Louis Pasteur, Cell Theory, and Photosynthesis Explained

Louis Pasteur (1822-1895)

Louis Pasteur made significant contributions to chemistry and microbiology. His key achievements include:

• 1858: Discovered germ theory.
• 1860: Studied bacteria and disproved the theory of spontaneous generation.
• 1862: Identified bacteria as the cause of diseases.
• 1880: Developed the vaccine against cholera.
• 1885: Successfully treated the first human for rabies and advanced anthrax research.
• Innovation: Pioneered the technique of pasteurization.

Cell Theory

Cell theory is based on the use of the microscope, starting with Antonie van Leeuwenhoek (17th century) who observed bacteria, and Robert Hooke (17th century) who coined the term cell. The core principles are:

1. Unity: All living beings are composed of one or more cells (Schleiden and Schwann).
2. Continuity: Every cell originates from a pre-existing cell (Virchow).
3. Individuality: The neuron doctrine (Ramón y Cajal).

Structure of the Nucleus

The nucleus is a spherical center containing the following components:

• Nuclear Envelope: A double membrane with pores that allow the exchange of substances between the nucleus and the cytoplasm.
• Nucleoplasm: The fluid content of the nucleus containing chromatin and nucleoli.
• Chromatin: A set of long filaments containing DNA. During cell division, these filaments condense into 46 chromosomes in the human body.
• Nucleoli: The site where ribosomes are produced.

Photosynthesis

Photosynthesis is a set of chemical reactions occurring primarily in plant chloroplasts. It utilizes carbon dioxide (CO2), water (H2O), and light energy, facilitated by photosynthetic pigments. The chemical equation is: 6CO2 + 6H2O → C6H12O6 + 6O2.

Light-Dependent Phase

This phase occurs during the day and involves:

• Photolysis of Water: Water is broken down by light; oxygen is released into the atmosphere, and hydrogen is transferred via ATP.
• Electron Transport Chain: Electrons are transferred to acceptors in the thylakoid membrane.
• Photophosphorylation: Energy is used to pump H+ ions inward. The resulting gradient releases energy through oxisomes to synthesize ATP.

The final products of the light phase are oxygen, ATP, and NADPH.

Dark Phase

Occurring in the stroma of chloroplasts, this phase functions day and night, requiring only ATP and NADPH.

Aerobic Respiration and Fermentation

Aerobic Respiration

Includes glycolysis, decarboxylation of pyruvic acid, the Krebs cycle, the electron transport chain (where oxygen is the final acceptor), and oxidative phosphorylation (ATP synthesis via oxisomes).

Fermentation

These are oxidative reactions that do not require oxygen:

• Lactic Fermentation: Involves lactose hydrolysis, glycolysis, and the reduction of pyruvic acid (e.g., Lactobacillus bulgaricus, Streptococcus thermophilus).
• Alcoholic Fermentation: Involves glycolysis, decarboxylation of pyruvic acid (releasing CO2), and the reduction of ethanal.