Photosynthesis & Cellular
Respiration
Chapters 8 and 9
Remember...
Autotrophs:
• can generate their own food
• are the base of many food chains
• include plants, bacteria, etc.
8-1 Energy and Life
• Autotrophs are any organism that can make their own
energy.
• Photoautotrophs undergo photosynthesis which
changes light energy
to chemical energy.
– Ex. Plants and cyanobacteria
• Chemoautotrophs undergo chemosynthesis which
changes inorganic
Chemical Energy
ATP
• We use Adenosine Triphosphate
Contains
 adenosine,
 ribose, and
3 phosphate groups
• When ATP loses a phosphate, it becomes ADP (only
has 2 phosphates) and energy is released
• What does ATP do?
– Movement in the cell (organelles)
Energy
• Most cells only contain small amounts of ATP,
they can’t store large amounts
• Get new ATP from carbohydrates
Where do the carbohydrates
get the stored energy?
8-2 Photosynthesis overview
Early discoveries:
Jan Van Helmont (1580-1644)...
Where does a plant get its mass as it grows?
From the soil?
Weighed the soil... Weighed the tree... Weighed the water...
After 5 years, the tree had gained 150 lbs.
The weight of the soil was nearly the same as when he started.
Van Helmont assumed the weight came from the water.
Joseph Priestley (1733-1804)...
Best known for his study of
the chemistry of gases
Plant releases a substance that
keeps the candle burning...
What was released by the plant?
Jan Ingenhousz (1730-1799)
Light is essential to plant respiration.
Aquatic plants produce oxygen bubbles
in the light,
but not in the dark.
Process of Science!
• White light from the sun is composed of a range of wavelengths.
• Only 1-3% of light energy is harvested by plants = not very efficient
• James Clerk Maxwell- 1st person to recognize electromagnetic spectrum
Properties of Light
The Photosynthesis Equation
Photosynthesis uses the energy of sunlight to convert water
and carbon dioxide into oxygen and high-energy sugars
Plants use the sugars to produce complex carbohydrates
Such as starches. Plants obtain CO2 from the air or water.
Figure 8-5 Chlorophyll Light Absorption
Section 8-2
page 207
Lights and Pigments
Absorption of Light by
Chlorophyll a and Chlorophyll b
In addition to
water and CO2,
photosynthesis
requires light and
chlorophyll, a
molecule in
chloroplasts.
Chlorophyll b
Chlorophyll a
Chlorophyll is
the plants
principle pigment
V
B
G
YO
R
Light Used in Photosynthesis
During photosynthesis, the chlorophyll pigments can absorb only
Some wavelengths of light...
The grana of the chloroplasts absorb mainly blue-violet and red-orange
Chlorophyll – main pigment absorbing
light for photosynthesis
Two types:
1. Chlorophyll a
2. Chlorophyll b
Chlorophyll does not absorb light well in the green region of the spectrum.
Why are leaves sometimes
red or yellow?
8-3 The Reactions of Photosynthesis
Photosynthesis takes place in the chloroplasts
Thylakoids are found
in the chloroplasts.
Thylakoids contain the
pigment chlorophyll that
captures light energy.
Text page 208
Photosynthesis occurs in two stages
The light-dependent reactions require light to work
= Light Reaction
The light-independent reactions do not require light
= Dark Reaction
Light
CO2
Chloroplast
See Text
Page 209
O2
Sugars
Light reactions are dependent on light
and occurs only during the day
Light reactions involve:
a. splitting water to release oxygen,
b. energy production (ATP), and
c. reduction of NADP+ to NADPH
The high energy NADPH is used to help build molecules the cell needs...
LIKE GLUCOSE!
Energy comes from
electrons “falling” to a
more stable energy level.
... Kinetic energy
Light-Dependent Reactions
(con’t)
 Produce oxygen gas
 Convert ADP and NADP+ into energy carriers ATP and NADPH
See Figure 8-10 (page 211)
1.
2.
3.
4.
Photosynthesis begins when pigments in photosystem II absorb light
Energy from the light excites electrons
Electron transport and H+ ions from water-splitting result in a positive
charge inside the thylakoid, and negative charge outside
This difference provides the energy to make ATP
(like a
battery!)
Light Independent Reactions
Stroma of the Chloroplast
• Also known as the Calvin Cycle
• They occur whether or not light is present.
• The The Calvin cycle uses ATP and energized ions from NADPH from
the light-dependent reactions to produce high-energy sugars.
• Uses 6 carbon dioxide molecules to make a single 6-carbon sugar
Text page 212-213
Photosynthesis review...
Factors affecting photosynthesis...
• shortages of water (reactant)
• temperature
• light intensity
Photorespiration
• Dark Reaction can’t tell difference between oxygen and
carbon dioxide.
If it uses Oxygen = waste
• It is only 30% efficient
Factors that Affect Rates- light
• At low light intensity,
photosynthesis occurs slowly
because only a small quantity of ATP
and NADPH is created by the light
dependent reactions.
• As light intensity increases, more
ATP and NADPH are created, thus
increasing the photosynthetic rate.
• At high light intensity,
photosynthetic rate levels out, not
due to light intensity but due to
other limiting factors, including
competition between oxygen and
carbon dioxide for the active site on
RUBP carboxylase.
Factors that Affect Rates- carbon
dioxide
• At high concentrations, the rate of
photosynthesis begins to level out
due to factors not related to carbon
dioxide concentration.
• One reason might be that some of
the enzymes of photosynthesis are
working at their maximum rate.
• In general, carbon dioxide is found
in low concentration in the
atmosphere, and so atmospheric
carbon dioxide levels may be a major
limiting factor on photosynthesis
when at low levels.
Factors that Affect Rates- temperature
• As temperature increases above freezing, the
rate of photosynthesis increases. This occurs
because molecules are moving more quickly
and there is a greater chance of a collision
resulting in a chemical reaction.
• At some point, a temperature is reached that
is an optimum temperature. The
photosynthetic reaction rate is at its quickest
rate at this point.
• Above that temperature, the enzymes begin
to denature, slowing the rate of photosynthesis
until a temperature is reached where
photosynthesis does not occur at all.
Cellular Respiration and Glycolysis
• Energy arrives from the sun and is captured by green
photosynthetic plants, and stored in the chemical
bonds of glucose.
• Non‐photosynthetic organisms must obtain their
energy by the breakdown of these energy rich storage
molecules in order to release the energy for their use.
• Photosynthesis stores this energy in glucose; glycolysis
and cellular respiration release it.
• These are the processes by which cells can "burn" or
breakdown glucose into CO2 and H2O and transfer
most of the energy to the phosphate bonds of ATP.
Cellular Respiration PREVIEW
• Glucose > ATP
• Anaerobic- w/o O2
• Aerobic- w O2
• C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + ATP
PHOTOSYNTHESIS BACKWARDS!