Cellular Respiration and Photosynthesis Processes

Posted on Jan 8, 2025 in Biology

New Ways to Share

Now you can send files to Slack or present them with Zoom without leaving Dropbox.

New Ways to Share

Now you can send files to Slack or present them with Zoom without leaving Dropbox.

Cellular Respiration

Process in which heterotrophic organisms obtain their energy at a cellular level, starting from a molecule of glucose.

  • Cellular Respiration starts with Glycolysis.
  • Most of the time, oxygen is available in the cell, and the Krebs Cycle follows glycolysis.
  • After the Krebs cycle, the Electron transport chain continues.
  • Two types of fermentation: Lactic Acid fermentation and Alcoholic fermentation.

Glycolysis

Anaerobic process that occurs in the cytoplasm of cells.

  1. Two molecules of ATP are broken down, and two phosphate groups are released to form ATP.
  2. The free phosphate groups join the molecule of glucose, forming a molecule of Fructose-biphosphate.
  3. This molecule is broken down into two, forming two molecules of Glyceraldehyde-Phosphate.
  4. Two free phosphate groups enter the cycle and join the molecules, forming two molecules of 1,3-biphosphoglycerate.
  5. Two molecules of NAD+ are transformed into NADH.
  6. Two phosphate groups from each molecule of 1,3-biphosphoglycerate are released and join two molecules of ADP.
  7. At the end of the process, two molecules of pyruvate are created.

Krebs Cycle

The Citric Acid cycle (occurs in the matrix of mitochondria).

  1. One atom of carbon is released from a molecule of pyruvate, creating a molecule of carbon dioxide.
  2. A molecule of NAD+ is converted into NADH.
  3. The two carbon atoms combine with coenzyme to form acetyl CoA.
  4. Coenzyme A is released from the molecule of acetyl CoA.
  5. A molecule of CO2 is released from the six-carbon molecule.

Electron Transport Chain

  • At this point, the molecules of NADH and FADH2 account for most of the energy extracted per molecule of glucose.
  • The electron transport chain is the final step in the breakdown process of glucose; it is also the point at which most of the ATP is produced.

Lactic Acid Fermentation

Process by which certain cells transform pyruvate from glycolysis into lactic acid or lactate.

  • This is the process that the dairy industry uses to produce yogurt.
  • Human skeletal muscles also carry out this process.
  1. Glycolysis starts with glucose.
  2. Glucose is split into pyruvates.
  3. Each molecule of pyruvate is transformed into lactate.

Alcoholic Fermentation

Process by which certain cells convert pyruvate from glycolysis into ethanol or ethyl alcohol and CO2.

  1. Glycolysis starts with glucose.
  2. Glucose is split into two pyruvates.
  3. One molecule of CO2 is released from each molecule of pyruvate.
  4. Acetaldehyde is transformed into ethanol as a final product.

Photosynthesis

Process by which autotrophic organisms transform light energy into organic compounds.

  • All the reactions occur mainly inside the chloroplast of plant cells.

It includes two main parts of pathways:

Phase 1: Light-Dependent Reactions, which occur in the thylakoids.

Phase 2: Light-Independent reactions of the Calvin cycle.

Phase 1: Light-Dependent Reactions

  • Light energy is converted into chemical energy.
  • During this phase, dihydrogen monoxide molecules (water) are transformed into oxygen molecules as byproducts.
  1. Light is absorbed by photosystems in the thylakoid membrane, and electrons flow through electron transport chains.
  2. This causes a molecule of water to split.
  3. A molecule of NADPH and a molecule of ATP are formed and stored to be later used in phase 2.

Phase 2: Calvin Cycle (C3 Cycle)

  • It occurs in the stroma of the chloroplast.
  • It uses the energy molecules obtained during phase 1 to begin the steps.
  1. Carbon from the atmosphere enters the stomata.
  2. Six molecules of CO2 combine with six molecules of ribulose.
  3. This molecule is immediately broken down into 12 molecules.
  4. The 12 free phosphate groups attach to the molecules.
  5. The previous molecules release 12 phosphate groups.
  6. Two out of the twelve molecules of G3P leave the cycle.
  7. The remaining molecules of G3P react with the enzyme rubisco.
  8. Six molecules of ATP are transformed into ADP.