Photosynthesis POGIL Lesson Key

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8th Grade Science POGIL Activity
Topic: Photosynthesis
Photosynthesis – From Light to Food
Why? Plants don’t eat food like you do. In this activity we will address the question:
How do plants get energy?
Group Instructions: When responding to each question, one group member should be assigned the task
of reading the question aloud for the rest of the group. Rotate the reading among the group members
throughout the assignment so that everyone gets several turns. Remember, allow everyone the chance to
respond, and respect each other’s ideas, feelings, and answers.
Model 1
Public Domain Image
1. Name two living (biotic) organisms you see clearly in Model 1.
A deer and flowers.
2. Explain how each organism in Model 1 gets the energy it needs to live.
a. The deer gets energy by…eating the flowers.
b. The flowers get energy from…changing sunlight into food for themselves.
3. The flowers are ____ producers ___ and the deer is a ____ consumer ___.
producers/consumers
producer/consumer
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8th Grade Science POGIL Activity
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Look at and discuss Model 2. Label the PRODUCERS and CONSUMERS in the picture.
Model 2
PRODUCERS
CONSUMERS
Public Domain Image
Compare and contrast the terms producers and consumers by listing at least 2 things they have in
common and at least 2 things they don’t have in common.
4.
PRODUCERS
Make their own food from sunlight.
CONSUMERS
Get their food from eating other organisms.
Autotrophs
Heterotrophs
Ex: plants, algae, & some bacteria
Ex: herbivores, omnivores, carnivores.
5. Do you think that the deer only uses the energy that is made by the plant using sunlight? Explain.
Answers will vary. By the end of the lesson students should explain that although the energy from
the plants can be used to fuel the deer when it eats them, the purpose of photosynthesis is for the
plant to make food for itself.
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6. Is there anything beneficial, other than food that the plant is providing to help the deer to breathe?
Oxygen
7. Do you think that the food and oxygen the plant is making from the sunlight were made on purpose
for the deer or for something or someone else? Explain.
Answers will vary. By the end of the lesson students should explain that although the energy from
the plants can be used to fuel the deer when it eats them, and the oxygen the plants make help the
deer breathe, the purpose of photosynthesis is for the plant to make food for itself and the some of
the oxygen the plant makes also is used by the plant to help break down the food as well.
8. What is the name given to the process whereby plants use sunlight to make food?
Photosynthesis
9. What steps do you think are involved in photosynthesis?
Step 1: Sunlight reaches the leaves of a plant.
Step 2: Carbon dioxide enters the bottom of the leaves through the stomata.
Step 3: Water enters the roots and travels around the rest of the plant.
Step 4: The sunlight is captured by the chloroplasts and converted into food (glucose) for the
plant.
Step 5: Oxygen is released as a by-product back out through the stomata
Think of a time when you may have helped your mother or someone else bake a cake and discuss with
your group what important pieces of information are needed before starting to make a cake. [NOTE:
When you are at this point, ask your teacher to show you an example of cake recipe and have your group
examine the back of a box a cake mix.]
Public Domain Image
10. A recipe is a set of instructions needed to make a food dish along with a list of ingredients needed to
make it. Do you think it’s important for the recipe to include how much of each ingredient you
need? Why or why not?
Yes, because if you don’t know how much of each ingredient to use the food won’t come out right.
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11. Once you mix all of the ingredients according to the recipe instructions, what still has to be done to
the mixture to make it look like a cake?
The cake batter still has to be cooked to bake the cake.
12. Did it take energy to mix all of the ingredients together? If so, where did that energy come from?
Yes, from the muscles in my arms and hands. Or, if using an electric mixer, from electricity and
mechanical energy.
13. Did it take energy to bake the cake? If so, where did that energy come from?
Yes, from the electricity powering the oven.
14. Does it take energy to eat the cake? If so, where did that energy come from?
Yes, it takes chemical energy and mechanical energy to chew and break down the food. It takes
more chemical energy in digestion to break the food down further into nutrients cells can use.
Reactants are the materials you use to make something new. The reactants often change into something
else once they are combined and many times don’t look the same as they did before. Products are the
materials that are made as a result of combining the reactants.
15. Think back to our cake example. What are some of the materials (reactants) needed to make the
cake? What product or products were made at the end?
REACTANTS
Flour, eggs, baking soda, salt,
PRODUCTS
The cake and gases that made the cake rise.
Some students might recognize that some
energy was lost as heat energy as well.
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PHOTOSYNTHESIS
Believe it or not photosynthesis helps keeps you alive. It is one of the most important processes on
Earth! Humans and plants are dependent on each other for survival. Can you figure out what
photosynthesis means just by reviewing its word parts? The prefix photo means “light” and the
synthesis means “putting together.”
16. Write your own definition for the word photosynthesis below.
Answers will vary. Students might respond: Photosynthesis puts together food from light.
But did you know that plants don’t make food for us to eat, but they use sunlight to make food for
themselves? Even though humans and other organisms eat plants for energy, that is not who they are
making the food for. Plants need to eat, too, to say alive. So, you could say that the process of
photosynthesis is like a plant cooking for itself. Many creatures just happen to like to eat plants and take
some of the energy as well. What’s even more wonderful, than plants providing us with yummy food
fuel, is that through photosynthesis, plants also provide us with oxygen, which we can’t live without.
Again, plants don’t make it on purpose just for us to breathe; it just happens to be what is made as a
result of combining the reactants together. Scientists call this a by-product. It’s kind of like when you
burn a piece of paper with a match and ash and smoke form which are both by-products. Oxygen just
resulted from the chemical change. The plant will use some of it to help break down glucose when it’s
ready to eat, very much like when we digest food. The process of breaking down food by plants and
animals will be dealt with in a future unit.
Model 3 is shows you the recipe for photosynthesis along with a list of the ingredients and their
amounts. This is the way scientists write recipes except they call them chemical equations instead. The
top row shows you the chemical symbols for each ingredient while the bottom row shows you the
common name for them. Study and discuss Model 2 in your groups now.
Model 3
Public Domain Image
17. List the reactants and products from Model 3 in the table below.
REACTANTS
PRODUCTS
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Carbon dioxide, water, and light
Sugar (glucose) and oxygen
18. Can you find the ingredient that doesn’t include how much of it to use? Why do you think that is?
Light. Students might say because you can’t measure how much light is made and that
possible different amounts of light are used depending on the weather.
19. Is light a reactant or product? Explain your answer.
A reactant because light is what the leaves need to start making food.
20.What do you think the big arrow pointing to the right in between Water and Glucose means in
Model 3?
The arrow means that the reactants are making the products and not the products coming
together to make the reactants. The equation only goes in one direction.
21. Think of our cake example. Can we turn our finished baked cake back into the original ingredients?
Once photosynthesis occurs, do you think it can be undone?
No, the cake can’t return back to the eggs, flour, and other original ingredients. No,
photosynthesis can’t get the sunlight and carbon dioxide back from the oxygen and glucose
that was made.
22. Remember the deer in Model 1? Using the chemical formula, which product does the deer use to
breathe?
Oxygen
23. Which product does the deer use for energy?
Glucose (sugar)
24. Which by-product do deer, humans, and many living organisms use to breathe?
Oxygen
ENERGY TRANSFER AND ENERGY TRANFORMATION
Recall that energy is the ability to do work and there are several types of energy. Living organisms need
energy to perform all their life functions. Larger organisms require more energy than smaller
organisms. Eating, breathing, talking, thinking, digesting, moving, even sleeping requires energy.
Mixing the cake batter required mechanical energy from the muscles in your arms and hands. Baking
the cake took heat energy from the oven.
Also, remember that energy can never be created or destroyed only transferred (sent somewhere else) or
transformed (changed into another form). For example, a car runs on fuel (gas). The liquid gas doesn’t
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stay in the tank forever. It eventually runs out. But we just said energy can never be destroyed so what
happened to the liquid gas? When a car is turned on it makes a controlled mini-explosion and starts
burning the gas. The chemical energy in the gas is being transformed into mechanical energy so the car
moves where you want it to go. Some heat energy is released as well as the car gets warm the more we
use it. Unfortunately, after the gas burns, carbon dioxide is sent up into the air and is bad for our
environment as. Chemical energy is also stored in food. It’s transformed after we eat it into
mechanical energy so we are able to do all of the things we want to do. Even we get warm the more we
move so some of the food energy we digest transforms into heat energy, too. Sometimes after we eat we
send gases into the air, too, that aren’t bad for the environment but they aren’t always pleasant to smell.

Circle the best answer.
25. What kind of energy is the plant making for itself when it makes glucose? Circle the portion of the
text (text evidence) above that helps you answer this question.
a.
b.
c.
d.
Light energy
Chemical energy
Sound energy
Mechanical energy
Review the following chemical equation again in your groups.
26. What type of energy change is happening between the reactants and the products?
Energy transformation
27. Is light energy transferring into chemical energy or is transforming into chemical energy?
Tranforming because it’s changing into something new.
You’ve already learned that food can be broken up into 3 main groups: Carbohydrates, proteins, and
fats. We eat carbohydrates for most of our chemical energy needs. Glucose is a carbohydrate,
specifically a sugar carbohydrate. Plants use this sugar as its source of fuel and when we eat plants we
are using them for fuel, too.
HOW DOES PHOTOSYNTHESIS WORK?
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Photosynthesis & Cellular Respiration – How do cells get and use energy?
Model 4
Public Domain Image
Photosynthesis happens in the leaves of the plant. The leaves are a lot like solar catching solar panels.
Sunlight isn’t enough though. Just like a cake requires more than flour, photosynthesis requires more
ingredients. Water is taken up into the rest of the plant parts through the roots and carbon dioxide
enters the bottom of the leaves through mouth-like structures called stomata.
CHLOROPLASTS
Have your group watch the Bill Nye the Science Guy video on chloroplasts to review what you learned
back in 6th grade using this link: http://www.youtube.com/watch?v=dax7v711qg0.
Model 5
Public Domain Image
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Photosynthesis & Cellular Respiration – How do cells get and use energy?
Inside the leaves the light is moving directly into the green chloroplasts where the sunlight will be
transformed into chemical energy in the form of glucose. This glucose will be used as a source of
energy for the plant itself to perform all of its life functions such as reproduction, growth, and the
making of more food.
In Model 5, the little green oval shaped organelles are the chloroplasts.
Circle the best answer.
28. In what part of the plant does most photosynthesis take place in?
a. The roots
b. The flowers
c. The stem
d. The leaves
29. What structure in plant leaf cells does the light energy transform into glucose (chemical energy)?
a. Cell wall
b. Chloroplasts
c. Nucleus
d. Water vacuole
30. What part of the plant takes in carbon dioxide?
Stomata in the underside (bottom) of the leaves.
VIDEO OPPORTUNITY
In your groups, watch and discuss the video entitled, “The Simple Story of Photosynthesis and Food”
only up to time marker 2:28 with the link http://www.youtube.com/watch?v=eo5XndJaz-Y.
HOMEWORK
For homework, go back and review your answers to every question. If you feel like you may have
answered any questions incorrectly, add your new answers in red pen next to your old answer. DO NOT
ERASE YOUR OLD ANSWERS. Then, summarize what you have learned in this lesson in a 1 page
essay. On the back of your essay, draw and label what happens during photosynthesis.
EXTRA CREDIT 2
In this lesson you learned that plants make food for themselves using sunlight through photosynthesis.
What is the cell process called that breaks down that food into nutrients the cells can use to live and
perform all of its functions? cellular respiration
EXTRA CREDIT 3
Write an extended answer to the following questions.
Why doesn’t a plant die at night when the Sun goes down? Does photosynthesis stop at night?
Yes, photosynthesis does not take place at night because photosynthesis requires sunlight and
when it’s dark there isn’t any. Plants have not used all of the glucose it has made while the Sun
was out so it has stored glucose to use for fuel when photosynthesis isn’t happening.
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