Cells Alive
www.cellsalive.com
Our next unit is the study of cells. We will now take our knowledge of molecules (proteins,
lipids, carbohydrates, and nucleic acids, as well as water) and determine how these
molecules are used and created within the cell.
This handout is both your lab and your notes. Be sure to study it carefully and to ask
questions as you complete this handout. Some of this will be assigned as classwork, some
as homework.
Studying Cells With High School Microscopes
Cells are difficult to study in high school, because the microscopes that we use don’t have
high enough magnification or resolution to be able to see most of the cell organelles. We
will be able to see the outline of the cell (which may be a cell wall, or a cell membrane (or
both), the nucleus of a cell, and chloroplasts in a plant cell.
The rest of the organelles we will examine via “real” microscopic pictures online (which
show a higher magnification and resolution than our own microscopes, drawings of cells
(which are more like “cartoons”, but do show the various organelles clearly, and, in some
cases, animation from youtube or other sources that show how organelles work.
Cell Size and Cell Complexity
It is important to keep in mind some basic concepts and pictures.
1). We will be looking at three types of cells.
Living cells are divided into two types - procaryotic and eucaryotic (sometimes spelled
prokaryotic and eukaryotic). This division is based on internal complexity. Cells Alive
contains interactive animations that allow you to identify internal structures (organelles)
contained within the cell.
You will need to do some exploring, drawing and writing to “get to know” these two types of
cells. First, let’s go to the section called “How Big Is A …. “ to get an idea of the size
difference between prokaryotic and eukaryotic cells.
Click on “How Big Is A…” to begin
Choose: Start the animation
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All pictures on these animations are scaled. You are beginning at a magnification of 1.
That means that the line you see on the screen represents 20 mm. If you increase the
magnification by 10, the same length of line now represents 2.0 mm. If magnified 10x
further (100x) the same line now represents 0.2 mm or 200 micrometers m). The first
letter of micrometer is represented by the Greek letter mu.
Look at the list of “things” we will be able to see on the head of the pin. Move the
magnification to 10 using the right arrow beside the word magnification (click on it).
1. At 10X what can you clearly see “laying” on the head of the pin? The magnification
scale is logarithmic. So the scale between 1-10 is by “twos” , the scale between 10 and 100
is by “ 200s” between 1000 and 10,000 is by 2000s, etc.
The list to the right of the picture on your screen indicates that order of the size of
“things” that can be found on the head of a pin. Since they are already in order, I want
you to identify when you see each organism clearly:
Human hair: 1st seen at magnification 8, seen in entirety at magnification 10
Dust mite: 1st seen at magnification 8, seen clearly at magnification 60 (legs apparent)
Ragweed pollen 1st seen at magnification 10, seen clearly at magnification 800-1000
A lymphocyte is a white blood cell: When do you see its shape clearly?
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Draw (to scale) the picture at 6000 magnification. Use colored pencils to clearly identify
the shapes and relative sizes of Pollen, lymphocyte, red blood cell, Baker’s yeast, E.coli,
Staphylococcus and the ebola virus (which you can barely see).
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E. coli and Staphylococcus are both bacteria.
How does the size of the bacteria compare to: (how many times bigger or smaller)
a. the virus (which is NOT a living thing) ?:
b. the yeast (a eukaryote),
c. a human red blood cell (small eukaryotic cell) and
d. a human white blood cell (average to large eukaryotic cell).
1. Viruses generally range from 30 – 250 nm(nanometers) – some are as large as
800 nm (mimivirus)
Look at the size of a rhino virus (common cold) as compared to a red or white blood
cell. It is very easy to see how these viruses can quickly get into our bodies
through infecting cells in the nasal passage.
2. Bacteria are general 1-10
m(micrometers)
Organelles within a eukaryotic cell are similar in size to bacterial cells
3. Eukaryotic animal cells can range from 10-30 m (human eggs are 100m)
4. Eukaryotic plant cells can range from 10- 100 m
Pollen is a large cell from a plant
5. Protista (like amoeba) can range for 100 – 900 m
Why are cells different sizes?
A cell grows to an “efficient size” (given its organelles or lack of them). By studying the
structure of each type of cell (prokaryote, eukaryote) and different types of eukaryotic
cells (plant vs. animal) we can begin to appreciate why plant cells can be so large, and
bacterial cells must remain small.
You can spend 5-10 minutes exploring the sizes of “organisms on a pin head, but then
you should move on to Cell Models (click on text on the left of the screen).
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What limits cell sizes?
Prokaryotes - Limited by efficient metabolism. They have no organelles and
can only use diffusion to move nutrients into a cell and waste out of a cell.
Animal Cells (Eukaryotic) - Limited by Surface Area to Volume ratio. The
cytoskeleton inside the cell helps to provide support for the cell membrane
and organelles and also helps to maintain cell shapel
Plant Cells (Eukaryotic) - Have large sizes due to large central vacuole which
is responsible for their growth (this is where food and many metabolic
processes occur and where water is stored). They also have a cell wall
which supports the cell membrane and protects it (to some degree) from
damage and additional stress. This allows the cell to be larger.
Addditionally, in eucaryotes, the nucleus can only “control” so much
cytoplasm. Because of this , some large or long cells (like muscle) are
multinucleated.
Click Cell Models. Choose Bacterial Cell Animation
Bacterial cells are prokaryotic cells. These cells are small, have few organelles and can be
divided into gram positive cells and gram negative cells (these two cell types have
different types of cell envelopes (Cell Wall/Cell Membrane).
Use the diagram provided at the end of this packet. Identify the following structures:
nucleoid, plasmid, cytoplasm, ribosomes, storage granules, cell envelope, capsule, pili,
flagella.
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What is the purpose of the organelles/ areas you have identified in prokaryotic cells?
nucleoid
plasmid
cytoplasm
ribosomes
storage
granules
cell envelope
Capsule
Pili
flagella
Be sure that you have chosen “Return to Cell Model” . At the top of the page choose Cell Model (Both
Bacterial Animation and Plant and Animal Cell Animation should now be red in color). Choose Plant and
Animal Cell animation.
Use the pictures provided to label structures
Animal cell Questions
1. Relate the following structures to each other (linking sentences):
Peroxisomes, lysosomes, secretory vesicles and vacuoles. What roles do they play in cell metabolism?
How do they transport materials out of the cell? What organelle creates these “packets”?
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2. How are the Rough ER, the Smooth ER, the nucleolus and the nucleus related?
3. How are the cell membrane and cytoskeleton (microtubules and filaments) related?
4. How are centrosomes, centrioles, and then nucleus related?
5. How are the nucleus, nucleolus and ribosomes in the cytoplasm related?
6. How are the cytosol and the cytoplasm related?
7. What is the role of the mitochondria? What molecules are required for the mitochondria to
generate ATP?
8. What are the two major components of the cell membrane. Describe at least 2 functions of the
proteins, What is the main job of the cell membrane?
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PLANT CELLS
1. Label the diagram provided
2. . During cell division, plants utilize the centrosome (MOTC) and microtubules. What is missing from
a plant cell that is present in animal cells during cell division?
3. What organelles are involved in storing energy, and converting chemical energy into ATP?
4. Why does the plant cell require both mitochondria and chloroplasts, but the animal cell only
requires chloroplasts?
5. How is the role and size of the vacuole different in a plant cell (as compared to an animal cell)?
6. How do the roles of the vacuole in the plant and the cell wall inter relate (hint: turgor pressure)
7. How are the roles of the cell membrane and the cell wall different?
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Based on the “average size” of bacterial, plant and animal cells.
Draw representative “circles” to ACCURATELY (to scale) represent
the size of each cell (all need to fit in the space below).
Show the scale:
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Eucaryotic Cell Organelles
The cells of protozoa, higher plants and animals are highly structured. These cells
tend to be larger than the cells of bacteria, and have developed specialized
packaging and transport mechanisms that may be necessary to support their larger
size.
Nucleus: The nucleus is the most obvious organelle in any eukaryotic cell. It is
enclosed in a double membrane and communicates with the surrounding cytosol
via numerous nuclear pores. Within the nucleus is the DNA responsible for
providing the cell with its unique characteristics. The DNA is similar in every cell
of the body, but depending on the specific cell type, some genes may be turned on
or off - that's why a liver cell is different from a muscle cell, and a muscle cell is
different from a fat cell. When a cell is dividing, the nuclear chromatin (DNA and
surrounding protein) condenses into chromosomes that are easily seen by
microscopy.
Nucleolus: The prominent structure in the nucleus is the nucleolus. The nucleolus
produces ribosomes, which move out of the nucleus and take positions on the rough
endoplasmic reticulum where they are critical in protein synthesis.
Cytosol: The cytosol is the "soup" within which all the other cell organelles reside
and where most of the cellular metabolism occurs. Though mostly water, the
cytosol is full of proteins that control cell metabolism including signal transduction
pathways, glycolysis, intracellular receptors, and transcription factors.
Cytoplasm: This is a collective term for the cytosol plus the organelles suspended
within the cytosol.
Centrosome: The centrosome, or MICROTUBULE ORGANIZING CENTER (MTOC),
is an area in the cell where microtubules are produced. Plant and animal cell
centrosomes play similar roles in cell division, and both include collections of
microtubules, but the plant cell centrosome is simpler and does not have centrioles.
During animal cell division, the centrioles replicate (make new copies) and the
centrosome divides. The result is two centrosomes, each with its own pair of
centrioles. The two centrosomes move to opposite ends of the nucleus, and from
each centrosome, microtubules grow into a "spindle" which is responsible for
separating replicated chromosomes into the two daughter cells.
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Centriole (animal cells only): Each centriole is a ring of nine groups of fused
microtubules. There are three microtubules in each group. Microtubules (and
centrioles) are part of the cytoskeleton. In the complete animal cell centrosome,
the two centrioles are arranged such that one is perpendicular to the other.
Golgi: The Golgi apparatus has a single membrane. It is important in packaging
macromolecules for transport elsewhere in the cell. The enzymatic or hormonal
contents of lysosomes, peroxisomes and secretory vesicles are packaged in
membrane-bound vesicles at the periphery of the Golgi apparatus.
Lysosome: Lysosomes contain hydrolytic enzymes necessary for intracellular
digestion. They are common in animal cells, but rare in plant cells. Enzymes of plant
cells are usually found in the central vacuole
Peroxisome: Peroxisomes are membrane-bound packets of oxidative enzymes. In
plant cells, peroxisomes play a variety of roles including converting fatty acids to
sugar and assisting chloroplasts in photorespiration. In animal cells, peroxisomes
protect the cell from its own production of toxic hydrogen peroxide. As an
example, white blood cells produce hydrogen peroxide to kill bacteria. The
oxidative enzymes in peroxisomes break down the hydrogen peroxide into water
and oxygen.
Secretory Vesicle: Cell secretions - e.g. hormones, neurotransmitters - are
packaged in secretory vesicles at the Golgi apparatus. The secretory vesicles are
then transported to the cell surface for release.
Cell Membrane: Every cell is enclosed in a membrane, a double layer of
phospholipids (lipid bilayer). The exposed heads of the bilayer are "hydrophilic"
(water loving), meaning that they are compatible with water both within the cytosol
and outside of the cell. However, the hidden tails of the phosopholipids are
"hydrophobic" (water fearing), so the cell membrane acts as a protective barrier to
the uncontrolled flow of water. The membrane is made more complex by the
presence of numerous proteins that are crucial to cell activity. These proteins
include receptors for odors, tastes and hormones, as well as pores responsible for
the controlled entry and exit of ions like sodium (Na+) potassium (K+), calcium
(Ca++) and chloride (Cl-).
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Mitochondria: Mitochondria provide the energy a cell needs to move, divide,
produce secretory products, contract - in short, they are the power centers
of the cell. They are about the size of bacteria but may have different shapes
depending on the cell type. Mitochondria are membrane-bound organelles, and like
the nucleus have a double membrane. The outer membrane is fairly smooth. But the
inner membrane is highly convoluted, forming folds (cristae). The cristae greatly
increase the inner membrane's surface area. It is on these cristae that food
(sugar) is combined with oxygen to produce ATP - the primary energy source for
the cell.
Vacuole: A vacuole is a membrane-bound sac that plays roles in intracellular
digestion and the release of cellular waste products. In animal cells, vacuoles are
generally small. Vacuoles tend to be large in plant cells and play several roles:
storing nutrients and waste products, helping increase cell size during growth, and
even acting much like lysosomes of animal cells. The plant cell vacuole also
regulates turgor pressure in the cell. Water collects in cell vacuoles, pressing
outward against the cell wall and producing rigidity in the plant. Without sufficient
water, turgor pressure drops and the plant wilts.
Cell Wall (plant cells only): Plant cells have a rigid, “protective” cell wall made up
of polysaccharides. In higher plant cells, that polysaccharide is usually cellulose.
The cell wall provides and maintains the shape of these cells and serves as a
protective barrier. Fluid collects in the plant cell vacuole and pushes out against
the cell wall. This turgor pressure is responsible for the crispness of fresh
vegetables.
Chloroplast (plant cells only): Found in all higher plant cells. Contain chlorophyll
which absorbs energy from sunlight (it does not absorb green light, which is why
chloroplasts are green!). The absorbed energy is used to convert water (which
comes into the leaf through roots) and atmospheric carbon dioxide into
metabolizable sugars (like glucose) using photosynthesis.
Ribosomes: Ribosomes are packets of RNA and protein that play a crucial role in
both prokaryotic and eukaryotic cells. They are the site of protein synthesis.
Each ribosome comprises two parts, a large subunit and a small subunit. Messenger
RNA from the cell nucleus is moved systematically along the ribosome where
transfer RNA adds individual amino acid molecules to the lengthening protein chain.
Some ribosomes are found on the rough ER, while others are found in the
cytoplasm.
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Endoplasmic Reticulum
Throughout the eukaryotic cell, especially those cells responsible for the
production of hormones and other secretory products, is a vast network of
membrane-bound vesicles and tubules called the endoplasmic reticulum, or ER for
short. The ER is a continuation of the outer nuclear membrane and has several
functions.
Smooth Endoplasmic Reticulum: Smooth ER plays different functions
depending on the specific cell type including lipid and steroid hormone
synthesis, breakdown of lipid-soluble toxins in liver cells, and control of
calcium release in muscle cell contraction.
Rough Endoplasmic Reticulum: Rough endoplasmic reticulum appears
"pebbled" by electron microscopy due to the presence of numerous
ribosomes on its surface. Proteins synthesized on these ribosomes collect
in the endoplasmic reticulum for transport throughout the cell.
Cytoskeleton: As its name implies, the cytoskeleton helps to maintain cell shape.
But the primary importance of the cytoskeleton is in cell motility. The internal
movement of cell organelles, as well as cell locomotion and muscle fiber contraction
could not take place without the cytoskeleton. The cytoskeleton is an organized
network of three primary protein filaments:
- microtubules
- actin filaments (microfilaments)
- intermediate fibers
Structure of the Cell Membrane:
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