Photosynthesis comes
from the word photon meaning light, and synthesis of the means set. So
photosynthesis can be interpreted as a preparation of complex chemical
compounds that require light energy. Energy source of natural light is the sun.
This process can take place because of a certain pigment with materials CO2 and
H2O. Sunlight consists of several spectra, each spectrum have different
wavelengths, so the effect on the photosynthetic process is also different
(Salisbury, 1995).
Photosynthesis is a
complex biological process, this process uses solar energy and light that can
be utilized by the chlorophyll contained in chloroplasts. Such as mitochondria,
chloroplasts have an outer membrane and inner membrane. Membrane in the
surrounding stroma containing an enzyme that dissolves in the membrane
structures called thylakoid. The process of photosynthesis is affected by
several factors such as water (H2O), CO2 concentration, temperature, leaf age,
translocation of carbohydrates, and light. But the major factor that
photosynthesis can take place is light, water, and carbon dioxide (Kimball,
1992).
Although photosynthesis
may take place in various ways in various species, some of the characteristics
are always the same. For example, the process always starts with the light
energy absorbed by chlorophyll proteins called photosynthetic reaction center.
In plants, protein is stored in organelles called chloroplasts, whereas in
bacteria, these proteins are stored in the plasma membrane. A portion of the
light energy gathered by chlorophylls is stored in the form of adenosine
triphosphate (ATP). The remaining energy is used to separate electrons from a
substance such as water. These electrons are used in a reaction that converts
carbon dioxide into organic compounds. In plants, algae, and cyanobacteria, was
conducted in a series of reactions called the Calvin cycle, but a series of
different reactions are found in some bacteria, such as reverse Krebs cycle in
Chlorobium. Many photosynthetic organisms have adaptations that concentrate or
store carbon dioxide. This helps reduce wasteful process called
photorespiration which can be spent most of the sugar produced during
photosynthesis.
The first
photosynthetic organisms likely evolved about 3,500 million years ago, early in
the evolutionary history of life when all life forms on Earth are
microorganisms and has a large amount of atmospheric carbon dioxide. Living
things when it is most likely utilize hydrogen or hydrogen sulfide - not water
- as a source of electrons. Cyanobacteria appeared later, around 3,000 million
years ago, and drastically change when they start oxygening Earth's atmosphere
at about 2,400 million years ago. This new atmosphere enables the evolution of
complex life are like protists. In the end, no less than a billion years ago,
one of the protists formed a symbiotic relationship with cyanobacteria and
produce common ancestor of all plants and algae. Chloroplasts in modern plants
are the descendants of this symbiotic cyanobacteria.
The
Light Reaction
Light reaction is a process to produce
ATP and NADPH2
reduction. This reaction requires water molecules and the light of the
Sun. The process begins with the
capture of photons by the antenna pigments.
Light reaction involves
two photosystems that
cooperate with each other, namely
photosystem I and II. [38] Photosystem
I (PS I) contains
the reaction center P700, which means that the
photosystem is optimally
absorb light at a wavelength of 700 nm, whereas photosystem
II (PS II ) containing P680
and the optimal reaction
center absorbs light at a
wavelength of 680 nm.
Light reaction mechanism begins with the stage where the photosystem II absorb
sunlight so that chlorophyll
in PS II electron
excited states and lead the charge to be
unstable. To stabilize the
back, PS II
will take electrons
from H2O molecules
around it. Water molecules
will be resolved by ion manganese (Mn),
which acts as an enzyme. This will result in the release of H + in the thylakoid lumen.
By using electrons from water, then
PS II would
reduce plastokuinon (PQ) form PQH2. Plastokuinon a quinone molecule
found in the thylakoid membrane lipid bilayer.
Plastokuinon will send electrons from PS
II to an H + pump called the cytochrome b6-f complex. The overall reaction that occurs in PS
II are:
2H2O
+ 4 + 2PQ + photon-4H → 4H + + O2 + 2PQH2
Cytochrome b6-f complex serves to carry electrons from PS II
to PS I by oxidizing PQH2 and reduction of small proteins that are very easy to
move and contain copper, which is named plastosianin (PC). This incident also led to pump H + from the stroma
to thylakoid membrane. The reaction in
the cytochrome b6-f complex is :
2PQH2 4PC + (Cu2 +) → + 2PQ 4PC (Cu +) + 4 H + (lumen)
Electrons from cytochrome b6-f complex to be received by photosystem I. is to
absorb light energy Photosystem apart from PS II, but it contains an integral
core complex, which receives electrons from H2O via the PS II core complex in
advance. For systems that rely on light,
PS I plastosianin oxidize reduced function and move the electrons to the Fe-S
protein called soluble feredoksin. the overall
reaction in PS I is :
Light
4PC + (Cu +) + 4Fd (Fe3 +) → 4PC (Cu2 +) + 4Fd (Fe2 +)
Further electrons from feredoksin used in the final stages
of the transport of electrons to reduce NADP + to form NADPH. [38] This
reaction is catalyzed by enzymes in the stroma-NADP + reductase feredoksin.
[38] The reaction is [38]:
4Fd
(Fe2 +) + 2H + + + 2NADP → 4Fd (Fe3 +) + 2NADPH
H + ions that have been pumped into the thylakoid membrane will go into the ATP
synthase. of ATP synthase will compare
the formation of ATP with the transport of electrons and H + across the
thylakoid membrane. The entry of H + on
the ATP synthase will make ATP synthase worked to change ADP and inorganic
phosphate (Pi) to ATP. overall reaction
that occurs in the light reaction is as follows
:
ADP
+ Pi + light + NADP + + 2H2O → ATP + NADPH + 3 H + + O2
The
scheme Z
In plants, light reaction occurs in the thylakoid membrane in chloroplasts and use
light energy to synthesize
ATP and NADPH.
Light reaction has two forms: the cycle and
nonsiklus. At nonsiklus
reaction, the photons are absorbed in the
antenna complex of photosystem
II by light-absorbing
pigment chlorophyll and other accessories. When
the chlorophyll molecules in photosystem
II reaction center
core obtain sufficient
excitation energy from the adjacent
antenna pigments, an electron is
transferred to electron acceptor molecules,
ie feopftin, through
a process called separation
of power terfotoinduksi. These electrons are transferred
through a series of electron transport, the
so-called Z scheme, which initially serves
to generate kemiosmosis potential along the
membrane. One enzyme ATP synthase using
kemisomosis potential to generate ATP during
photophosphorylation, whereas NADPH is a product
of the terminal redox
reaction in the scheme
Z. Electrons into
the chlorophyll molecules in fofosistem
II. Electrons are
excited because the light is absorbed by the photosystem.
The second electron carrier receives electrons,
which again is passed to lower energy electrons
penerim. The energy generated by the electron acceptor used to move hydrogen ions
across the thylakoid membrane to the lumen. Electrons are used to
reduce the coenzyme NADP, which has the
function of the light reaction.
The reaction cycle nonsiklus similar, but
differ in shape because it only produces
ATP, and no NADP
(NADPH) produced reduced.
The reaction cycle only lasts in photosystem
I. Once the electrons
transferred from photosystem,
the electron is moved through the electron-accepting molecules and returned
to photosystem I, that's where the electron was originally issued, so
the reaction is named in the reaction cycle.
Photolysis of Water
NADPH is the main reducing
agent in chloroplasts, providing a source of energetic electrons to other
reactions. Its production leaves
chlorophyll with a deficit of electrons (oxidized),
which must be
obtained from some other reducing agents. Electrons
lost from chlorophyll in photosystem I are
replaced from a
series of electron transport
by plastosianin. However,
since photosystem II includes the first phase of the scheme Z,
an external electron source to reduce molekuk
siperlukan its chlorophyll
a has been oxidized. Source of electrons in photosynthesis
of green plants and cyanobacteria is water. Two water molecules are oxidized by the reaction of the separation-energy four in a row
by photosystem II
to produce one
molecule of oxygen diatom and four hydrogen ions;
electrons generated at each stage was transferred to a redox-active tyrosine
residue that then
reduces the paired
species of chlorophyll
a has been called the P680 terfotooksidasi useful
as the primary electron
donor (driven by
light) on the photosystem
II reaction center.
Catalyzed the oxidation
of water by photosystem
photosystem II by
a redox-active
structure that contains four manganese ions
and one calcium
ion; complex evolution
of oxygen is bound to two molecules of
water and store the equivalent of four that
has been oxidized is required
to perform water
oxidation reaction. Photosystem II is the
only enzyme known to carry out biological oxidation
of water. Hydrogen ions contribute to the transmembrane
potential kemiosmosis that led to the synthesis of ATP. Oxygen is the
residue of the reaction
product of light, but most organisms on
Earth use oxygen for cellular respiration, including photosynthetic organisms.
The Dark Reaction
Dark reactions in plants can
occur via two
pathways, the Calvin-Benson
cycle and the Hatch-Slack cycle. In the
Calvin-Benson cycle plants convert ribulose
1.5 bisphosphonate compound into a compound with three carbon
atom number of the
compound 3-phosphogliserat. Hence plants that run
through the dark reaction
pathway is called C-3 plants. Belay
CO2 as a carbon source in plants is aided by the enzyme RuBisCO. Plants
are dark reactions following the Hatch-Slack pathway is called C-4
plants due to a
compound formed after mooring
CO2 is oxaloacetate,
which has four carbon atoms. Enzymes that play a role is the phosphoenolpyruvate carboxilase.
Calvin-Benson cycle
Mechanism of the Calvin-Benson cycle begins with the fixation of CO2
by ribulose diphosphate carboxylase (RuBP) to form 3-Phosphoglyceric. is an enzyme RuBP alosetrik stimulated by
three types of lighting changes
resulting from chloroplast. First, the reaction of this
enzyme is stimulated by an increase in pH. If the chloroplasts were light, the ion H + is
transported from the stroma into the thylakoid result in an increase in pH of
the stroma that stimulates enzyme carboxylase, is located on the outer surface
of the thylakoid membrane. Second, this
reaction stimulated by Mg2 +, which enters the stroma of leaves as H + ions, if
the chloroplasts were light. Third, the
reaction was stimulated by NADPH, generated by photosystem I light during
administration. CO2 fixation is a dark reaction is stimulated by light
chloroplasts. Fikasasi CO2 through the
process of carboxylation, reduction, and regeneration. carboxylation involves the addition of CO2 and
H2O into RuBP to form two molecules of 3-Phosphoglyceric (3-PGA). Later in the reduction phase, the carboxyl
group in 3-PGA is reduced to an aldehyde group in 3-fosforgliseradehida
(3-Pgaldehida).
This reduction does not occur directly, but the carboxyl group of 3-PGA is
first converted into the acid anhydride ester type 1.3-bifosfogliserat acid
(1,3-bisPGA) with the last addition of phosphate groups from ATP. ATP was arising from photophosphorylation and
ADP is released when the 1.3-bisPGA formed, which rapidly converted back to ATP
by the addition reaction of photophosphorylation. reducing the actual material
is NADPH, which accounts for two electrons. Taken together, Pi released and re-used
to convert ADP to ATP.
In the phase of regeneration, the regenerated RuBP is required to react with
additional CO 2 that diffuses constantly into and through the stomata. At the end of the reaction of Calvin, a third
ATP is required for each molecule of CO2 is tethered, is used to change the
ribulose-5 -phosphate to RuBP, then the cycle begins again.
Three rounds will cycle tether 3 molecules of CO2 and the end product is a
1.3-Pgaldehida. Some used the chloroplast to form starch, while others were
carried out. This system makes a
constant amount of total phosphate in the chloroplasts, but led to the
emergence of triosafosfat in the cytosol. Used the cytosol trioses phosphate to form
sucrose.
Experiments Ingenhousz
Tool :
Medium-size bottle of mineral water (pict.1)
Timekeeper
Material :
Plant of Hydrilla
Verticillata
Water
Time : 09.10 Wita until finish
Place : Schoolyard of Junior
High School 2 Maros
Work Steps of experiment Ingenhousz :
§
Water bottle with water filled to the brim
§
Enter the plant Hydrilla verticillata into a bottle of mineral water
§ .
Close the bottle
tightly
§
Place the bottle
that had been given Hydrilla plants in areas of direct
sunlight
§
Observe what happens
§
After 1 hour
later, again observe
the changes in the bottle and its content
§
Write the results of observations on a sheet of paper
§
And the conclusion
was the result of photosynthesis experiments are you doing.
The Result of Experiment Ingenhousz
day/
date
|
time
|
Hour
|
duration
of observation
|
number
of bubbles
|
Thursday/
05-04-2012
|
morning
|
09.10
– 09.11
Wita
|
1minute
|
34
bubbles
|
Thursday
/
05-04-2012
|
Afternoon
|
12.09
– 12.10
Wita
|
1minute
|
121
bubbles
|
Thursday
/
05-04-2012
|
Afternoon
|
13.00
– 13.01
Wita
|
1minute
|
106
bubbles
|
Thursday
/
05-04-2012
|
Evening
|
16.04
– 16.05
Wita
|
1minute
|
65
bubbles
|
Thursday
/
05-04-2012
|
Evening
|
19.00-19.01
Wita
|
1minute
|
no bubble
|
Important things resulted
from the experiment, which are :
§
The gas released by plant is O2
§
Sunlight is needed in the process
§
Only the green part releases 02
When the bottle
containing the Hydrilla verticillata plant and water, will soon
appear bubbles of
air that meets the surface of the
bottle. Bubbles generated in
the experiment was a oxygen. This gas is formed
by the photolysis process in which water is decomposed into oxygen gas that will
appear in the form of bubbles with the
following equation:
2H2O (l) 4H + (aq) + O2 (g)
Of the equation appears to O2 gas produced from the decomposition of
molecules of water. After left
for one hour under a hot sun in a bottle of water decreases
1 cm and create your bottle becomes
bloated and can not stand anymore.
CONCLUSION
From experiments have been carried out it
can be concluded
photosynthesis is a
biochemical process in which
plants, algae, and some types of bacteria
used to produce
energy (nutrients) by utilizing light energy. Almost all living things depend on energy produced in photosynthesis. Photosynthesis is one way in photosynthetic
carbon assimilation due to CO 2 bonded carbon-free
(fixed) into sugars as energy storage
molecules. In photosynthesis,
the chemical energy converts carbon
dioxide into sugar and takes place in the stroma.
Glucose not only provides an energy savings
of chemical bonds, but also provide
a molecular basis for generating thousands
of other molecules needed by plants. Oxygen is
released as a byproduct of
photosynthesis. The overall chemical process of photosynthesis can be simplified into the
following equation:
6CO2 + 12H2O + light energy C6H12O6 +6 O2 +6 H2O
Here are some key factors that determine the rate of photosynthesis:
1. Light Intensity
The maximum photosynthetic rate when a lot of light.
2. Concentration of carbon
dioxide
The more carbon dioxide in the air, the more the amount of material used DAPT plants to continue
photosynthesis.
3. Temperature
Enzymes that work in the process of photosynthesis can only work at optimum
temperature. Generally fotosintensis rate increases
with increasing temperature up to
the tolerance of the enzyme.
4. Water Content
Water shortage or
drought cause stomata
to close, blocking the absorption
of carbon dioxide, thereby
reducing the rate of photosynthesis.
5. Fotosintat Levels (of photosynthesis)
If fotosintat such
as reduced carbohydrate levels,
photosynthetic rates will rise. If levels of fotosintat increases or even saturated, the
rate of photosynthesis will decrease.
