B1.4 - Photosynthesis

• • During photosynthesis, photosynthetic organisms, such as green plants and algae use energy from the Sun or an artificial source to make glucose.
  • Some of the glucose is used to make larger, complex molecules that the plants or algae need to grow. These make up the organism's biomass - the mass of living material.
  • The energy stored in the organisms' biomass then works its way through the food chain as animals eat them and each other.
• Photosynthesis

  • Photosynthesis happens inside chloroplasts - they contain chlorophyll which absorbs light.
  • Energy is transferred to the chloroplasts from the environment by light.
  • This is the equation for photosynthesis: Carbon dioxide + water --> glucose + oxygen 6O2 + 6H20 --> C6H12O6 + 602
• Photosynthesis is an endothermic reaction, energy is transferred from the environment during it
• Stages of photosynthesis

  1. Energy from light is used to split water into oxygen and hydrogen ions

  2. Carbon dioxide gas combines with the hydrogen ions to make glucose
• The rate of photosynthesis is affected by light intensity, CO2 concentration, and temperature. Any of these three factors can become the limiting factor. This just means that it's stopping photosynthesis from happening any faster.
• Investigating the rate of photosynthesis using pondweed

  • As the pondweed photosynthesises, the oxygen released will collect in the capillary tube.
  • At the end, the syringe is used to draw the gas bubble in the tube up alongside a ruler and the length of the gas bubble is measured. This is proportional to the volume of O2 produced.
  • Repeat experiment to test a range of values for the factor being investigated, e.g. a range of different temperatures. 
  • Variables other than the one being investigated should be kept the same. E.g. the other limiting factors, the time the pondweed is left for.
• light intensity

  •  Light transfers the energy needed for photosynthesis.
  • As the light level is raised, the rate of photosynthesis increases, but only up to a certain point.
  • Beyond that, it won't make any difference it'll be either the temperature or the CO2 level which is the limiting factor.
  • You can investigate light intensity by moving a lamp closer to or further away from your plant. You can't plot the rate of photosynthesis against "distance of lamp from the plant", you either need to measure the light intensity at the plant using a light meter or do math.
• CO2 concentration

  • CO2 is one of the raw materials needed for photosynthesis.
  • As with light intensity the concentration of CO2, will only increase the rate of photosynthesis up to a point. After this, the graph flattens out showing that CO2 is no longer the limiting factor.
  • As long as light and CO2 are in plentiful supply then the factor limiting photosynthesis must be temperature.
  • There are loads of different ways to control the concentration of CO2 E.g. dissolve different amounts of sodium hydrogen-carbonate (which gives off CO₂) in the water.
• Temperature

  • Usually, if the temperature is the limiting factor, it's because it's too low the enzymes needed for photosynthesis work more slowly at low temperatures.
  • But if the plant gets too hot, the enzymes it needs for photosynthesis and its other reactions will be denatured - the rate of reaction decreases dramatically.
  • This can start to happen at about 45°C 
  •  Experimentally, the best way to control the temperature of a boiling tube is to put it in a water bath.
• Pondweed:

  -The rate at which the pondweed produces oxygen corresponds to the rate at which it's photosynthesising - the faster the rate of oxygen production, the faster the rate of photosynthesis.

  • The amount of oxygen collected is not the total amount produced by photosynthesis, some of it is used up in respiration.

  A) capillary

  B) O2

  C) O2 bubble

  
• Inverse square law:

  The distance from the lamp and light intensity are inversely proportional to each other this means that as the distance increases, the light intensity decreases. However, light intensity decreases in proportion to the square of the distance. This is called the inverse square law and is written like this: 

  A) light intensity

  B) 1

  C) distance

  D) 2

  
• Temperature:

  A) denatured

  
• Light Intensity:

  A) light intensity

  B) CO2

  C) temp

  
• Carbon Dioxide:

  A) light

  B) light

  C) temp

  D) CO2