Download 04 Cell Structure and Function

05. Cell Structure & Function
Name: ______________________________
Concepts in Biology (BIOL 100)
04. Cell Structure and Function
Learning Objectives:
• To examine size and structure differences between prokaryotes and eukaryotes.
• To examine plant and animal cells, and recognize key structures of these cells.
• To review cell structures and functions, and recognize them on diagrams.
• To understand the rules governing movement of particles and water with diffusion and
osmosis.
• To relate diffusion and osmosis rules to their effects on plant and animal cells.
• To differentiate between isotonic, hypertonic and hypotonic solutions, and recognize their
effects on water movement in cells.
Prokaryotes and eukaryotes
The cell is the smallest unit of life; a cell may be an independent life form, or a part of a larger
organism. Prokaryotes are cells that lack nuclei (bacteria, archaea), whereas eukaryotic cells are
more complex and have nuclei (plant cells, fungal cells, animal cells and single-celled protists).
Prokaryotes
1. What is the most obvious structural difference between prokaryotic and eukaryotic cells?
______________________________________________________________________
2. What are two organelles that eukaryotes have, but prokaryotes do not?
________________________
______________________
3. Which is generally larger, a prokaryotic cell or a eukaryotic cell? _________________
4. For a compound microscope we can calculate the field of view at higher magnifications, using
our measurements at lower magnification from last week, and our ability to easily convert
within the metric system to complete the table below.
Conversion: 1mm = 1,000µm
Objective
Total Magnification
Field of View (mm)
4x
40x
4mm
Field of View (µm)
10x
40x
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05. Cell Structure & Function
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Look at the bacterial slides. Note that there are two bacterial shapes set up on the
microscopes – rods (ovals with flat sides – in 3D, shaped like pill capsules) and cocci (circles –
in 3D, spheres). Even at 1000x magnification the bacteria are very tiny – they will be visible
as clusters (cocci) or chains (rods) with hundreds if not thousands of bacteria visible per field of
view.
Draw just a few rods (bacilli) and spheres (cocci) in your fields of view, approximately to scale.
Enter the total magnification, as this is good practice when drawing microscope views. Next,
estimate the length/diameter of each bacterium based on the diameter of the field of view.
Start by estimating the number of bacteria that can be lined up end-to-end in a straight line
across the field of view. Then use the following formula to estimate individual size.
𝑪𝒆𝒍𝒍 𝒔𝒊𝒛𝒆 =
𝑫𝒊𝒂𝒎𝒆𝒕𝒆𝒓 𝒐𝒇 𝒕𝒉𝒆 𝒇𝒊𝒆𝒍𝒅 𝒐𝒇 𝒗𝒊𝒆𝒘 (𝝁𝒎)
𝑵𝒖𝒎𝒃𝒆𝒓 𝒐𝒇 𝒄𝒆𝒍𝒍𝒔 𝒍𝒊𝒏𝒆𝒅 𝒆𝒏𝒅 𝒕𝒐 𝒆𝒏𝒅
Bacterial shape:
Bacterial shape:
_______________
_______________
Bacterial length/diam.
Bacterial length/diam.
____________
____________
Total magnification:
__________
Total magnification:
__________
Plant cells: Elodea
You will now examine cells in leaves of the plant Elodea (scientific names for plants and animals
are written in italics if typed, or underlined if handwritten), and in thin pieces of onion or potato.
Since you will be trying to focus on individual cells, you want samples that are as thin as possible
– when examining Elodea, look at the edge of the leaf, and when you are taking onion layers or
cutting potato sections, aim for sections so thin that you can see through them.
1. What are the three cell structures that are generally found in plant cells but not animal cells?
_______________________
_______________________
______________________
2. Take two Elodea leaves and place them on microscope slides. Add a drop of water to one,
and a drop of salt solution (10% NaCl) to the other. Cover with cover slips.
3. Use the low-power (4x) objective to initially focus on the plant in water (save both for the
Tonicity exercise). Move the slide until you find a thin region of the leaf, then increase the
magnification so that you can better examine the cells. Note that the central vacuole will
often occupy most of the space in the cells, but you should be able to see the chloroplasts
squeezed between the central vacuole and the cell membrane. Sometimes the cell membrane
is tight against the cell wall; at other times you may be able to see these structures separately.
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05. Cell Structure & Function
Name: ______________________________
4. Draw at least two Elodea cells to scale in your field of view below. Be sure to indicate the total
magnification and calculate average cell size using the formula above. Label the central
vacuole, chloroplasts, cell membrane and cell wall in your diagram.
Objective: ______________
Total magnification: ______
Plant cell length: _________
5. Using the diameter for the fields of view provided earlier, estimate the length of an Elodea cell
and write it above.
Which is larger, the plant cell or the bacterial cell? __________________________
By approximately what factor (2x, 10x, 100x, 1000x etc.)? ___________________
6. Save the Elodea slide for use in the osmosis activity.
Plant cells: potato and onion
In this exercise you will again look at plant cells, this time from potatoes and onions. You will
also observe storage vacuoles containing starch.
1. Obtain a very thin slice of either potato or onion (your lab partner will take the other). For the
potato, cut a paper-thin slice with the knife or scalpel. The whole slice need not be paper-thin
– a super-thin edge of a slice will work fine. For the onion, use a fingernail or knife to peel off
a super-thin (see-through) layer of onion. Put your sample on a microscope slide – try to keep
it flat, with minimal folding. Cover with a cover slip.
2. Examine the onion/potato cells under the microscope. Draw the outlines of at least four cells
to scale in your field of view below. Repeat for the other plant, using your labmates’ slide.
Plant: ________________ Mag: ______
Plant: _________________ Mag: ______
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05. Cell Structure & Function
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3. Do you see any chloroplasts in these cells? _________
Why not? (hint: where do these parts of the plant grow?)
4. Iodine is a substance that will stain starch molecules Purple/brown/black. Add a drop of
iodine solution to one edge of the coverslip; you should see the iodine move across the
sample. Iodine can temporarily stain your skin and permanently stain clothes, so please be
careful.
5. Look at the potato and onion slides again. Which has starch storage? ____________________
Flavor aside, if you wanted a starchy meal, would you eat a potato or an onion?
____________________
6. Draw a plant cell with starch vesicles/vacuoles/sacs below.
Plant: ________________
Magnification: ________
7. Dispose of your plant slides.
Animal cells: cheek cells
To obtain your animal cell sample, you will collect cells from the inside of your cheek. You will
stain the cells with the dye methylene blue to make the nuclei visible (Methylene blue stains
nucleic acids, and cell membranes). You may have noticed that it was difficult or impossible to
see the nuclei in the plant slides – we didn’t add methylene blue then because it does not
penetrate the plant cell wall. Note: Methylene blue, like iodine, will temporarily stain your skin
and permanently stain clothes, so please be careful.
1. To obtain a cheek scraping, gently rub a
toothpick along the inside of your cheek. (You
should NOT draw blood or otherwise gouge
out a chunk of cheek tissue!)
2. Place the drop of cheek cells onto the
microscope slide. Add a drop of the methylene
blue dye and cover with a cover slip. If you
get methylene blue on your skin, wash your
hands.
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05. Cell Structure & Function
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3. Find an individual cell. There will probably be clusters of cells scattered around on the slide.
Try to find one by itself, or at the edge of a cluster, to look at – it will probably look like a fried
egg (sunny-side up) with a light/medium blue yolk (the nucleus). For the hair follicle cell, look
at the root end of the hair.
4. Draw your animal cell below. Label the nucleus and cell membrane.
Cell: ________________
Magnification: _______
5. How does the animal cell differ in shape from the plant cells?
___________________________________________________________________
6. Dispose of your slide and toothpick in the biohazard waste.
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05. Cell Structure & Function
Name: ______________________________
Cell organelles
Describe the basic functions for the following cell structures, and check whether they are found in
plant cells, animal cells or both.
Structure
Function
Plant
cells?
Animal
cells?
cell membrane
cell wall
nucleus
ribosome
rough ER
smooth ER
Golgi apparatus
storage vesicles
central vacuole
mitrochondria
chloroplasts
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05. Cell Structure & Function
Name: ______________________________
Label the diagrams below with the structures in the table.
(Fluid'filling'the'cell)'
(Fluid'filling'the'cell)'
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05. Cell Structure & Function
Name: ______________________________
Diffusion and Osmosis
Dialysis: diffusion (and a little osmosis)
With diffusion, particles move from areas of high concentration to areas of low concentration. For
this exercise, we will look at simulated (fake) blood in a bag made of dialysis tubing – thin plastic
sheeting with very tiny holes. The holes are large enough to allow water and small yellow waste
particles to move through, but are too small to allow red blood cells to move through. This is
similar to what happens in your kidneys while urine is produced (and it is why blood in the urine
often indicates some sort of damage to the kidneys – the holes in the kidney’s filtration membranes
should not be large enough for red blood cells to pass through!)
1. Note the appearance of the dialysis bag before it is placed into the water. Is the bag
completely full (it looks like a ready-to-burst water balloon), or is it mostly full with some
expansion room?
2. Draw the beaker and dialysis bag as they appear at the beginning of the demonstration in the
space at left below. Indicate where the concentrations of red particles and yellow particles are
the highest (in the bag or in the beaker).
Beginning
End
3. Given the information provided above, what do you expect to happen to the colors in the
beaker over the course of the lab period, and why?
4. Draw the beaker and dialysis bag as they appear at the end of the lab period in the space
provided in step 2 above.
5. Examine the fullness of the dialysis bag. Has it become more full or less full? _____________
Why?
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05. Cell Structure & Function
Name: ______________________________
Tonicity basics
The cell membrane is selectively permeable; that is, it allows some substances to pass through,
and holds other substances inside – or outside – the cell. Animal cell membranes are almost
always permeable to water, since they have water channels passing through the lipid bilayer, but
the phospholipid cores are impermeable to polar molecules (e.g. sugars) and charged ions (e.g.
sodium). When a concentration gradient of particles cannot be resolved by diffusion, water will
move to dilute the more concentrated solution in an effort to restore equilibrium.
1.
Isotonic solutions have concentrations of particles similar to those found inside the cell.
Will there be net (overall) movement of water into or outside the cell? __________
2. Hypertonic solutions have a higher concentration of particles than are found inside the cell.
In which direction will water move? _______________________________
3. Hypotonic solutions have a lower concentration of particles than are found inside the cell.
In which direction will water move? _______________________________
4. Label the images of red blood cell solutions below as isotonic, hypertonic and hypotonic –
note the concentrations of the large circles. The arrows indicate flow of water.
Tonicity: Elodea
1. Take out the Elodea leaf in plain water that you prepared earlier and examine. Note the
distribution of organelles within the cell (in particular chloroplasts)
Is this leaf in a hypertonic or a hypotonic solution? _______________________
As water flows into a plant cell, it is stored in the central vacuole. Go back to your labeled
diagram of a plant cell. Does the central vacuole likely take up a large space or small space
in this cell? ______________
2. Take out the Elodea leaf in the salt solution slide. The leaf is in a _______________________
solution. You would therefore expect water to move __________________ the cell.
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05. Cell Structure & Function
Name: ______________________________
3. Draw a representative cell from each leaf below.
WATER
Mag: ______
SALT SOLUTION
Mag: ______
4. Where are the cell membrane and chloroplasts located for the cell in salt water, compared to
the cell in plain water? Why?
Tonicity: Celery
At the beginning of the lab period, celery stalks were placed in fresh water and salt water.
1. Is the freshwater celery in a hypertonic, hypotonic, or isotonic solution?
2. Is the saltwater celery in a hypertonic, hypotonic, or isotonic solution?
3. Pick up the strips and gently bend them. How are they different, and why?
4. If you wanted to “perk up” some slightly wilted lettuce, would you put it in freshwater or
saltwater?
5. Sailors use to salt meat to preserve it for long voyages. Why would packing fresh meat in salt
help to preserve it?
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05. Cell Structure & Function
Name: ______________________________
Endocytosis
Endocytosis is the process of taking particles into the cell by pinching an inward fold of the plasma
membrane to form a vesicle around the particles. In this exercise you will observe endocytosis of
colored yeast by the single-celled animal Paramecium.
1. Make a wet mount by placing a drop of the Paramecium culture on a slide. Next, add a drop
of the red-dyed yeast (be sure to take from the bottom of the flask). Before adding the
coverslip, add a drop of Protoslo – this will slow the organism down, as it is a fast swimmer.
2. Examine the Paramecium using the medium and/or high-power objective. You may see
organelles and the nucleus, as well as the blur of beating cilia at the external surface. Find a
Paramecium that is feeding on the yeast, and look for the red-dyed food particles in vesicles
within the cell.
3. Draw one of the Paramecium that you observe and
label all identifiable cell structures.
Objective: __________
Total magnification: ______
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05. Cell Structure & Function
Name: ______________________________
Notes:
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