This experiment allows you to see protozoa, tiny-single celled organisms, in your compound microscope. While I can go in my backyard and find a lot of interesting pond scum and dead insects, I realize that not everybody has a thriving ecosystem on hand, especially if you live in a city.

I am going to show you how to grow a protozoa habitat that you can keep in a window for months (or longer!) using a couple of simple ingredients.

Once you have a protist farm is up and running, you’ll be able to view a sample with your compound microscope. If you don’t know how to prepare a wet mount or a heat fix, you’ll want to review the microscope lessons here.

Protozoa are protists with animal-like behaviors. Protists live in almost any liquid water environment. Some protists are vital to the ecosystem while others are deadly.

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Download Student Worksheet & Exercises

Here’s how you can grow your own to look at under a compound microscope:

1. Leave a glass of water out overnight, to get rid of chlorine. If you are in a hurry, use filtered water (not distilled) instead.

2. Add dead grass to the glass of water. Stir.

3. Add yeast to the glass. Stir again.

4. Allow the glass to sit overnight in a warm place. For best results, let grow and ferment for several weeks.

5. Each day for a week, observe a sample of water and/or grass under the microscope, after the first 24 hours.

6. Sketch the protozoa you see, and note if there are more or less of a certain type as time goes on in your science journal.

Exercises

1. What is a cell?
2.  Why are cells so small?
3.  What is a protozoa?
4.  How does it develop?

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If you think of celery as being a bundle of thin straws, then it’s easy to see how this experiment works. In this activity, you will get water to creep up through the plant tissue (the celery stalk) and find out how to make it go faster and slower.

The part of the celery we eat is the stalk of the plant.  Plant stalks are designed to carry water to the leaves, where they are needed for the plant to survive.  The water travels up the celery as it would travel up any plant.

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Download Student Worksheet & Exercises

1. First, find four celery stalks about the same size with leaves still attached.

2. Mix up a four-cup batch of colored water (try purple).

3. Place your celery stalks in the water, leaf-end up. After an hour or two, take it out and place it on the paper towel. Label your celery stalk with the each time length it was in the water.

4. Repeat this for different increments of time. Try one overnight!

5. Use a ruler and measure how high the water went. Record this in your science journal.

6. Now make a graph that compares the time to distance traveled by placing the time on the horizontal axis and the distance traveled on the vertical.

7. What happens if you start with hot water? Ice cold water? Salt water?

8. What happens if you cut the celery stalk at the base high enough so it straddles two cups of different colors?

Exercises

1. What two types of transport move substances into a cell?
2. How does water get into the celery?
3. What are the tubes in celery called?
4. In what direction does air flow? Hint: Think of the balloon example.
5. What happens to the water after it travels through a plant?
6. Use answers 1-4 to describe the process of water traveling through a celery stalk.

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One way substances can get into a cell is called passive transport. One special kind of passive transport is osmosis, when water crosses into the cell. This experiment allows you to see the process of osmosis in action. Are you ready?

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Download Student Worksheet & Exercises

1. Cut two thin slices of potato. The pieces should be about the same thickness and be slightly flimsy.

2. Place both slices in separate glasses of water.

3. Add salt to one of the glasses.

4. Wait about 15 minutes.

5. Pull out the two pieces of potato and make observations in our science journal.

Did you notice that the potato slice in the fresh water became a little stiffer, while the potato in salt water became rather flimsy?  Remember that cells are made of water, and that the water in the cells flows from areas of low salt concentration to high salt concentration.  That means that if the water outside the cell is saltier than the water inside, water will move from the inside of the cell to the outside. As the water left the cell it was like letting the air out of a balloon. As more and more of the cells lost water, the slice of potato became soft and flexible.  If the water inside was saltier, the opposite happens, and some water goes into the cells, stiffening them up.

Osmosis is the diffusion of water molecules through a membrane, where the water molecules move from high water concentration to areas of low water concentration.

Salt starts osmosis by attracting water and causing the water to move toward and across the membrane. Remember that salt is a solute, and when water is added to a solute, it spreads out (diffuses) the concentration of salt, and that creates a chemical solution.

Imagine the salt concentration inside a cell being the exact same as the salt concentration outside the cell – what would happen? Right – the water level will stay the same and nothing would happen. Now imagine there’s more salt inside of a cell than outside it. What happens now? The water moves through the membrane into the cell causing it to swell with water.

If the cell is placed in a higher concentration of salt (like sticking a carrot in a salt bath), the water will leave the cell, and that’s why the plant cells shrink and wilt. This is also why salt kills plants, because it takes water from the cells. This doesn’t just happen in plants, though. Animals can also get dehydrated if they drink ocean water.

Questions to Ask:

1. How was the concentration of salt different in each cup?
2. Which direction was water flowing in each cup?
3. Why did one potato become stiff, while the other became flimsy?

Let’s do this experiment again, but use beans instead of potatoes.

1. Place enough beans and water in a glass to completely fill it

2. Place the glass on a cookie sheet

3. Leave the glass alone for several hours… even overnight!

4. While you wait, take out your science journal and write about what you expect to happen. When your experiment is ready, record what you found.

Questions to Ask:
1. The beans should begin to fall out of the water. If you look at them, you will see that they have expanded. What happened?

2. Where was the concentration of water greater – inside or outside of the beans? Explain.

Exercises

For Potatoes

1. How was the concentration of salt different in each cup?
2. Which direction was water flowing in each cup?
3. Why did one potato become stiff, while the other became flimsy?

For Beans

4. If you look at the beans, you will see that they have expanded. What happened?
5. Where was the concentration of water greater – inside or outside of the beans? Explain.

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The carrot itself is a type of root—it is responsible for conducting water from the soil to the plant. The carrot is made of cells. Cells are mostly water, but they are filled with other substances too (organelles, the nucleus, etc).

We’re going to do two experiments on a carrot: first we’re going to figure out how to move water into the cells of a carrot. Second, we’ll look at how to move water within the carrot and trace it. Last, we’ll learn how to get water to move out of the carrot. And all this has to do with cells!

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Osmosis is how water moves through a membrane. A carrot is made up of cells surrounded by cell membranes. The cell membrane’s job is to keep the cell parts protected. Water can pass through the membrane, but most things can’t.

And water always moves through cell membranes towards higher chemical concentrations. For example, a carrot sitting in salt water causes the water to move into the salty water. The water moves because it’s trying to equalize the amount of water on both the inside and outside of the membrane. The act of salt will draw water out of the carrot, and as more cells lose water, the carrot becomes soft and flexible instead of crunchy and stiff.

You can reverse this process by sticking the carrot into fresh water. The water in the cup can diffuse through the membrane and into the carrot’s cells. If you tie a string around the carrot, you’ll be able to see the effect more clearly! Here’s what you do:

Download Student Worksheet & Exercises

Experiment #1: Water moving INTO the carrot via osmosis and UP the carrot.

In this experiment we will see the absorption of water by a carrot. Make note of differences between the carrot before the experiment, and the carrot afterward.

Materials

• 2 carrots
• Sharp knife (be careful!)
• Cutting board
• Glass
• Water
• Food coloring

Procedure :

Step 1: Cut the tip off of a carrot (with adult supervision).

Step 2: Place the carrot in a glass half full of water

Step 3: Place the carrot somewhere where it can get some sunshine.

Step 4: Observe the carrot over several days.

What’s going on?

When surrounded by pure water, the concentration of water outside the carrot cells is greater than the concentration inside. Osmosis makes water move from greater concentrations to lesser concentrations. This is why the carrot grows in size—it fills with water!

Procedure:

Step 1: Re-do the four steps above in a new cup, and this time put several (10-12) drops of food coloring into the water.

Step 2: With the help of an adult, cut the carrot in half length-wise.

What’s going on?

Carrots are roots. They conduct water from the soil to the plant. If we were to repeat this experiment several times—first cutting the carrot at half a day, then one day, then one day and a half, etc—we would see the movement of the water up the root.

Experiment #2: Water moving OUT of the carrot via osmosis

In this experiment we answer the question “what if the concentration of water is greater inside the carrot?”

Materials

• Large carrot
• 3 tablespoons of salt
• Two glasses
• String
• water

Procedure

Step 1: Snap the carrot in half and tie a piece of string around each piece of carrot (make sure they’re tied tightly).

Step 2: Place each half in a glass half full of warm water.

Step 3: In one of the glasses, dissolve the salt.

Step 4: Leave overnight.

Step 5: The next morning pull on the strings. What do you observe?

What’s going on?

The salt-water carrot shrunk while the non-salt-water carrot bloated!

This is because of osmosis. Carrots are made up of cells. Cells are full of water. When the concentration of water outside the cell is greater than the concentration of water inside the cell, the water flows into the cell. This is why the non-salt-water carrot bloated—the concentration was greater outside the cell than inside. The concentration of water was greater inside the salt-water carrot than outside (because there was so much salt!) so the water flowed out of the cell. This made the salt-water carrot shrink.

Questions to Ask:

1. What happens if you try different vegetables besides carrots?
2. How do you think this relates to people? Do we really need to drink 8 glasses of water a day?
3. What happens (on the osmosis scale) if humans don’t drink water?
4. Use your compound microscope to look at a sample and draw the cells (both before and after taking a bath in the solution) in your science journal.
5. What did you expect to happen to the string? What really happened to the string?
6. Which solution made the carrot rubbery? Why?
7. Did you notice a change in the cell size, shape, or other feature when soaked in salt water? (Check your journal!)
8. Why did we bother tying a string? Would a rubber band have worked?
9. What would happen to a surfer who spent all day in the ocean without drinking water?
10. What do you expect to happen to human blood cells if they were placed in a beaker of salt water?

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Here’s a fun experiment that shows you how much stuff can pass through a membrane. Scientist call it the  semi-permeability of membranes.

Before we start, take out your science journal and answer this question: What do you think will happen when we stick a piece of celery into a glass of regular water. Anything special?

What if we add a teaspoon of salt to the water? Now do you think anything will happen?
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Let’s find out. First, you’ll need:

• 2 pieces of celery stalk
• salt
• 2 glasses
• a sensitive scale to weigh the celery

Note: If you don’t have a scale, you can rig up a balance by suspending two cups from a either end of of a pencil. Balance the center on a point (like another pencil) and you’ll be able to tell which is heavier at the end of this experiment (see image below).

You’ll need to measure the celery both before and after this experiment since you won’t be able to “read” the weight.

Trim your celery to be the same weight before you start your experiment.

Download Student Worksheet & Exercises

1. First, weigh the celery (both pieces) and record this in your journal.
2. Next, make your hypotonic solution (plain water). Fill a glass with water and stick your celery in for ten minutes.
3. Remove the piece of celery and pat dry. Weight it again and record your results. If you don’t see a weight difference, dip it in again for ten more minutes. Pat dry and weigh again.
4. Now make your hypertonic solution (salt water). Add a small amount of salt to the water (keep adding until no more can be dissolved and a small amount remains on the bottom).
5. Weight the second celery stalk and record it in your journal. Add this new celery stalk to the water. Wait impatiently for ten minutes. Remove and record the weight. Did you notice a difference? (Note – if you left the first one in for 20 minutes, make sure to leave this one in for the same amount of time.)

What effect did the salt solution have on the celery?  Did it change in appearance?  Did it feel different? Record your results in your journal!

Osmosis is the diffusion of water molecules through a membrane, where the water molecules move from high water concentration to areas of low water concentration.

Salt starts osmosis by attracting water and causing the water to move toward and across the membrane. Remember that salt is a solute, and when water is added to a solute, it spreads out (diffuses) the concentration of salt, and that creates a chemical solution.

Imagine the salt concentration inside a cell being the exact same as the salt concentration outside the cell – what would happen? Right – the water level will stay the same and nothing would happen. Now imagine there’s more salt inside of a cell than outside it. What happens now? The water moves through the membrane into the cell causing it to swell with water.

If the cell is placed in a higher concentration of salt (like sticking a carrot in a salt bath), the water will leave the cell, and that’s why the plant cells shrink and wilt. This is also why salt kills plants, becaise it takes water from the cells. This doesn’t just happen in plants, though. Animals can also get dehydrated if they drink ocean water.

Exercises

1. In what direction does water move?
2. What is the process by which water crosses membranes by itself?
3. What are all living things made of?
4. Did the celery in the fresh water weigh more or less? Why?
5. Did the celery in the salt water weigh more or less after a few minutes?

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