1.

It is a key
product of
photosynthesis.
GLUCOSE
 2. It is a plant
organelle that is used
in photosynthesis
CHLOROPLAST
3. It is an energy
carrying
molecule
NADPH
 4. It is a green
pigment found in
plants
CHLOROPHYLL
 5. It is a sac-like
membrane that make up
the grana within the
chloroplast.
THYLAKOID
MEMBRANE
 6. It is the process in
which sunlight is used to
make food.

PHOTOSYNTHESIS
 7. These are groups of
molecules absorbing
sunlight during the light
reactions.
PHOTOSYSTEMS
 8. It is the stage of
photosynthesis in which
sunlight is stored in ATP
and NADPH.
LIGHT REACTION
 9. These are transport
molecules which transfer
electrons from molecule to
molecule.
ELECTRON
TRANSPORT CHAIN
10. It is the stage of
photosynthesis in
which glucose is
produced.
CALVIN CYCLE
 11. It is a type of
photosystems in which
the special pair is called
P680.
PHOTOSYSTEMS II
12. It is the primary
electron acceptor of
photosystems I.
CHLOROPHYLL A
13. It is the process of
creating ATP using
energy stored in a
chemical gradient.
CHEMIOSMOSIS
14.It is the primary
electron acceptor of
photosystems II.
PHEOPHYTIN
 15. It is a process of
light reactions in
which the chemical
energy created is ATP
only.
CYCLIC
PHOTOSYNTHESIS
Light, energy and life
Table of contents:
Introduction

Timeline

Photosynthesis

Harnessing sunlight

Transforming energy

Photosynthetic organisms

Importance
 Have you ever stayed
out too long under the
sun? What happened to
you?
 Necessary components for
photosynthesis to proceed
• visible light (solar energy)
• leaves which are the food-producing sites of a plant
• chloroplasts which are organelles where
photosynthesis occurs.
• Chlorophyll is a green pigment located in the thylakoid
membrane of the chloroplast which is responsible in
capturing the visible light.
• Plant pigments (just like chlorophyll) are organic
molecules that selectively absorbs light of specific
wavelength.
 The word comes from Greek:

Photo synthesis SYNTHESIS: COMPOSITION

PHOTO: LIGHT
 TIMELINE
17th Century Year 1779 Year 1854
First description of Identification of
Experiments on plant growth
photosynthesis, process by which Chlorophyll as the primary
reveal that plants absorb
green plants absorb carbon pigment responsible for
water, but not soil, for their
dioxide and release oxygen, and photoshynthesis.
development.
water into glucose.

18th Century Year 1845 Year 18960

First theory of photosynthetic Consolidation of photosynthesis
Discovery of oxygen and its
metabolism, stating that plants as a fundamental biochemical
relationship with the release of
convert light into chemical process that sustains life
"vital air" by plants.
energy. on Earth.
 Photo synthesis
It is a chemical process that involves the conversion of
inorganic matter into organic matter through the energy
provided by sunlight.

6CO 2 + 6H 2 O C6 H12 O 6 + 6O 2
CARBON DIOXIDE WATER GLUCOSE OXYGEN
ACTIVITY
Directions: After reading the experiment conducted
by Jan Van Helmont, let us answer the following
questions:
1. How did van Helmont’s results invalidate the
prevailing idea about plant growth?
__________________________________________
2. How did van Helmont describe his results?
__________________________________________
3. What is the appropriate interpretation of van
Helmont’s results?
__________________________________________
1. The willow tree gained a lot
of mass but the soil lost none.
Therefore, the gain in mass of
the tree could not be due to
matter absorbed from the soil.
2. He deduced that the
tree gained mass from
the water he gave.
3. The tree gained mass by
changing water and carbon
dioxide in the air to glucose
and other organic
compounds needed for
growth.
Describe the patterns of
electron flow through
light reaction events
 Stages of
Photosynthesis
 1. Light Dependent
Reaction (or simply Light
Reactions)
2. Light Independent
Reaction (commonly
known as Calvin cycle).
 LIGHT REACTION
Light dependent reactions, as the
name implies, use light energy to
make molecules needed for the
next stage (light independent
reactions) of photosynthesis
 PHOTOSYSTEMS
Photosystems are multiprotein complexes
found in the thylakoid membrane.
The processes involve in converting light
energy to chemical energy takes place here.
Photosynthetic pigments that act as light-
harvesting molecules, such as chlorophyll a,
chlorophyll b and carotenoids are organized
into photosystems.
 PHOTOSYSTEMS
There are two types of photosystems in
the light reactions,
Photosystem II (PSII) and Photosystem I
(PSI). PSII comes first in the path of
electron flow, but it is named as second
because it was recognized after PSI.
PHOTOSYSTEMS
PHOTOSYSTEMS
 Stage 1: Light Reactions

termed as “Light-Dependent
Reaction” and is the first stage of
photosynthesis.
Stage 1: Light Reactions
 Stage 1: Light Reactions
It utilizes sunlight to initiate
electron transfer, thereby reducing
NADP+ to NADPH and splitting
water to give off oxygen as by-
product.
 Stage 1: Light Reactions
It utilizes sunlight to initiate electron
transfer, thereby reducing NADP+ to
NADPH and splitting water to give off
oxygen as by-product. It occurs in the
thylakoids of the chloroplast
Stage 1: Light Reactions
A. Linear Phosphorylation or Non-
cyclic Phosphorylation-
B. Cyclic phosphorylation-
. Linear Phosphorylation or Non-cyclic
Phosphorylation-
light is absorbed and converted to chemical
energy in the bonds of NADPH (Nicotinamide
Adenine Dinucleotide Phosphate) and ATP
(Adenosine Triphosphate).
 Cyclic phosphorylation-
light is absorbed and converted to
chemical energy in the bonds of
ATP only.
. Linear Phosphorylation or Non-cyclic
Phosphorylation-

Electrons travel in a line from water

through PSII and PSI to NADPH
(Photophosphorylation means light-
driven synthesis of ATP)
STEP 1
When the P680
special pair of
photosystem II
consumes
energy (photons
from sunlight),
it enters an
excited (high-
energy) state.
STEP 1
Excited P680 is a
good electron
donor and can
shift its excited
electron to the
primary
electron
acceptor,
pheophytin
STEP 1
From Pheophytin,
the electron will
be transferred on
through the first
leg of the
photosynthetic
electron transport
chain in a series of
redox, or electron
transfer,
reactions.
STEP 2
Step 2: Once the
special pair gives up
its electron, it has a
positive charge and
requires a new
electron. This
electron is provided
through the splitting
of water molecules,
a process carried out
by a portion of PSII.
STEP 2
About 10 percent of the oxygen is
utilized by mitochondria in the leaf
to support oxidative
phosphorylation. The remainder
escapes to the atmosphere where
it is used by aerobic organisms to
aid in respiration.
STEP 3
When an electron
leaves PSII, it is
transferred first to a
small organic
molecule
(plastoquinone, Pq),
then to a
cytochrome complex
(Cyt), and lastly to a
copper containing
protein called
plastocyanin (Pc).
STEP 4 As the electron
travels through
this electron
transport chain,
it goes from a
higher to a
lower energy
level, releasing
energy.
STEP 4
Some of the
energy is used
to pump
protons (H+)
from the stroma
(outside of the
thylakoid) into
the thylakoid
interior.
STEP 5 After an
electron has
gone down the
first leg of the
electron
transport chain,
it arrives at PSI,
where it joins
the chlorophyll
a special pair
called P700.
STEP 5
Since electrons
have lost energy
before their
arrival at PSI,
they must be re-
energized
through
absorption of
another photon.
STEP 6
Excited P700 is a
good electron
donor, and it
gives its
electron to
chlorophyll Ao
and then down
to short
electron
transport chain.
STEP 6
In this series of
reactions, the
electron is first
transmitted to a
protein called
ferredoxin (Fd),
then to an
enzyme called
NADP+
reductase.
STEP 7
NADP+ reductase
moves electrons
to the electron
carrier NADP+ to
make NADPH.
NADPH will travel
to the Calvin
cycle, where its
electrons are used
to create sugars
from carbon
dioxide
STEP 8
The other ingredient
required by the Calvin
cycle is ATP, and this too
is administered by the
light reactions. H+ ions
build inside the
thylakoid interior and
make a concentration
gradient.
STEP 8 Protons "want" to diffuse
back down the gradient
and into the stroma, and
their only route of passage
is through the enzyme ATP
synthase. ATP synthase
harnesses the flow of
protons to create ATP from
ADP and phosphate (Pi).
This process of creating
ATP using energy stored in
a chemical gradient is
called chemiosmosis
Cyclic phosphorylation-
Electrons break the
pattern and loop back
to the first part of the
electron transport
chain, repeatedly
cycling through PSI
instead of ending up
in NADPH.
Cyclic phosphorylation-
The electrons then
flow down the
chain to PSI
normally, driving
proton pumping
and the production
of ATP.
Cyclic phosphorylation-
The cyclic pathway does
not make NADPH, since
electrons are moved away
from NADP+ reductase.
After leaving PSI, cyclically
flowing electrons travel
back to the cytochrome
complex (Cyt) or
plastoquinone (Pq) in the
first leg of the electron
transport chain.
 Cyclic phosphorylation-
Why does the cyclic pathway exist? In some cases,
chloroplasts assume to switch from linear to cyclic
electron flow when the ratio of NADPH to NADP+ is too
high (when too little NADP+ is available to accept
electrons); Finally, cyclic electron flow may perform a
photoprotective role, preventing excess light from
damaging photosystem proteins and promoting repair of
light-induced damage;
Harnessing sunlight
Light capture:
Pigments like chlorophyll absorb light energy, propelling
electrons in photosystems.

ATP generation:
The released electrons create a flow that drives ATP
synthesis, storing chemical energy.

NADPH production:
Another stream of electrons generates NADPH, an energy
and electron carrier molecule.

Oxygen release:
The water molecule splits, releasing oxygen crucial for the
atmosphere and respiration.
 Transforming energy
CO2 capture:
The enzyme RuBisCO fixes carbon dioxide (CO2) into
organic compounds in the Calvin cycle.

Sugar formation:
The resulting molecules convert into sugars, utilizing ATP
and NADPH from the light-dependent phase.

RuBisCO regeneration:
Molecules enabling CO2 capture regenerate, ensuring cycle
continuity.

Readying for new cycles:

The cycle persists, creating sugars and regenerating
molecules for CO2 fixation in future iterations.
 Sunlight

Graphic summary
Carbon
Water dioxide

NADP+

ADP

Thylakoid Photosystem II

Stroma
Pi
Grana

Calvin cycle
Lamella
Electron
Transport Chain
Photosystem I
ATP

NADPH

Oxygen Glucose
 Photosynthetic organisms

MI CROALGAE PLANTS MACROALGAE BACTE RI A

The primary producers of They are the primary terrestrial Habitat and food for various Some cyanobacteria perform
oxygen on Earth, and they also photosynthetic organisms, marine organisms, also photosynthesis, being
form the foundation of aquatic sustaining life and regulating contributing to ecological essential for the carbon and
food webs. the climate. balance. oxygen cycle.
Importance
Vital energy source:
Photosynthesis converts sunlight into chemical energy,
nourishing plants and initiating food webs on Earth.

Oxygen production:
Photosynthetic organisms release oxygen as a byproduct,
sustaining the respiration of most living beings and
enriching the atmosphere with this gas.

Climate regulation:
Photosynthesis absorbs carbon dioxide, aiding in climate
change control and maintaining the balance of the
greenhouse effect.
 THANK YOU FOR
YOUR ATTENTION!

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