Download Looking at Types of Cells

173
Looking at Types of Cells
While we will focus in depth on human body cells, it’s useful
and interesting to know that all living things on Earth are
divided into a few basic groups based on the kinds of cells
they have. We will use the microscope to look at
representatives of the Animal Kingdom, Plant Kingdom and
Protist Kingdom.
The Animal Kingdom, represented by....human cheek cells!
You are a member of the Animal Kingdom, and your cheek cells are easy to examine.
1. Put on gloves.
2. Use a toothpick to gently scrape the inside of your cheek.
(Why are we doing this?)
3. Wipe the contents on a small portion of a microscope slide.
4. Ask me for a drop of methylene blue stain.
(Why are we adding a “stain”?)
5. Add a cover slip to the slide.
6. Examine the slide under the microscope (low power, then medium power, then
high power) for evidence of your cells.
(What do you expect your cheek cells to look like?)
7. Draw your cheek cells here. See if you can label the cell membrane, nucleus, and
cytoplasm. You may also see some other organelles as well.
Why do you think that animal cells have a flexible cell membrane as their outer covering
instead of a sturdy cell wall like you will soon see in plant cells?
8. OPTIONAL FUN: What is the effect of salt on your cheek cells? Introduce a drop
of salt water onto your slide just as you did with the stain. Wait a few minutes.
What happens to the cells? Why is this?
174
The Plant Kingdom, represented by... Anacharis (seaweed), Onion and Lettuce!
Here are pictures of cells of three plants – (Anacharis) seaweed, onion and lettuce:
http://science.exeter.edu/jekstrom/WEB/CELLS/Epith/JPEG/
http://www.ecok.edu:9045/repository/unmanaged_content/biology/russo/
http://www.luc.edu/depts/biology/111/
175
1. Make slides of each of the three plant types and observe them under the
microscope.
2. Determine which photograph depicts which plant type and label each photograph
correctly.
3. In the Anacharis (seaweed) photograph, label cell wall, cell membrane (tricky!!),
cytoplasm and chloroplasts. In the slide you prepare, you may also see the
nucleus of some cells and vacuoles in other cells. Draw those in on the
photograph of the Anacharis cells.
4. In the onion photograph, label cell wall, nucleus, cytoplasm and cell membrane
(tricky!!).
5. In the lettuce photograph, label cell wall, cell membrane (tricky!!), nucleus (very
tricky!!), cytoplasm, and chloroplasts.
Thinking questions:
1. Why do plant cells have a sturdy cell wall in addition to their cell membrane?
2. Why do Anacharis cells and the cells of many other plants have the green sacs
called chloroplasts in them?
3. Why, then, are there no chloroplasts in the section of onion you looked at?
4. Look closely at the lettuce. Notice that there are a few special round cells in
addition to the squarish or blobby cells. Which cells in the lettuce contain
chloroplasts – the round or the square? What do you think these round cells might
be for?
5. OPTIONAL FUN: What is the effect of salt on plant cells? Add a drop of salt
water to the plant cells. Wait a few minutes. What happens to the cells?
176
Microscopic Life in the Park Pond
A drop of pond water can yield hundreds of
exciting and interesting organisms. These
include microscopic animals, microscopic
plants and a group of single-celled creatures
called Protists. A few common types of
protists you might find are Paramecium,
Vorticella and Amoeba. Many of “The Far
Side” cartoons feature Protists!
Obtain a drop of pond water that contains
some chunks of debris and place this on a
slide with a cover slip. Here are some things
you might see:
Organism
Comments
These are members of the Animal Kingdom because
Interesting adaptations include
Bristle Worm
http://www.environmentalleverage.com/Bristle%20Worms.htm
http://mblaquaculture.com/assets/images/content/photo_Daphnia
_magna.jpg
These are members of the Animal Kingdom because
Interesting adaptations include
Daphnia (water flea)
177
http://cache.eb.com/eb/image?id=9298&rendTypeId=4
These are members of the Plant Kingdom because
Interesting adaptations include
Various species of Algae
These are members of the Protist Kingdom because
http://serc.carleton.edu/images/microbelife/k12/cedarswamp/A
WCS_microbes.jpg
Various species of Protists
http://serc.carleton.edu/images/microbelife/k12/cedarswamp/A
WCS_microbes.jpg
Interesting adaptations of Protists include
More Protists
What Kingdom do you think this belongs to?
Interesting adaptations include
Your discovery here
What Kingdom do you think this belongs to?
Interesting adaptations include
Your discovery here
178
Questions:
1. Now that you’ve seen some cells firsthand, what do you think is a good definition
of “cells”?
2. What are some differences that you saw between plant and animal cells? Why do
these differences exist?
3. Why are our bodies made up of so many cells? Why are there not, say, a hundred
or a few thousand?
4. One of the big remaining mysteries of human biology is the issue of cell
differentiation. When a sperm cell fertilizes an egg and a little embryo is first
developing, it is just a ball of identical cells. Somehow, as these cells divide, these
identical early cells (often called stem cells) differentiate and turn into different
cells like cheek cells, blood cells, heart cells, pancreas cells, etc. How do you
think stem cells “know” what kind of cell to turn into? (I know this is a hard
question! I’m just curious about your ideas.)