Photosynthesis and respiration are two processes that underlie life. They both occur in the cell. The first - in plant and some bacterial, the second - in animals, and in plant, and in mushroom, and in bacterial.
We can say that cellular respiration and photosynthesis are processes opposite to each other. This is partly correct, since oxygen is absorbed and carbon dioxide is released in the first , and vice versa in the second. However, it is incorrect to even compare these two processes, since they occur in different organoids using different substances. The goals for which they are needed are also different: photosynthesis is necessary for obtaining nutrients, and cellular respiration for energy production.
Photosynthesis: where and how does this happen?
This is a chemical reaction aimed at obtaining organic substances from inorganic. A prerequisite for the occurrence of photosynthesis is the presence of sunlight, since its energy acts as a catalyst.
Photosynthesis characteristic of plants can be expressed by the following equation:
- 6CO 2 + 6H 2 O = C 6 H 12 O 6 + 6O 2 .
That is, from six molecules of carbon dioxide and as many water molecules in the presence of sunlight, a plant can get one glucose molecule and six oxygen.
This is the simplest example of photosynthesis. In addition to glucose, other more complex carbohydrates can be synthesized in plants, as well as organic substances from other classes.
Here is an example of the production of amino acids from inorganic compounds:
- 6CO 2 + 4H 2 O + 2SO 4 2- + 2NO 3 - + 6H + = 2C 3 H 7 O 2 NS + 13O 2 .
As you can see, from six molecules of carbon dioxide, four water molecules, two sulfate ions, two nitrate ions and six hydrogen ions using solar energy, you can get two molecules of cysteine and thirteen - oxygen.
The process of photosynthesis occurs in special organoids - chloroplasts. They contain the pigment chlorophyll, which acts as a catalyst for chemical reactions. Such organelles are found only in plant cells.
The structure of chloroplast
This is an organoid that has the shape of an elongated ball. The size of the chloroplast is usually 4-6 microns, however, in the cells of some algae you can find giant plastids - chromatophores, the size of which reaches 50 microns.
This organoid belongs to the two-membrane. It is surrounded by outer and inner shells. They are separated from each other by intermembrane space.
The internal environment of the chloroplast is called the "stroma". It contains thylakoids and lamellae.
Thylakoids are flat, disc-shaped sacs made of membranes containing chlorophyll. This is where photosynthesis takes place. Gathering in piles, thylakoids form grana. The number of thylakoids in the facets can vary from 3 to 50.
Lamellas are structures formed by membranes. They represent a network of branched channels, the main function of which is to provide communication between the grains.
Chloroplasts also contain their own ribosomes necessary for protein synthesis, and their own DNA and RNA. In addition, there may be inclusions consisting of reserve nutrients, mainly starch.
Cell respiration
There are several types of this process. There are anaerobic and aerobic cellular respiration. The first is characteristic of bacteria. Anaerobic respiration is of several types: nitrate, sulfate, sulfuric, iron, carbonate, fumarate. Such processes allow bacteria to receive energy without the use of oxygen.
Aerobic cellular respiration is characteristic of all other organisms, including animals and plants. It occurs with the participation of oxygen.
In representatives of the fauna, cellular respiration occurs in special organoids. They are called mitochondria. In plants, cellular respiration also occurs in the mitochondria.
Stages
Cellular respiration takes place in three stages:
- Preparatory stage.
- Glycolysis (anaerobic process, does not require oxygen).
- Oxidation (aerobic phase).
Preparatory stage
The first stage is that complex substances in the digestive system are split into simpler ones. Thus, amino acids are obtained from proteins, fatty acids and glycerin from lipids, and glucose from complex carbohydrates. These compounds are transported to the cell, and then directly to the mitochondria.
Glycolysis
It lies in the fact that under the action of enzymes, glucose is broken down to pyruvic acid and hydrogen atoms. In this case, ATP (adenosine triphosphoric acid) is formed. This process can be expressed by the following equation:
- 6 12 6 = 2 3 3 3 + 4 + 2.
Thus, in the process of glycolysis from one glucose molecule, the body can get two ATP molecules.
Oxidation
At this stage, pyruvic acid formed during glycolysis under the action of enzymes reacts with oxygen, resulting in the formation of carbon dioxide and hydrogen atoms. These atoms are then transported to cristae, where they are oxidized, forming water and 36 ATP molecules.
So, in the process of cellular respiration, a total of 38 ATP molecules are formed: 2 in the second stage and 36 in the third. Adenosine triphosphoric acid is the main source of energy with which mitochondria supply the cell.
Mitochondrial structure
Organoids in which respiration occurs are found in animals, and in plant, and in fungal cells. They have a spherical shape and a size of about 1 micron.
Mitochondria, like chloroplasts, have two membranes separated by intermembrane space. What is inside the shells of this organoid is called a matrix. It contains ribosomes, mitochondrial DNA (mtDNA) and mtRNA. Glycolysis and the first stage of oxidation undergo in the matrix.
Creases similar to ridges form from the inner membrane. They are called cristas. Here the second stage of the third stage of cellular respiration takes place. During it, most ATP molecules are formed.
The origin of two-membrane organoids
Scientists have proven that the structures that provide photosynthesis and respiration appeared in the cell through symbiogenesis. That is, once they were separate organisms. This explains the fact that both mitochondria and chloroplasts have their own ribosomes, DNA and RNA.