B1.4 - Photosynthesis

    Cards (11)

    • What is photosynthesis?
      To make food plants need:
      • CO2 - diffuses from air into plant through stomata
      • Water - Enters roots through root hair cells by osmosis
      • These substances react to make glucose, which is used by plants for food
      • Oxygen is also made and used for respiration
    • Where does photosynthesis happen?
      • Happens in chloroplasts
      • Mainly in the leaf but some happens in the stem
      • Light transfers energy from Sun to Chlorophyll where CO2 + H2O makes Glucose
      Stage 1 (light dependent) - Energy transferred from lights splits water into Oxygen and H+ ions
      Stage 2 (light independent) - CO2 combines with H+ ions to make glucose
    • Photosynthesis is an endothermic reaction
    • How is the glucose used
      • Used immediately in respiration
      • Converted into sugar molecules e.g fructose/sucrose
      • Glucose that is not needed straight away turns into starch which can be used at night for respiration
      • Cellulose to form cell walls
    • Testing for starch
      • You can show light, chlorophyll and CO2 are needed for photosynthesis by testing presence of starch in a leaf
      Steps:
      • Place leaf in boiling water to kill it
      • The place it in tube of boiling ethanol to remove chlorophyll
      • Wash leaf to remove ethanol
      • Drop iodine onto leaf
      • If it turns blue-black then starch is present
      If starch is not present then it is unable to photosynthesise
    • Proving chlorophyll is needed for photosynthesis
      • Variegated leaves only have chlorophyll on some parts which means only parts are green
      • To prove chlorophyll is needed place destarched variegated plant in sunlight for several hours
      • Then test for starch
    • Proving light is needed for photosynthesis
      • Take a destarched plant and cover part of it with black card
      • Place plant in sunlight for several hours and test for presence of starch
    • Proving CO2 is needed for photosynthesis
      • Take destarched plant and place it in a polythene bag with soda lime(which absorbs water + CO2)
      • Place in sunlight for several hours before testing for starch
    • Proving Oxygen is given off in photosynthesis
      • Place upside down tube above an aquatic plant
      • Put it in light for maximum photosynthesis
      • Then put a glowing split in the tube and if it relights oxygen is present
    • Factors affecting the rate of photosynthesis
      Light Intensity:
      • The higher the light intensity the greater the rate of photosynthesis
      • This continues until light reaches maximum rate
      CO2:
      • Greater the CO2 concentration, the greater the rate of photosynethesis
      • But there is little CO2 in atmosphere so it is a limiting factor
      Temperature:
      • As it increases so does rate of photosynthesis
      • But it is controlled by enzymes so once optimum rate passes enzymes denature slowing it down
    • Interaction of limiting factors
      To check effects on photosynthesis
      • Light intensity - place light sources at diff distances from plant
      • CO2 - Add diff masses of KHCO3 to H2O as it releases CO2
      • Temperature - Place apparatus in water bath at diff temperatures