Examine the following figure and answer the questions below 38 mg \' . 4.3 ng .

Question

Examine the following figure and answer the questions below 38 mg ' . 4.3 ng . . . . : . .- No addition 0 10 20 30 40 50 60 Hours of illuminatior Figure 1. The influence of added phosphates on photosynthetic oxygen produc- tion by the marine diatom Phaeodactylum tricornutum (= Nitschia closterium). Flasks containing dense concentrations of the diatom were illuminated by two 500 watt lamps and incubated in a water bath at 15C. Numbers on the graph indicate the amount of added phosphate, in mg added per m3 of seawater 1. Looking only at the axes and the data, what do you know about how the study was done? 2. Looking now at the entire graph, including the figure caption, what else do you ow about how this study was done? What can't you tell about how the study was done? What specific question is being addressed in the portion of the study represented by the graph? Why would anyone want to ask the question referred to in Question 4? What is the most important result shown by the graph? 3. 4. 5. 6.

Explanation / Answer

1) From the above graph, it is understandable that, with no addition it has a steady increase in the amount of oxygen evolved. With increase in the amount added, the steepness of the graph increases. At very high level i.e at 38 mg after 30th hour of illumination there is no oxygen evolved. After the 50th hour of illumination it is seen that the oxygen evolution becomes quite slow as the line in the graph starts bending down.

2) This graph shows the relation between the amount of oxygen evolved after the addition of phosphate to the dense concentration of the diatom Phaeodactylum tricornutum which is already exposed to light. As per the given observation it is clear that at a particular hour of illumination there is a constant increase in the amount of oxygen evolved. With the addition of phosphate there is a rise in amount of oxygen evolving, As seen with the increase in steepness of the graph. At very high amount of phospates i.e at 38 mg the water gets saturated early i.e till 30th hour, hence, there is no evolution of oxygen beyond that. Similarly, in 8.7mg and 4.3mg addition it is seen that till 50th hour the saturation point is close. As a result, the line starts bending, due to slight decrease in oxygen production by the diatom. At 8.7mg the graph reaches the maximum distance, showing a high rate of oxygen evolved.

3) Whether it is just the addition of phosphates, that affects the oxygen production or some other factors are also involved.

4) The dependency of phosphate addition on the oxygen evolution in a photosynthetic diatom.

5) Phosphorus being an essential element of all life forms, plays a major role in biological reactions of any organism. Hence,it becomes important to understand it.

6)Phosphate addition enhances the oxygen evolution by the diatoms.

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