Lesson 2

• Photosynthesis

  • Capturing and using solar energy
  • Store energy
• • From the Greek words:
  • PHOTO = produced by light
  • SYNTHESIS = a whole made of parts put together
• PHOTOSYNTHESIS is the process whereby plants, algae, some bacteria, use the energy of the sun to synthesize organic compounds (sugars) from inorganic compounds (CO, and water).
• What photosynthesis does:

  • Converts sunlight into stored chemical energy.
• What photosynthesis does:

  • Makes carbon compounds that can be broken down for energy or used to build tissue.
• • Photosynthesis is an Endergonic process because energy is consumed by the process.
• This diagram shows that photosynthesis is an endergonic reaction because it takes in energy.

  
• • Carbon for making carbon compounds (such as sugar) comes from the atmosphere. Oxygen, hydrogen, and minerals are needed also.
• • Oxygen and hydrogen come from water. Minerals comes from the soil
• Plants make carbon-based molecules from raw inorganic compounds.

  
• • Plants use the organic carbon compounds as “food” and to build cell parts.
• Organic molecules are molecules that contain Carbon and Hydrogen
• • The function of the chloroplast is to gather light energy and convert it into chemical energy
• • Light energy is “captured" by chlorophyll, which is embedded in the thylakoid membranes.

  
• • Energy from the light-dependent reactions drives the reactions where carbon compounds are produced.
• ATP and NADPH are used to move energy from one part of the chloroplast to another.

  
• • ATP made in the chloroplast is ONLY used to power production of carbon compounds. It is not available to the rest of the cell
• Note: The Light and “Dark” or Carbon reactions happen at different sites in the chloroplast.
• I. The Light Reactions

  1. Light dependent
  2. Occur in the thylakoid membrane of chloroplast
  3. Water is split into oxygen gas (O2) and H+
  4. Use light energy (photons) to generate two chemical energy compounds: ATP & NADPH
• II. The“Dark” or Carbon Reactions

  1. Light independent (can occur in light or dark; some enzymes require activation by light)
  2. Occur in the stroma of chloroplasts
  3. Use the chemical energy produced in Light -Reactions (ATP; NADPH) to reduce CO2 to carbohydrate (sugar).
  4. CO2 is converted to sugar by entering the Calvin Cycle
• The Calvin Cycle - Named after Melvin Calvin

  
• Calvin cycle has 3 phases, 13 steps
• In calvin cycle, CO2 goes 6 cycles to produce 1 glucose
• • First product is a 3-carbon molecule: 3-PGA (phosphoglyceric acid). That’s why it’s also called C-3 cycle.
• • Enzyme RUBISCO (ribulose bisphosphate carboxylase/oxygenase) is the main enzyme that catalyzes the first reactions of the Calvin Cycle.
• • RUBISCO: Is the most abundant protein on earth!
• Summary - Light Dependent Reactions

  1. Overall input light energy, H2O.
  2. Overall output ATP, NADPH, O2.

  
• Summary - Light Independent Reactions

  1. Overall input CO2, ATP, NADPH.
  2. Overall output glucose.

  
• Overall, the light-dependent reactions capture energy.
• Overall, the light-independent reactions make carbon compounds.
• In photosynthesis, water is split in order to release oxygen.
• In photosynthesis, light energy is captured by Chlorophyll.
• The membrane protein that makes ATP is ATP synthase.
• The source of carbon to make carbon compounds in photosynthesis is Carbon dioxide. 
• The breaking down of ATP to power molecule synthesis happens in C3 cycle.
• Plant cells need ATP to run cell processes. These ATP came from Cellular respiration.
• • Photosynthesis does NOT supply energy to the cell. Photosynthesis USES light energy to make organic compounds.
• To get energy for the cell, plant cells must use cellular respiration to break down glucose and make ATP.
• While animals can only do cellular respiration,

  plants make “food” using photosynthesis and break the “food” down for energy in cellular respiration.
• Cellular Respiration