The aim of the investigation is to determine factors affecting the rate of photosynthesis in plants, by using Canadian pondweed and counting the number of bubbles of O2 given out during a minute.

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Alexander Boothroyd 10iii        Biology Practical Assessment        07/05/2007

PLANNING

Introduction:

        The aim of the investigation is to determine factors affecting the rate of photosynthesis in plants, by using Canadian pondweed and counting the number of bubbles of O2 given out during a minute.

Variables:

As I am going to investigate the effect of CO2 concentration on the rate of photosynthesis, all other factors must be made constant; these include temperature, light intensity, length of shoot and as far as possible, the amount of foliage on each shoot, and the colour (how green) of the shoot. Any major changes in the above could result in a false set of readings.

Pilot Studies and Use of Knowledge:

        A pilot study explaining the effect of light intensity on photosynthesis of Canadian pondweed shows that as light intensity increases, the rate of photosynthesis follows suit.

In another pilot study, I found that a similar pattern emerges with rising temperatures. However, after a certain temperature (slightly lower than most enzymes), the rate slows down and, behaving according to the enzymes in the plant eventually stops as these enzymes are denatured.

        

Hypothesis/Prediction:

        I predict that as the concentration of CO2 will increase the rate of photosynthesis, thus the number of bubbles of O2 per minute will increase in number as the concentration of sodium hydrogen carbonate increases. However, I believe that past a certain concentration at a specific temperature and light intensity, the rate of O2 bubbles given out will not increase as there will be a maximum rate at which photosynthesis can be carried out, as for example there is a maximum rate at which a certain job can be done. Thus I predict that past a certain concentration the graph will level out to a plateau.

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Method:

        I shall cut a shoot of Canadian pondweed (with an approximate length of 5 cm) and place it in a boiling tube (containing 40 cm3 of distilled water), placing this in a water bath, heated to 25°C. To keep the shoot down below the surface of the water, we attached a paper clip. To keep the experiment fair, I shall try to cut shoots of similar ‘greenness’, length, and width, when the experiment carries over to another lesson. Then, having let the water equilibrate for half a minute, I shall count the number of bubbles given out at the ...

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