The process of photosynthesis – The word photosynthesis comes from the Greek. Photo means
light and synthesis means combination. Photosynthesis is a biochemical
process of forming carbohydrates from inorganic materials carried out by plants, especially plants that
contain a green substance, namely chlorophyll.
In addition to organisms that contain greening substances, there are also organisms that carry out
photosynthesis, namely algae and several types of bacteria that use nutrients, carbon dioxide, water and need to
use solar energy.
Almost all living things depend on the energy produced during photosynthesis. As a result,
photosynthesis is essential for life on earth. Photosynthesis is also credited with producing
most of the oxygen in Earth’s atmosphere. Organisms that produce energy through photosynthesis
(Photos means light) are called phototrophs.
Photosynthesis is a means of assimilation of carbon because in photosynthesis the free carbon from CO2 is
bound (fixed) to sugar as an energy storage molecule. Another way organisms use to assimilate
carbon is through chemosynthesis, which is carried out by some sulfur bacteria.
Photosynthesis lessons are usually given when someone enters junior high school (SMP).
However, there is nothing wrong if this material is reviewed again because it is closely related to
everyday life. Summarized from several sources, the following is an explanation of what
photosynthesis is and how this natural process occurs in plants. So, read the explanation of
photosynthesis until it’s finished, Sinaumed’s friends .
Definition of Photosynthesis
In KBBI, the definition of photosynthesis is the use of solar energy (artificial sunlight) by green leafy
plants or bacteria to convert carbon dioxide and water into carbohydrates. Photosynthesis is a
biochemical process that uses sunlight and occurs only in organisms that have chlorophyll.
Examples are plants and phytoplankton. This condition is a combination of two compounds CO2
(carbon dioxide) and H2O (water) to produce chemical energy using light energy and chlorophyll.
From the various definitions above, we can conclude that photosynthesis is the process of producing
food using carbon dioxide, water, sunlight and chlorophyll.
However, photosynthesis is not only carried out by plants. Several species of bacteria,
protozoa, and algae are also capable of photosynthesis. These organisms are able to carry out
photosynthesis because they have color pigments that can absorb sunlight, ranging from purple to red.
Color pigments are not only green, but also xanthophyll (orange) and carotene (yellow).
Organisms that are capable of photosynthesis are called autotrophs.
In this chemical transformation process, it really needs these 4 things: water, carbon dioxide, chlorophyll
and the last is sunlight. The following is the process of photosynthesis:
- Plants take water from the soil, then it is taken up by the roots, and from the roots
it is metabolized by the transport system, namely xylem and phloem tissues. Distributed to
all organs of the plant body, including leaves.
- Carbon dioxide is obtained from the air that enters through the stomata.
Place the stomata on the underside of the leaf.
- Photosynthesis occurs when the chlorophyll in the leaves receives sunlight and then the light
is used to convert water and carbon dioxide into sugar and oxygen.
- The sugar produced can be used directly by plants, or it can be stored in other plant organs,
such as fruits.
- In addition to sugar, the oxygen that is formed passes through the stomata and then
into the air. This oxygen is used by humans to breathe.
- Through polymerization, the glucose or sugar produced from this process will be
converted into starch or starch. The essence or starch will be stored in the roots
Types of Reactions in the Process of
Until now photosynthesis is still being studied because there are still several stages that have not been
explained, although much is known about this important process. The process of photosynthesis
is complex because it involves all the main branches of natural science, such as physics, chemistry and
In plants, the main organ where photosynthesis takes place is the leaf. But in general, all
cells with chloroplasts are capable of this reaction. This organelle is where photosynthesis
takes place, precisely in the buffer. The results of photosynthesis (known as photosynthesis)
are usually delivered first to nearby tissues.
Basically, the chain reaction of photosynthesis can be divided into two main parts:
light reactions (because they need light) and dark reactions (which don’t need light but do need carbon
dioxide). The light reactions occur in the grana (singular: particles), while the dark
reactions occur in the stroma. In the light reactions, light energy is converted to chemical
energy and produces oxygen (O2).
Whereas in the dark reaction, a series of cyclic reactions occur which form sugar from the building blocks
of CO2 and energy (ATP and NADPH). The energy used in this dark reaction is obtained from the
light reaction. During the dark reaction, sunlight is not needed. Black reaction
to convert compounds containing carbon atoms into sugar molecules.
The light reaction is the reaction that produces ATP and reduces NADPH2. This reaction
requires water molecules and sunlight. The process begins with the capture of photons by
pigments that act as antennas.
The light reactions involve two optical systems operating together, namely photosystems I and II.
Photosystem I (PS I) contains the P700 reaction center, meaning photosystem absorbs light optimally
at 700 nm, whereas photosystem II (PS II) contains photosystem II (PS II). P680’s response and absorption of
light is optimal at 680 nm.
The light reaction mechanism begins with the stage where photosystem II absorbs sunlight so that the
chlorophyll electrons in PS II are excited and cause the charge to become unstable. To
stabilize again, PS II will take electrons from H2O molecules around it. Water molecules will
be broken down by manganese ions (Mn) which act as enzymes. This will result in the release of
H+ in the thylakoid lumen.
By using electrons from water, then PS II will reduce plastoquinone (PQ) to form PQH2.
Plastoquinone is a quinone molecule found in the lipid bilayer of the thylakoid membrane.
This plastoquinone will send electrons from PS II to an H+ pump called the cytochrome b6-f complex.
The overall reaction that occurs in PS II is:
2H2O + 4 photons + 2PQ + 4H- → 4H+ + O2 + 2PQH2
The cytochrome b6-f complex functions to carry electrons from PS II to PS I by oxidizing PQH2 and reducing
a small, highly mobile, copper-containing protein called plastocyanin (PC). This event also
causes an H+ pump from the stroma to the thylakoid membrane. The reactions that occur in the
cytochrome b6-f complex are:
2PQH2 + 4PC(Cu2+) → 2PQ + 4PC(Cu+) + 4H+ (lumen)
Electrons from the cytochrome b6-f complex will be accepted by photosystem I. This photosystem absorbs
light energy separately from PS II, but contains an integral core complex, which accepts electrons coming
from H2O through the PS II core complex first. As a light-dependent system, PS I functions to
oxidize reduced plastocyanin and transfer electrons to a soluble Fe-S protein called ferredoxin.
The overall reaction on PS I is:
Light + 4PC(Cu+) + 4Fd(Fe3+) → 4PC(Cu2+) + 4Fd(Fe2+)
Furthermore, electrons from ferredoxin are used in the final stage of electron transport to reduce NADP+
and form NADPH. This reaction is catalyzed in the stroma by the enzyme ferredoxin-NADP+
reductase. The reaction is:
4Fd (Fe2+) + 2NADP+ + 2H+ → 4Fd (Fe3+) + 2NADPH
H+ ions that have been pumped into the thylakoid membrane will enter into the ATP synthase.
ATP synthase will couple the formation of ATP with the transport of electrons and H+ across the
thylakoid membrane. The entry of H+ into ATP synthase will make ATP synthase work to convert
ADP and inorganic phosphate (Pi) into ATP. The overall reaction that occurs in the light
reaction is as follows:
Rays + ADP + Pi + NADP+ + 2H2O → ATP + NADPH + 3H+ + O2
The dark reaction is known as the Calvin-Benson cycle. In the dark, the Calvin reaction or
reaction does not require sunlight to produce sugar and oxygen. The dark reaction occurs after
the light reaction. The dark reaction is the process by which ATP and NADPH are fertilized by
CO2 and then converted into sugar. The substrate is where the dark reaction occurs.
In the buffer immobilization, reduction and regeneration processes occur. These stages
include: 4,444 CO2 bonds (bonding) – Reduction – Formation of RuBP (Ribulose Bisphosphate).
The dark reaction is divided through several processes, namely:
- Carbon dioxide is bound by RuBp to give rise to phosphoglycerate (PGA).
- PGA is reduced giving birth to PGAL (phosphoglyceraldehyde).
- PGAL will be regenerated into glucose and RuBp.
Photosynthesis in Plants
Plants are autotrophic organisms. Autotrophs mean that they can synthesize food directly from
inorganic compounds. Plants use carbon dioxide and water to produce the sugars and oxygen they
need for food. The energy to carry out this process comes from photosynthesis. The
following is the equation for the photosynthesis reaction that produces glucose:
6H2O + 6CO2 + light → C6H12O6 (glucose) + 6O2
Glucose can be used to form other organic compounds such as cellulose and can also be used as a fuel.
This process takes place through cellular respiration which occurs in animals and plants.
In general, the reaction that occurs in cellular respiration is the opposite of the equation above.
During respiration, sugar (glucose) and other compounds react with oxygen to produce carbon
dioxide, water, and chemical energy.
Plants capture light using a pigment called chlorophyll. This pigment gives plants their green
color. Chlorophyll is found in organelles called chloroplasts. Chlorophyll absorbs
light to be used in photosynthesis.
Although all the green parts of the plant body contain chloroplasts, most of the energy is produced in the
leaves. Inside the leaf is a layer of cells called the mesoderm which contains half a million
chloroplasts per square millimeter.
Light passes through a transparent, colorless cuticle to the dermis, where most photosynthesis takes place. The
leaf surface is usually covered by a waxy impermeable cuticle to prevent absorption of sunlight or excessive
evaporation of water.
Photosynthesis in Algae and Bacteria
Algae range from multicellular algae such as seaweed to microscopic algae consisting of a single cell.
Although algae do not have the complex structures of land plants, photosynthesis in both species
occurs in a similar way.
Simply because algae have different types of pigments in their chloroplasts, the wavelengths of light they
absorb also vary more. All algae produce oxygen and most are autotrophs. Only a
minority are heterotrophs, meaning they depend on materials made by other organisms.
Factors Affecting Photosynthesis
The process of photosynthesis is influenced by several factors, namely those that can affect directly such
as environmental conditions and factors that do not have a direct effect such as disruption of several
organic functions that are important for photosynthesis. Photosynthesis is actually sensitive
to a number of environmental conditions including the presence of sunlight, ambient temperature, and carbon
dioxide (CO2) concentrations. These environmental factors are also known as limiting factors
and have a direct effect on the rate of photosynthesis.
This limiting factor can prevent the photosynthetic rate from reaching optimal conditions even when other
photosynthetic conditions have improved, which is why this limiting factor affects the photosynthetic rate
by controlling the optimal photosynthetic rate. In addition, factors such as carbohydrate
translocation, leaf age, and nutrient availability affect the function of the important organs in
photosynthesis and thus indirectly affect the photosynthetic rate.
The success of plants and autotrophs in making food through photosynthesis is influenced and required by several
Light is the main ingredient for good photosynthesis.
A. Light intensity
Every plant has different light requirements. C3 plants (beans, cotton, soybeans, potatoes,
wheat) have low light tolerance, so when exposed to high light intensity photosynthesis does not increase.
Meanwhile, the light tolerance of C4 plants (sugarcane, corn and sorghum) is high. At
high light intensity will increase the intensity of photosynthesis.
B. Wavelength of Light
Each color spectrum has a different wavelength. However, chlorophyll can absorb more red and
blue colors because the wavelength of light is very efficient.
All plants require different temperatures. For C3 plants, the optimum temperature needed is
around 20-26 ℃. Meanwhile for C4 plants, the optimum temperature required for photosynthesis is
around 35-40 ℃.
3. Plant Age
When the plant is mature, the tissues will form more and more perfectly, this helps increase the effectiveness
and rate of the photosynthesis process.
4. Concentration of Carbon Dioxide (CO2) and
Carbon dioxide greatly affects photosynthesis. The higher the concentration of carbon dioxide
in the air will increase the rate of photosynthesis. In contrast to carbon dioxide, the more O2
concentration will make the photosynthetic intensity decrease.
5. Water and Nutrient Content
Photosynthesis will be disrupted if the plant lacks water. Likewise, abundant water also
inhibits photosynthesis. Chlorophyll actually requires the elements Mg (magnesium) and Nitrogen
n). If these two elements are lacking, then the rate of photosynthesis will decrease.
Benefits of Photosynthesis
1. Produces Oxygen for Living Things
During photosynthesis, plants also release oxygen as a by-product. Oxygen is needed by living
things to breathe. In addition, during this chemical change, plants will absorb carbon dioxide
from pollution. When carbon dioxide is absorbed, the air around plants becomes cleaner and
2. Forming Fruits and Tubers in Plants
Fruits and tubers are food reserves produced by this chemical process. Fruits and tubers can
also be used by humans and animals as a food source. Fruits and tubers contain many vitamins
and compounds that are beneficial to the human body.
3. Produce Glucose
In addition to oxygen, fruit contains glucose. Glucose in plants is used as fuel to make other
food substances. Like fat or protein. Both substances are equally important for
animals and humans. Protein is very good for the body. Protein can repair cells
and enhance human immunity.
4. Humidify the Air in the Surrounding Environment
10% natural humidity caused by vegetation. Increased air humidity has an impact on humans,
namely helping sedation, overcoming fatigue and helping people sleep better.
5. Produce Food Ingredients
The main function of photosynthesis is to produce food. Examples are fruits, tubers and
glucose. The nutritional composition of plants is very beneficial to humans and animals.
This is why the ability of plants to convert solar energy into chemical energy (nutrients) is
always a link in the food chain.
Based on all the explanations above, it can be concluded that photosynthesis is the process of compiling simple
compounds into complex compounds, in plant parts which then contain chlorophyll.
The photosynthesis process will also help produce the main product in the form of stored carbohydrates as
food, including fruit. This process will also require the help of sunlight. When
fruit is eaten by other organisms, there will be a transfer of energy.
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