Understanding Fermentation and Cellular Respiration

Posted on Dec 7, 2024 in Biology

  1. Fermentation: The process by which the glucose molecule is broken down by enzymatic action, giving rise to simpler compounds and a net gain of two molecules of ATP. This process may occur in the absence of oxygen.
  2. Importance of Fermentation: The most important aspect is that this allows cells to obtain energy without the need for oxygen.
  3. Utility: It enriches the diet through the development of flavors, aromas, and textures in food substrates, food preservation, and converts the wort into beer, barley, wine, carbon dioxide, and so on.
  4. Autotrophic Hypothesis: This hypothesis holds that the first life forms must have existed in the absence of oxygen and probably possessed primitive organisms capable of absorbing light energy for photosynthesis. It is believed that contemporary green plants, including algae and bacteria, evolved from these photosynthetic organisms.
  5. Heterotrophic Hypothesis: This hypothesis posits that the large amount of organic matter present in the primitive seas, formed by abiogenic processes, was the source of energy for the first organisms. Photosynthetic bacteria have been observed to give rise to mutant non-photosynthetic (heterotrophic) forms.
  6. 1st Law of Thermodynamics: States that energy can neither be created nor destroyed; it can only be transformed.
  7. 2nd Law of Thermodynamics: States that energy tends to increase, increasing the degree of disorder (entropy) of the elements of the system.
  8. Photosynthesis: The basis of most current life on Earth, it is the process by which plants, algae, and some bacteria capture and utilize light energy to convert inorganic matter from their external environment into organic matter used for growth and development.
  9. Chlorophyll: Chlorophyll is a family of pigments found in cyanobacteria and in all organisms that contain plastids, including plants and various groups of protists known as algae.
  10. Chloroplasts: Chloroplasts are cell organelles in eukaryotic photosynthetic organisms involved in photosynthesis.
  11. Structure of Chloroplasts: The two membranes of the chloroplast have a completely different structure, delimiting the chloroplast. Both are separated by a space, sometimes incorrectly called the intermembrane space, known as the periplastidial space. The outer membrane is highly permeable due to the presence of porins, while the inner membrane contains proteins specific to the internal cavity called stroma, where reactions of fixing CO2 occur. It contains circular DNA, ribosomes (70S type, similar to bacterial), granules of starch, lipids, and other substances. Additionally, there are a number of membrane-bound sacs called thylakoids, which are arranged in stacks called grana (plural of granum, grain). The thylakoid membranes contain substances such as photosynthetic pigments (chlorophyll, carotenoids, xanthophylls) and other lipids, proteins of the electron transport chain, and photosynthetic enzymes such as ATP synthase. By observing the structure of the chloroplast and comparing it with that of the mitochondria, we note that it has two sets of membranes delimiting an internal compartment (matrix) and an outer space (perimitochondrial), while the chloroplast has three, forming three compartments: the intermembrane space, the stroma, and the intrathylakoidal space.
  12. Anaerobic Respiration: It is a biological process of oxidation-reduction of sugars and other compounds where the terminal electron acceptor is an inorganic molecule other than oxygen, and more rarely an organic molecule.
  13. Aerobic Respiration: This is a type of energy metabolism in which living organisms extract energy from organic molecules such as glucose, through a complex process in which carbon is oxidized and the oxygen present is used as the terminal electron acceptor.
  14. Mitochondria: Membranous bodies found in most eukaryotic cells. Their size varies between 0.5-10 micrometers in diameter.
  15. Stages of Respiration: Glycolysis – Krebs cycle – Respiratory chain.


  1. Glycolysis: The metabolic pathway responsible for oxidizing or fermenting glucose to obtain energy for the cell. It consists of 10 enzymatic reactions that convert glucose into two molecules of pyruvate, which can follow other metabolic pathways to continue delivering energy to the body. At this stage, glucose is reduced to pyruvic acid.
  2. Krebs Cycle: The Krebs cycle (also called citric acid cycle or tricarboxylic acid cycle) is a metabolic pathway, a sequence of chemical reactions that is part of cellular respiration in all aerobic cells. In aerobic organisms, the Krebs cycle is part of the catabolic pathway for the oxidation of carbohydrates, fatty acids, and amino acids to produce CO2, releasing energy in usable forms (reducing power and GTP).
  3. Respiratory Chain: The electron transport chain is a series of electron carriers found in the plasma membrane of bacteria, in the inner mitochondrial membranes, or in thylakoids, mediating biochemical reactions that produce adenosine triphosphate (ATP), the energy compound used by living things. Only two sources of energy are used by living organisms: oxidation-reduction reactions (redox) and sunlight (photosynthesis). Organisms that use redox reactions to produce ATP are known as chemoautotrophs, while those that use sunlight for this process are known as photoautotrophs. Both types of organisms use their electron transport chains to convert energy into ATP.
  4. Stages of Photosynthesis: Light phase – during this phase, the source of light energy is converted into energy usable by the plant and produces oxygen as waste.
  5. Dark Phase: During this phase, carbon dioxide is used by the plant through the stomata, along with hydrogen taken up by the NADPH molecule and the energy stored as ATP from the previous phase.