Background for Teachers
It's easy for kids (and adults!) to think of leaves as kinds of umbrellas that make great shelter from the sun and rain, but this month you can help your students understand just how important they really are. Leaves actually play a crucial role in sustaining all life on Earth.
It begins with photosynthesis and photosynthesis begins with sunshine. And, since you've taught your students about prefixes and suffixes you can introduce photosynthesis this way: The prefix "photo" means "light." The suffix "synthesis" means "change." So...Plants change light! (Sunlight).
As you review the following diagram with the children, make sure you help them connect the concept of "light" with "energy." In fact, this is a good time to review of the concept of energy. Remind students of the two main principles of energy: 1) That it is either kinetic (in motion), or; 2) stored. Look for ways to relate the principles of energy to the discussions you’ll have about leaves.
Also, as you discuss this diagram, point out that light (energy) isn’t the all leaves need to do photosynthesis. They also need carbon dioxide from the air and water from the soil.
This animated photosynthesis diagram does a good job of reminding students why plants do photosynthesis in the first place: http://earthguide.ucsd.edu/earthguide/diagrams/photosynthesis/photosynthesis.html
Leaves and Light
When leaves do photosynthesis they change energy into something else. But, what exactly do leaves change energy into?
For the sake of elementary-aged children we've simplified the answer into:
- OXYGEN – one of the gases in the air that all living creatures need to survive.
When plants "exhale," they breathe out oxygen. Most children won’t know what "exhale" means so you'll probably need to teach this concept.
- GLUCOSE – a sugary food that the plant either uses right away or stores for later.
Take this opportunity to discuss some of the fruits, vegetables, and nuts the children eat. Discuss how some of them have a sweet flavor and why. Help the children make the connection that, while fruits, vegetables, and nuts are now stored energy, they started out as kinetic energy when they were sunlight.
Leaves and Us
Check out this chart that shows the relationship between leaves and animals (including humans).
NOTE: We suggest you do this activity before discussing this chart:
You may be surprised to discover how few of your students understand the meaning of inhaling and exhaling. That's why we suggest that you first play with the concept of breathing for a little bit before jumping into a discussion about how leaves and humans/animals help one another with regard to oxygen and carbon dioxide.
Take 5 minutes for some breathing lessons. The kids will love them and, if nothing else, when you're all done you'll have a much calmer group of children!
Tell the children to take a deep breath IN and slowly breathe OUT. Then, explain what they just did. They just inhaled and then exhaled.
Do it again and this time tell them WHAT they inhaled and what they exhaled. They inhaled OXYGEN and exhaled CARBON DIOXIDE. (The kids will want to say they are breathing in and out "air" so be sure to explain that air contains both gases, but their bodies breathe in oxygen and out carbon dioxide – IMPORTANT DISTINCTION!)
Do it over and over until you feel that everyone understands what inhaling and exhaling mean and what the difference between oxygen and carbon dioxide are. As you do this exercise, continue explaining the relationship between oxygen and carbon dioxide and also how that relates to leaves and humans/animals.
If you have a classroom plant, have some fun by making a dramatic show of breathing out (exhaling) on it. Can you make your plant act out a big "Thank you!," as if you're doing it a huge favor?
VIDEO: Even though this 4-minute video is called "Respiratory System" it focuses on inhaling deeply in order to get oxygen and exhaling in order to get rid of carbon dioxide. http://www.youtube.com/watch?v=u7pYMD6or70. It will help kids understand that it’s not simply "air" that us and plants breathe.
Losing Leaves & Keeping Leaves
Ask your students to think about the trees they see each winter in their yards and near school. Can they think of any that lose their leaves? What happens as they lose them? What happens as they get them back?
Ask your students to think about the trees they see each winter in their yards and near school. Can they think of any that do NOT lose their leaves? How about bushes or other types of plants that get to keep their leaves? Remind them that pine needles are a type of leaf.
Anatomy of a Leaf
In a simplified fashion, a leaf has three main parts:
- Epidermis –
- This see-through skin protects the leaf and helps it breathe. One of the biggest jobs of the epidermis is to protect the leaf against water loss. This is particularly true of plants in west and south Texas where water can be scarce. In those regions, many of the plants tend to have leaves with thicker epidermis.
- Mesophyll –
- This is the part of the leaf where chlorophyll changes sunlight into the nutrients the plant will use for food. Here, within a spongy texture, gases are exchanged and energy is temporarily stored until it can be transported by the veins. Leaves get their green color from this portion of their anatomy.
- Veins –
- Veins carry water and the food the leaf made (called "glucose") to other parts of the plant. Made up of vascular tissue, veins also help give the leaf its form and provide support to its structure. While veins will be arranged differently in different kinds of plants, most leaves have one major vein, which runs down the middle and acts as a sort of major highway.
Leaves and Colors
Leaf colors come from "pigments," which are what give the leaf its colors – just as pigments are what give paints their colors. The green color in leaves comes from the pigment chlorophyll, which is the most important pigment, for without it no photosynthesis could be done. N/p>
Leaves always have orange and yellow pigments in them, but we can't see these colors until leaves stop making green chlorophyll. That usually happens in the fall.
Various pigments are responsible for the color yellow, but overall, most attribute the fall yellows to the pigment xanthophyll. Red and purplish fall colors generally come from anthocyanin pigments, while orange leaves get their colors from carotenoid pigments.
Why do leaves change color?
Leaf color variations depend upon the part of the state and many other factors and scientists still do not completely understand all there is to know about why and how leaves change colors.
However, a simplified answer is this: As we get closer to the winter solstice, days get shorter and nights get longer. When this starts to happen leaves get the message that winter is coming and that it's time to stop making chlorophyll. Why? Because, for the most part, during the winter, the light needed to perform photosynthesis is scarce, so plants won't need chlorophyll. Thus, to keep from wasting precious resources that plants need to conserve in order to survive the winter, they stop making chlorophyll until such time as they need it again.
Why do some leaves change color in the fall?
Leaf colors will depend on three things:
- How much chlorophyll they have in them
The more chlorophyll leaves have the greener they will be.
- How much sugar they have in them
The amount of sugar and sunlight leaves get in the autumn determine the colors they become.
The more sugar and sunlight the more red you will see in the leaves. Some leaves don’t change colors. They just become dry and shrivel up.
- The weather
The weather throughout the year will also affect the colors of the autumn leaves.
No Lazy Leaves Here!
Leaves Work Hard To...
...provide food for other living things.
Ask your students to talk about insects they’ve seen eating leaves.
Revisit your yoga lessons to see how much your students remember about inhaling and exhaling...oxygen and carbon dioxide...the connection that leaves and humans/animals have with one another.
...clean the air.
SOMETHING FOR YOU, THE TEACHER: Check out this interesting article, from NASA about what indoor plant do for us: http://www.zone10.com/nasa-study-house-plants-clean-air.html
...help plants grow....make new soil.
NOTE TO TEACHERS ABOUT THE SLIDE SHOW ON THEIR STUDENT RESEARCH PAGE (Composting is a way you can help the leaves make new soil. Check out this cool slide show: http://aggie-horticulture.tamu.edu/kindergarden/kidscompost/kid1.html). Don’t let the "kindergarten" part of the URL turn you or your students off – this really is suited for all elementary school children. You can connect this slide show into the other things leaves do including the fact that dead leaves add carbon to the soil. Carbon helps plants grow better.
Are You Ready for the Challenge?
NOTE TO TEACHERS: This quiz has a couple of terms that we have chosen not to include (i.e. "transpiration"), but given that we have discussed the majority of them, your students can be successful if they have read all parts of the Student Research Page thoroughly. http://www.neok12.com/quiz/PHOSYN01