The fascinating process of photosynthesis
Hypothesis: Autotrophs
Various circumstances led to the appearance and development of autotrophs, including:
A. – Initiation of Photosynthesis
As primitive organisms multiplied, the substances available to them in the seas decreased, leading to increased competition. Organic synthesis likely continued to occur in the atmosphere, but too slowly to restore equilibrium in the consumption of energy reserves in the seas.
Under these conditions, any variation that allowed an organism to manufacture its own food was favored. It is assumed that some variations allowed certain organisms to utilize solar energy.
This synthesis was possible because CO2 from fermentation was abundant and dissolved in water. This simple molecule (CO2) is a building block in the formation of more complex compounds.
The appearance of autotrophic organisms was made possible by variations and natural selection. It is assumed that the first organisms capable of using solar energy acted partly as heterotrophs, taking organic compounds from the environment for energy, and partly as autotrophs, processing organic compounds with cellular energy.
All organisms that require sunlight to form organic compounds are called photosynthetic. As chlorophyll is involved, it is called chlorophyll. Autotrophic organisms must have resembled certain bacteria with simple cellular structures that derived energy from organic matter or sunlight for their metabolism.
Photosynthesis
Photosynthesis irreversibly modified the environment with the production of oxygen, which is a byproduct of the process. The appearance of oxygen radically altered the conditions of life.
Formation of the Ozone Layer
It is believed that the ozone layer could have formed before the appearance of photosynthetic organisms by the slow accumulation of oxygen from the photodissociation of water vapor.
This layer, by retaining UV radiation, paralyzed the formation of synthetic organic compounds. Organisms capable of producing their own food were at an advantage. This ozone layer made it possible for organisms to conquer the earth and air. Organisms no longer relied on substances accumulated in the seas for years; they were already autonomous.
Photosynthesis as a Result of Evolution
Photosynthesis was a higher stage of evolution. Organisms could produce sugars from CO2, H2O, and sunlight, and no longer needed to depend on organic substances stored in the seas. They were already trained to perform organic synthesis and could produce the necessary energy through fermentation. However, fermentation was inefficient and left much of the potential energy contained in organic compounds unused. Additionally, it produced a series of byproducts that were neutralized in the water. For organisms living on land and in the air, these substances posed a danger.
Photosynthesis is an oxidation-reduction reaction between CO2 and H2O, using sunlight as an energy source and chlorophyll as a catalyst.
Dark Phase
In the light phase, oxygen is released from the ionization of water, and hydrogen will serve to reduce CO2. With the help of ATP and NADPH2, reserve substances are formed in plants. All these reactions are carried out independently of light, hence the name “dark phase.”
Process
Ribulose phosphate enters the dark reactions and is activated by ATP, forming ribulose diphosphate. Ribulose diphosphate reacts with CO2 to form a 6-carbon sugar molecule that breaks down into two PGA compounds, each with 3 carbon atoms. In the next step, PGA is reduced by NADPH2 to form PGAL, a 3-carbon molecule. This results in 6 PGAL molecules, 5 of which are used to form 3 new ribulose phosphate molecules, and the cycle begins anew.
Factors Affecting Photosynthesis
A. Presence of Sunlight
As light intensity increases, the photosynthetic process accelerates until it reaches an optimal intensity, after which the process begins to decline.
B. CO2 Concentration
Plants living in a clean environment with a normal CO2 content of about 0.04% of the air volume reach their photosynthetic optimum at a concentration of 0.17% to 0.18%. When CO2 concentration increases further, photosynthesis decreases.
C. Effect of Temperature
Photosynthetic reactions are activated with increasing temperature until they reach an ideal point, after which further increases in temperature cause a decrease in photosynthesis.
D. Concentration of Moisture
Humidity can influence the dilation of the stomata, where gas exchanges occur between the plant and the external environment.
Light Stage
The first step of photosynthesis is the absorption of light by chlorophyll. The absorption capacity of chlorophyll determines the efficiency of photosynthesis.
Stages of the Light Phase
- Cyclic phase
- Acyclic phase