Part 1: Photosynthesis
Section 4.2 & 4.3
Important molecules in cellular
energy:
• CO2 = carbon dioxide gas
• H2O = water
• C6H12O6 = glucose (sugar)
• O2 = oxygen gas
Important molecules
in cellular energy:
• ATP = chemical
energy
• NADPH = energy
molecule that
receives and gives
away e- (electrons) to
drive chemical
reactions
ATP gets recycled
AdenosineTriphosphate
ATP
Loses a
P to use
energy
Gains a P
to make
energy
ADP
ADP = AdenosineDIphosphate – It’s ATP that is missing 1 P!
NADPH gets recycled, too
Nicotinamide Adenine Dinucleotide Phosphate(+ Hydrogen)
 It cycles from NADPH to NADP+ back to
NADPH, etc.
 It carries electrons (held by H) and gives
them away during the second stage of
photosynthesis – the Calvin Cycle.
NADPH
NADP+
Photosynthesis: the process for
the conversion of light energy into
chemical energy (ATP) stored in
organic compounds (glucose)
Photosynthesis Equation
Carbon Water
dioxide
Glucose
PHOTOSYNTHESIS
Oxygen
gas
Photosynthesis happens in
2 parts:
Step 1: Light Dependent- light is
absorbed to make energy for light
independent.
•
Happens in the thylakoid membrane of a
chloroplast
Step 2: Light Independent
(Calvin Cycle)– uses energy
from the light reactions to make
sugar.
•
Happens in the stroma of a chloroplast
Sketch this chloroplast!
Chloroplasts
Overview of Photosynthesis
H 2O
CO2
Chloroplast
Light
NADP+
ADP + P
LIGHT
REACTIONS
(in grana)
CALVIN
CYCLE
(in stroma)
ATP
NADPH
O2
Sugar
Light Reactions – Detailed steps:
1) Light is absorbed by chlorophyll
2) H2O molecules are split to provide eand H+ that will enter an electron
transport chain to produce:

ATP
 NADPH
Will be used in the Calvin Cycle
3) Oxygen from the splitting of H2O is
released as waste
2 H2O  e- + 4 H+ + O2
Time for video clips!
• http://youtu.be/sQK3Yr4Sc_k
(2:42)
Check for
Understanding
1. What happens to the oxygen
created during the light reactions of
photosynthesis?
a. It is used in the next step of
photosynthesis
b. It is discarded as a waste product
c. It is used to make water
d. It becomes a part of glucose
Check for
Understanding
2. What is the general purpose of
the light reactions of
photosynthesis?
a. To make oxygen
b. To convert chemical energy into light
energy
c. To convert light energy into chemical
energy
d. To make glucose.
The Calvin Cycle
The Calvin Cycle
(sometimes called “the Dark Reactions”)
 Calvin Cycle: Creates glucose using
ATP and NADPH from the light
reactions as well as CO2 from the air
 Happens in the liquid stroma of a
chloroplast
 Carbon Fixation: the incorporation
(adding) of CO2 into organic
compounds
 Happens in Calvin Cycle
Plant Food
 The plant stores the
excess sugar as
starch in the roots,
seeds, and fruit of
the plant.
Check for
Understanding
2. What is the general purpose of
the light independent reactions
(Calvin cycle) of photosynthesis?
a. To make oxygen
b. To convert chemical energy into light
energy
c. To convert light energy into chemical
energy
d. To make glucose.
Energy overview
sun
Photosynthesis
plants
CO2
glucose
H2O
animals, plants
Cellular Respiration
The Great Circle
of Life,Mufasa!
ATP
O2