Let’s dive into studying life and living organisms with a new set of biology experiments for kids! These are all easy and simple to do at home or in your classroom, and all of them are liquid or water-based, so you’ll likely have everything you need on hand to bring these science projects to life. We’ll be exploring osmosis, chromatography, homogenization, transpiration, capillary action, and evaporation.
Gummy Bear Osmosis
“Solute” is a general term that refers to a molecule dissolved in a solution. In a salt water solution, for example, the salt molecules are the solutes. The more salt we put in the solution, the more we increase the concentration of solutes.
Water moves from an area with a lower concentration of solutes to an area with a higher solute concentration. This movement of water molecules is called “osmosis.” In order to examine the process of osmosis and observe how it works, we can look at what happens to gummy bears when they are left to soak in different solutions overnight.
What you’ll need:
- Two container such as bowls, cups, or jars
- Measuring cup
- Gummy bears
- Add ½ cup of water to each of the two empty containers. Add 1 teaspoon of salt to one of the containers and stir well.
- Drop a gummy bear into each container and leave it 8 hours or overnight.
- Observe what happened to each gummy bear. Compare the gummy bears to each other, and also to a gummy bear that was not left to soak overnight.
The concentration of solutes inside the gummy bear is higher than the concentration of solutes in plain water. As a result, in our experiment, the water flowed into the gummy bear causing it to swell, and that’s why the gummy bear grew overnight.
The same is true for the gummy bear placed in the salt water solution. However, the difference in solute concentration wasn’t as great, so less water flowed into the gummy bear. In other words, it took less water to balance out the solute concentration inside and outside the gummy bear. Thus, the gummy bear in the salt water solution grew less than the bear in the plain water solution.
You can experiment with different solute concentrations to see how it affects the outcome. What happens when you add twice as much salt to the overnight water bath? Is there any amount of salt that can be added to keep the gummy bear the same size?
Chromatography is a technique used to separate out the components of a mixture. The technique utilizes two phases – a mobile phase and a stationary phase. There are several types of chromatography, but in this experiment, we will be looking at paper chromatography.
In paper chromatography, the stationary phase is filter paper. The mobile phase is the liquid solvent that moves over the filter paper. For this experiment, we will use marker ink to examine how chromatography works.
What you’ll need:
- Three clear containers such as drinking glasses or mason jars
- Coffee filters
- Rubbing alcohol
- Vegetable oil
- Water-soluble marker, any color
- Sharpie marker, any color
- Mark one container with an “A,” a second container with a “W,” and a third container with an “O.” Fill the bottom of the “A” container with rubbing alcohol, the “W” container with water, and the “O” container with vegetable oil. Make sure the liquid in each container comes up no more than ½ an inch from the bottom.
- Take three coffee filters out and measure out 1 inch from the bottom. Mark this spot by drawing a line with the pencil. Make one dot on this line using the water-soluble marker. Do the same with the Sharpie marker.
- Place one coffee filter in each container so that the bottom of the coffee filter is submerged in the solvent but the solvent DOES NOT touch the dots of marker ink. The solvent will travel up the coffee filter and past the dots. Watch what happens to the dots as the solvent moves over them.
Like dissolves like, so substances will interact with solvents that are similar to it. Water-soluble marker ink is polar, so it will interact with polar mobile phases such as water and alcohol. When a non-polar solvent such as vegetable oil moves over it, it will not interact, and therefore will not move.
Sharpie marker ink is “permanent” in the sense that it can’t be washed off with water. It isn’t water-soluble. When the rubbing alcohol moves over it, however, we see that the Sharpie ink interacts with it. This is because Sharpie ink contains alcohols in it. Following the principle of “like dissolves like,” it interacts with the rubbing alcohol.
Using Tie-Dyed Milk to Observe Homogenization
Molecules in a solution tend to aggregate with other molecules that are similarly charged. Fat molecules, for instance, will cluster together with other fat molecules. Milk is made up of different types of molecules, including fat, water, and protein. In order to keep these molecules from completely separating to form layers, milk undergoes a process called homogenization.
Even after undergoing homogenization, however, fat molecules floating free in solution will come together when milk is left sitting undisturbed. To visualize this process, and what happens when those molecules are dispersed, we can use food coloring and dish soap.
What you’ll need:
- Full fat milk
- Dish soap
- 1 small bowl
- Cotton swabs
- Pour some milk into a small bowl. You don’t need a lot of milk for this, just enough to fill the bottom of your bowl. Allow the milk to settle so the surface of the milk is still before moving on to Step 2.
- Add a drop of food coloring to the surface of the milk.
- Dip a cotton swab in dish soap and touch the swab to the surface of the milk, directly adjacent to the drop of food coloring. What happens to the food coloring?
Have you ever tried to mix oil and water? The fat molecules in oil, just like the ones in milk, are “hydrophobic,” meaning they don’t like to be near charged molecules such as water, and will do whatever they can to keep away from them. To achieve this, they clump together. Because the fat molecules are less dense than water, the fat globules float up and form a layer above the water. In our experiment, we added food coloring to this layer of fat globules.
Dish soap is a detergent. Detergent molecules have a hydrophobic end and a hydrophilic end. Because of this, they are able to form a bridge between the fat molecules and the water molecules, causing the fat globules to break up and disperse. What we’re seeing when we add the dish soap is this dispersal of the fat clusters, carrying the food coloring with it and resulting in a beautiful tie-dyed pattern. The result is more dramatic if you add several drops of food coloring and include a variety of colors.
Making water travel through capillary action
Paper towels are designed to pick up spills quickly, absorbing lots of liquid with only a few sheets. But what is it about paper towels that makes them so absorbent? The answer is, in part, capillary action.
In this experiment, we’ll observe how capillary action works to make paper towels efficient. Using nothing but paper towels and the principles governing capillary action, we’ll make water travel from one container and into another.
What you’ll need:
- 3 containers (cups or jars)
- Paper towels
- Food coloring
- Line up the three containers. Fill the two containers on either end about ¾ full of water. Add several drops of food coloring to each of the jars. Whatever color you use is up to you, but the effect works best if the two colors combine to make a third color. (For instance – yellow and blue make green.)
- Fold a paper towel in 4 lengthwise. Place one end of the folded paper towel in one of the containers filled with colored water (make sure the end is immersed in the water) and let the other end hang into the empty container. Repeat using a second paper towel and the remaining filled container.
- Let the containers sit for four hours. Check them after 1 hour, 2 hours, and 4 hours. What do you see?
Paper towels are highly porous. These pores function like tiny tubes, or capillaries, to draw up water. Two properties allow this to happen. The first is adhesion. Water molecules are attracted to the walls of the capillaries and “stick” to them. This is enhanced in our experiment because paper towels are made of cellulose molecules that are highly attractive to water. The second property is cohesion. The water molecules like to stick to each other. Together, these two properties allow the water to “travel” along the paper towel against gravity, moving out of one container and dropping into the other.
Efficient paper towels are more porous than less efficient brands, giving them a higher degree of absorbency. Taking this into account, how do you think the progress observed at each time point would differ if you used low quality paper towels instead of highly absorbent ones? How would you expect the color in the middle jar to change if you use a less absorbent paper towel to make the blue water travel, and a more absorbent paper towel to make the yellow water travel?
Observing Xylem in Celery
All plants need water to survive. In order to move water up from the soil and into their shoots and leaves, plants have developed a system of water transport. This system is called “xylem.” We can observe the movement of water through xylem transport by placing stalks of celery in colored water. The colored water moves through the stalk and up into the leaves, making the path of the water through this system visible.
What you’ll need:
- A container such as a jar or vase
- Food coloring
- Measuring cup
- Add 1 cup of water to the empty container. Add 2 drops of food coloring to the water (or however many it takes to achieve the color desired) and stir well to mix.
- Choose a celery stalk that has leaves attached to the top. Cut about 1 inch off the bottom of the stalk.
- Place the stalk upright in the container, making sure the bottom of the stalk is immersed in the water.
- Leave the celery out over night. Observe what happens. Take the celery out of the water and cut it open to get a better look at the path the water took.
Plants use a system called xylem to pull water up from the ground and transport it up through the shoot into their leaves. This process is passive, meaning it doesn’t require any energy in order to occur. That’s why the celery was able to pull water up overnight. The celery pulled colored water through its stalk via the xylem transport system. The colored water traveled all the way into the leaves, staining them.
The xylem transport system can be seen more clearly when the celery is cut. The colored water stains the xylem cells, making them visible.
One phenomenon that drives the flow of water through a plant is transpiration. Transpiration is the name given to the process by which water evaporates from the leaves of a plant. What do you think would happen if we repeated the experiment using a celery stalk whose leaves had been cut off? Try it and see!
How to Make it Rain Indoors
One of the properties of water is that it can exist in different phases. It can exist as a liquid, which is the form we’re most familiar with, and it can also exist as a solid (ice), or gas (water vapor). In this experiment, we’ll take water through two of its phases – liquid and gas. We’ll observe how temperature causes water to move from one phase into another. This will allow us to get a better idea of what happens to water in nature, and the role temperature plays in the water cycle.
What you’ll need:
- Large container such as a jar
- A ceramic plate
- Heat approximately eight cups of water to just steaming. This can be done on the stovetop or the microwave, but a stovetop will give you more control over the heating process.
- Pour the water into the jar until it is completely full and allow the jar to sit for five minutes. This will heat the jar for the experiment. After five minutes, discard the water.
- Add enough heated water to fill the jar up approximately halfway. Cover the jar opening with the plate, making sure no steam can escape. Let the jar sit for 3 minutes. Observe what happens to the water in the jar. Note any changes you see.
- After 3 minutes have passed, place enough ice on top of the dinner plate to cover its surface. Watch what happens to the jar.
The water cycle is responsible for producing rain. Liquid water evaporates, sending water vapor into the atmosphere. When the water vapor reaches the cooler air in the upper atmosphere, it condenses back into water droplets, forming clouds. If too much water condenses, or if the temperature becomes colder, the condensed water will fall back down to earth in the form of rain.
In this experiment, we replicated these conditions to produce “rain.” First, we let the heated water form water vapor inside the jar. The water vapor filled the space between the water surface and the plate. We then added ice to our plate, initiating a quick temperature drop. The lower temperature caused the water vapor to condense. This was visible as water droplets that beaded and ran down the sides of the jar. This is how rain happens. We made it rain inside our jar!