Cellular Physiology: Transport, Respiration, and Division

Posted on Feb 18, 2025 in Biology

Cellular Physiology

It deals with the study of each and every one of the functions performed by the cells. The most important focuses on the movement of substances across their membranes, which form the barrier between the intracellular and extracellular fluid.

Passive Transport

Passive transport involves the movement of substances in different media concentration with no need to expend energy.

  • Simple diffusion: Moving from a place of higher to lower concentration.
  • Facilitated diffusion: Large molecules pass through a pore.
  • Osmosis: Is the diffusion of water through a selectively permeable membrane, depending on a concentration gradient of the solute. When osmosis occurs toward the side of the membrane where there is more concentration, the volume and pressure increase until the water diffusion is slowed and even stopped.

Active Transport

Active transport is performed by the cell with an energy expenditure.

Endocytosis

Endocytosis is a cellular process in which large molecules or particles enter the cell. It is encompassed by an invagination of the cytoplasmic membrane, forming a vesicle that eventually breaks off and enters the cytoplasm.

  • When endocytosis leads to the capture of particles, it is called phagocytosis.
  • When only portions of the captured liquid are involved, it is called pinocytosis.

Cellular Respiration

In the mitochondrial matrix and mitochondrial cristae, the following processes are performed, respectively: the Krebs cycle and respiratory chain.

Meiosis

Meiosis is necessary for sexual reproduction. In all sexually reproducing individuals, at some point in their life cycles, meiosis occurs.

  • Glycolysis is characteristic. It occurs in the cytosol. Produces NADH2 and ATP.
  • Glycolysis is characterized by pyruvic acid having 2 AC, 2 ATP, and 2 NADH2.
  • Glycolysis occurs in all previous cases.
  • Glucose comes from two sources: Food (generates 2 ATP) and glycogen (the way we store glucose, 3 ATP).
  • The reduction of CO2 in photosynthesis is achieved thanks to NADPH.
  • The enzymes that catalyze the reactions of the Krebs cycle are in the mitochondrial matrix of eukaryotic cells.
  • Mitochondria and chloroplasts differ in that the latter produce ATP.
  • The end products of fermentation that follow the glycolytic pathway are always smaller organic compounds than pyruvic acid.
  • DNA and RNA are required for manufacturing, which is called transcription (takes place in the nucleus), and translation and protein synthesis take place in the ribosome.
  • Products of the Krebs cycle: GTP, NADH2, FADH2, CO2.

Mitosis

Mitosis is the process by which a mother cell produces two daughter cells with the same number and kind of chromosomes as the parent cell. It is a continuous process with four phases:

  • Prophase: Chromatin condenses by spiraling, thus the chromosomes become visible. The nuclear membrane and nucleolus disappear. Each centriole moves to opposite poles of the cell, linked by aster fibers, forming the mitotic spindle.
  • Metaphase: Centrioles occupy opposite poles, and the chromosomes are placed on the spindle, causing the equatorial plate.
  • Anaphase: The centromeres divide. Each daughter centromere goes to the opposite side of the cell with a chromatid and initiates reabsorption of the spindle filaments. Therefore, anaphase chromosomes have one chromatid. We had 3 chromatids at first, and now we have 6 chromatids. At the end, there are two groups of 3.
  • Telophase: Chromosomes become invisible by the unwinding of the chromatids.