Photosynthesis

PHOTOSYNTHESIS
Discussant:
KENNETH D. BARRIENTOS
MAED-BIO SCI
1BIO SCI 103 - Advanced Molecular and Cellular Biology

INTRODUCTION
In order for plants to grow, they need
inputs of Carbon dioxide (CO2), water
and energy.
The chemical process by which plants
use these resources to manufacture
glucose, the building blocks of plants, is
called photosynthesis.

6𝐶𝑂2 + 12𝐻2 𝑂 𝐶6 𝐻12 𝑂6 + 6𝑂6 + 6𝐻2 𝑂
Chemical Equation:
Sunlight
4
Chlorophyll
BIO SCI 103 - Advanced Molecular and Cellular Biology

Continued…
Green plants, algae, euglenoids protists
and some bacteria are autotrophs and
carry out photosynthesis on their own.
Animals and other protists, and most
bacteria cannot produce their own food
but depend on other organisms to
produce food - called heterotrophs.

Requirements for photosynthesis
The energy of photosynthesis originates
in the sun and arrives at the earth in the
form of sunlight. This light has both a
wave and a particle nature. The
particles, called photons, are the
smallest unit of light. The light emitted
from the sun contains photons
A. Light

The light emitted from the sun contains
photons in a wide spectrum of
wavelengths, called electromagnetic
spectrum.
Chlorophyll molecules capture energy
from a range of varying wavelengths of
light. The total light composition is made
up the visible light, called BIVGYOR,
ultraviolet (invisible spectrum) and the
infrared. 7

The spectrum of colors carry different
amount of energy depending on the
wavelengths – that is – the shorter the
wavelength the higher the energy level.
During photosynthesis all colors are
absorbed by plants except green and
yellow which are reflected. Red and Blue
wavelengths of light are absorbed by the
pigments and provide the energy used in
the process. 8

Chlorophyll and carotenoids are two
most important groups in
photosynthesis. They are considered
primary light gatherers because they
capture light energy and use it directly to
power the process.
Carotenoids absorb light energy which
the chlorophyll cannot gather, then later
pass the energy to the chlorophyll.
B. Pigment
10

Chemical reactions of photosynthesis
occur within the plant cells in
specialized structures known as
chloroplast.
The chloroplast it is composed of two
parts: stroma and grana.
C. Chloroplast

Stroma – is a large central compartment
which contains fluids and enzymes.
12
Grana – contains the thylakoids.

Light-Dependent
Reaction

The light-dependent reaction occur in
the thylakoid. It is here that the
conversion of light energy to chemical
energy is initiated.
In most photosynthetic organisms,
thylakoid contain pair of photosystems:
Photosystem I and Photosystem II. They
work in tandem to produce the energy
that will later be used in the stroma to
manufacture sugars. 17

Photons of light strike PSI & PSII
simultaneously; but the photons strikes
PSII first.
The absorbed light energy excites
electrons to higher state.
It is then passed from the reaction
center of PSII to an electron transport
chain. 18

Electrons lost in PII process are replaced by a
processed called, photolysis.

The energy from the electron is used to
pump hydrogen ions from the stroma to
the thylakoid, creating a concentration
gradient, called the ATP synthase.

The low energy electron from PSII is
shuttled to PSI where it is again
reenergized to be used in reducing
NADP+ to NADPH.

The resulting product of light-dependent
reaction are ATP and NADPH.
 They are used in the stroma to fuel the
Light-independent reaction (Calvin
Cycle).

Light-Independent
Reaction
(Calvin Cycle)

The Calvin Cycle consists of series of
reactions that reduce Carbon dioxide to
produce the carbohydrate
glyceraldehyde-3-phosphate.
Consists of 3-steps: Carbon fixation,
Reduction, and Regeneration of RuBP

Carbon Fixation
29
Carbon dioxide is attached to 1,5-
biphosphate resulting in a six carbon
molecule that splits into two three-carbon
molecules.

31
 A sequence of reaction using electrons
from NADPH and some of the ATP to
reduce CO2. Finally, ribulose 1,5-
biphosphate is regenerated.
 For every three turns, five molecules of
glyceraldehyde-3-phosphate (G3P) are
used to reform three molecules of
ribulose 1,5-biphosphate.
Reduction

34
 Finally, ribulose 1,5-biphosphate is
regenerated.
 For every three turns, five molecules of
glyceraldehyde-3-phosphate (G3P) are
used to reform three molecules of
ribulose 1,5-biphosphate.
Regeneration of RuBP

36
 The remaining G3P is then used to
make glucose, fatty acids, or glycerol.
 It takes two molecules of G3P to make
one molecule of glucose phosphate.

38
 Calvin cycle must run 6 times to
produce one molecule of glucose.
 The glucose phosphate can remove
their phosphate and add fructose to
form sucrose.
 Glucose phosphate is the starting
molecule for the synthesis of starch
and cellulose

41
 Therefore, plants are the primary
producers of glucose on the planet.
 They also produce food and oxygen
thus serve as the foundation of life in
both land and ocean.

THANK YOU…

Photosynthesis

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