Teacher's Pages
ACTIVITY 11 - " How Plants Use Sunlight To Make Their Own Food"
ACTIVITY 11 - STUDENT'S PAGE
(It may be helpful to view the student page alongside this teacher
page.)
Purpose:
This activity introduces the idea of photosynthesis for
the first time. Students are encouraged to see the idea of photosynthesis in contrast with many of the
hypotheses they suggested.
Materials:
Post a chart listing the rules for the active reading of this
section.
Mixing bowl (preferably green)
Hand mixer or wire whisk
Sugar cubes
Bottle of water
Zip loc baggy filled with exhaled breath (carbon dioxide)
Flashlight
Optional costume ideas: chef's hat, apron
FRAME
"Today we are going to learn about some ideas that
scientists have discovered through their research about how plants get their food. Before we read about their
ideas, however, let's see where we stand in our thinking about our chart of hypotheses about how plants get their
food." [Point to class hypotheses chart]
Individual Work
Have students fill out the chart in the Masters section: Our
Hypotheses About Food for Plants.
Working Toward Consensus
Take a quick hand raising vote of how each student is thinking
about each hypothesis. Students may ask for a third category in addition to "yes" and
"no". This is fine, but encourage them to take a yes/no
position whenever they can.
Write down the polling results on the chart.
With the students look at patterns: Where are our ideas changing?
What are we agreeing about? Where does there seem to be a lot of uncertainty? How do we explain
that uncertainty?
Scientists' Explanations
Use this section to frame this activity. This text sets the stage
for the introduction of the concept of photosynthesis.
"We're going to read about something that scientists are
figuring out about how plants get their food. As we read, check each paragraph to see if that makes sense to you.
Does it make sense in terms of our experiments -- the bean seeds, the grass plants in the light and
dark, the vitamin labels, the Van Helmont experiment? "
ACTIVITY
1. Give directions for students to read this section aloud
together in small groups. To foster active reading comprehension, you might assign the following rules:
a. Go around your circle and take turns reading the paragraphs.
b. After reading a paragraph, the reader should ask the group:
Did this paragraph give you any ideas about how plants get their
food? Give examples.
Did this paragraph say something different than you thought
before? Give examples.
Did this paragraph challenge any of the hypotheses on our class
data chart? Which ones?
Do you have any questions about this paragraph? Is it clear?
Could it be clearer?
ACTIVITY
As another way of representing photosynthesis, do a teacher
demonstration model of the photosynthesis process:
"I'm going to show you a model of how I think photosynthesis
happens. I want you to listen carefully and give me feedback based on my model. Based on what you have read
about photosynthesis, is my model accurate? In what ways? In what ways is it inaccurate?"
For extra effect, you might want to wear an apron and a chef's
hat!
Have a student helper pour water in the bowl.
Have another student helper pour carbon dioxide in the bowl.
Have another student helper shine a flashlight on the contents of
the bowl.
Use wire whisk or mixer to mix up the water and carbon dioxide.
Then surreptitiously (magically!?) throw out a sugar cube from
the bowl.
"Look what was made from water and carbon dioxide and
light!!! What is it? "
Ask students to name what each part of this model represents.
Bowl: Leaf and cells in the leaf
Wire whisk: what starts the chemical reactions between the water
and carbon dioxide
What are the strengths of this model?
Shows that water and carbon dioxide get turned into something
completely new -- sugar!
Helps you imagine what is going on inside of each cell.
What are the limitations /inaccuracies of this model?
There is no human chef cooking the sugar in photosynthesis -- it
is done by each green,
leaf cell. The water and carbon dioxide are not poured into the leaf by
humans. It is more than just simple mixing that occurs in the leaf -- the
mixing involves a chemical change from one substance to another.
Work through these 4 questions with the students. You might want
to take extra time with #3 and make a whole day's session focus on this activity. You could have
different groups read different explanations of photosynthesis and then have them compare findings.
Alternatively, you could read an explanation to them and ask them to listen for new or different ways of explaining
photosynthesis.
How Do Plants Get Food by Meish Goldish (Raintree Steck-Vaughn
Publishers, Austin TX, 1992) is a picture book that you could read to the class.
A More Detailed Explanation -- Cells (OPTIONAL)
If you want students to think more about cells and cell activity
in photosynthesis, use Transparency Masters 13. 1 through13.8. This series helps students zoom in
closer to a leaf and its cells. You could pair this discussion with work with microscopes and looking at leaf
cell cross sections.
A More Detailed Explanation -- Molecules (OPTIONAL)
If you get into more about the molecules and chemistry of the
photosynthesis reaction, you could use the factory analogy as represented on the last handout in the
blackline masters section of this guide.
Photosynthesis and Our Bean Experiment
Purpose:
This activity begins a series of activities in which
students get help in trying to use the concept of photosynthesis to explain different real-world situations. This
activity focuses on explaining the bean experiment using photosynthesis.
Teacher Role: Modeling how to use photosynthesis to explain our
experiment.
Materials:
Overhead Transparencies 1A-B through 5A-B
Students' hypotheses from Activity Seven (where does the food in
the cotyledon come from?)
FRAME
Beginning to USE the Idea of Photosynthesis
Use Transparency Masters 1A-1B through 5A-5B to give students
practice using the idea of
photosynthesis to explain what happens to water, air, and
sunlight in a plant.
How the Transparencies work. Make transparencies of 1A and 1B.
Show 1 A. Have students explain what they think. Then put Transparency 1B over top of 1A to show the
scientific way of explaining what is happening.
Looking at the Bean Experiment With New Eyes
Use this section to consider where the food in the cotyledon came
from. Help students revisit the
hypotheses they generated in Activity Seven (Bean skits). Does
the idea of photosynthesis give them any new ideas about where that food comes from?
Students 'Hypotheses: The food in the cotyledon is soaked up from
the water and soil.
Scientific Concept: The food in the cotyledon was made in the
leaf and stored in the seed.
Apply -- Teacher Modeling
Analyzing at the Amazing Leaf
The Amazing Leaf's Secret
Purpose:
This activity provides a lot of structure and
scaffolding to help students analyze and use their new knowledge about photosynthesis.
This would be a good small group activity.
Apply -- Teacher Coach
Putting it Altogether -- Food for Plants
Let students read the introductory text. Do not provide any more
modeling or scaffolding for the questions. Let the students answer the questions. Then have
students share their responses. Provide feedback to coach students in using the idea of photosynthesis to
answer these questions.
1. Desired student response: Water is not food for the plant by
itself. We know that because water does not have any calories -- it has no food energy to give the plant. But
it is important in helping the plant to make food. The water needs to combine with the carbon dioxide in the
air and the energy from the light to make energy-providing food.
In addition, water serves other purposes for the plant -- like
helping it support itself so its' leaves can reach the sunlight they need for photosynthesis.
2. Desired student response: A cow cannot make food like plants
can. Only plants can use water and carbon dioxide and light energy to create energy-giving food. The
cow gets its energy (which order to turn foods into milk) from plants who make food during
photosynthesis.