SAM Teachers Guide
Harvesting Light for Photosynthesis
Overview
This activity focuses on how certain molecules called pigments interact with light and
determine the color of plants. Students explore how molecules such as chlorophyll
interact with light and gain energy. Students are then introduced to the concept that this
energy is used by plants to make sugar and release oxygen—which is the beginning of
the photosynthesis process.
Learning Objectives
Students will be able to:
 Interpret a model of photons emitted by sunlight.
 Describe how different colored leaves absorb, reflect, and transmit different
photons due to the presence or absence of a variety of pigments.
 Correlate the energy of a photon to the change in energy levels of electrons in
molecules.
 Observe the structure of a chlorophyll molecule and explain how it can transfer
energy to other molecules.
Possible Student Pre/Misconceptions
 Plants are green because they absorb only green light.
 Photosynthesis can take place at night.
 Plants get their food from soil, not through sunlight.
Models to Highlight
After completion of the activity:
Models to Highlight:
 Page 2 – What Happens When Light Shines on Leaves
o Review with students how the red leaf absorbs photons of any
color but red while the green leaf absorbs photons of any color but
green. This observation is the foundation for understanding the rest
of the activity.
 Page 3 – 3D Structure of Chlorophyll Molecule
o Point to the two parts of the molecule: the light-catching head and
the hydrocarbon tail. Talk about the structure and the function of
these different parts of the molecule.
o Link to other SAM activities: Intermolecular Attractions and
Solubility. Help students relate the structure of the molecules to
how they function.

Page 5 – How Does Chlorophyll Work?
o Students will most likely need to consult the “Help” link in order to
clarify how to complete this task. It is worthwhile to discuss what
the students are doing and why they are doing it. Compare this
process to what is really going on in the photosystems of leaves.
o Link to other SAM activities: Excited States and Photons and
Spectroscopy. Explain the correlation between the energy of the
photons and the excited states of the electrons.
Possible Discussion Questions:
 How would leaves look different if chlorophyll was not the primary
pigment present in chloroplasts?
 How does the process of photosynthesis connect to the idea of energy
being converted from one form to another?
Connections to Other SAM Activities
Harvesting Light for Photosynthesis is a biology capstone activity that deals with light
being captured and the light-matter interaction. It has many supporting activities.
Atomic Structure introduces students to atoms, orbitals, and excited states. Excited
States and Photons and Spectroscopy help students grasp the concept that certain
atoms and/or molecules can only absorb certain photons or wavelengths of light. Lipids
and Carbohydrates and Proteins and Nucleic Acids look at the structure and function
of biomolecules and help students explore the chlorophyll molecule. Cellular
Respiration describes a different part of the photosynthesis process—the electron
transport chain.
Activity Answer Guide
Page 1:
1. What color light has the highest
frequency?
(d)
2. Which photon has the lowest amount of
energy?
(a)
Page 2:
1. Based on the model, which of the
following must be true? (Check all that are
true.)
(c) (d)
2. What will happen if we put a plant in a
dark room and only shine green light on it?
Explain your answer.
A green leaf will absorb photons of any color but
green. Since the light is green, the leaf will
reflect the green light and not absorb any
photons. The plant will die.
Page 3:
1. Based on your observation of the above
model, which molecule is responsible for
absorbing light in the leaf?
(c)
2. Click the “Whole Leaf” button and
describe three things you have observed
about photons after they hit a leaf.
Sample responses:
1. The green photons are bounced back.
2. The other color photons are absorbed.
3. Non-visible light photons are absorbed.
4. Some photons pass through the leaves. (This
is why leaves are semi-transparent.)
3. In the cell, chlorophyll binds to other
molecules in a large complex. Based on the
structure of chlorophyll's tail, with which of
the following would chlorophyll associate?
(Check all that apply.)
(a) (b)
4. Heme is a functional group similar to
chlorophyll's head, but it has iron in place of
magnesium. Heme is what makes blood look
red. What colors of light does iron help heme
absorb? Explain your answer. (Hint)
Heme must absorb all colors of light except red.
That is why blood looks red as red photons are
reflected back. Chlorophyll absorbs colors other
than green. Leaves look green because green
photons are reflected back.
Page 4:
1. How do additional pigments help
chlorophyll to transfer energy for
photosynthesis?
(c)
2. Compared to the other pigments, there is
so much chlorophyll in leaves that they
appear green. In the autumn, pigments start
to break down. How can you explain the
other colors in autumn leaves?
With a lack of sunlight in the fall (as compared to
summer) comes a lack of chlorophyll. Without
the presence of chlorophyll the other colored
pigments can be seen in autumn leaves. The
principle of light being reflected back is the
same.
Page 5:
1. Describe what you need to do in order to
produce a blue pigment.
You need to prevent blue photons from being
absorbed. The energy levels that represent blue
photons being absorbed must be deleted to
create a gap in energy levels.
2. Place the snapshot of the energy level
diagram you have designed that produces a
blue pigment.
Sample snapshot:
plant to make its own food? Explain your
answer.
Indian pipe plants must not make their own food,
but rather, they must get food in some other way
such as parasitism. Without chlorophyll, they
cannot excite the electrons to go through the
process of photosynthesis. This makes the
Indian pipe plant more similar to an animal or
fungus.
Page 6: Summary
1. What color of light is LEAST effective in
causing photosynthesis? Why?
Green, because it is reflected back.
2. If a substance is blue, then what is true
about the photons it absorbs?
(b)
3. Water tends to absorb more red photons
than blue ones. Red algae are the known
photosynthetic organisms that live deepest
in the sea (as deep as 600 feet). Why do they
have a red color when we observe them
under sunlight?
Because they are reflecting the red light when
they are put in the sunlight.
4. Which of the following must be true about
photon absorption and energy levels of
pigments?
(a)
5. Indian pipe plants (see the image on the
left) contain no chlorophyll. What can you
conclude about the ability of the Indian pipe
SAM HOMEWORK QUESTIONS
Harvesting Light for Photosynthesis
Directions: After completing the unit, answer the following questions to review.
1. A lichen is a symbiotic association of a fungus and green algae. Lichens are considered to
be producers and primitive plants. Given what you have learned in this lesson, what role
do you think the green algae play?
2. The snapshot shows the energy levels of a blue pigment. Explain how the gap
in energy levels accounts for the pigment absorbing any photons but blue
ones.
3. Describe what a photosystem is.
4. What determines the frequencies of the photons a pigment molecule absorbs?
SAM HOMEWORK QUESTIONS
Harvesting Light for Photosynthesis – With Suggested Answers for Teachers
Directions: After completing the unit, answer the following questions to review.
1. A lichen is a symbiotic association of a fungus and green algae. Lichens are considered to
be producers and primitive plants. Given what you have learned in this lesson, what role
do you think the green algae play?
The green algae can go through photosynthesis to make food for the symbiotic association. The fact that the
algae are green is a clue that they contain chlorophyll, the pigment necessary to start the photosynthetic
reactions.
2. The snapshot shows the energy levels of a blue pigment. Explain how the gap in
energy levels accounts for the pigment absorbing any photons but blue ones.
The gap shown makes it impossible for blue photons to be absorbed. If a photon's energy is not equal to
the energy difference between any two energy levels in the molecule, then the photon cannot be absorbed.
Instead, it will bounce back or pass through. Since blue photons have frequencies in the range where
there is a gap of energy levels, so they are reflected back and seen as a blue pigment.
3. Describe what a photosystem is.
A photosystem is a group of chlorophyll molecules held together by proteins.
4. What determines the frequencies of the photons a pigment molecule absorbs?
When a pigment molecule absorbs a photon, one of the molecule’s electrons gains energy and the electron jumps
from a lower energy state to an excited state. The difference between the lower energy and the higher one is equal to
the energy of the absorbed photon.