Photosynthesis

• What is photosynthesis?

  Photosynthesis is a process where carbon dioxide and water is used to create glucose and oxygen
• What is the word equation for photosynthesis?

  A) Carbon dioxide

  B) Water

  C) light

  D) Chlorophyll

  E) Glucose

  F) Oxygen

  
• What is the symbol equation for photosynthesis?

  6CO2 + 6H2O -> C6H12 O6 + 6O2
• Photosynthesis is an endothermic reaction.
• The light energy required is absorbed by a green pigment called chlorophyll
• Chlorophyll is located in chloroplasts in plant cells
• What are the limiting factor of photosynthesis?

  carbon dioxide concentration, temperature, amount of chlorophyll, light intensity
• Initially, increasing temperature increases the rate of photosynthesis, as more energy is provided. Above a certain temperature (about 45 degrees Celsius), the enzymes involved in the reaction begin to denature and, consequently, the rate of the reaction begins to drop sharply until it stops altogether.
• Photosynthesis takes place inside the chloroplasts that are found in plants and algae. The reaction is endothermic, meaning that it requires energy. The source of this energy is sunlight, which is trapped in the chloroplasts by the chemical, chlorophyll.
• In an experiment using pondweed to investigate the effect of light intensity on the rate of photosynthesis, the light intensity is the independent variable and the number of bubbles is the dependent variable.
• The aim for the photosynthesis practical would be to investigate the effect of light intensity on the rate of photosynthesis.
• What would the independent variable be for the photosynthesis practical?

  Distance from light intensity
• what is the dependant variable for the photosynthesis practical?

  the number of bubbles produced per minute.
• what is the control variable for the photosynthesis variable

  Temperature of the pondweed
• increasing the temperature will increase the rate of photosynthesis up to a certain temperature because the enzymes will have more kinetic energy and are therefore more likely to successfully collide with the substrate. This means that temperature is the limiting factor.

  When it reaches the optimum temperature, the enzymes are most active and the rate of photosynthesis is at its highest – temperature is not the limiting factor. 

  Temperature becomes the limiting factor once again when raised above the optimum because the enzymes will start to denature.  
• Plants require carbon dioxide to photosynthesise. 

  If the carbon dioxide concentration is too low, it becomes the limiting factor. In order to increase the rate of photosynthesis, carbon dioxide concentration must be increased.

  After a certain point, increasing the carbon dioxide concentration will not increase the rate of photosynthesis because other factors will become limiting. 
• More than one factor can influence the rate of photosynthesis. 

  The graph shown the effect of both temperature and light intensity on the rate of photosynthesis.

  Increasing the light intensity increases the rate of photosynthesis up to a point. When the lines begin to level off, light intensity is no longer limiting. 

  However, low temperature can also limit the rate of photosynthesis. The 10°C10°C line levels off at a much lower rate that the 20°C20°C line. 

  
• Doing the experiment 

  1. Place a piece of freshly cut pondweed in a boiling tube filled with sodium hydrogen carbonate solution.  
  2. Place the boiling tube 10 cm away from a lamp.
  3. Switch the light on and leave for 5 minutes, bubbles should start appearing from the end of the pondweed.
  4. Start the stopwatch and count and record the number of bubbles produced in 1 minute.
  5. Repeat the count at this distance twice more in order to calculate the mean number of bubbles per minute. 
  6. Repeat the experiment with the boiling tube at different distances from the lamp.
• as the temperature increases, the enzymes can move faster and carry out their jobs more efficiently
•  When the temperature gets too high, the enzymes can denature
• When the carbon dioxide concentration is increased, the rate of photosynthesis also increases
• if we increase the carbon dioxide concentration after it reaches its optimum, the rate of photosynthesis will not increase any further.