Earth came into existence some 4.5 billions year ago and based on the fossil evidence from ancient rocks of Greenland, the life on earth dates to 3.7 billion years ago.
The organisms that existed for the first two billions years, after the origin of life, were all anaerobic organisms.
These organisms managed to survive and flourish even in absence of oxygen (anaerobic).
They lived on the chemicals that were abundant in the early atmosphere and oceans, such as molecular hydrogen (H2), ammonia (NH3), and water (H2O).
These anaerobic organism devised an oxygen independent metabolism – Glycolysis and fermentation.
The efforts of these microbes created the conditions for all subsequent life to evolve across the earth.
Photosynthesis and its role in altering life forms on earth:
Around 2,5 billion years ago, a different kind of bacteria evolved, which eventually changed the whole picture of our planet.
As more and more sunlight was starting to penetrate the earth’s toxic atmosphere, the Cyanobacteria appeared – a new kind of bacteria which had the ability to split water, fix Carbon di oxide and form carbohydrates (food) plus release of oxygen as byproduct. This was all done in presence of sunlight and process is called Photosynthesis.
Slowly the earth’s atmosphere bean to change with accumulation of released oxygen in significant levels, which set the platform for a dramatic change in the types of organisms that begin to inhabit our planet and saw a shift from anaerobic to aerobic life forms (see Cambrian explosion).
The photosynthetic producers take in energy in the form of light (solar energy) and convert it into chemical energy in the form of glucose, which stores this energy in its chemical bonds.
The glucose formed during photosynthesis can be extracted for energy by a series of metabolic pathways termed as “Cellular respiration”. By means of cellular respiration, organism can convert the energy present in chemical bonds of glucose and convert it into a useable form for the all activities of life forms.
Hence all the energy required for all our activities such as movement, transport, absorption of food, biochemical processes, reproduction , breathing etc. is obtained from oxidation of macromolecules (carbohydrates, proteins, fats) that we call “food”.
All organisms (bacteria, plants, animals etc.) will extract energy from food, by means of cellular respiration.
The production of energy from food is connected to our process of breathing (in take of oxygen).
We all know that only Plants, Algae and Cyanobacteria can produce their own food and release oxygen by a process termed as Photosynthesis.
All the other organisms are dependent on photosynthesis directly (herbivores) or indirectly ( carnivores) for food and ultimately for extraction of energy in the form Adenosine Tri Phosphate (ATP) and release carbon di oxide (CO2)through cellular respiration.
So it is important to remember that all the food which organisms use for respiration comes from photosynthesis.
Respiration is of two types : Anaerobic and Aerobic respiration
Anaerobic Respiration :
In this kind of respiration, organisms oxidize the food without the help of oxygen and form energy-rich products such as lactic acid and ethanol, which they fail to metabolize further. Anaerobic respiration yields only a limited amount of energy is extracted from their food.
Glycolysis and Fermentation are two major pathways involved in anaerobic respiration
Aerobic respiration is a biological process in which food (glucose) is converted into energy in the presence of oxygen.
Aerobic organisms that use O2 into their metabolism, devised a way to completely oxidize carbohydrates (food) into CO2 and H2O .
The big advantage of this kind of aerobic respiration is that it allows the cells to extract a much larger percentage of energy content from their foodstuffs.
Glycolysis, Krebs cycle and oxidative phosphorylation are important pathways in aerobic reparation.
Glycolysis, which is common to both anaerobic and aerobic respiration, occurs in cytoplasm.
Krebs cycle and Oxidative phosphorylation takes place in Mitochondria.
Next parts of Cellular Respiration
Image Credit :
Animals and plants – Correlation. Modified from (pixabay)