Lesson Plan: Teaching Photosynthesis and Cellular Respiration in Tandem
Timeline: 2+ class periods
MO Content Standards:
Strand 3: Characteristics and Interactions of Living Organisms
2. Living organisms carry out life processes in order to survive
B. Photosynthesis and cellular respiration are complementary processes necessary to
the survival of most organisms on Earth
a. Explain the interrelationship between the processes of photosynthesis and
cellular respiration (e.g., recycling of oxygen and carbon dioxide), comparing and
contrasting photosynthesis and cellular respiration reactions
b. Determine what factors affect the processes of photosynthesis and cellular
respiration (i.e., light intensity, availability of reactants, temperature)
D. Cells carry out chemical transformations that use energy for the synthesis or
breakdown of organic compounds
a. Summarize how energy transfer occurs during photosynthesis and cellular
respiration as energy is stored in and released from the bonds of chemical
compounds (i.e. ATP)
Overarching Enduring Understanding:
• A direct relationship exists between structure and function in living systems.
Enduring Understanding:
• Photosynthesis and cellular respiration are complementary processes necessary
to the survival of most organisms on Earth.
Essential Question:
• How do cells transform, store, and use energy to maintain the survival of
organisms?
Lesson Description:
A primary goal of these two lessons is to introduce students to the ideas behind these
two processes. In most cases, I would follow up with hands on labs and/or activities to
further the development of these two processes. I would also assign textbook readings
to complement the lessons we were doing in class.
Day 1:
Introduce the concept with the Cell Energy lesson (see below). The point of this
exercise is to uncover prior knowledge find out (as the teacher) where student
understanding is at this point. This information will not only be helpful for this two-day
lesson, but also helpful in deciding what to do after these two days. For instance, if you
discover students really have trouble understanding CO2 has mass, a short demo or lab
on gas properties may be appropriate. After the class discussion of the first question,
students go online to learn about a few basic ideas. For this, find a few good websites
you find suitable for your students’ ability levels. Use websites with introductory
information and use a website like www.portaportal.com to host the links. This site is
easy to set up and easy for students to use. Students should be able to work in pairs
and find the answers to many of the questions before the end of the hour. Part three of
the first day is handing out the word sort cards marked “A”. Students should work in
pairs and try to make some sense of the words and what they mean. As they sort their
words into groups, circulate and ask lots of probing questions. Encourage them to sort
them any way they see fit. Lastly, have them record the pattern they sorted their words
into in the box on their paper. Collect the cards and the student’s Cell Energy handouts.
Day 2:
Return their papers and “A” cards. Have them reassemble their cards into their original
pattern. Next, handout the “Photosynthesis and Respiration: How Cells Make and
Use Energy” reading and the second set of cards marked “B”. This time, students
should use their reading and try to build a concept map using both sets of cards. They
may choose to use their original layout or go with another plan. After this, students can
move to a larger piece of paper to build a concept map or use computer software (such
as Inspiration or SMART Ideas) to build their final map. On Day 3, students can share
their maps and compare differences and similarities as you sort out the events taking
place in both processes.
Day 3 and Beyond – Follow Up:
Based on student understanding of the concepts and time available, students could
perform a photosynthesis lab (floating disks or elodea) and/or respiration labs (human
respiration). Most labs suitable for high school measure O2 or CO2 production
(depending on which process). However, these sorts of labs depend upon or improve
upon students being able to understand the concepts of photosynthesis/respiration
themselves. Doing labs in absence of a concept development activity (like the lesson
described here) or doing the concept development activity without a lab lessens the
chance students will actually understand the ideas. In the interest of time and materials,
there are several other ways to visualize these processes. Students can build models or
use computer software simulations. Logal software company created an excellent series
called “Explorer” that offered computer simulations in which students could manipulate
and control different variables that affected the rate of photosynthesis. The company
sold their product to Riverdeep software who in turn made the software web-based.
There are many other animations and/or simulations on the web that can assist
students with these concepts.
Personal Reflections on Lesson Design:
(1) What I learned as I designed this lesson:
In designing this lesson, I attempted to recall my own experiences with learning
photosynthesis and respiration. I remembered really struggling with the
terminology and details involved in the processes. I remembered being taught
the two reactions as reciprocal in nature. While reflecting on the experiences of
my students during the last 15 years, I can honestly say some students “learned”
both reactions, but still had no recollection of “what goes in” and “what goes out.”
In preparing for the development of this activity, I modified many of the text
resources my students already had access to. I was very selective in the amount
of information I wanted to expose them to. I also reviewed in my own mind the
relationships between photosynthesis and respiration. Making concept maps
really helped me with this. This translated into taking the word sort idea into a
concept mapping exercise. My goal is for the students to focus on the big ideas
and not get lost in the details. I’m very excited to try this out!
(2) How used to teach this lesson before:
While teaching this content before, I remember students struggling with the
details. In the past, I usually presented students with the content via notes and
video animations. Students memorized the reactions as I taught them separately.
I have always taught photosynthesis first because it has only two reactions (light
reaction and Calvin cycle). Since photosynthesis is also the metabolic driving
force for most producers (something students will already have learned in
ecology) it only seems fitting that cellular respiration follows after photosynthesis
is presented. Also, cellular respiration actually has three reactions (glycolysis,
Kreb’s cycle, and the electron transport chain). I’ve done some lab activities in
the past with limited success. Again, it seems most labs mainly focus on
assessing the presence or absence of CO2 or O2 (depending on which process
we are demonstrating). While I think the labs are great learning experiences, it’s
really easy for students to collect data, analyze results and still walk away with a
limited understanding of metabolism and the relationships between
photosynthesis and cellular respiration. I’m still searching for good framing and
synthesizing activities to help students develop and mentally assess their
conceptualization of the ideas we are studying. Like a proverbial “mental
container” that I provide to students. As they learn material through readings,
visuals, lab experiences, and discussions, they “fill” their containers. In the end
however, they need to be able to access these containers and build new
knowledge and/or self-assess their own understanding. This notion is what
inspired me to try this new design and attempt to teach both metabolic processes
in tandem. Ultimately, my goal is for deeper understanding of the principles and
generalizations surrounding cellular metabolism (photosynthesis, cellular
respiration, and fermentation).
Cell Energy!
Due Date:
Enduring Understanding:
Cells use distinct and separate structures to perform chemical processes essential
towards maintaining homeostasis.
Essential Question:
How do cells transform, store, and use energy to maintain the survival of
organisms?
Assessing Prior Knowledge:
From Seed to Tree ?
Answer the questions in your own words individually. Afterwards, discuss your answers
with members at your tables.
1. Estimate how much you think a seed weighs.
2. Estimate how much you think a full-sized tree weighs.
3. Estimate the difference in mass between a seed and a tree.
4. Where do you think the mass of the tree comes from?
Procedure:
Using your computer, visit some websites to learn more about how cells make and use
energy. Be sure to answer the following questions as you explore these concepts. Use
the following site to find the recommended list of URLs for this activity:
www.portaportal.com sign in as guest with: ______________________
A. How do plants and animals obtain energy?
B. In what organelle does the process of Photosynthesis occur?
C. In what organelle does the process of Respiration occur?
D. In what type of cells do Photosynthesis and Respiration take place? For each
process describe if it is: Plant, Animal, Both, Neither
E. Why are animal cells not capable of carrying out Photosynthesis?
F. Photosynthesis and Respiration can be summarized into equations. Write the
equations and how do they relate to one another.
G. Analyze why leaves change color in autumn.
H. Identify the parts of the plant involved in Photosynthesis.
I. Describe how glucose is broken down during Respiration.
J. Name 3 interesting facts you learned from the websites:
Concept Assessment:
1.
2.
3.
4.
5.
Your teacher will give you a stack of words.
Lay all the words out on your table and sort them out.
Talk with a partner at your table and try to look for patterns.
Look for general and specific words.
Finally, once you think you have the words arranged in a way that sums up what
you understand so far about cell energy, record the way you arranged the words
on the next page.
6. Give the word cards back to your teacher at the end of the class.
Results from Cell Energy Word Sort:
Photosynthesis and Respiration:
How cells make and use energy
In order for cells to do any work, they need energy! Where does this
energy come from? How do they store it? How do they use it? The
answers to these questions and more are found in the
complementary processes of photosynthesis and respiration. In
photosynthesis, energy is stored in chemical bonds, while in
respiration, those same chemical bonds are broken and energy is
released for use by the cell.
Before going into the details of photosynthesis and respiration, let’s
review a little bit about energy and light and how they are used by
cells.
Energy
Energy can be stored in the form of covalent bonds between atoms. Remember that
covalent bonds are bonds created when two atoms share a pair of electrons between
them. When these bonds are broken by enzymes, the energy is released for the cell to
use.
In photosynthesis, plants take energy from the sun and store it in the chemical bonds of
glucose, a simple sugar. In respiration, the energy in the glucose bonds is released.
The energy released from glucose through respiration is transferred to a molecule
called ATP. Think of ATP as a kind of money used by the cell. ATP is used to power
some cellular processes, like active transport or enzyme activity, that cost energy.
Only plants can photosynthesize, but all organisms carry out some form of cellular
respiration because all organisms need to get energy for their cells to use.
Key point:
All organisms, including plants, use cellular respiration to get energy from the chemical
bonds in food.
Light
Light travels from the sun across 93 million miles of space to get to use here on earth.
That’s pretty far, but it only takes 8 minutes for light to travel that distance! A single unit
of light is called a photon, and it carries energy. It is the energy of light photons that is
harnessed by the plant through photosynthesis.
Photosynthesis
The production of glucose in photosynthesis can be summarized by the following
equation:
6 CO2
+
12 H2O + light  C6H12O6 + 6 O2 + 6 H2O
carbon dioxide + water + light energy  glucose + oxygen gas + water
Let’s break this equation down a little bit. On the left side of the equation, where does
the carbon dioxide come from? It is present in the air, and is brought into the plant
through tiny pores in the leaf called stomata. How about water, where does it come
from? It comes from the soil, and is drawn in by the roots. And, as mentioned above,
the light comes from the sun, and provides the energy for the chemical reaction
between carbon dioxide and water.
On the right side of the equation, notice that photosynthesis gives off oxygen, the very
substance we need to breathe. As we will see later, oxygen is a necessary component
of cellular respiration. This is why the word ‘respiration’ is used for both breathing and
for the release of energy from glucose molecules.
Photosynthesis takes place in the chloroplasts of plant cells. In most plant chloroplasts
are most abundant in the leaves and give them their green color. Therefore the leaves
are the major site of photosynthesis in most plants. Inside the chloroplasts, there are a
number of flattened structures that look like
stacks of green pancakes. A single
“pancake” is called a thylakoid, and the
whole stack is called a granum. The
chlorophyll pigment, which is very
important in photosynthesis, is located in the
thylakoid membranes. The rest of the space
inside the chloroplast is called the stroma.
The process of photosynthesis can be
divided into two main parts: the light-dependent reaction and the Calvin cycle. The
light-dependent reaction is the energycapture part of photosynthesis, while the
Calvin cycle uses that energy to build
sugar molecules.
In the light-dependent reaction, which
takes place in the thylakoid membrane,
electrons in a chlorophyll molecule directly
absorb the energy in a photon from the
sun. These high-energy electrons are
carried from the thylakoid to the stroma on
special carrier molecules. It is in the
stroma where the glucose-building step of photosynthesis, the Calvin cycle, occurs.
In the Calvin cycle, the solar energy in those electrons is used
combine carbon dioxide and hydrogen into glucose. The
energy that was absorbed from solar photons has now been
stored in the stable chemical bonds of a glucose molecule.
to
After glucose is synthesized, it is often processed into sucrose
disaccharide) or starch (a polysaccharide) for long-term
storage or transport to other parts of the plant.
(a
Respiration
How do plants and animals use the energy stored in glucose? Cellular respiration!
While only plants can photosynthesize, all organisms perform some kind of respiration.
Respiration in eukaryotes is the breakdown of glucose in the presence of oxygen and
can be summarized by the following equation:
C6H12O6 + O2
 6 CO2 + 6 H2O + energy
glucose + oxygen  carbon dioxide + water + energy
Notice that oxygen is required for cellular respiration, which is why we breathe it in, and
that carbon dioxide is one of the waste products. Notice also that this is the reverse of
photosynthesis, where carbon dioxide is taken in and oxygen is a product. In other
words, we exist in a beautiful mutualism with plants – they provide us with exactly what
we need and vice versa!
Respiration consists of three main steps:
glycolysis, the Krebs cycle (a.k.a. the
citric acid cycle), and oxidative
phosphorylation. The end product of
these three steps in 36 molecules of
ATP, the cell’s energy “money”, per
molecule of glucose.
Respiration mostly takes place in the
mitochondria, but the first step in the
breakdown of glucose, glycolysis,
actually occurs out in the cytoplasm. In
glycolysis, enzymes split a molecule of
glucose, which has 6 carbon atoms, into two 3-carbon molecules called pyruvate. A
small amount of energy is released in glycolysis, and two molecules of ATP are created.
After glucose is split into pyruvate, the pyruvate is transferred to the inside of a
mitochondrion, where the Krebs cycle is carried out. In the Krebs cycle, pyruvate is
further broken down by enzymes into carbon dioxide and water and 2 more molecules
of ATP are generated.
The final step of respiration, oxidative phosphorylation, is where the big payoff in ATP
happens. As glucose is broken down in glycolysis and the Krebs cycle, high-energy
electrons are transferred to special electron carriers very similar to the ones found
photosynthesis. These electrons are passed to electron transport proteins
embedded in the internal membrane of the mitochondrion. These proteins are able to
use the energy of these protons to make ATP molecules. In this final stage of
respiration, 32 molecules of ATP are generated for each molecule of glucose that we
started with. The cell now has a big supply of energy money to spend on whatever
activities it wants!
Summary:
Photosynthesis:
light-dependent reaction – energy from sunlight is harvested, water is split into H and
O2, occurs in thylakoid membrane
Calvin cycle – glucose is created from CO2 and H, energy is stored chemically, occurs
in stroma
Respiration:
glycolysis – glucose is split into 2 molecules of pyruvate, 2 ATP generated, occurs in
cytoplasm
Krebs cycle – pyruvate is broken down into CO2, 2 ATP generated, occurs in
mitochondria
electron transport – electrons transferred to membrane proteins in mitochondria, 32
ATP generated, O2 required
“A” Group Word List
•
•
•
•
•
•
•
•
•
•
photosynthesis
glucose broken down
light energy
energy released
respiration
chloroplast
glucose created
mitochondrion
energy stored
carbon dioxide
“B” Group Word List
•
•
•
•
•
•
•
•
•
•
stroma
oxidative phosphorylation
water
cytoplasm
Krebs cycle
glycolysis
thylakoids
oxygen
Calvin cycle
light-dependent reaction
glucose broken
photosynthesis
down
light energy
energy
released
respiration
chloroplast
glucose
created
mitochondrion
energy stored
carbon dioxide
A
A
A
A
A
A
A
A
A
A
stroma
oxidative
phosphorylation
water
cytoplasm
Krebs cycle
glycolysis
thylakoids
oxygen
Calvin cycle
lightdependent
reaction
B
B
B
B
B
B
B
B
B
B
An example of Concept Map using both the “A” and “B” cards: