Chapter 8
Photosynthesis
8-1 Energy and Life
8-1 Energy and Life
8-1 Energy and Life
Autotrophs
• Make their own food
8-1 Energy and Life
Heterotrophs
• Cannot make their own food
8-1 Energy and Life
Chemical Energy and ATP
• The principal chemical compounds
that cells use to store and release
energy is called ATP adenosine
triphosphate
8-1 Energy and Life
Storing Energy
• ATP stores energy in the third
phosphate
• ATP is like a fully charged battery
8-1 Energy and Life
Releasing Energy
Q: How is the energy in ATP released?
A: Break bond between the second and 3rd
phosphates
2
ADP
8-1 Energy and Life
8-1 Energy and Life
Using Biomechanical Energy
• Active Transport
• Movement of organelles through cell
• Sythesis of proteins and nucleic acids
• Produce light
– Blink of firefly caused by an enzyme
powered by ATP
8-1 Energy and Life
ATP Availability
• Most cells only have enough ATP for a few
seconds of activity
• Why?
– Not good at storing energy over the long term
– Glucose stores 90X the chemical energy of ATP
– Cells generate ATP from ADP as needed by
using the energy in foods like glucose
8-2 Photosynthesis:
an Overview
8-2 Photosynthesis an Overview
During Photosynthesis…
• Organisms (plants) absorb light energy
from the sun and store it in organic
compounds.
• Energy is crucial to all life, without it work
could not be done.
8-2 Photosynthesis an Overview
AN OVERVIEW OF PHOTOSYNTHESIS
Photosynthesis is the process by which autotrophic organisms
use light energy to make sugar and oxygen gas from carbon
dioxide and water
8-2 Photosynthesis an Overview
An example of basic photosynthesis…
8-2 Photosynthesis an Overview
The Photosynthesis Equation
CO2 + H2O
(Carbon Dioxide)
(Water)
light
(Sun)
C6H12O6 + O2
(Glucose)
(Oxygen)
8-2 Photosynthesis an Overview
Because light is a form of energy…
• Anything that absorbs light also absorbs
the energy from that light
• When chlorophyll absorbs light, much of
the energy is transferred to electrons in
the chlorophyll molecule, raising the
energy level of these electrons
• These high-energy electrons make
photosynthesis work
8-2 Photosynthesis an Overview
Photosynthesis
8-2 Photosynthesis an Overview
Chloroplasts
•
The site of Light Dependent Reactions
•
These organelles are surrounded by a double membrane and contain an
inner membrane separate into disk like sacs called thylakoids
•
Thylakoid are arranged into granum, or neat stacks
•
Each thylakoid contains the green pigment chlorophyll
•
The light absorbing pigments are organized into photosystems, which
transfer energy during the light reactions
8-2 Photosynthesis an Overview
8-2 Photosynthesis an Overview
Pigments in chloroplasts
•
Chloroplasts absorb all other color pigments, leaving green to be reflected
resulting in a plant’s color.
•
Chlorophyll a and b are
two are the 2 most
common types of chlorophyll
Light
•
Reflected
light
Chlorophyll b absorbs colors or
light energy NOT absorbed by
chlorophyll a
Absorbed
light
Transmitted
light
Chloroplast
8-2 Photosynthesis an Overview
Absorption of Light by
Chlorophyll a and Chlorophyll b
Chlorophyll b
Chlorophyll a
V
B
G
YO
R
8-3 The Reactions of
Photosynthesis
8-3 Reactions of Photosynthesis
8-3 Reactions of Photosynthesis
Thylakoids
• Sac-like photosynthetic
membranes arranged in stacks
8-3 Reactions of Photosynthesis
Grana
• Stacks of thylakoids
8-3 Reactions of Photosynthesis
Stroma
• The region outside the thylakoid
8-3 Reactions of Photosynthesis
Scientists describe the reactions
of photosynthesis in two parts
1. Light – dependent reactions
(in the thylakoid membranes)
2. Light – independent reactions
(takes place in stroma)
8-3 Reactions of Photosynthesis
8-3 Reactions of Photosynthesis
Photosynthesis Consists of 2 Stages
•
Light dependent reactions
•
Non-light dependent (dark) reactions
•
Take place in the Thylakoid Membrane
•
Takes place in the Stroma
•
Depends on sunlight for activation energy
•
Includes the Calvin cycle
•
Responsible for the absorbing of light
in Photosynthesis
•
Does not literally occur in the dark, but
requires no light to occur
• Water is split,
• giving off oxygen
• Carbon dioxide is split,
• Carbon to make sugars
• H2O + O2 + ATP + NADPH2
•
ATP + NADPH2 + CO2 + C6H12O6
8-3 Reactions of Photosynthesis
8-3 Reactions of Photosynthesis
Carrier Molecule
• Compound that can accept a pair
of high energy electrons and
transfer them along with most of
their energy to another molecule
• Ex.) NADP+
8-3 Reactions of Photosynthesis
8-3 Reactions of Photosynthesis
Q: What does this do?
• NADP + H
NADPH
A: this traps sunlight in
chemical form
8-3 Reactions of Photosynthesis
Light Dependent Reactions
• Uses energy from light to produce
1. Oxygen gas
2. ATP
3. NADPH
8-3 Reactions of Photosynthesis
Watch The Light Reaction Video
8-3 Reactions of Photosynthesis
8-3 Reactions of Photosynthesis
Watch The Light Reaction Video
8-3 Reactions of Photosynthesis
The Calvin Cycle
• The ATP and NADPH formed by the lightdependent reactions contain an
abundance of chemical energy, but they
are not stable enough to store that energy
for more than a few minutes.
• The Calvin cycle uses ATP and NADPH
from light – dependent reactions to
produce high energy sugars
8-3 Reactions of Photosynthesis
The Calvin Cycle
• These reactions don’t require
light, therefore these reactions
are called
• Light – independent reactions
8-3 Reactions of Photosynthesis
Watch The Calvin Cycle Video
8-3 Reactions of Photosynthesis
Watch The Calvin Cycle Video
8-3 Reactions of Photosynthesis
Factors Affecting Photosynthesis
• Not enough water
• Temperature
• Light intensity
8-3 Reactions of Photosynthesis
Review: Photosynthesis uses light
energy to make food molecules
Chloroplast
Light
Stroma
NADP
Stack of
thylakoids
ADP
+P
Light
reactions
Calvin
cycle
Sugar used for
 Cellular respiration
 Cellulose
 Starch
 Other organic compounds
8-3 Reactions of Photosynthesis