What is the dark phase of photosynthesis?

Photosynthesis is a process that only plant beings can carry out, and on which all animals depend to be able to breathe and, therefore, exist. Although humans tend to think that terrestrial plants are the main responsible for life, something that is not entirely strange since we ourselves are terrestrial and non-aquatic beings, in reality it is those that inhabit the seas, rivers and swamps that produce the higher percentage of this vital gas.

But beware, that does not mean much less that trees, palm trees, and others are not important… because they are. Everything counts. And the more plants there are on the planet, both in its waters and in the earth’s crust, the greater the diversity of life. But how do they survive? Well, transforming the carbon dioxide obtained from the air into food, during what is known as the dark phase of photosynthesis.

How is the dark phase of photosynthesis carried out?

Image – Wikimedia/ Cheveri

Although its name can be misleading, it is a reaction that takes place both day and night in structures called chloroplasts. In this phase , ATP (adenosine triphosphate), essential for obtaining energy, and NADPH (nicotinamide adenine dinucleotide phosphate) are taken mainly, which is a coenzyme thanks to which carbon dioxide is fixed. With them, more chemical processes are carried out on them, divided into two parts:

Carbon fixation

Although it does not depend on the fact that there is sunlight at that time, it is important to note that without it it could not be given, since certain enzymes involved depend on light. When it comes to fixing carbon, plants can do it in different ways. In fact, botanists have identified three CO2 fixations:

  • C3 plants: they are the most common. They fix it during the Calvin cycle (which we will now see), without any prior fixation.
  • C4 plants: these are those in which carbon dioxide, after reacting with fossoenolpyruvate, produces oxaloacetate, which later becomes malate (4-carbon molecules). This malate is what will be carried into the cells, and where the carbon dioxide necessary for the Calvin cycle and pyruvate will be produced.
  • CAM plants: occurs in succulent plants. Living in regions where maximum temperatures are really high, and where there is also little rain, the stomata remain closed during the day to reduce water loss. At night they open, and that is when they absorb the CO2. But, as in C4 plants, this first gives rise to malate after a series of chemical reactions, which ends up supplying the CO2 during the day. More information here.

Calvin cycle

The Calvin cycle is a process during which carbon dioxide is transformed into glucose, which will be used by the plant for breathing and also as a source of carbon. It is the second phase of photosynthesis, and the most important for most animals, because thanks to it, plant beings can exist, and, therefore, expel oxygen throughout the day and all night.

Where does the dark phase of photosynthesis take place?

The dark phase takes place in chloroplasts. These are cellular structures found in eukaryotic organisms, and they have an oval or spherical shape. Its main function is the transformation of energy from the sun into chemical energy, something that occurs during photosynthesis and, to be more exact, during its dark phase.

It is composed of an envelope made up of two membranes which contain pigments such as chlorophyll, as well as other essential substances so that it can fulfill its function.

What is the structure of the chloroplast?

  • Outer membrane: it is permeable and has proteins. It keeps it separate from the cytoplasm.
  • Inner membrane: contains stroma, which is its watery region.
  • Thylakoid membrane: in it are located the thylakoids, which are like flattened sacks. When these are stacked, they form sprinkles.

What function does it have?

Photosynthesis takes place inside the chloroplasts, both its light phase (producing ATP and NADPH in the tylokoid membrane), and the dark phase (fixation of carbon dioxide in the stroma). But not only that, but they also synthesize amino acids and make fatty acids, essential for plants to obtain food. With this food, that is, with these carbohydrates, sugars and starches, they have the opportunity to grow, flourish and produce their seeds.

So without photosynthesis our world would be very different. That is why it is convenient, as well as interesting, to learn more about the flora that surrounds us, since without them surely none of us would be here today.

We hope that what you have learned about the dark phase of photosynthesis has been helpful to you.

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