Cells: The Importance of Cell Walls

 Cell walls prevent plant cells from bursting. 

Blow up a balloon until it pops.  An animal cell (or a plant cell that's missing a cell wall for some reason) is like this balloon.  Water can flow into the cell until the membranes bursts. 

Now place a balloon into a length of pantyhose and proceed to blow it up.  It will be harder and harder to blow up the balloon because the nylon restricts the balloon.  Virtually impossible to blow it up enough to pop it.  In the same way, the cell wall prevents the cell from reaching its bursting point. 

Cells: Semipermeable Membranes

You don't have to get very far into your study of cells before your students are presented with the term "semi-permeable," used to describe cell membranes.  Just as easily as you can define it for your students, you can show them!

Before class mix together 1/2 cup of sand (or salt) and 1/2 cup of marbles (or dried beans, pebbles, or other objects larger than the holes in a colander).  Place the mixture in a beaker or glass jar.

When you get to semi-permeable membranes during class, show the students your mixture.  Then pour the mixture through a colander (make sure you have a bowl or pan underneath!).

The beans stay in the colander while the salt/sand passes right through.  Just like a cell membrane, particles that are small enough to pass through the holes do so and particles larger than the holes stay put.

Candy Cell Models

One week of candy wasn't quite enough, so here's one more!  Happy Halloween!

A good friend did this with her 5th grade students following Halloween one year, and it was a great success. 

The students were studying cells and they were placed in groups and instructed to make a cell model using different types of candy.  The students rationalized what would work best for each organelle and each contributed some candy from their own stash to create the finished product. 

The students enjoyed their work and their parents were quite happy to have the candy put to use other than eating!

And, this activity could be adapted to whatever you happe to be studying right around Halloween.  Students could use candy to make models of body parts/systems, atoms, viruses, bacteria, etc.

Microscopes: Elodea Lab

Elodea is an aquatic plant that can be found at most fish stores. It is great for looking at under the microscope because the leaves are so thin, only a couple of cell layers thick and light can pass through the leaf.

Place an elodea leaf on a clean slide. Place a drop of water on the leaf and then the cover slip. View under the microscope. You will note the regular, retangular shape of the plant cells, the cell wall, the chloroplasts, and the nucleus.

Microscopes: Onion Skin Lab

One variety of plant cells…

Cut some onion into small pieces and separate each layer. Each layer of the onion contains a thin layer of cells that can easily (usually!) be peeled off the rest of the onion. Place the layer of cells onto a clean slide, make sure not to fold the onion skin over on itself. Place a drop of iodine on top of the onion skin and then a cover slip. View under the microscope. You will note regular, rectangular shape of the plant cells, the cell wall and the nucleus.

One question to ask your students…. They are plant cells, why are there no chloroplasts? [Think about where onions grow…]

Cell Processes: Modeling Endocytosis: The Jelly Bean Problem

I just refer to this activity as modeling endocytosis, but you might not want to refer to it that way, as it may give too much away to your students.  

It comes from the Access Excellence collection and is named The Jelly Bean Problem.

In short, the students are trying to get a handful of candy into a plastic bag following these rules:

• The candy must enter through a solid part of the bag.
• The inside of the bag may not be directly open to the external environment.
• The candies entering the bag must remain clustered together.
• Students may work with their hands in the bag to act as the inside of a cell.
• The candy may be eaten only if it enters the bag "cell" under the specified conditions. 

Check out the original version for a nice illustration of how to accomplish this goal.

It's fun, candy is always an attention-getter, and it relates directly to cells.

Organism Organization

Cells make tissues.

Tissues make organs.

Organs make organ systems.

Organ systems make organisms.

Get your students up and moving, while helping them understand the organization of organisms. 

Prepare the following 2 of each of the following signs (Notice I didn't do much to prepare these - printed them out and stapled them to a piece of construction paper, just for a little added weight - this was a last-minute idea that was quickly assembled after lunch one day).

Blood Cell  I
Blood Cell II
Heart Cell I
Heart Cell II
Brain Cell I
Brain Cell II
Nerve Cell I
Nerve Cell II
Stomach Cell I
Stomach Cell II
Intestine Cell I
Intestine Cell II

Hand each student a sign.  They are each a cell, wandering around the classroom on their own. 

Cells make tissues, so have them find their matching cell, in order to make a tissue.  You now have pairs of students walking around together.

Tissues make organs.  Have all the heart tissues combine, all the stomach tissues combine etc.  You now have organs, a.k.a. groups of four students.

Organs combine to make organ systems.  The heart and blood make the circulatory system.  The brain and nerves make the nervous system.  The stomach and intestine make the digestive system. 

And finally, organ systems combine to make an organism.  At this point all the students (cells) come to gether to create one organism. 

If you wanted to have a little more fun, you could turn it into a game of Simon Says and call out the different levels of organization (i.e. cell, tissue, organ, organ system, organism) and students would have to quickly assemble into the appropriate grouping. 

Turn Your Students Into a Protein

This one takes a little prep work the first time 'round.  But after that, you're set forever.  It's a great way to include a little kinesthetic activity into the study of DNA.

First, the prep work: 
On a long strip of paper* write out a string of DNA bases (actually, you're making the mRNA).  You want to make sure your letters are evenly spaced - I actually marked the paper.

Keep a codon chart handy - make sure you begin with a start codon and don't come to a stop codon immediately.  And, don't make the mistake of using T instead of U, as someone did...

Now you need to make a ribosome through which your strip of paper can fit.  I made mine out of fun foam.  It has magnets on the back, so it sticks to the white board.  Cut the window in the ribosome, so that you can see 3 bases at a time (hence the reason for evenly spacing your letters).  Use this picture to guide you:

Now you need to make the amino acids.  Once again I used fun foam.  I wrote the amino acid on the foam, punched holes in it and strung string through the holes so the students could wear them. 

For the activity: 
Draw a huge circle on the board - a cell.  Sketch in a nucleus and stick your ribosome in the middle as well. 

Show your students the mRNA (your paper strip) moving from the nucleus to the ribosome.

Feed the mRNA into the ribosome.

Have your students translate the first 3 mRNA bases into an amino acid.

Have a student put the appropriate amino acid placard on and stand in front of the room.

Move the mRNA to the next three bases.  Determine the amino acid.  Have another student put on the appropriate placard, then stand next to the first student and hold his/her hand.

Proceed this way until you come to a stop codon, or until you've made your point.

Your students will have a better feel for how a ribosome translates mRNA, how proteins are formed, and understand that proteins are long chains of amino acids. 

* I got a few sentence strips from an elementary teacher in my building - they're the perfect size and shape for this, I didn't have to cut them, and they have lines marked on them!

******
I learned this from a fellow teacher at a NJ Science Teachers Association Convention several years ago.  I don't know who that teacher is - but if you're out there, please let me know - I'd like to give you credit.

Cell Building Blocks: Testing Food for Fat

Gather a variety of food items (fruits, veggies, crackers, chips, cheese, bread, lunchmeat, condiments, etc.).

Spread open a brown paper bag on your work surface. Rub a small amount of each food item on the bag and label the spot with the type of food. After you have completed all of the food items, look for transparent spots – this is evidence of fat. Beware of spots that are just wet – they will dry out, transparent spots due to fat will not. You may want to rub a small amount of oil (a known fat) onto brown paper bag as a source for comparison.


Have students record data and look for patterns in the items that contain fat and those that don’t (think plants vs. animals).

Cell Building Blocks: Testing Food for Starch

Gather a variety of food items (fruits, veggies, crackers, chips, cheese, bread, lunchmeat, condiments, etc.-whatever you can find in your house).

Place a drop of iodine on each food item. If the item contains starch, the iodine will turn black (you may have to wait a minute or two. If there is no starch present, the iodine will remain dark purple/brown. The difference can be subtle... look carefully. Also consider the color of your food choices... it's easier to discern the difference on lighter colored foods.



Have students record data and look for patterns in the items that contain starch and those that don’t (think plants vs. animals).

Microscopes: Cheek Cell Lab

View some animal cells under the microscope: your own!

Place a drop of iodine on a clean slide. Rub a toothpick along the inside of your cheek (not need to poke or jab, just a gentle rub). Dip the toothpick into the drop of iodine. Place a cover slip over the iodine and view under the microscope. You will note the irregular shape of the animal cell, as well as being able to identify the cell membrane and nucleus.