Lesson 2

What did you do last time?

unicellular

lineage

divides

multicellular

cell

LUCA

PRINT the word next
to the image on the next slide.

Looking at CELLS!

To look at cells,
you will need to use
microscope slides.

Let’s begin with plant cells --
onion cells.

Start with a pre-made slide.

Find these items.

Onion Cells

Look at the slide
of onion cells.
What do you see?

Not much! The cells are too small to see.

On this slide
is a thin layer
of cells
pealed from
an onion.

Magnifying Cells

magnifyer

the pre-made microscope
slide labeled
onion cells

To test this, begin with your magnifier.

First, look at the tip
of your finger WITHOUT
the aid of the magnifier.

You cannot see cells with just your eyes! Cells are too small.
You will need to make the cells appear to be larger than they really are.

Do you see the grooves?
You may see more if you rub
your fingertip with a pencil.

Now use
the magnifier
to look at your finger.

How MUCH magnification is needed?

Use your magnifier
to examine your
fingerprint.
Observe coins and
other objects
around your home.

Use

Use your magnifier
to examine
the lettering
on this screen.

Now use your magnifier to look
at the onion cells on your slide.
What do you see?

NOT MUCH, because your magnifier does not magnify
the cells enough for you to see them! Your magnifier only
makes objects appear 3 to 5 times larger than they are.

You will need a much more POWERFUL magnifier to see your onion cells.
What magnification will you need

Click for answer.

To see most cells,
you need a light microscope.

Compound microscopes start
at 100x and typically go to 1000x.

You will need
a smartphone or
tablet to use
this microscope.

Assemble
as directed.

Locate
the clip-on microscope
and the light attachment.

Now look at your slide
using a smartphone or a tablet.

Summary of Direction

1. Use the two metal clips to hold
the microscope slide in place.

2. Center the sample over
over the microscope lens.

3. Turn on the light source.

4. Pinch open the clamp.

5. Gently line up the microscope
lens with the camera lens.
The cells will come into view
WHEN the two lenses are lined up.

6. Now use the clamp to hold
the microscope in place over the camera lens on the device.

To use your microscope,
follow the directions in the video.

Turn on the light source!

Use the photo app
to further enlarge and
enhance the photos
of your slides.

You can take
photos of your cells
with the standard
camera app.

Onion Cells

Do they look like stacked bricks?
The interlocking of many
cells gives strength
and form to the roots,
stems and leaves of a plant.

Now look at your slide of onion
cells. Do you see a number of individual onion cells?

Cells are the building blocks of plants.

close-up view
of one section
in a photo app

Draw it on a
sheet of paper.

This is a close-up view
of a few onion cells
as seen in the photo app.

What do you see?

Click for answer.

The NUCLEUS contains the recipe
for making each cell. This information is called “genetic” information.
The genetic information in the nucleus is encrypted in the molecule called -- Deoxyribo Nucleic Acid -- DNA!

Do you see a dense round structure
inside each onion cell?
This is a NUCLEUS. Label it.

What does the nucleus DO

Close up view
of onion cells.

Do you see that each individual plant cell
is surrounded by a thick surface or wall?
Label this the CELL WALL.

What does the cell wall DO

Plant cells have CELL WALLS that:

• protect the cell
• maintain the cell’s shape
• prevent excessive water uptake
• are made up of cellulose

Inside the cell wall is an inner sack
that encircles the cell. It is difficult
to distinguish at this magnification
but label it the PLASMA MEMBRANE.

What does the plasma membrane DO

It performs many functions in a cell.
The CYTOPLASM of onion bulbs is packed with energy stored in the form of sugar. The sugar stored in each cell of the bulb allows the onion plant to survive over the winter without leaves.

The PLASMA MEMBRANE
controls what goes in and out of a cell.

The CYTOPLASM is the area INSIDE each cell
that is OUTSIDE the nucleus.
Label it on your onion cell diagram.

What does the cytoplasm DO

plasma membrane

cytoplasm

Find these items:

Now make your own
microscope slides.

1 microscope slide

1 coverslip

You may need help with the onion skin.

tweezers

onion

toothpick

one pipette

PRACTICE squeezing water
in and out of the pipette.

Squeeze the air
out of the bulb.

Lower the pipette tip
into a cup of water.

Suck in water by reducing your
finger pressure on the bulb.

Squeeze the bulb to
release one small drop
at a time onto a penny.

How many drops
can you put on
the head of a penny?
The record is almost
100 tiny droplets.

Try it.

Peel a small
section of this
THIN layer with
a fingernail or tweezers.

HOW THIN? As thin as peeling skin
after a sunburn.

To make your own slide,
begin by slicing
your onion into halves
and then quarters.

Pull off
a single
segment of onion.
Snap the onion segment back
toward the outer smooth side.
Notice that there is a THIN layer
of cells on the inside of each piece.

Carefully flatten
the THIN onion layer
onto the center
of the slide.

Do NOT allow this THIN
piece to fold up into a wad.
It should be flat and smooth.

NOTE: It may
take a few minutes for the stain to be absorbed
into the cells.

Be sure the coverslip lays flat and that there are no air bubbles.
Use a small piece of paper to blot up any excess liquid.

Position one edge
of the coverslip
over the layer of onion,
as shown.

Gently drop the coverslip onto the stained onion.

Use the pipette to add a drop
of iodine OR food coloring stain
onto the onion tissue.

The drop of Iodine is the “wet” part of what is called a wet mount.

Iodine is a different stain than
the one used in the pre-made slide.
Do your iodine stained cells look different than the blue stained cells?

The iodine you added to your slide reacted with the starch stored in the cytoplasm of the onion cells. This made the otherwise transparent onion cells visible under the microscope.

The pre-made slide used
a blue stain that attaches
to negatively charged particles.
This stain tends to attach
to the DNA in the nucleus,
turning it an intense blue color.

You may also see the nucleolus,
a dark spot in the nucleus.

Do you see the differences?
Go back and look.

In your science classes, you will use different stains to hi-light different regions within a cell.

nucleolus