Method
To show the effects of oxygen and temperature: on the rate of germination.
Take a damp piece of cotton wool.
Roll in cress seeds.
Attach cotton wool to a piece of thread.
Attach thread to a rubber bung with a bent pin.
Add solutions to flasks A and B.
Put in the bung making sure that the cotton wool goes inside the flask.
Check once a day for six days.
Place in different places (for temperature experiment only).
To give a range of temperatures place them:
Freezer: -5 degrees Celsius
Fridge: -3 degrees Celsius
Windowsill: 12 degrees Celsius -17 degrees Celsius
Airing cupboard: 30 degrees Celsius
Oven: 50 degrees Celsius
If the moist cotton wool is rolled in the cress seeds, they will stick to it. The cotton wool must not touch the solution that is in the flasks and the bungs must make an airtight seal in the flask. Pyrogallic acid and sodium hydroxide absorb oxygen from the air, so the cress seeds in flask A are deprived of oxygen. Flask B is the controller. In the experiment germination is counted as when the seeds swell and spit open. To make it a fair test cover the seeds on the windowsill with black paper so the seeds have the same condition, like the rest. Check rate of germination after the given time. For the temperature experiment I used water in the flasks to make it a fair test.
Apparatus:
- Damp cotton wool, dampening is important to keep water available to the seeds.
- Seven flasks and bungs, to contain the experiment.
- Lots of cress seeds.
- Some thread, to hang the cotton wool.
- Bent pins to hang thread from.
- Pyrogallic acid.
- Sodium hydroxide.
- Black paper, to cover flask on windowsill.
Figure 1: The need for oxygen in germination
Oxygen:
Is necessary for germination because it is needed for respiration to perform both chemical and mechanical work. It must constantly make new cells and physically drive its roots downward and its shoot upwards. The energy required for this is released as a result of oxidation, which cannot start without a supply of oxygen.
Equation: Oxygen + Glucose= Carbon dioxide + Water
Results
Graph 1
Conclusion
The seeds in this experiment followed my predictions. As I predicted, no germination took place in flask A containing Pyrogallic acid and sodium hydroxide. This makes sense since seeds cannot respire without oxygen and this solution removes oxygen and carbon dioxide for the atmosphere. My second prediction was that the sodium hydroxide in Flask B would allow the cress seeds germinate faster as the solution removes carbon dioxide for the atmosphere, this could be because the oxygen will be acting as a catalyst, increasing respiration and therefore giving the seed more energy.
However, my results could have been inaccurate because:
The rubber bungs could have been fitted loosely in which case the solutions could have been contaminated.
The seeds that did not germinate could have been duds- meaning they could not germinate due to natural cause
Results
Graph 2
CONCLUSION
As expected, no seeds germinated in the freezer and the fridge. This is because the water in the seed could have frozen due to the low temperature. Also with low temperatures there will be no enzyme reaction and therefore the necessary processes cannot go on. No germination took place in the oven as predicted, this is because the temperature in there was 50 degrees Celsius, this high temperature denatures the enzymes which stops them fitting into their substrates and therefore the necessary processes cannot go on. In the airing cupboard 50% of the seeds germinated, this was 35% less then the seeds that germinated on the windowsill. My prediction for the airing cupboard was that the rate of germination should be double then that of the windowsill since the temperature is doubled. However my prediction proved incorrect the seeds on the windowsill germinated much faster then the airing cupboard and not all of the seeds in the airing cupboard germinated. There could be a number of reasons for this:
The seeds in the airing cupboard could have received less water compared to the windowsill. Which resulted in an unfair test since there was not enough water for the process of respiration etc.
After a day or so the temperature in the airing cupboard could have reached to 45 degrees Celsius, in which case the enzymes would have denatured stopping the seeds from germinating.
Some of the seeds in the airing cupboard may have been duds - which are naturally weak and unable to germinate.
Looking at the two variables together, I have come to the conclusion that temperature can be said to be the most important limiting factor in the rate of germination providing all other factors are constant. This is because when the seeds were put in two different solutions there was a huge difference between the total numbers of seeds germinated, the 0% of oxygen on seeds germination because if there is on oxygen available to the seeds no germination can take place, as the seeds cannot respire. I think temperature has quite a distinct effect on the rate of germination and is the main limiting factor. This is because {providing that no factors limit the process of germination} there is a particular range of temperatures in which seeds will germinate, 3 degrees Celsius – 45 degrees Celsius and if it the temperature dose not come in this range the enzymes will be denatured. Therefore looking at my results for the temperature experiment there is a huge difference between the total numbers of seeds that germinate in different areas, proving my theory that temperature is the main limiting factor in the rate of germination. However, it is not sensible to be sure that the predictions made are accurate, without having a wider range of oxygen solutions and temperatures. For example, in the temperature experiment the ranges of temperatures were -7C (freezer), -3C (fridge), 12C ---17C (window sill), 30°C (airing cupboard) and 50°C (oven). I do not think these are good ranges of temperature because there is a lot of difference in temperatures between the windowsill and the airing cupboard and it is possible that there is a big difference in the rate of germination that cannot be investigated, as the resources are not available.
Bibliography
G.C.S.E Biology second edition D.G. Mackean
ICS Biology Module B