photosynthesis

• Plants and algae are the main ​producers​ of food, which they synthesise from sunlight in a process called ​photosynthesis​. They are also therefore the primary producers of ​biomass in all food webs and food chains.
• • Photosynthesis occurs in ​plants​ and ​algae​.
• • It is an ​endothermic​ ​reaction​, meaning that it takes in more energy than it releases.
• • Light energy from the environment is transferred to ​chloroplasts​ in leaves.
• The equation for photosynthesis is:

  lightcarbon dioxide + water → glucose + oxygen
• 1. Each compound has its own ​chemical symbol​: Carbon dioxide: ​CO​2Water: ​H​2O​Oxygen: ​O​2Glucose: ​C​6H​ ​12O​ ​6
• effect of temperature:

  With an increase in temperature, the rate of photosynthesis increases. As the reaction is controlled by ​enzymes​, this trend continues up to a certain temperature until the enzymes begin to ​denature​ and the rate of reaction decreases.
• effect of light intensity:

  For most plants, the higher the light intensity, ​the faster the rate of the reaction.
• effect of carbon dioxide concentration :

  For most plants, the higher the light intensity, ​the faster the rate of the reaction.
• By carrying out an experiment measuring​ ​the ​oxygen production ​of a plant, you can calculate the rate of photosynthesis.
• What is placed in the test tube for the experiment?

  Pondweed
• Why is the top of the test tube sealed with a bung?

  To prevent gas escape during photosynthesis
• What connects the test tube to the syringe in the experiment?

  A capillary tube with water
• What is the purpose of the lamp in the experiment?

  To provide light for photosynthesis
• How is the volume of oxygen produced measured in the experiment?

  By measuring the distance the bubble has moved
• What factors can be changed to observe their effect on photosynthesis?

  Temperature, time, and light intensity
• How can temperature be controlled in the experiment?

  Using a water bath
• What is the independent variable in this experiment?

  The factor being observed, like light intensity
• Why is it important to control all factors except the independent variable?

  To ensure a valid experiment
• What is the procedure for measuring oxygen production in the experiment?

  1. Place pondweed in a sealed test tube with water.
  2. Connect a capillary tube to a syringe.
  3. Position a lamp at a measured distance.
  4. Observe oxygen bubble movement in the capillary tube.
  5. Measure the distance moved to calculate oxygen volume.
• Light intensity is measured in lux
• Farmers can use the knowledge of limiting factors to enhance the conditions in the greenhouse for a greater rate of photosynthesis. This will increase growth leading to increased profits.
• We can set up a simple experiment to measure the rate of photosynthesis in a plant:We will need a ​sealed 100ml flask​ filled with ​water at room temperature​, a ​gas syringe​, a

  small amount of ​pondweed​, a small ​lamp​ and a ​1m ruler​.

  1. Use the ruler to place the flask and pondweed 15cm from the lamp.

  2. Leave the apparatus for around 10 minutes to allow the pondweed to adjust.

  Connect the gas syringe to the flask and record the change in volume on the syringe after 5 minutes.Move the lamp 10cm further away and measure the volume change again. Repeat.
• As mentioned above, light intensity is directly proportional to the rate of photosynthesis. This is because the greater the intensity of light, ​the more photons (light energy) hit the chloroplasts in the leaf​, and the ​more photosynthesis can occur at once
• It makes sense, then, that the opposite pattern can be seen between the rate of photosynthesis and the distance from the light source: ​inverse proportion​ describes a relationship between two factors which involves one increasing whilst one decreasing. As the distance between the light source and the plant increases, the light intensity decreases. The light intensity is inversely proportional to the square of the distance- called the ​inverse square law​.