Chloroplasts are organelles found in plant cells and other eukaryotic cells that are the site of photosynthesis. They contain chlorophyll and have a double membrane structure, with stacks of internal membranes called thylakoids that are the site of the light-dependent reactions of photosynthesis. During photosynthesis, chloroplasts capture energy from sunlight and use it to convert carbon dioxide and water into oxygen and energy-rich molecules like glucose through a two-stage process of light-dependent and light-independent reactions.

1. Chloroplast
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2. Chloroplast
•the site of photosynthesis in eukaryotic
cells
•disk-like structures
•composed of a single membrane
•surrounding a fluid containing stacks of
membranous disks
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3. •SOLAR energy radiated from the sun
is captured by plants(chloroplast)
•Then it is instantaneously changed
Chloroplast
into ELECTRICAL energy
•Then packaged as CHEMICAL
energy
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5. The structure of the chloroplast , function and
photosynthetic membranes
• Inner membrane- highly impermeable, substances moving
through this membrane with the aid of a variety of
transporters
• Outer membrane- outer covering of the chloroplast, it
contains several different porins (proteins with large
channels, 1 nm), exhibit selectivity towards various
solutesThe thylakoid is the structural unit of photosynthesis.
• Intermembrane space- a narrow space between inner and
outer membrane
• Thylakoids- flattened membranous sacs which contains
the photosynthetic chemicals
• Granum/Grana- are stacks of thyllakoids
• Stroma- the areas between grana which contains the
enzymes responsible for carbohydrate synthesis. It contains
small, double-stranded, circular DNA molecules and
prokaryotic-like ribosomes 5

6. Chloroplast
•photosynthesis takes place inside the chloroplast
the process in which plant use wate
Photosynthesis- carbon dioxide, and energy form the
sun to make food
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7. Photosynthesis is the conversion of light energy to chemical
energy or the production of carbohydrates from carbon dioxide and water
in the presence of chlorophyll
the overall reaction of this process is: 6H2O + 6CO2 ----------> C6H12O6+
6O2
Leaves and Leaf Structure
Plants are the only photosynthetic organisms to have leaves (and not all
plants have leaves). A leaf may be viewed as a solar collector crammed
full of photosynthetic cells.
The raw materials of photosynthesis, water and carbon dioxide, enter the
cells of the leaf, and the products of photosynthesis, sugar and oxygen,
leave the leaf.

8. Photosynthesis is a two stage process.
1. Light Dependent Process (Light Reactions), requires
the direct energy of light to make energy carrier
molecules that are used in the second process.
it occurs in the grana of the chloroplast
the energy (light) is absorbed and stored in ATP &
NADPH
2. The Light Independent Process (or Dark Reactions)
occurs when the products of the Light Reaction are
used to form C-C covalent bonds of carbohydrates.
The Dark Reactions can usually occur in the dark, if
the energy carriers from the light process are present.
Recent evidence suggests that a major enzyme of the
Dark Reaction is indirectly stimulated by light, thus the
term Dark Reaction is somewhat of a misnomer. It
takes place in the stroma of the chloroplasts.
* ~ 500t kg of CO2 to carbohydrates/year

9. The Nature of Light White light is separated into the different
colors (=wavelengths) of light by passing it through a prism.
Wavelength is defined as the distance from peak to peak (or
trough to trough). The energy of is inversely proportional to the
wavelength: longer wavelengths have less energy than do
shorter ones.

10. The order of colors is determined by the wavelength of light.
Visible light is one small part of the electromagnetic
spectrum. The longer the wavelength of visible light, the more
red the color. Likewise the shorter wavelengths are towards
the violet side of the spectrum. Wavelengths longer than red
are referred to as infrared, while those shorter than violet are
ultraviolet.
Light behaves both as a wave and a particle. Wave properties
of light include the bending of the wave path when passing
from one material (medium) into another (i.e. the
prism, rainbows, pencil in a glass-of-water, etc.). The particle
properties are demonstrated by the photoelectric effect. Zinc
exposed to ultraviolet light becomes positively charged
because light energy forces electrons from the zinc. These
electrons can create an electrical current. Sodium, potassium
and selenium have critical wavelengths in the visible light
range. The critical wavelength is the maximum wavelength of

11. WHAT IS PHOTOELECTRIC EFFECT?
Photoelectric Effect is the formation and liberation of
electrically charged particles in matter when it is irradiated by
light or other electromagnetic radiation. The term
photoelectric effect designates several types of related
interactions. In the external photoelectric effect, electrons are
liberated from the surface of a metallic conductor by
absorbing energy from light shining on the metal's surface.
The effect is applied in the photoelectric cell, in which the
electrons liberated from one pole of the cell, the
photocathode, migrate to the other pole, the anode, under
the influence of an electric field.

12. Light travels in packets or quanta of energy called photons, which can be
thought of as “particles” of light.
The absorption of light is the first step in a photochemical
process. When a photon is absorbed by a molecule, an electron
becomes sufficiently energetic to be pushed from an inner to an outer
orbital. The molecule is said to have shifted from the ground state to an
excited state. Because the number of orbitals in which an electron can
exist is limited and each orbital has a specific energy level, it follows that
any given atom or molecule can absorb only light of certain specific
wavelengths.
The excited state of a molecule is unstable and can be expected
to last only about .0000000009 second. There is a tendency that the
electron of an excited chlorophyll molecule drops back to a lower
orbital, the energy it had absorbed will be dissipated or released as heat
or reemitted at a longer wavelength.
Instead, the excited electrons of chlorophyll molecules are
transferred to electron acceptors within the chloroplast membranes
before they have a chance to drop back to lower energy orbitals.
Thus, the chloroplasts are able to harness the absorbed energy before it
dissipates.

13. Chlorophyll and Accessory Pigments
A pigment is any substance that absorbs light. The color of the
pigment comes from the wavelengths of light reflected (in other words,
those not absorbed). Chlorophyll, the green pigment common to all
photosynthetic cells, absorbs all wavelengths of visible light except
green, which it reflects to be detected by our eyes. Black pigments
absorb all of the wavelengths that strike them. White pigments/lighter
colors reflect all or almost all of the energy striking them. Pigments
have their own characteristic absorption spectra, the absorption
pattern of a given pigment.
Absorption and transmission of different wavelengths of light by a
hypothetical pigment.

14. Chlorophyll is a complex molecule. Several modifications of chlorophyll occur
among plants and other photosynthetic organisms. All photosynthetic organisms
(plants, certain protistans, prochlorobacteria, and cyanobacteria) have chlorophyll
a. Accessory pigments absorb energy that chlorophyll a does not absorb.
Accessory pigments include chlorophyll b (also c, d, and e in algae and
protistans), xanthophylls, and carotenoids (such as beta-carotene). Chlorophyll a
absorbs its energy from the Violet-Blue and Reddish orange-Red wavelengths,
and little from the intermediate (Green-Yellow-Orange) wavelengths.

15. Molecular model of chlorophyll. The above image is
from
http://www.nyu.edu:80/pages/mathmol/library/photo
Molecular model of carotene.

16. Carotenoids and chlorophyll b absorb some of the energy in the green
wavelength. Why not so much in the orange and yellow wavelengths? Both
chlorophylls also absorb in the orange-red end of the spectrum (with longer
wavelengths and lower energy). The origins of photosynthetic organisms in
the sea may account for this. Shorter wavelengths (with more energy) do
not penetrate much below 5 meters deep in sea water. The ability to
absorb some energy from the longer (hence more penetrating)
wavelengths might have been an advantage to early photosynthetic algae
that were not able to be in the upper (photic) zone of the sea all the time
The molecular structure of chlorophylls

17. The action spectrum of photosynthesis is the relative effectiveness of different
wavelengths of light at generating electrons. If a pigment absorbs light energy,
one of three things will occur. Energy is dissipated as heat. The energy may
be emitted immediately as a longer wavelength, a phenomenon known as
fluorescence. Energy may trigger a chemical reaction, as in photosynthesis.
Chlorophyll only triggers a chemical reaction when it is associated with
proteins embedded in a membrane (as in a chloroplast) or the membrane
infoldings found in photosynthetic prokaryotes such as cyanobacteria and
prochlorobacteria.
Absorption spectrum of several plant pigments (left) and action spectrum of
elodea (right), a common aquarium plant used in lab experiments about
photosynthesis.

18. PHOTOSYNTHETIC UNITS AND REACTION CENTERS
Several hundred chlorophyll molecules act together as
one photosynthetic unit in which only one member of the
group- the reaction center chlorophyll- actually transfers
electrons to an electron acceptor.
Pigment molecules are responsible for light
absorption. These pigment molecules form a light-harvesting
antenna that absorbs photons of varying wavelength and
transfers that energy very rapidly to the pigment molecule at
the reaction center.
The energy can only be passed to a pigment molecule
that absorbs light of equal or longer wavelength (lower
energy) than that absorbed by the donor molecule. The
energy is ultimately transferred to a chlorophyll of the
reaction center, which absorbs light of longer wavelength
than any of its neighbors. Once the energy is received by the
reaction center, the electron excited by light absorption can
be transferred to its acceptor.

19. PHOTOSYTEMS
The light absorbing reactions of photosynthesis occur in large
pigment-protein complexes called photosystems.
Photosystems are arrangements of chlorophyll and other
pigments packed into thylakoids.
2 Types:
1. PSI- raises electrons from a midway point to an energy
level well above that of NADP+
- the reaction center is chlorophyll a with a wavelength of
P700 nm
2. PSII- boosts electrons from an energy level below that of
water to a midway point
- the reaction center is a chlorophyll a with a wavelength of
P680 nm

20. Photophosphorylation is the process of converting energy
from a light-excited electron into the pyrophosphate bond of
an ADP molecule. This occurs when the electrons from water
are excited by the light in the presence of P680. The energy
transfer is similar to the chemiosmotic electron transport
occurring in the mitochondria. Light energy causes the
removal of an electron from a molecule of P680 that is part of
Photosystem II. The P680 requires an electron, which is
taken from a water molecule, breaking the water into H+ ions
and O-2 ions. These O-2 ions combine to form the diatomic O2
that is released. The electron is "boosted" to a higher energy
state and attached to a primary electron acceptor, which
begins a series of redox reactions, passing the electron
through a series of electron carriers, eventually attaching it to
a molecule in Photosystem I.

21. Chloroplast
•No energy transformation is 100% efficient
•Not all the solar energy captured is
converted to electrical and then chemical
energy.
•Some of it gets lost as heat or other forms
of energy (light)
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