Chapter 6: Photosynthesis

• Photosynthesis


  The process by which green plants, algae, some protists, and cyanobacteria use solar energy, carbon dioxide, and water to produce carbohydrates and oxygen
• Photo = light, Synthesis = to make
• Photosynthesis (balanced chemical equation)

  6CO2(g) + 6H2O(l) → C6H12O6(s) + 6O2(g)
• Photosynthesis (word equation)


  Carbon Dioxide + Water → Glucose + Oxygen
• Light


  A type of electromagnetic radiation (EMR)
• Common forms of EMR

  • X-rays
  • Microwaves
  • Radio waves
• Photon


  A packet of light
• Photons with short wavelength

  High energy (Gamma rays, X-rays, UV)
• Photons with long wavelengths

  Low energy (Infrared, Microwaves, Radio Waves)
• The sun's energy is a mixture of different wavelengths. When passed through a prism, the different wavelengths separate forming the electromagnetic spectrum
• Humans can only see a narrow band of visible light from 380 nm (violet light) to 750 nm (red light)
• Photosynthetic organisms (autotrophs, producers)


  Capture solar energy and store it as chemical energy in bonds of glucose molecules
• Chlorophyll


  The light-absorbing green-coloured pigment that begins photosynthesis
• Types of chlorophyll


  • Chlorophyll a (blue-green)
  • Chlorophyll b (yellow-green)
• Chlorophyll a


  Primary light-absorbing pigment, only pigment that can transfer solar energy to photosynthetic reactions
• Chlorophyll b


  Acts as an accessory pigment, absorbs photons that chlorophyll a can't absorb
• Chlorophylls a and b absorb visible light in red and blue regions of the spectrum and reflect visible light in the green region, which is why plants appear green
• In spring and summer, leaves are green due to lots of chlorophyll in their chloroplasts. Accessory pigments are still present but their colours are masked by the green light reflected by chlorophyll
• In fall, plants stop producing chlorophyll, and colours of accessory pigments are revealed, revealing yellow, red, and brown in the leaves
• Chloroplasts


  A membrane-bound organelle in green plant and algal cells that carries out photosynthesis
• Leaves are the primary photosynthetic organs of most plants
• Stroma


  The protein-rich semiliquid material in the interior of a chloroplast
• Thylakoids


  A system of interconnected flattened membrane sacs forming a separate compartment within the stroma of a chloroplast
• Grana


  Stacks of thylakoids
• Lamellae


  Groups of unstacked thylakoids between grana
• Photosynthesis occurs partly in the stroma and partly in the thylakoid membrane
• Thylakoid Membrane


  The photosynthetic membrane within a chloroplast that contains light-gathering pigment molecules and electron transport chains
• Thylakoid Lumen


  The fluid-filled space inside a thylakoid
• The thylakoid system's structure in a chloroplast increases the surface area of the thylakoid membrane, significantly increasing the photosynthesis efficiency
• Other compounds, called carotenoids, also act as accessory pigments. These and other accessory pigments transfer energy they absorb back to a molecule of chlorophyll a
• ATP (Adenosine triphosphate)


  A molecule containing three high-energy phosphate bonds that acts as the primary energy-transferring molecule in living organisms
• ATP

  • Used by plant and animal cells
  • Provides immediate energy for cellular functions, such as growth and movement, synthesis of needed chemicals, transport of materials across cell membranes
• Formation of ATP

  1. Addition of an inorganic phosphate group (PO4^3- or Pi) to a molecule of lower-energy ADP

  2. When ATP loses a phosphate group, it forms ADP and releases energy which is used for cellular processes
• ADP (adenosine diphosphate)


  A molecule containing two high-energy phosphate bonds that may be formed by breaking one of the phosphate bonds in ATP
• NADPH


  A compound that donates 1 hydrogen atom and 2 electrons to another molecule to reform NADP+
• NADP+ (nicotinamide dinucleotide phosphate)


  A compound that accepts 1 hydrogen atom and 2 electrons, forming NADPH
• The gain and loss of electrons (e-) from NADP+ and NADPH contributes to photosynthesis in several steps
• Overall Stages of Photosynthesis

  1. Capture solar energy and transferring it to electrons

  2. Using captured solar energy to make ATP and to transfer high-energy electrons to NADP+; yields NADPH, which is then used as a high-energy electron carrier molecule

  3. Use energy stored in ATP and high-energy electrons carried by NADPH to form energy-rich organic molecules, such as glucose from CO2
• Light-dependent reactions


  The first set (stages 1 and 2) of reactions of photosynthesis in which light energy excites electrons in chlorophyll molecules, powers chemiosmotic ATP synthesis, and results in the reduction of NADP+ to NADPH
• Light-independent reactions


  The second set (stage 3) of reactions in photosynthesis (the Calvin cycle); these reactions do not require solar energy