PHOTOSYNTHESIS 1
B-3.1: SUMMARIZE PHOTOSYNTHESIS &
INTERPRET THE FORMULA
CHAPTER 8 SECTION 1

Essential Question:
 What
 SC
is the role of ATP in cellular activity?
B- 3.3:recognize the overall structure of ATP,
namely, adenine, the sugar ribose, & three phosphate
groups – and summarize its function(including ATPADP cycle
PHOTOSYNTHESIS
AUTOTROPHS

Organisms that can
make their own food
(energy source)
 plants
 some bacteria
 algae
HETEROTROPHS

Organisms that cannot
make their own food;
they have to consume
food (energy source)

Animals


have to eat other
organisms
Fungi

decomposers
AUTOTROPHS
HETEROTROPHS
ATP
Adenosine
Triphosphate
is the principle
chemical
compound
cells use to
store and
release energy
DRAW & LABEL FIGURE 8-3 ON PAGE 203 ONTO TOP ½ 0F
PAGE 53 OF NOTEBOOK
ATP  ADP + P releasing
energy in the 3rd phosphate
bond. This is a reversible
reaction:
ADP + P ATP
PHOTOSYNTHESIS OVERVIEW
CHAPTER 8-2

How would you
describe the
relationship
between
chlorophyll and the
color of plants?
EQ:
Photosynthesis
uses the energy
in sunlight and
carbon dioxide
from the air to
make glucose
and releases
oxygen into the
air.
Draw, color, label
figure 8-4 from
page 206 on page
55 of your
notebook
Pigments are also a
necessary part of
photosynthesis.
Pigment: any light
absorbing molecule
Chlorophyll:
principle pigment of
plants; absorbs light
energy
PHOTOSYNTHESIS REACTIONS
CHAPTER 8-3

EQ: What happens in the light reactions of
photosynthesis?
Inside a Chloroplast:
thylakoids: saclike
membrane folds;
appear like coins
granum: stack of
thylakoids
stroma: space
between granum
and inner
membrane
PHOTOSYSTEMS
• clusters of
pigments in
thylakoid
membrane that
capture energy
from light
•Photosystem I &
II
LIGHT REACTIONS

Use energy from light to excite
electrons. Electrons absorb
energy from light and go from
their ground state to their
excited state. These excited
electrons then jump out of that
atom & move through a series
of molecules called the
electron transport chain
NOTICE THIS IS HAPPENING IN THE THYLAKOID MEMBRANE
LIGHT REACTIONS: STEP 1



Photosynthesis begins when photons of
light are absorbed by pigments in
Photosystem II
Ground state electron  excited
electrons enter electron transport chain
The electrons that left must be
replaced: Enzymes breakdown 2 water
 4H+ + O2 + 4 electrons
LIGHT REACTIONS: STEP 2
The excited electrons move thru the
electron transport chain to
Photosystem I
 Their energy is used to move H+ from
the stroma to inner thylakoid space

Light Reactions: Step 3
( in Photosystem I now)

 One
of the electron carrier
molecules is NADP+
 NADP+
carries 2 excited electrons
with a H+
 In the process NADP+ 
NADPH thus converting some of
the light energy into chemical
energy
 NADPH carries excited electrons
to other molecules
LIGHT REACTIONS: STEP 4
Over time the inside of the thylakoid
membrane fills with H+ making the
outside of the membrane relatively
negative compared to the inside
(creating a difference in charge across
the membrane)
 The difference in charges provides
energy to make ATP

LIGHT REACTIONS: STEP 5
The thylakoid membrane is impermeable
to H+
 Membrane protein called ATP synthase
allows H+ to pass through membrane
 As H+ is passing through ATP synthase
changes shape & in the process binds
ADP + P  ATP

OVERVIEW OF LIGHT REACTIONS

Things required




Light
Water
NADP+
ADP + P

Things produced



Oxygen
NADPH
ATP
LIGHT REACTIONS ANIMATIONS
Harvesting Light
 Photosynthetic Electron Transport and ATP
Synthesis

TIME FOR THOUGHT

How would you compare the role of
Photosystem II and Photosystem I
LIGHT-INDEPENDENT REACTIONS
 aka:
Thermochemical
cycle
Calvin Cycle
LIGHT-INDEPENDENT REACTIONS:
PART 1


6 carbon dioxide
molecules enter
chloroplast from
atmosphere
Each combines with
a 5-carbon sugar
which then splits 
(12) 3-carbon
molecules
LIGHT-INDEPENDENTREACTIONS:
PART 2


Energy source for
Dark reactions is the
ATP made in light
reactions
H added to carbon
molecules is from
NADPH made in
light reactions
LIGHT-INDEPENDENT REACTIONS:
PART 3

2 of the (12) 3-carbon
molecules leave the
cycle & are used by
the plant to make
compounds needed by
the plant for
metabolism and
growth
LIGHT-INDEPENDENT REACTIONS:
PART 4

(10) C-C-C + 6 ATP
 (6) C-C-C-C-C +
6 ADP


The remaining (10) 3carbon molecules are
converted back into
5-carbon sugars in a
series of reactions
powered by 6 ATP
These are used in the
next turn of the cycle
LIGHT-INDEPENDENT REACTIONS
OVERVIEW

Things required:
 6 CO2
 18 ATP
 12 NADPH

Things produced:
 1 glucose (6carbon)
 18 ADP
 12 NADP+
PHOTOSYNTHESIS EQUATION
FACTORS AFFECTING
PHOTOSYNTHESIS


availability of
water
1. too much
2. too little
temperature
1. Photosynthesis
enzymes work
best 0 ◦C – 35 ◦C
FACTORS AFFECTING RATE OF
PHOTOSYNTHESIS-2
3. light intensity
as it increases rate
of photosynthesis
increases but only to
a certain point, then
it levels off
RAINFORESTS


About 2 ½ acres of
Amazon rainforest
absorbs 1 ton of CO2
per year
20% of world’s O2
produced in Amazon