Photosynthesis

• The ultimate source of all energy for every organism on Earth comes from the Sun
• The survival of all organisms depends on the survival and presence of plants (underwater and terrestrial, including algae) and cyanobacteria (photosynthetic bacteria)
• This is because these organisms undergo PHOTOSYNTHESIS
• Photosynthesis


  The process of converting the energy from the sun into chemical energy
• Photosynthesis

  6CO2 + 6H2O → C6H12O6 + 6O2
• How photosynthesis works

  1. Water is absorbed through the plant's roots, then transpirated to the leaves

  2. Carbon dioxide is taken in through the leaves' stomata

  3. Water and carbon dioxide are transferred to the chloroplast

  4. Plants use the light from the sun to synthesize ATP

  5. ATP is then used to rearrange and combine atoms to create carbon dioxide into glucose molecules

  6. Oxygen is then released as a waste product through the stomata

  7. The glucose is then either converted into starch, cellulose or consumed by an animal
• Chloroplast


  • Made of TWO membranes, an outer and an inner membrane
  • Contains specialized discs of membranes called "thylakoids"
  • A stack of thylakoids is known as a granum
  • The fluid that surrounds the granum and occupies the space within the chloroplast is called the "stroma"
• Why are chloroplasts green?

  • Thylakoid (and granum) have a specialized pigment called "chlorophyll" embedded into their membranes
  • Chlorophyll is specialized to absorb red and blue light spectrums, reflecting green wavelengths and hence giving leaves their green color
• Light-Dependent Photosynthesis

  1. Sunlight is absorbed via chlorophyll in thylakoid

  2. Energy from sun is used to produce ATP to drive light-independent phase

  3. Water molecules are split into H+ ions (needed) and O2 gas (waste)
• Light-Independent Photosynthesis

  1. ATP from light dependent phase drives the Calvin Cycle

  2. Monosaccharides (e.g. glucose) is produced with the CO2 and H+ inputs

  3. Monosaccharides are fused together to make long chains of polysaccharides (e.g. starch)