Photosynthesis &
Cellular Respiration
Chapter 5 Section 1
Objectives




Analyze the flow of energy through living
systems.
Compare the metabolism of autotrophs with
that of heterotrophs.
Describe the role of ATP in metabolim.
Describe how energy is released from ATP.
Key Terms




Photosynthesis
Autotroph
Heterotroph
Cellular Respiration
Capturing the Energy of Life



All organisms require energy
Some organisms obtain energy directly from
the sun
This energy is used to make organic
compounds that will serve as food for the
organisms
Autotrophs




Organisms that use energy from the sunlight or
form chemical bonds in inorganic substances
to make organic compounds.
Only 10% of the Earth’s 40 million species are
autotrophs.
Includes plants and some other types of
organisms.
Also known as producers.
Heterotrophs



Organisms that must get energy from food
instead of directly from sunlight or inorganic
substances.
Includes animals, humans & even mushrooms.
Also known as consumers
Flow of Energy
Photosynthesis

Process in which plants use the energy of
sunlight to convert water & carbon dioxide
into high-energy carbohydrates (sugars &
starches) and oxygen (waste product)
Cellular Respiration

Process by which cells produce
energy from carbohydrates to do
chemical work in the cell.
ATP

Principal chemical compounds that cells use
to store and release energy. The only source
of energy to do chemical work in the cell.
Storing Energy


ADP (adenosine diphosphate) is a compound that looks
almost like ATP.
When a cell has energy available, it can store small
amounts of it by adding a phosphate group to ADP
molecules.
Releasing Energy for
Chemical Work

Energy is released by breaking the bond
between the 2nd and 3rd phosphate.
Mitochondria
ATP + Enzymes
ADP + P+ Energy
PHOTOSYNTHESIS
Objectives




Summarize how energy is captured from
sunlight in the first stage of photosynthesis.
Analyze the function of electron transport
chains in the second stage of photosynthesis.
Relate the Calvin cycle to carbon dioxide
fixation in the third stage of photosynthesis.
Identify three environmental factors that affect
the rate of photosynthesis.
Key Terms





Pigment
Chlorophyll
Carotenoid
Thylakoid
Electron Transport
Chain



NADPH
Carbon Dioxide
Fixation
Calvin Cycle
Photosynthesis

Carbon dioxide (CO2) requiring process
that uses light energy (photons) and
water (H2O) to produce organic
macromolecules (glucose).
SUN
photons
6CO2 + 6H2O  C6H12O6 + 6O2
glucose
Where does
Photosynthesis occur?



Plants/Autotrophs – produce their own
food (glucose)
Process called photosynthesis
Mainly occurs in the leaves:
a. stoma - pores
b.mesophyll cells
Mesophyll
Cell
Chloroplast
Stoma
The Stages of Photosynthesis

Stage 1


Stage 2


Energy is captured from sunlight by chlorophyll and other
pigments present.
Light energy is converted to chemical energy, which is
temporarily stored in ATP & the energy carrier molecule
NADPH
Stage 3

The chemical energy stored in ATP & NADPH powers the
formation of organic compounds, using the CO2 to make
Glucose.
Stages of Photosynthesis
The Photosynthesis Equation
6CO2 + 6H20
Carbon
Dioxide
Water
Light
C6H12O6 + 6O2
Sugars
(High Energy)
Oxygen
Stage 1: Absorption of
Light Energy
How does a human eye or leaf absorb
light?
Visible Spectrum


Sunlight contains a
mixture of all the
wavelengths (colors) of
visible light.
When sunlight passes
through a prism, the
prism separates the light
into different colors.
Visible Spectrum




When light strikes an object, it is, absorbed,
transmitted or reflected.
When all colors are absorbed the object
appears black.
When all colors are reflected the object
appears white.
If only one color is reflected the object appears
that color.
Pigments


Light-absorbing substances
Absorb only certain wavelengths and reflect all
others.
Chlorophyll




The primary pigment in plants.
Absorbs mostly blue & red light
Reflects green & yellow light
2 Types of chlorophyll


Chlorophyll a - blue green
Chlorophyll b -yellow green
Carotenoids
Accessory pigments:
-Carotenoids - orange
-Xanthrpphyll – yellow
-Anthocyanin – red
-Lutein – grey/brown
 Absorb wavelengths of light different from
those absorbed by chlorophyll a & b.

Light Absorption During
Photosynthesis
Thylakoids


Saclike photosynthetic membranes located
inside the chloroplasts.
Arranged in stacks known as grana (singular:
granum).
Thylakoids



When light strikes a thylakoid in a chloroplast,
energy is transferred to electrons in
chlorophyll, exciting the chlorophyll.
This energy transfer causes electrons to jump
to a higher energy level.
Electrons with extra energy are said to be
“excited”
Excited Electrons



Excited electrons jump from chlorophyll
molecules to other nearby molecules in the
thylakoid membrane.
These electrons must be replaced by other
electrons.
Plants get these replacement electrons from
water molecules.
Replacement Electrons



Water molecules are split by an enzyme
inside the thylakoid.
Chlorophyll molecules take the electrons from
the hydrogen atoms.
Oxygen from the disassembled water
molecules combine to form oxygen gas and
this is given off at the end of stage 1 as a waste
product of photosynthesis.
Stage 2: Conversion of
Light Energy
Light Dependent
Conversion of Light Energy

Excited electrons that leave chlorophyll
molecules are used to produce new molecules,
including ATP, that temporarily store chemical
energy.
Electron Transport Chains



Excited electrons are passed through a series
of molecules along the thylakoid membrane.
This is called the electron transport chain.
This provides the energy needed to make ATP.
NADPH


A second electron transport chain provides
energy used to make NADPH
NADPH is an electron carrier that provides the
high-energy electrons needed to make carbonhydrogen bonds in the 3rd stage of
photosynthesis
Light-Dependent Reactions
Summarized
1.
2.
3.
Pigment molecules in the thylakoids of
chloroplasts absorb light energy.
Electrons in the pigments are excited by light
& move through electron transport chains in
thylakoid membranes.
These electrons are replaced by electrons
from water molecules that are split.
Light-Dependent Reactions
Summarized (cont)
4.
5.
Oxygen atoms from water molecules
combine to form oxygen gas.
Hydrogen ions accumulate inside thylakoids,
setting up a concentration gradient that
provides the energy to make ATP and
molecules of NADPH to be used in the Dark
Reaction, the third stage.
Stage 3: Storage of
Energy
“Dark Reaction”
Dark Reaction (third stage)
of Photosynthesis


Carbon atoms from carbon dioxide in the atmosphere
and the H molecules from the NADPH of the light
reactions are used to make organic compounds in
which chemical energy is stored in glucose
molecules.
The transfer of carbon dioxide to organic compounds
(glucose) is called carbon dioxide fixation or the
Calvin Cycle.
Calvin Cycle


Most common method of carbon dioxide
fixation.
Series of enzyme-assisted chemical reactions
that produce a three-carbon sugar.
Dark Reaction Summarized
1.
2.
Each molecule of carbon dioxide is added to
a five-carbon compound by an enzyme using
the energy from the ATP and the splitting of
the NADPH from the Light Reaction.
The resulting six-carbon compound splits
into two three-carbon compounds.
Phosphate groups from ATP & electrons from
NADPH are added to the three-carbon
compounds, forming three-carbon sugars.
Calvin Cycle Summarized (cont)
3.
The resulting three-carbon sugars
are used to make organic
compounds— glucose —in which
energy is stored for later use by the
organism.
Factors that Affect Photosynthesis

Light


Concentration of carbon dioxide


Rate increases as light intensity increases until all
the pigments are being used.
Once a certain concentration of carbon dioxide is
present, photosynthesis cannot proceed faster
Temperature

Most efficient within a certain range of
temperatures.
Question:
During the fall,
what causes the
leaves to change
colors?
Fall Colors



In addition to the chlorophyll
pigments, there are other pigments
present
During the fall, the green
chlorophyll pigments are greatly
reduced revealing the other pigments
Carotenoids are pigments that are
either red, orange, or yellow
Brought to you by Captain Friday