Summary of Photosynthesis from Biological Science Chapter 10

Photosynthesis Notes

Overview of Photosynthesis

  • Definition: Photosynthesis is the process by which sunlight is used to manufacture carbohydrates.
  • Autotrophs vs. Heterotrophs:
  • Autotrophs: Organisms that make their own food (e.g., plants).
  • Heterotrophs: Organisms that consume organic materials for energy.

Key Components

10.1 Photosynthesis Process

  • Converts sunlight, carbon dioxide (CO2), and water into glucose and oxygen.

  • Overall equation:

    CO2 + H2O + light energy → (CH2O)n + O2

10.2 Light Reactions & Calvin Cycle
  • Photosynthesis consists of two linked sets of reactions:
  • Light Reactions: Convert light energy to chemical energy (ATP, NADPH) and produce oxygen by splitting water.
  • Calvin Cycle: Uses ATP and NADPH to fix CO2 and produce sugars.

Photosynthetic Structures

Chloroplasts
  • Components:
  • Thylakoids: Membrane-bound structures containing chlorophyll.
  • Granum: Stack of thylakoids.
  • Stroma: Fluid-filled space surrounding thylakoids.
Pigments
  • Types of Pigments:
  • Chlorophylls: Main pigments, absorb red and blue light, reflect green.
  • Carotenoids: Accessory pigments, absorb blue and green light, reflect yellow and red.

Light Absorption and Energy Transfer

  • When chlorophyll absorbs light:
  • Electrons become excited and may be transferred to an electron transport chain.
  • Some energy is released as heat or fluorescence.

Photosystems and Electron Flow

Photosystem I & II
  • Photosystem II: Captures light energy, splits water to replace electrons and produce O2.
  • Photosystem I: Reduces NADP+ to produce NADPH, crucial for carbohydrate production.
Electron Transport Chain (ETC)
  • Excited electrons flow through ETC, generating ATP via chemiosmosis.
  • Photophosphorylation: Light energy used to synthesize ATP.

The Calvin Cycle

  • Phases:
  • Fixation: CO2 combines with RuBP.
  • Reduction: ATP and NADPH convert 3PGA into G3P.
  • Regeneration: G3P used to regenerate RuBP.
  • Key enzyme: Rubisco (Ribulose-1,5-bisphosphate carboxylase/oxygenase).

CO2 Concentration Mechanisms

  • C4 Pathway: Fixes CO2 using PEP carboxylase, separating initial fixation and the Calvin cycle into different cells.
  • CAM Pathway: Similar to C4, but CO2 fixation occurs at night to minimize water loss.

Summary of Products

  • G3P from the Calvin cycle can be converted into glucose or fructose and then into sucrose or starch, crucial for energy storage in plants.

Regulation of Photosynthesis

  • Photosynthesis proteins are produced in response to light availability; high sugar levels can inhibit these proteins to balance energy production with utilization.