Thoughts on Trees

This is another post that comes from the Science Photo of the Day. It worked well there, but has great potential for a full blown Experiment of the Week activity. To try this, you will need:

• a plant or some seeds
• a pot to grow the plant in
• potting soil
• a scale to weigh the plant, pot, and soil

We will explore how plants grow, by growing a potted plant. You can use a plant from your local garden shop, or you can plant seeds from your favorite plant.

Start by weighing the pot. Then put the soil into the pot and weigh it again. Finally, add the plant or seeds to the pot, and weigh it one more time. This will let us calculate the weight of the plant (weight of everything minus weight of the pot and soil) as well as the weight of the soil (weight of the pot and soil minus weight of the pot.) Be sure to write everything down, as we will need that information later.

Then all you have to do is get the plant to grow. Give it water, and plenty of sunlight, but don't add anything else. As the plant gets larger, weigh it again. You should find that it has gained weight, even though you have not added any soil. Where did that extra weight come from?

To find out, start by looking at trees. Don't just think about trees. Look out the window, or even better, go outside. Notice how big trees are. Wrap your arms around the trunk, and get a feel for how strong it is. Think about how much wood is in that tree. Think about all the leaves that it produces and drops on your lawn. Think about how heavy those leaves are when you rake them up and haul them away.

Where does all that stuff come from? Your first thought is probably that it comes from the soil. After all, our bodies build up their mass from the food that we eat, and plants eat by taking in nutrients from their roots, don't they? Think about that for a minute. Look at the ground around the tree. If the tree had removed enough matter from the soil to build its trunk and branches, there would be a huge hole around the tree. Then think about your potted plant. It gained weight, which did not come from the soil in the pot.

Plants are not like us. They don't take in food. Instead, they make their own food, through the process of photosynthesis. To do that, they need energy, which they get from sunlight. They also need hydrogen, oxygen, and carbon as the chemical building blocks to make their food. They get those chemicals from water (hydrogen and oxygen) and carbon dioxide (carbon and oxygen.) During photosynthesis, these chemicals are recombined to form sugar. That sugar can be used as it is to provide energy for the plant, or it can be converted into other substances such as starch and cellulose, which make up the trunk, branches, roots, and leaves of the tree. Almost the entire tree is made of the chemicals from rain water and carbon dioxide from the air, and the same is true for your potted plant. It is also true for apples, peaches, strawberries, etc. When you think about it, even chocolate is made from plants. The sugar from plants, and so is the cocoa. That means that chocolate is mostly made up of sunlight, water, and air! Sounds yummy to me!

Have a wonder-filled week.