Photosynthesis and Cellular
Respiration
AHSGE Standard II-1:The students will understand the concepts
dealing with matter. Objective: Trace the transfer of matter and energy
through biological systems.
AHSGE Standard V-1: The student will understand concepts of cells.
Overview
In one way or another all of the energy that
your body needs comes from the sun. Plants
take in energy from the sun through the
process of photosynthesis. Other living
organism take in food and break it down to
make energy through the process of cellular
respiration. All of this energy flows through
different organisms either through the food
web or the food chain.
Photosynthesis
Photosynthesis is a process in which plants
take in energy from the sun, carbon dioxide,
and water and convert them all to make
glucose (sugar), and oxygen.
 Photosynthesis takes place in the chloroplast
of plant and algae cells and in the
membranes of certain bacteria.

3 Stages of Photosynthesis
1.
2.
3.
Energy is captured from sunlight.
Light energy is converted to chemical
energy, which is temporarily stored in ATP
and the energy carrier molecule NADPH.
The chemical energy stored in ATP and
NADPH powers the formation of organic
compounds, using carbon dioxide (CO2).
Photosynthesis Formula
Reactants
Products
6CO2 + 6H2O---------> C6H12O6 + 6O2
Carbon
Dioxide
Water
Glucose
Oxygen
OR
3CO2 + 3H2O---------> C3H6O3 + 3O2
Carbon
Dioxide
Water
Glucose
Oxygen
Note: The left hand side of the formula represents the reactants and
the right side the products.
Photosynthesis Stage One
Light Energy is Absorbed
The chemical reactions that occur during the
first and second stages of photosynthesis are
sometimes referred to as “light reactions” or
“light dependent reactions”.
Pigment and Wavelengths of Light
Pigments are molecules that absorbs
wavelengths of light.
 Pigments only absorbs only certain
wavelengths and reflects all others.
 Chlorophyll is the primary pigment that is
involved in photosynthesis.

Pigment and Wavelengths of Light
Chlorophyll
During photosynthesis the primary pigment which
is chlorophyll, absorbs mostly the blue and the red
light and reflects the green and yellow light. The
reflection of the green and yellow light is what
make plants look green.
There two types of chlorophyll. You have
chlorophyll A and B.
Pigment and Wavelengths of Light
Carotenoids
Carotenoids are the yellow and orange plant
pigments that aid in photosynthesis. These are the
colors of most fruits, vegetables, and flowers.
Carotenoids absorbs wavelengths of light differently
than the chlorophyll. So, in conjunction with
chlorophyll they are able to absorb more light.
These pigments are located in the chloroplast of the
plant cell in the thylakoid membranes.
Stage II of Photosynthesis
Light Energy is Converted to Chemical Energy
The electron transport chain is used to pump hydrogen ions
into the thylakoid (membrane inside the chloroplast). The
ions will accumulate so much that they will diffuse back out
of the thylakoid membrane down their concentration
gradient through carrier proteins. (This is passive transport)
When this happens the carrier proteins also serving as
channels catalyzes (speeds up) the reaction in which a
phosphate group is added to ADP (adenosine diphosphate)
turning it into ATP (energy molecule). The movement of the
hydrogen ions across the thylakoid membrane through the
carrier proteins gives the energy needed for the third stage
of photosynthesis.
Stage II of Photosynthesis
Light Energy is Converted to Chemical Energy
While one electron transport chain is working
to provide the energy needed to make ATP
the second one is providing energy to make
NADPH. NADPH is an electron carrier that
provides the high energy electrons need to
make carbon-hydrogen bonds in the third
stage of photosynthesis. In this second chain
the excited electrons along with hydrogen
and the electron acceptor NADP+ to form
NADPH.
Summary of Photosynthesis
STAGES OF PHOTOSYNTHESIS
Used
Stage 1
Light, water
Stage 2
Electrons,
hydrogen ions
ATP, NADPH,
Carbon Dioxide
Stage 3
Produced
Oxygen,
hydrogen ions
ATP, NADPH
Organic
Compounds
Cellular Respiration
Most of the foods that we eat contains
energy. Before our bodies are able to use
that energy it has to be first broken down into
a more usable form. That energy will be in
the form of ATP. The process that is used to
break those foods that are high in energy
down is called cellular respiration. Cellular
respiration takes place in the mitochondria
(powerhouse of the cell).
Cellular Respiration Formula
Reactants
Products
C6H12O6 + 6O2 ----- 6CO2 + 6H20 + energy
Glucose
Oxygen enzymes
Carbon
Dioxide
Water
ATP
Stages of Cellular Respiration
Stage 1: Glucose is converted to pyruvate helps in
energy production and starts the krebs cycle. Once
converted, a small amount of ATP and NADH is
formed.
Stage 2: When oxygen is present (aerobic) the NADH
and pyruvate is used make a large amount of ATP.
This is called aerobic respiration which occurs in
the mitochondria of the cell for eukaryotes and in
the cytoplasm (cytosol) of the prokaryotes. If
oxygen is not present the pyruvate is converted to
lactate or ethanol and carbon dioxide.
Glycolysis
In the first stage of cellular respiration
glucose is broken down through a process
called glycolysis ( a process that breaks
down glucose into pyruvates).
Cellular Respiration Summary




Cellular Respiration has two stages. First glucose is
broken down to pyruvate during glycolysis to make
some ATP. Then a large amount on ATP is made
during aerobic respiration.
The Krebs Cycle is a series of reactions that
produce energy storing molecules during aerobic
respiration.
During aerobic respiration, large amounts of ATP
are made in an electron transport chain.
When oxygen is not present, fermentation follows
glycolysis, regarding NAD+ needed for glycolysis to
continue.