Photosynthesis

• The equation for photosynthesis is the reverse of aerobic respiration: carbon dioxide + water → glucose + oxygen
• Photosynthesis occurs in chloroplasts in the leaves, which contains a green pigment called chlorophyll that absorbs light energy from the sun.
• Stomata are tiny holes found on the underside of the leaf that opens for carbon dioxide to diffuse in and oxygen (a waste product) to diffuse out. The stomata are controlled by guard cells which open and close the stomata.
• Root hair cells cannot photosynthesise because they do not contain chloroplasts. There is no chlorophyll in the root hair cells so they cannot absorb light. Root hair cells have adapted to not contain this because they are found in the roots of the plant which is underground so they are unable to absorb light energy.
• The three organelles that only plant cells contain are chloroplasts, a vacuole and a cell wall
• The (balanced) symbol equation for photosynthesis is: 6CO2 + 6H20 → C6 H12 O6 + 6O2. The reaction requires light energy for it to take place.
• Photosynthesis is an endothermic reaction as it takes in energy from the environment to the chloroplasts by light.
• Water is taken up from the soil by the roots and transported to the leaves via the xylem.
• The glucose made during photosynthesis can be used for storing starch for later use (such as when photosynthesis isn't happening as much like in the winter), and for respiration.
• Plants get the water required for photosynthesis from the soil by absorbing it through their roots into the root hair cells by osmosis.
• Starch is a useful long term storage molecule because:

  • It is compact
  • It can easily be broken down when needed
  • It is insoluble in water
• There are 5 main uses of glucose in plants:

  • Cellular respiration - breaks down the glucose to release energy
  • Makes cellulose - used to make strong cell walls
  • Makes starch - used to store glucose for a later time
  • Makes amino acids - used to make proteins
  • Makes lipids - stores the energy as fats or oils for later use