Ixia-Ayne T.
Luyun
PHOTOSYNTHESIS
12/5/2023
PHOTOSYNTHESIS
▪An anabolic, endergonic, 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
PHOTOSYNTHESIS
• Almost all plants, some
bacteria and protists
(c) Euglena (d) Cyanobacteria
(b) Kelp
(a) Mosses, ferns, and
flowering plants
PHOTOSYNTHESIS
▪Photosynthesis is the process by which
autotrophic organisms use light energy
to make sugar and oxygen gas from
carbon dioxide and water
Carbon Water Glucose Oxygen
dioxide gas
PHOTOSYNTHESIS
6 CO2 + 6 H2O + light energy → C6H12O6 + 6
O2
Food Chain
THE FOOD WEB
QUESTION:
▪Where does
photosynthesis
take place?
PLANTS
▪Autotrophs: self-producers.
▪Location:
1. Leaves
a. stoma
b. mesophyll cells
Mesophyll Chloroplast
Cell Stoma
STOMATA (STOMA)
▪Pores in a plant’s cuticle through which
water and gases are exchanged
between the plant and the atmosphere.
Oxygen
(O2)
Carbon Dioxide
(CO2) Guard Cell Guard Cell
MESOPHYLL CELL
Nucleus
Cell Wall
Chloroplast
Central
Vacuole
CHLOROPLAST
▪Organelle where photosynthesis takes place.
Stroma
Outer Membrane Thylakoid Granum
Inner Membrane
CHLOROPLAST Chloroplast
LEAF CROSS SECTION MESOPHYLL CELL
LEAF
Mesophyll
CHLOROPLAST Intermembrane space
Outer
membrane
Granum Inner
membrane
Grana Stroma Thylakoid
Stroma Thylakoid compartment
THYLAKOID Thylakoid
Membrane
Thylakoid
Space
QUESTION:
▪Why are
plants
green?
WHY ARE PLANTS GREEN?
It's not that easy bein' green
Having to spend each day the color of the leaves
When I think it could be nicer being red or yellow or gold
Or something much more colorful like that…
Kermit the Frog
Gamma Infrared &
rays X-rays UV Microwaves Radio waves
Visible light
Wavelength (nm)
WHY ARE PLANTS GREEN?
Different wavelengths of visible light are seen
by the human eye as different colors.
Gamma Micro- Radio
X-rays UV Infrared
rays waves waves
Visible light
Wavelength (nm)
The feathers of male
cardinals are loaded with
carotenoid pigments. These
pigments absorb some
wavelengths of light and
reflect others.
Sunlight minus absorbed
wavelengths or colors
equals the apparent color
of an object.
❑A molecule that absorbs
Certain wavelength of
light and reflects or transmit
Others.
❑They vary in colors because of their
specific combinations of pigments
❑Ripe orange ( absorbs most of the
wavelength of light except color orange )
Why are plants green?
Transmitted light
▪Transmitted , Reflected, Absorbed
❑An object that reflects all wavelengths,
or colours, of light appears white.
❑An object that absorbs all colors of
light appears black
WHY ARE PLANTS GREEN?
Plant Cells
have Green
Chloroplasts
The thylakoid
membrane of the
chloroplast is
impregnated with
photosynthetic
pigments (i.e.,
chlorophylls,
carotenoids).
THE COLOR OF LIGHT SEEN IS THE COLOR
NOT ABSORBED
▪Chloroplasts
absorb light Light
Reflected
light
energy and
convert it to
chemical
energy
Absorbed
light
Transmitted Chloroplast
light
CHLOROPHYLL
MOLECULES
▪Located in the thylakoid membranes.
▪Chlorophyll have Mg+ in the center.
▪Chlorophyll pigments harvest energy
(photons) by absorbing certain
wavelengths (blue-420 nm and red-660
nm are most important).
▪Plants are green because the green
wavelength is reflected, not absorbed.
WAVELENGTH OF LIGHT (NM)
400 500 600 700
Short wave Long wave
(more energy) (less energy)
ABSORPTION OF CHLOROPHYLL
Absorption
violet blue green yellow orange red
wavelength
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 or yellow.
REDOX REACTION
▪The transfer of one or more
electrons from one reactant to
another.
▪Two types:
1. Oxidation
2. Reduction
OXIDATION REACTION
▪The loss of electrons from a substance.
▪Or the gain of oxygen.
Oxidation
6CO2 + 6H2O → C6H12O6 + 6O2
glucose
REDUCTION REACTION
▪The gain of electrons to a
substance.
▪Or the loss of oxygen.
Reduction
6CO2 + 6H2O → C6H12O6 + 6O2
glucose
BREAKDOWN OF
PHOTOSYNTHESIS
▪Two main parts (reactions).
1. Light Reaction or
Light Dependent Reaction
Produces energy from solar
power (photons) in the form of
ATP and NADPH.
BREAKDOWN OF
PHOTOSYNTHESIS
2. Calvin Cycle or
Light Independent Reaction or
Carbon Fixation or
C3 Fixation
Uses energy (ATP and NADPH) from
light rxn to make sugar (glucose).
PHOTOSYNTHESIS
▪ The light reactions
Light
convert solar Chloroplast
energy to chemical
energy NADP+
▪ Produce ATP & NADPH ADP
+P
Calvin
• The Calvin cycle makes Light
reactions
cycle
sugar from carbon
dioxide
1. LIGHT REACTION
(ELECTRON FLOW)
▪Occurs in the Thylakoid membranes
▪During the light reaction, there are
two possible routes for electron flow.
A. Cyclic Electron Flow
B. Noncyclic Electron Flow
PSII PSI
Reaction Center
(Special pairs of P680 P700
chlorophyll a)
Primary electron
Pheophytin A
acceptor
0
ETC from PS
Source of electron HO
II
2
ETC Pq, Cyt, Pc Fd, FNR
A. CYCLIC ELECTRON FLOW
▪Occurs in the thylakoid membrane.
▪Uses Photosystem I only
▪P700 reaction center- chlorophyll a
▪Uses Electron Transport Chain (ETC)
▪Generates ATP only
ADP + P ATP
A. CYCLIC ELECTRON FLOW
Primary e-
SUN Electron
Acceptor
e- e- ATP
produced
Photons by ETC
e-
P700
Accessory
Pigments
Photosystem I
B. NONCYCLIC ELECTRON FLOW
▪Occurs in the thylakoid membrane
▪Uses PS II and PS I
▪P680 rxn center (PSII) - chlorophyll a
▪P700 rxn center (PS I) - chlorophyll a
▪Uses Electron Transport Chain (ETC)
▪Generates O2, ATP and NADPH
B. NONCYCLIC ELECTRON FLOW
Primary
Electron 2e-
Acceptor
Enzyme
Primary Reaction
2e-
Electron
Acceptor
2e-
ETC
SUN 2e-
2e- NADPH
P700
Photon ATP
P680 Photon
H2O Photosystem I
1/2O2 + 2H+ Photosystem II
B. NONCYCLIC ELECTRON FLOW
▪ADP + P → ATP
(Reduced)
▪NADP+ + H → NADPH
(Reduced)
▪Oxygen comes from the
splitting of H2O, not CO2
H2O → 1/2 O2 + 2H+
(Oxidized)
CHEMIOSMOSIS
▪Powers ATP synthesis.
▪Located in the thylakoid
membranes.
▪Uses ETC and ATP synthase
(enzyme) to make ATP.
▪Photophosphorylation: addition of
phosphate to ADP to make ATP.
CHEMIOSMOSIS
SUN
H+ H+ (Proton Pumping)
Thylakoid E
PS II T PS I
C
high H+
H+ H+
concentration
H+ H + H+ H+
Thylakoid
H+ ATP Synthase Space
ADP + P low H+
ATP
H+ concentration
CALVIN CYCLE
▪Carbon Fixation (light independent
rxn).
▪C3 plants (80% of plants on earth).
▪Occurs in the stroma.
▪Uses ATP and NADPH from light rxn.
▪Uses CO2.
▪To produce glucose: it takes 6 turns
and uses 18 ATP and 12 NADPH.
CHLOROPLAST
Stroma
Outer Membrane Thylakoid Granum
Inner Membrane
CALVIN CYCLE (C3
FIXATION) (36C)
(6C) 6C-C-C-C-C-C
6CO2 (unstable)
6C-C-C 6C-C-C 12PGA
(36C)
6ATP 6ATP
(30C)
6C-C-C-C-C
6NADPH 6NADPH
RuBP
(36C)
6C-C-C 6C-C-C
6ATP 12G3P
C3 (30C)
(6C)
glucose C-C-C-C-C-C
Glucose
CALVIN CYCLE
▪ Remember: C3 = Calvin Cycle
C3
Glucose
PHOTORESPIRATION
▪Occurs on hot, dry, bright days.
▪Stomates close.
▪Fixation of O2 instead of CO2.
▪Produces 2-C molecules instead
of 3-C sugar molecules.
▪Produces no sugar molecules or
no ATP.
PHOTORESPIRATION
▪Because of photorespiration:
Plants have special
adaptations to limit the effect
of photorespiration.
1. C4 plants
2. CAM plants
C4 PLANTS
▪Hot, moist environments.
▪15% of plants (grasses, corn,
sugarcane).
▪Divides photosynthesis
spatially.
▪Light rxn - mesophyll cells.
▪Calvin cycle - bundle sheath cells.
C4 PLANTS
Malate Malate
C-C-C-C C-C-C-C
Transported CO2
CO2 C3
Vascular
Tissue
glucose
C-C-C
PEP ATP
C-C-C
Pyruvic Acid
Mesophyll Cell Bundle Sheath Cell
CAM PLANTS
▪Hot, dry environments.
▪5% of plants (cactus and ice plants).
▪Stomates closed during day.
▪Stomates open during the night.
▪Light rxn - occurs during the day.
▪Calvin Cycle - occurs when CO2 is present.
CAM PLANTS
Night (Stomates Open) Day (Stomates Closed)
Vacuole
C-C-C-C C-C-C-C C-C-C-C
CO2 Malate Malate
Malate
CO2
C3
C-C-C
ATP C-C-C glucose
PEP
Pyruvic acid
QUESTION:
▪Why would CAM plants close their
stomates during the day?
