, the cell membrane may pull away from the cell
wall, this is called plasmolysis - the plant wilts.
If the solution surrounding a cell has less dissolved
substances in it than the cell’s interior, the solution is
hypotonic and water will try to enter the cell. If the cell
bursts, it’s called cytolysis.
A solution is isotonic if the concentration is equal on both
sides.
Osmosis Cont.
• Hypertonic-more concentrated solution
• Isotonic- same concentration solution
• Hypotonic- less concentrated solution
Substances may also move in or out of the cell via vesicles.
When the cell draws substances in, it is called endocytosis
To do this, the cell membrane indents and then
surrounds a substance that has triggered a receptor site,
creating a membrane encased vesicle..
If a liquid is drawn in this way, it’s called pinocytosis.
If a solid is drawn in this way, it’s called phagocytosis.
To export large substances or large amounts of a
substance, the cell builds a membrane enclosed vesicle
around the substance. Then the vesicle attaches to the
cell membrane, fuses with it while opening up to the
outside environment. This is called exocytosis.
Figure7-20 Active Transport
Endocytosis- cell membrane folds in to itself to
take in particles
-Phagocytosis- type of endocytosis
Exocytosis- removal of large amounts of
material from a cell
Cells
prokaryotic
Examples
Example
Fungi & Protists
Which have no true…
Organelles
not found in animal cells
Organelles found in
plant & animal cells
Analogy: How is a factory like a cell?
nucleus
cafeteria
mitochondria
walls
cytoskeleton
Shipping Dept.
Cell
membrane
Electric
generator
Golgi Body
Recycling
center
ribosome
Main Office
lysosome
Doors &
Windows