photosynthesis

• Mitochondria produce energy through aerobic respiration.
• Carbon Dioxide + Water → Oxygen + Glucose
• Photosynthesis takes place in the chloroplasts of leaf cells. These contain chlorophyll to absorb light energy. Leaves are broad + flat so there is a large surface area for maximum exposure to absorb light. The chemical reactions of photosynthesis within the cells are controlled/catalysed by enzymes
• Testing a leaf for starch

  1. Place leaf in boiling water to kill the leaf - stop photosynthesis
  2. Boil leaf in ethanol to remove chlorophyll
  3. Place leaf in boiling water to soften it
  4. Place leaf on white tile to see colour change
  5. Add Iodine to leaf surface to test for starch
  6. If it is present it will turn blue black - if not it will stay brown
• The three main factors that affect the rate of photosynthesis are :

  • CO2 concentration
  • Light intensity
  • Temperature
• Between points A and B we can see light intensity is the limiting factor - as light intensity increases, rate of photosynthesis increases. However through point B and C we can see that light intensity is not the limiting factor - It must be temperature or CO2 concentration

  
• Carbon dioxide is needed for photosynthesis. Increasing the carbon dioxide concentration increases the rate of photosynthesis, provided the plant is warm enough, and has plenty of light and water. However at points B and C we can see that CO2 concentration is no longer the limiting factor, so it must be light intensity or temperature.

  
• During photosynthesis:

  • light energy is absorbed by chlorophyll - a green substance found in chloroplasts in the palisade cells in the leaf
  • absorbed light energy is used to convert carbon dioxide (from the air) and water (from the soil) into a sugar called glucose
  • oxygen is released as a by-product
• We can see as temperature increases, rate of photosynthesis increases - more enzyme-substrate-complexes are made and more successful collisions. However as it increases it reaches optimum temp at 25 degrees and further than that, enzymes will start to denature (active site changes shape), less successful collisions and the rate of photosynthesis decreases

  
• (1) - What it is

  Experiment to investigate effect of light intensity in rate of photosynthesis - light is a factor that affects rate of photosynthesis, in this investigation a green plant (canadian pondweed - eldoea)will produce bubbles as a result of photosynthesis. Number of bubbles produced is affected by light intensity
• (2) - Equipment needed

  1 250cm.  beaker, 1 lamp

  1 glass funnel, 1 plasticine

  1 boiling tube, 8cm length of pondweed (Elodea)

  1 metre ruler ± 1mm, sodium hydrogen carbonate powder

  1 clamp stand, clamp and boss, 1 spatula
• (3) -method

  1. Place elodea in beaker containing 200cm³ of water
  2. Add on spatula of sodium hydrogen carbonate to the water
  3. Stick 3 small piece of plasticine to rim of funnel and place upside down over the plant
  4. Place lamp 5 cm away from apparatus
  5. Start stopwatch and record number of bubbles of oxygen produced in one minute
  6. Repeat experiment with lamp 10cm to 30 cm from apparatus - (every 5cm)
  7. Repeat steps 5-7 one more time
• (4) - Experiment

  A) Lamp

  B) boiling tube

  C) metre ruler

  D) Clamp stand

  E) glass funnel

  
• How to alter method of light intensity on photosynthesis to see effect of temperature on photosynthesis

  • Repeat experiment the same except this time lamp stays same distance away because it is a control variable
  • Put beaker containing plant into a thermostatically controlled water bath or place a bunsen burner underneath to vary temp (5 temperatures is range minimum)
  • use thermometer to monitor temperatures
• What happens to the glucose made in photosynthesis by plants?


  Glucose is broken down during respiration to release stored energy for life processes. Glucose is stored as starch in plants but as glycogen in animals.
• Light Intensity

  light intensity x 1/distance²
• Process of photosynthesis

  Light energy absorbed by chlorophyll

  Light energy is used to convert CO2 and Water to Glucose and Oxygen

  Oxygen released as by product

  Glucose is used or stored as starch
• PHOTOSYNTHESIS is the chemical reaction plants use to make food from light energy, CO2 and water. Oxygen is a waste product from this reaction
• If CO2 conc. and temp are at optimum levels for photosynthesis, increasing light intensity will increase rate of photosynthesis but up to a point explain why?

  Light is no longer a limiting factor and its not CO2 or temp so t must be that all chlorophyll is saturated and cannot absorb any more light
• Light energy → Chemical energy
• The leaf is the organ of the plant which carries out photosynthesis
• Why is the leaf considered an organ

  Leaves are the main photosynthetic organs of plants and are filled with palisade cells that have the chloroplasts needed for photosynthesis. 
• The role of CO2 in photosynthesis is to provide the Carbon and Oxygen found in glucose
• light is required in photosynthesis because it provides energy required for the chemical reactions
• Why is photosynthesis important?

  • produces glucose which is used in respiration to release energy
  • Glucose used to make complex organic molecules which are used for growth in plants
  • These organic molecules are transferred between organisms in the food chain
  • Produces oxygen why is required by organisms for respiration
• Glucose can be used for respiration to release energy

  Glucose can also be transformed into -

  • Starch for storage
  • Cellulose for cell walls
  • Proteins for growth
  • Oils for storage
• Photosynthesis alone cannot supply the plant with protein. What else is necessary?

  Proteins need nitrogen as well, but that is absorbed from the soil in the form of nitrates.
• A student said that plants photosynthesise during the day, but respire at night. Why is this statement incorrect?

  Photosynthesis in plants occurs only during the day when there is the sunlight but plants respire throughout the day and night. To carry out the process of photosynthesis, sunlight is important for the plant.
• In the daytime, water loss is bound to happen, but at night, when no photosynthesis can occur, the loss of water would be a complete waste. To reduce this water loss, the guard cells around each stoma can change shape and cause the stomata to close