In-Depth Notes on Fermentation and Photosynthesis

Fermentation

• Definition: Metabolism that occurs without oxygen (Anaerobic).

• Glycolysis:

  • Occurs in both aerobic and anaerobic environments.

  • NAD+: An input in glycolysis, regenerated during oxidative phosphorylation in the presence of O2.

  • In the absence of O2, fermentation regenerates NAD+.

  • Importance: No NAD+ leads to no glycolysis, resulting in far fewer ATP (2 ATP are produced).

• Types of Fermentation:

  1. Lactic Acid Fermentation:

  • Examples: Animals, yogurt bacteria.

  • Process: NADH transfers electrons directly to pyruvate, forming lactate as a byproduct.

  1. Alcohol Fermentation:

  • Examples: Yeasts, some fungi, and bacteria.

  • Sequence: From pyruvate to acetaldehyde then to ethanol.

Muscle Fiber Types

• Muscle cells can switch between aerobic cellular respiration and fermentation (facultative anaerobes).

• Types of Muscle Fibers:

  • Slow twitch (Type 1):

  • Function: Endurance.

  • Characteristics: More mitochondria/myoglobin, long and thin.

  • Energy Production: Aerobic.

  • Fast twitch (Type 2):

  • Function: Sprinting.

  • Characteristics: Less mitochondria, short and fat.

  • Energy Production: Anaerobic.

Alcoholic Fermentation

• Processes similar to glycolysis, producing ethanol:

  • Glucose → 2 Pyruvate → 2 Acetaldehyde → 2 Ethanol + 2 CO₂ + Heat.

• Important reaction for yeast in sugar fermentation, especially in low oxygen environments.

Fermentation Adaptations

• Example: Some fish (e.g., crucian carp) can ferment sugars into alcohol for survival in low-oxygen environments by converting lactate into ethanol.

Photosynthesis Overview

• Definition: Transformation of light (radiant) energy to chemical energy (sugars).

• Location: Plant cell chloroplasts.

  • Reactants: Sunlight, Water (H2O), Carbon Dioxide (CO2).

  • Products: Sugars, Oxygen.

Photosynthesis Equation

1. Light Reactions:

   • Convert light energy into ATP & NADPH.

   • Occur in the thylakoid membranes.

2. Calvin Cycle:

   • Utilize ATP & NADPH to produce sugars.

   • Occur in stroma.

Light Energy and Absorption

• Definition: Electromagnetic energy composed of photon particles traveling as waves.

• Visible Range: Only a fraction of light energy that plants utilize for photosynthesis:

  • Main pigments:

  • Chlorophyll a: Absorbs at 430 nm & 662 nm.

  • Chlorophyll b: Absorbs at 453 nm & 642 nm.

  • β-carotene: Absorbs at 400-500 nm, protects chlorophyll.

• Accessory Pigments: Broaden the light spectrum for photosynthesis and protect chlorophyll and DNA.

Mechanism of Light Reactions

1. Photosystem II (PS II):

   • Absorbs light at 680 nm (P680).

   • Transfers excited electrons to primary electron acceptor.

   • Water is split to replace lost electrons, producing O2.

2. Electron Transport Chain (ETC):

   • Electrons flow from PS II to PS I, creating a proton gradient.

   • This gradient drives ATP synthesis.

3. Photosystem I (PS I):

   • Absorbs light at 700 nm (P700) to excite electrons for NADPH production.