2013
Jul 03

How Do Plants Make Food

by Hannah Holt »

6 comments


Last summer we regrew green onions and celery from stubs.It worked so well that the celery is now as tall as my two-year-old:

celery

We wanted to see if we could do the same thing with lettuce. We put a Romain lettuce stub in a small bowl of water and waited…

Lettuce growth

It’s day 14 and we have some respectable looking lettuce leaves. Cool. Huh?

Along with this project we read The Magic School Bus Gets Planted. After reading the book, my five-year-old asked, “How do plants make food out of water and air?” Or…

How Question

I could have given him a one word answer (photosynthesis!). But he asked a thoughtful question and I thought it deserved an equally thoughtful answer.

First we talked about what is water made of?

Atoms: atoms are tiny, tiny building blocks. They are like the mini-legos of life. Atoms are so small you cannot see them with your eyes or even a magnifying glass. You need a special looking machine (an electron microscope) to see the biggest atoms. Some atoms like to hangout with other atoms:

hydrogen

And others prefer to keep to themselves:

argon

When a group of atoms hang out together, it is called a molecule.

Water is made of molecules. Water molecules look like this:

water molecule

Air is also made of molecules. It is made of lots of different molecules, but the molecule that plants use is called carbon dioxide. It is a carbon atom with two oxygen atoms:

carbon dioxide molecule

Now let’s talk about food, like sugar. Yup, that’s right… some plants use sugar for energy. But they don’t eat it. They make it. Here is what one type of sugar looks like:

sucrose molecule

Let’s check if we have all the right building blocks. To make sugar we need carbon, hydrogen, and oxygen. Can we get all of those atoms from water and air?

YES! From water we get hydrogen and oxygen, and from air we get more oxygen and carbon. Here is how plants use air and water to make food:

photosynthesis2

The “big dance” that rearranges the atoms is called PHOTOSYNTHESIS. Photosynthesis means light (photo) and making-stuff (synthesis). Plants take water and air and use light to turn atoms into food. If you have the right building blocks and the right conditions, you can make almost anything.

Note: My seven-year-old liked this discussion, but it was a bit too much for my five-year-old. If this is too much detail for your tykes, here is the two sentence explanation:

Q: How do plants make food out of air and water?

A: Under the right conditions air and water can be turned into sugar (and other foods). The process of turning air and water into food for plants is called photosynthesis.

Extension activity: Playdoh Molecules

playdoh molecules

What you’ll need

  • Different colors of playdoh
  • Cut up straws

Form the playdoh into balls and connect them using bending straws bits. See if you can make all the different molecules in this posts.


  1. Tina Cho

    Amazing, Hannah! I hope this is one of your nonfiction ms for WOW! You really need to write a sciency-type book!

    • Hannah Holt

      Tina, yes this is one of my WoW ms. How did you know? ;)

  2. julie rowan zoch

    I wish we had you around when mine were younger. You come up with the funnest ways of teaching! Those atoms are toooooo cute!

  3. Susanna Leonard Hill

    Hannah this is amazing! You manage to make science fun and understandable! I love that playdoh activity, and the way you compare atoms to mini legos – perfect for relating to a child (or very non-sciency adult! :) )

  4. Romelle

    Hannah, you outdid yourself again! An amazing explanation. Your daughter is lucky to have a mommy like you. You make learning fun!

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