Electrons for this reduction reaction ultimately come from water (factor 4), which is then converted to oxygen and protons. If there is not enough water then carbon dioxide, the plant wouldn’t be able to produce any carbohydrates.
Energy for this process is provided by light (factor 1), which is absorbed by pigments (primarily chlorophylls and carotenoids). If there were not any light then the whole process could not take place.
Temperature increase (factor 2) affects the other key factors. As the temperature increases it increases the temperature of the water. As water temperature increases the:
- Rate of photosynthesis increases until plant suffers from heat stress
- Rate of plant growth increases
- Amount of dissolved oxygen decreases
- Metabolic rate of organisms increases thereby increasing the oxygen demand
- Vulnerability to toxic wastes can increase due to decrease in dissolved oxygen and stress of higher temperatures.
Therefore if the temperature increases the demand of oxygen increases.
I have chosen to investigate the light intensity further because light determines the whole process of photosynthesis and is the easiest to control in experimental conditions.
I am going to investigate how fast the rate of photosynthesis is by counting the bubbles of oxygen given off by the plant. My method for the experiment is as follows: I will shine a lamp on a test tube of water with a sample of Elodea in it, the lamp will act as the sun and will provide energy for the plant. I will test the elodea at different stages of light intensity by moving the distance from which the light shines. This should affect the rate of photosynthesis. When the light shines on the plant it acts with the chlorophyll in the plant and the carbon dioxide from water (taken up by the roots) and from the air to make glucose and oxygen.
6CO2 + 6H2O C6H12O6 + 6O2
Carbon Dioxide + Water Glucose + Oxygen
The glucose is then stored in the plant for energy and the oxygen is given off in bubbles.
To find out what range of results I should take I’m going to conduct a preliminary experiment. The method will be the same as above and I will start off by using the lamp very close and working my way back to a distance where the bubbles will be slower.
The results were:
We counted at 2cm but because the rate of bubbles given off were more than 2 per second we decided it would inaccurate to have the lamp so close because the readings would be wrong. This forced to decide to start our readings at 10cm. We stopped at 60cm because the rate of photosynthesis had halved its pace. We decided this would be a good area to study. We finally decided that it would be best going up in tens from ten to seventy.
To make sure are results are as accurate as possible we have decided to take three lots of readings and take an average. This would improve the accuracy in case we had accidentally counted wrong and had an anomaly.
I predict that the further away the lamp is, the slower the rate of photosynthesis will be because when the light is further away the light intensity is less and this would cause the rate of photosynthesis to slow because there will be less energy given by the light and taken in by the chlorophyll.
I plan to make my test as fair as possible by:
- Using the same lamp – this will make sure the same voltage of light is being used for each reading.
- Using the same sample of Elodea on the same day - This makes sure the Elodea is the same age for the experiment, if we left it too long it will become older and will grow bigger. Therefore making the rate of photosynthesis differ.
- Taking all the readings in the same lesson – This will make sure the CO2, temperature of water and the quantity of water remain the same, they will remain the same because there isn’t enough time for them to differ.
- Measuring correctly to the nearest millimetre - Otherwise the readings will be incorrect because the light intensity can be different if the lamp isn’t the correct distance away.
- Having the classroom lights turned off so the lights don’t affect the experiment – the rate of photosynthesis will be wrong if other lights interfere.
- Doing all the experiment in one room so the temperature is the same - keeping the temperature constant will make sure its only the change in light I am testing.
Equipment
Test tube, WaterElodea, Test Tube rack, Ruler, Lamp, Tweezers, Bucket and a Desk
Diagram
Test tube
Water Lamp
Elodea
Light
Test tube rack
