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Investigate which surface of a leaf loses more water by transpiration.

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Introduction

PLAN SECTION 1 An investigation into which surface of a leaf transpires more by transpiration. Brief statement of investigation I am going to investigate which surface of a leaf loses more water by transpiration. I will do this by covering certain sides in a layer of Vaseline. The Vaseline will prevent transpiration occurring on that particular side allowing me to see which side transpires more. Risk assessment The number of risks in this assessment is minimal but the following risks will be present: * Any leaves must not be consumed * Extreme care must be taken when handling glass Vaseline pots * Paper clips must be handled with care and must not be uncoiled * All personal property should be tucked away while the experiment is being carried out Independent variable The surface(s) covered by Vaseline i.e. topside or underside. Dependent variable The amount of transpiration that occurs from a particular surface and therefore the amount of weight lost due to transpiration from one particular surface. Number and range of readings I will be making one reading for each leaf after about 20 hours. SECTION 2 Prediction I predict that the underside of the leaf will transpire more. I also predict that the amount of transpiration that occurs from the two leaves with one surface vaselined will be roughly the same as the amount that occurs from the leaf with neither of its side's vaselined. ...read more.

Middle

ANALYSING EVIDENCE SECTION 1 Graphs Section 2 Process data and evidence The first graph shows that leaf 1 had the highest percentage weight loss followed by leaf 4 and then leaf 2 and 3. This supports my prediction that the underside of the leaf will transpire the most because leaf 1 is the leaf with just the underside showing. However, I did expect leaf three, the leaf with none of its surfaces Vaseline to transpire more than leaf 1 so this is an anomalous result. Also, this graph does not support my second prediction that the percentage weight loss of leaves 1 & 2 should roughly add up to the percentage weight loss of leaf 4 as they add up to a significant amount more. This all suggests that leaf 4 is a large anomaly. Section 3 Conclusion based on section 1 & 2 above From my evidence I conclude that more transpiration occurs from the underside of the leaf where the stomata are situated. Relate conclusion to detailed scientific knowledge The reason for my conclusion, similar to that of my first prediction since it proved to be right, is that the underside is covered in stomata pores, making it possible for water to leave the leaf when the pores are open. On the topside however, there are no pores, just a waxy layer instead. ...read more.

Conclusion

would result in the normal side receiving a boost from the wind (leaf 1), upsetting the balance. One may argue that if the unvaselined underside is facing the draught and so transpires extra, this is fair since you would expect it to transpire more anyway but we are not only looking for which side transpires more, we are also looking for particular relationships in the amount of transpiration between the leaves. Another way of curing this apart from putting the leaves in a draught free environment would be to point all of the vaselined sides the same way. All of what I have said here also applies to sunlight, and sources of either temperature or humidity. The only reason that we didn't do all this when we were carrying out our experiment was because we didn't think of it. Also, it may be necessary to revise the time period that I leave the leaves to transpire, because some of the smaller leaves may reach the end of their 'transpiration period' and so the bigger, chunkier leaves will have a larger percentage weight loss because they will continue to transpire for longer. A period of around 6 hours may have been a lot more suitable. Additional evidence Additional evidence such as results obtained by previous groups carrying out this same experiment would have been useful for me to compare my results with and see if they showed similarities. However, I did not have any previous results so I wasn't able to do this. ...read more.

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Here's what a teacher thought of this essay

3 star(s)

***
A sound summary of the investigation but results are not reliable and it lacks a detailed discussion of factors affecting the rate of transpiration. This gives the impression the author is not completely familiar with relevant concepts.

Marked by teacher Adam Roberts 18/07/2013

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