Cognogeny and Formation of First Cell: Natural selection was effective even at the time of life’s emergence. Bacteria, moulds, and cyanobacteria were the dominant and maybe only forms of life on the planet for a long time. Blue-green algae evolved into different types of algae over time. Around 1600 million years ago, eukaryotes are estimated to have evolved. By mutation (Raff and Mahler, 1972) or symbiotic relationship, this organism evolved from prokaryotes (Raff and Mahler, 1972). According to Margulis (1970), eukaryotic cilia were once spirochetes, and cytoplasm originated from a symbiotic interaction between eubacteria and archaebacteria. Later on, algae, fungi, protozoans, and other living things evolved. Continue reading to learn more about cognogeny, or the origins and evolution of primitive life.

Origin of Life

The Modern Theory of Origin of Life, commonly known as the Oparin-Haldane theory, was suggested by a Russian biochemist, Alexander I. Oparin (1923 A.D.), and backed by a British scientist, J.B.S. Haldane (1928 A.D.).

It stated that primitive life on Earth arose from non-living organic molecules (e.g., RNA proteins, etc.) in early Earth water bodies through chemical evolution through a series of chemical reactions around 4 billion years ago (during the Precambrian era) (i.e. about 500 million years after the formation of the Earth). It is the most satisfactory theory because it has a scientific explanation and has been practically tested. Oparin’s theory is also known as primary abiogenesis.

The following are some of the steps in modern theory:

A. Chemogeny (Chemical Evolution)– Chemogeny, or life’s chemical evolution, is the process of forming complex organic molecules from simpler inorganic molecules in the oceans during the Earth’s early history; it is the first step in the evolution of life on this planet.

B. Biogeny (Formation of Primitive Life)– Biological evolution is another term for biogeny. Any genetic change in a population that is passed down through generations is referred to as biological evolution. These modifications could be minor or significant. To be called an instance of evolution, changes in a population’s genetic makeup must occur and be passed down from generation to generation.

C. Cognogeny (Nature of Primitive Life and Its Evolution)- It involves the evolution of prokaryotic and eukaryotic cell diversity. Anaerobic and chemoheterotrophic cells were the first to arise. The creation of the first cell was most likely caused by the selection of more successful eobionts together with the modification of the membrane system.

Origin of Autocatalytic Systems, Genes, Viruses and Primordial Life

1. Nucleoproteins first arose as self-replicating (=autocatalytic) complexes in the primordial seas. As a result, once produced, nucleoproteins must have steadily increased in the marine soup.
2. These are capable of performing hereditary duties due to their self-replicating property. Nucleic acids, therefore, revealed the earliest hint of self-perpetuating life.
3. The nucleotide monomers of nucleic acids are thought to have first formed tiny chains, similar to today’s genes.
4. A group of such genes may have eventually collected into a big unit known as a protovirus, which is similar to today’s viruses.
5. Protoviruses are thought to be the earliest or most rudimentary creatures.

Origin of Primordial Cellular Forms of Life (Prokaryotes)

Fig: Prokaryotic cell structure

1. Conditions favorable for the evolution of cell-like organisms existed in the ancient ocean after the formation of self-duplicating systems in the form of nucleoproteins.
2. According to Oparin, the first cellular organisms were coacervates with nucleoproteins. These primitive cellular organisms were similar to modern-day bacteria.

Origin of Autotrophism

1. As anaerobic heterotrophs, the early bacteria-like prokaryotes gradually absorbed all of the marine soup’s abiotically generated organic resources and struggled for survival. Some early prokaryotes developed enzymes that catalyzed the production of simple carbohydrate molecules from inorganic chemicals found in oceanic water during this struggle. This marked the start of autotrophism.
2. The early autotrophism is called chemoautotrophism because the energy utilized in the synthesis of organic molecules came from anaerobic breakdown.
3. In the conditions that existed at the time, natural selection favoured the creation of these anaerobic autotrophs.
4. These anaerobic autotrophs are similar to modern-day deep-sea Sulphur bacteria.
5. From the magnesium porphyrin in sea water, certain autotrophic bacteria-like primitive organisms develop chlorophyll-like green pigments (bacteriochlorophylls).
6. These pigments were able to absorb sunlight, which provided solar energy for carbohydrate synthesis. Photosynthetic autotrophism has been discovered in some marine planktonic sulphur bacteria today.
7. Bacteriochlorophylls then underwent chemical modifications, resulting in the formation of real chlorophyll, which was arranged into lamellar units along with the photosynthetic system’s enzymes.
8. Using water instead of sulphides or other inorganic compounds, early prokaryotes were able to manufacture carbohydrates.
9. The original ocean’s chlorophyll-bearing prokaryotes can be compared to today’s blue-green algae.
   \({\text{6C}}{{\text{O}}_{\text{2}}}{\text{ + 6}}{{\text{H}}_{\text{2}}}{\text{O}} \to {{\text{C}}_{\text{6}}}{{\text{H}}_{{\text{12}}}}{{\text{O}}_{\text{6}}}{\text{ + 6}}{{\text{O}}_{\text{2}}}\)

Fig: Photosynthesis & Cellular respiration.

Origin of Eukaryotic Cells

1. In the early history of the Earth, the liberation of oxygen (O2) into the primitive atmosphere by blue-green alga-like prokaryotes constituted a revolutionary change.
2. Methane and ammonia were oxidised by oxygen, resulting in carbon dioxide, nitrogen, and water, and the reducing atmosphere became oxidising.
3. As a result, the primitive atmosphere’s composition differed from that of today’s atmosphere. With the changing composition of the atmosphere, it seems doubtful that the circumstances for life to emerge will reappear.
4. Oxygen Revolution- As the number of photoautotrophs grew, oxygen wasd and began to build up in the atmosphere. This results in the conversion of a reducing to an oxidizing atmosphere, as well as the conversion of dominating methane and ammonia to carbon dioxide and nitrogen, respectively.
   \({\text{C}}{{\text{H}}_4} + 2{{\text{O}}_2} \to {\text{C}}{{\text{O}}_2} + 2{{\text{H}}_2}{\text{O }}\)
   \(2{\text{N}}{{\text{H}}_4} + 2{{\text{O}}_2} \to {{\text{N}}_2} + 4{{\text{H}}_2}{\text{O}}\)
5. The oxygen revolution was caused by the emergence of an oxidizing atmosphere. Finally, abiotic synthesis and the genesis of new forms were stopped.
6. The oxygen generated an ozone layer, shielding the ultraviolet light and allowing life to travel from the sea to the land.
7. Around 27 billion years ago, when oxygen was liberated from the atmosphere, circumstances favourable for aerobic respiration were developed.
8. Prokaryotes evolved a real nucleus, mitochondria, and other specialized organelles over time, and so-living eukaryotic cell-like animals emerged about 15 billion years ago in the primordial ocean.

Summary

The creation of the first cell was most likely caused by the selection of more successful eobionts together with the modification of the membrane system. The first cells were anaerobic (obtained energy by fermentation of some organic molecules due to lack of oxygen), prokaryotic (containing nucleoid as in bacteria), and chemoheterotrophic (obtained energy by fermentation of some organic molecules due to a lack of oxygen) (derived food from existing organic molecules). Some chemoheterotrophs evolved into anaerobic, prokaryotic, and chemoautotrophs to cope with the depletion of organic molecules.

Sulphate-reducing bacteria, nitrifying bacteria, iron-bacteria, and others began producing organic food from inorganic compounds in the presence of chemical energy (also from the degradation of inorganic compounds) and enzymes. Mutations are thought to be the driving force behind this type of evolution. Chemoautotrophs produced porphyrins and bacteriochlorophyll (a green photosynthetic pigment), and they began photosynthesis (synthesis of carbohydrate). As a result, anaerobic, prokaryotic, and photoautotrophic organisms evolved.

FAQs on Respiratory Balance Sheet

Q.1. What is Cognogeny in evolution?
Ans: Cognogeny is the process of prokaryotic and eukaryotic cells diversifying over time. Anaerobic and chemoheterotrophic cells were the first to arise.

Q.2. What came first in the evolution of cells?
Ans: The early cells were little more than an organic molecule like RNA enclosed in a lipid membrane. The last universal common ancestor (LUCA) is a single cell (or collection of cells) that gave rise to all subsequent life on Earth. 3 billion years ago, photosynthesis evolved and delivered oxygen into the atmosphere.

Q.3. What is primordial soup?
Ans: The primordial soup is a broad term that refers to an aqueous solution of organic chemicals that accumulated in early water bodies.

Q.4. When and how did life begin?
Ans: As the oldest rocks having fossil evidence of life on Earth is at least 3.5 billion years old. Hence we can say life began there at least 3.5 billion years ago. Because subsequent geologic processes have changed the surface of our planet, removing older rocks and creating new ones, these rocks are rare.

Q.5. What is chemogeny?
Ans: Chemogeny, or life’s chemical evolution, is the process of forming complex organic molecules from simpler inorganic molecules in the oceans during the Earth’s early history; it is the first step in the evolution of life on this planet.

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