Comparing Photosynthesis
and Cellular Respiration
-Biochemical Pathways for Energy
Section 8-3
Remember that our cells must have ATP to run
cellular chemical reactions.
Where does the energy needed to
make ATP come from?
1.To make ATP, cells must constantly break
down glucose. (Glucose = 650 kilocalories).
2.The highly-energized bonds in glucose must
be handed over to ATP because ATP holds a
much smaller, more manageable amount of
energy for the cell to use.
3.This process of making ATP from glucose is
called cellular respiration.
Where does the Glucose come from?
The highly-energized bonds in glucose are
formed in a process called
photosynthesis, which stores solar
energy from the sun in those chemical
bonds.
Comparing Cellular Respiration
and Photosynthesis
Photosynthesis and cellular respiration are
life’s most important processes.
Reason: energy!
In photosynthesis, energy is stored in
the bonds of glucose (C6H12O6).
In cellular respiration, energy is
released from glucose and stored in ATP
molecules for the cell to use.
Molecule Key
CO2
Carbon Dioxide
O2
Oxygen
H2O
Water
C6H12O6
Glucose
ATP/ADP
Energy carrier
Photosynthesis
Reactants
Transforms solar energy into
chemical energy by creating
energy-storing bonds found in
C6H12O6
6CO2 and 6H2O
Products
C6H12O6 and 6O2
Reactants
Cellular Respiration
36 ATP
Energy released for
Cellular
Reactions*
*Some lost as heat
Products
36 ADP
& 36 P
Breaks bonds in
C6H12O6 to
transfer and store
chemical energy
in ATP
Notes over Comparison Diagram
1. Solar energy is
constantly required for
this energy cycle to
continue supporting life.
2. Carbon, oxygen, and
hydrogen atoms are
recycled in the
environment in order to
transfer chemical bond
energy.
Photosynthesis and cellular respiration form
a cycle-the products of one are used as the
reactants for the other.
Photosynthesis
Happens
In the
Chloroplast!
Cellular Respiration
Happens
In the
Go to
Section:
Mitochondria!
Chloroplast
Photosynthesis produces glucose and oxygen,
which are used as reactants in cellular respiration.
Photosynthesis Equation
Light Energy
6 CO2 + 6 H2O — C6H12O6 + 6 O2
Reactants
Go to
Section:
Chlorophyll
Products
Mitochondria
Cellular Respiration produces carbon dioxide
and water, which are used as reactants in
photosynthesis. (the process of obtaining energy)
Cellular Respiration Equation
Enzymes
C6H12O6 + 6 O2— 6 CO2 + 6 H2O + 36 ATP
Reactants
Products
A Closer Look at
Photosynthesis
Photosynthesis
Overview Animation
Photosythesis from leaf
into grana animation
Photosynthesis
Animations tutorials
Photosynthesis is the
process producers use
to transform solar
energy into chemical
energy (stored in
food)
(used or stored)
Why study photosynthesis
Requirements for Photosynthesis
H
O
C
H
O
O
1. Light -- Light is a form of energy.
2. Chloroplasts – are green organelles in
plants where photosynthesis occurs.
3. Pigments—colored molecules that help
absorb light.
4. Chlorophyll -- green pigment found in
chloroplasts that absorbs light energy.
5. Water – source of hydrogen atoms to
make glucose.
6. Carbon Dioxide – source of carbon
atoms to make glucose
Chlorophyll Light Absorption
1. Chlorophyll BEST
absorbs energy of
red & blue light
Absorption of Light by
Chlorophyll a and Chlorophyll b
2. Plants appear
green because they
REFLECT green
light
Chlorophyll b
Chlorophyll a
• Plants grown in
green light don’t
grow very well.
Why?
Go to
Section:don’t
Plants
absorb the energy in green light!
V
B
G
YO
R
Light Intensity and Photosynthesis
1. In each of the above beakers there is a submerged
water plant under a funnel. As the light enters the cells
of these plants photosynthesis occurs producing oxygen
bubbles that can be seen coming out of the top of the
funnel.
•
Which beaker will produce the most oxygen bubbles?
•
Which beaker will product the least oxygen bubbles?
1
3
How does Light Intensity effect the
rate of photosynthesis?
As the intensity of light increases the
rate of photosynthesis also increases.
Benefits of Photosynthesis
1. Plants obtain energy DIRECTLY
from sun
a. Plants will breakdown
glucose for energy using
cellular respiration
b. Plants store extra glucose as
starch to use later
c. Plants use glucose to make
cellulose for cell walls
Go to
Section:
Benefits of Photosynthesis
2. Animals obtain energy
INDIRECTLY from sun
a. Animals can feed on plant’s
stored glucose
b. Animals get O2 from plants
Go to
Section:
Comparison Chart
Chloroplast
Store solar energy
into food
Cellular
Respiration
Mitochondria
Release energy in
food to make ATP
Reactants
6H2O & 6CO2
C6H12O6 & 6O2
Reactants
Water, carbon dioxide,
& light energy
Glucose (chemical
energy) & oxygen
Products
C6H12O6 & 6O2
6H2O & 6CO2
Products
Glucose & oxygen
Water, carbon dioxide,
& 36 ATP (energy)
Photosynthesis
Location
Purpose
What about the animal cells?
Mitochondria – power plant of the cell
Glucose from food sources
Oxygen in  fuel molecules (food)
burned  ATP synthesized  CO2
out