Photosynthesis Notes

Photosynthesis

Origin and Importance:

• Photosynthesis likely originated in blue-green algae.
• These algae converted carbon dioxide into oxygen, enabling the development of multicellular organisms.
• Photosynthesis is crucial for managing the planet sustainably, ensuring food, water, and habitable conditions.

Location

• Takes place in chloroplasts within multicellular plants.

Autotrophs vs. Heterotrophs:

• Autotrophs: Organisms that produce their own food (e.g., plants).
• Heterotrophs: Organisms that rely on other organisms for food (e.g., animals).

Photosynthesis vs. Cellular Respiration:

• Photosynthesis is essentially the reverse of cellular respiration.
• Photosynthesis: converts CO_2 into Glucose, requires Light and Water
• Cellular Respiration: converts Glucose into CO2, requires O2.

Two Major Steps of Photosynthesis:

1. Light Reactions:

• Light is captured by pigments (similar to rod and cone cells in eyes).
• Photons excite electrons to higher energy levels.
• Excited electrons are passed along an electron transport chain.
• Products: ATP (energy) and NADPH (reducing molecule).
  • NADPH donates electrons to carbon dioxide for carbon fixation.

2. Carbon Fixation:

• Fixing carbon: Removing carbon dioxide from the atmosphere and attaching it to other carbon molecules.
  • This proces is aided by NADPH

3. Photosystems:

• Light reactions involve two photosystems working together.
  • These maximize light use for ATP generation.
• Photosynthetic bacteria utilization:
  • Some bacteria only use one photosystem (I or II).
  • This results in ATP generation, but no NADPH production. Thus, they are less efficient in producing energy independently as plants.

4. Calvin Cycle:

• Products from the light reactions (ATP and NADPH) are used to generate sugar.
• Molecules involved in photosynthesis are recycled in cycles.

Alternative Electron Sources:

• Some bacteria use hydrogen sulfide (H_2S) instead of water as an electron source.
• These bacteria produce solid sulfur instead of oxygen.

Chloroplasts:

• The organelle where photosynthesis takes place.
• Similarities to Mitochondria:
  • Believed to have originated as free-living bacteria.
  • Engulfed by larger bacteria, leading to a symbiotic relationship.
• Symbiotic Relationship:
  • Internalized bacteria (with grana) provide energy for the larger cell through photosynthesis.
  • Larger cell protects the bacteria and provides nutrients.
• Genetic Correlation:
  • Chloroplasts and mitochondria have their own DNA and genes.
  • Genes were lost from the original bacteria, now rely on the host cell for needed proteins.
• Chloroplast Structure:
  • Possess internal membranes, similar to the inner membrane of mitochondria.

Basic Photosynthesis Reaction:

• Reactants: carbon dioxide (CO2), water (H2O), and light.
• Products: one molecule of glucose (C6H{12}O6), six molecules of oxygen (6O2), and six molecules of water (6H_2O).
• Chloroplasts are designed to capture carbon dioxide (CO2) and split water (H2O).
• Redox Reaction:
  • Carbon dioxide (CO_2) is reduced during photosynthesis.