Photosynthesis of plants – Understand this process and its phases

The  photosynthesis  is the process by which  plants , which are autotrophs beings synthesize their own food. This process occurs from internal reactions in the plant, involving inorganic substances and sunlight. The substance responsible for this phenomenon is  chlorophyll , which is also responsible for the green pigment of the leaves, as it is where it is most present in vegetables. There are some exceptions, like the cactus, which has no leaves and chlorophyll is concentrated in the stem.

Photosynthetic beings are the captors and fixers of light energy and, through a set of chemical reactions, transform light energy into chemical energy, forming organic compounds that serve as food for living beings.

With the exception of photosynthetic bacteria (cyanobacteria), whose chlorophyll is dispersed throughout the cytoplasm, in other autotrophic photosynthetic organisms, chlorophyll is located inside the chloroplasts or more specifically in the chloroplast lamellae or grass.


  • The stages of photosynthesis
  • The process of photosynthesis
  • Process equation performed by plants and cyanobacteria
  • Light and photosynthetic pigments
  • Exceptions
  • How important are photosynthesizers?

The stages of photosynthesis

Photosynthesis takes place in two stages : the light stage or the photochemical stage (depends directly on light) and the dark or chemical stage (where light is not needed). The chemical stage depends on the products made in the photochemical stage to occur.

Photosynthetic beings are the captors and fixers of luminous energy (Photo: depositphotos)

The photochemical stage occurs in thylacoids, with the participation of photosynthetic pigments and the chemical stage occurs in the stroma of chloroplasts.

The process of photosynthesis

There are factors necessary for photosynthesis to happen, they are:

  • Temperature- Up to 35º C, the levels of production of photosynthesis are good, but after that temperature, the proteins begin to denature, making the process unprofitable.
  • CO2 amount- The more CO2 in the atmosphere, the more potential the process will take. Scientists have already managed to increase the amount of CO2 by 10 times (in the laboratory), enhancing photosynthesis.
  • Light- The most important factor in the process. Without it there is no photosynthesis. The more light present in the environment, the more intense and productive the process will be.

Other photosynthetic beings

There are some protists, bacteria and cyanobacteria that are also capable of carrying out this process, however there are aspects that are different, such as bacteria, which do not release oxygen.

See also : Reino Plantae

Process equation performed by plants and cyanobacteria

6 CO 2 + 12 H 2 O   (light and chlorophyll →) C 6 H 12 O 6 + 6 O 2 + H 2 O

The equation shows that when there is light and chlorophyll, CO2 and water are converted to glucose and water and oxygen is released. We can conclude that for photosynthesis to occur there is a need for light, water and carbon dioxide , the reaction being above the endergonic type, that is, it needs to gain energy to occur.

The oxygen gas released by photosynthesis carried out by eukaryotes and cyanobacteria comes from water and not from carbon dioxide, as previously thought. These organisms then perform oxygen photosynthesis .

In bacterial photosynthesis the equation is different, as bacteria do not release oxygen and do not need water. The first researcher who proposed this was Cornelius Van Niel (1897 – 1985), during the 1930s. The bacteria he studied used CO2 and H2S (hydrogen sulfide) and produced carbohydrate and sulfur. This process has the following equation:

6 CO 2 + 2 H 2 S    (light →)     CH 2 O + H 2 O + 2 S

Using this formula, Van Niel suggested the general photosynthesis equation (shown above).

Van Niel found that red sulfur bacteria, or purple sulfobacteria, performed a particular form of photosynthesis in which there was no formation of oxygen gas. He noted that these bacteria use carbon dioxide and hydrogen sulfide (H 2 S) and produce carbohydrate and sulfur (S). Because it does not produce oxygen, the photosynthesis of these bacteria is called anoxygen .

Light and photosynthetic pigments

Light can only be used in photosynthesis thanks to the presence of specialized pigments, which are able to capture light energy.

The solar radiation is composed of several wavelengths. Among them, the human eye can only distinguish those that make up visible light or white light. When passing through a prism, the light is decomposed and the seven colors that make up white light can be perceived. Each color covers a wavelength range. Photosynthesis is the spectrum of white light.

White light and photosynthesis

White light (from the sun) is formed by a set of electromagnetic radiation of various wavelengths, which vary on a 350 nm scale (namometer), corresponding to violet, at 760 nm, corresponding to red (spectrum visible to our eyes) .

The radiation, which goes from one extreme to the other, is not absorbed with the same intensity by chlorophyll, measuring the amount of energy absorbed by chlorophyll in each radiation wave that makes up the visible spectrum.

Through a device called a spectrophotometer, it was found that blue and red radiation (wavelengths from 450 nm to 700 nm respectively) are the most absorbed and where the rate of photosynthesis is relatively high. Green and yellow radiation (wavelength 500 nm to 580 nm respectively) are the least absorbed. Therefore, a plant subjected to green light practically does not perform photosynthesis.

See also : Reproduction of plants


Although most plants are capable of photosynthesis, there are plants that do not have all the necessary conditions. For this reason, some plants have adapted to capture small insects and remove nutrients that are still missing for their survival. Examples of these carnivorous species are the Dioneias .

These plants have leaves that give off an odor that attracts insects and when the animal lands on the leaf, it automatically closes, thus preventing the animal from flying and escaping. Another well-known example is the plant called the ” jarrinha “. It is a plant of the Nepenthes species, has several colors and a sugary liquid inside. When the insect falls on that plant, it is absorbed and transformed into nutrients.

How important are photosynthesizers?

Oxygenic photosynthetic beings are fundamental for the maintenance of life on our planet, because, in addition to being the basis of most food chains, they produce oxygen, gas kept in the atmosphere in adequate concentrations, thanks mainly to photosynthetic activities.


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