3.4 biology

• Photosynthesis


  The process by which green plants make their own food
• Light reactions


  First stage in photosynthesis producing hydrogen and ATP required in the carbon fixation stage
• Chloroplasts


  An organelle containing chlorophyll which is the site of photosynthesis
• Chlorophyll


  Green pigment in chloroplasts that absorbs light energy for the process of photosynthesis
• ATP


  Adenosine triphosphate; a substance that transfers chemical energy in cells
• Enzyme controlled reaction


  A reaction which needs the presence of certain enzymes to continue
• Carbon fixation stage


  The second stage in photosynthesis in which ATP, hydrogen and carbon dioxide are involved in the production of sugar
• Carbohydrate


  A substance such as sugar, starch or cellulose, containing the elements carbon, hydrogen and oxygen
• Starch


  Storage carbohydrate in plants
• Respiration


  A way in which sugar is used in a plant to produce energy
• Cellulose


  A structural carbohydrate of which plant cell walls are composed
• Limiting factors


  • A variable that, when in short supply, can limit the rate of a chemical reaction such as photosynthesis
  • Examples are carbon dioxide concentration, light intensity and temperature
• Water


  The substance that is split up during the light reactions
• Hydrogen and oxygen


  The two substances that are produced when light energy is used to split up water
• Chemical energy


  The type of energy which is stored in sugar
• Uses of glucose made in photosynthesis

  • Used to make cellulose in cell walls
  • Used for respiration
  • Stored as starch
• Stages of Photosynthesis


  1. Light Reactions

  2. Carbon Fixation
• Light Reactions


  1. Occur in the chloroplasts

  2. Splitting of water into oxygen and hydrogen

  3. Oxygen is produced and excess oxygen diffuses into the air

  4. Light energy is converted to chemical energy in the form of ATP

  5. ATP and hydrogen are transferred to stage 2
• Carbon Fixation


  1. It is a series of enzyme controlled reactions that form a cycle

  2. ATP from stage 1 provides energy for this process

  3. Hydrogen from stage 1 combines with CO2 from the air to form glucose
• Limiting factors of photosynthesis

  • Temperature
  • Carbon dioxide concentration
  • Light intensity