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Edexcel AS Biology Unit 3 9th May 2016 Official Thread

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Guys, any tips for answering question 2? I always lose marks on it. I'm literally freaking out.


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Original post by bdoon esm
When to draw a bar chart and when to draw a scatter graph and a straight line graph?


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Draw a bar chart when the data you have been given are in groups usually when the x-axis aren't numbers but words like the experiment for deficiency in each mineral, the x axis would be mineral ions and y axis would be mean mass of plants. Draw a line graph if the data links with one another usually when x-axis are numbers like the experiment for effect of temperature of enzyme activity, x-axis would be temperature and y-axis would be enzyme activity. Anyways, I have noticed that for part two of the unit 3 biology paper, bar chart is usually the answer.
Reply 22
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this refers to the mineral ion deficiency practical...if they ask "what variables to control and how?" then that's the answer :smile:
Original post by Hiyoriiki
How do you increase the validity of an experiment and how does controlling variables increase reliability? 😦😦


To increase validity:
1) Compare experimental results with other similar experiments
2) Use of control in experiment.
3) Check bias of sponsors.
4) No overlapping of standard deviation.
5) Large sample.
6) Peer review.
7) Methodology to which the data is obtained.

Keeping all other factors constant increases reliability because we would without doubt know that all changes within an experiment is due to the specific factor. For example: Mineral deficiency, we need to find out the effect of mineral deficiency in plants so variables to keep constant are light intensity and temperature. Now, we want to make sure that all changes in growth of plants is due to mineral deficiency but not light intensity and temperature, therefore makes the results more reliable.

Hopefully this helps as I am also going to take the exam.
Original post by willandy123
to increase validity:
1) compare experimental results with other similar experiments
2) use of control in experiment.
3) check bias of sponsors.
4) no overlapping of standard deviation.
5) large sample.
6) peer review.
7) methodology to which the data is obtained.

Keeping all other factors constant increases reliability because we would without doubt know that all changes within an experiment is due to the specific factor. For example: Mineral deficiency, we need to find out the effect of mineral deficiency in plants so variables to keep constant are light intensity and temperature. Now, we want to make sure that all changes in growth of plants is due to mineral deficiency but not light intensity and temperature, therefore makes the results more reliable.

Hopefully this helps as i am also going to take the exam.

thank u for this OMGG
Original post by Saima Hasnain
Guys, any tips for answering question 2? I always lose marks on it. I'm literally freaking out.


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omg same :frown:
Original post by Willandy123
To increase validity:
1) Compare experimental results with other similar experiments
2) Use of control in experiment.
3) Check bias of sponsors.
4) No overlapping of standard deviation.
5) Large sample.
6) Peer review.
7) Methodology to which the data is obtained.

Keeping all other factors constant increases reliability because we would without doubt know that all changes within an experiment is due to the specific factor. For example: Mineral deficiency, we need to find out the effect of mineral deficiency in plants so variables to keep constant are light intensity and temperature. Now, we want to make sure that all changes in growth of plants is due to mineral deficiency but not light intensity and temperature, therefore makes the results more reliable.

Hopefully this helps as I am also going to take the exam.


Thanks a lot😊
How do you answer when you are told to compare the students experiment and another source? Like do you talk about the similarities and differences? Also, do you have to manipulate data in that question?


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Original post by Saima Hasnain
How do you answer when you are told to compare the students experiment and another source? Like do you talk about the similarities and differences? Also, do you have to manipulate data in that question?


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Yes, when comparing sources we have to talk about the similarities and differences and we have to manipulate the data as there will always be one mark for data manipulation.
Original post by Willandy123
Yes, when comparing sources we have to talk about the similarities and differences and we have to manipulate the data as there will always be one mark for data manipulation.


Thank you😊
Do you have any tips on question 2, I usually mess up there?


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Original post by Willandy123
Yes, when comparing sources we have to talk about the similarities and differences and we have to manipulate the data as there will always be one mark for data manipulation.


Data manipulation means calculating % difference??
When we draw graph with SD we add and subtract from that point
Eg. SD is 0.9 and mean is 66
So we add and subtract 0.9 from 66



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(edited 7 years ago)
Original post by bdoon esm
Data manipulation means calculating % difference??
When we draw graph with SD we add and subtract from that point
Eg. SD is 0.9 and mean is 66
So we add and subtract 0.9 from 66



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Data manipulation is when you use the graph and its data to explain e.g when you have a graph of temperature against mean vol. of juice needed to decolourise DCPIP, you explain using the numbers how as the temp increases the vol. also increases.


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How can we manipulate standard deviations? 😕
Original post by Hiyoriiki
How can we manipulate standard deviations? 😕


I'm not really sure, but when you talk about reliability usually you talk about whether the standard deviations are overlapping or their range.


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does standard deviation effect validity or reliability
Reliability.
If the standard deviation is low then data is reliable.
If the standard deviation is high then data is unreliable.

Also i was wondering if anyone has any notes (general) and any specific Vitamin C notes, seeing as though that's the expected experiment to come tomorrow.
Original post by Ali Bizri
Reliability.
If the standard deviation is low then data is reliable.
If the standard deviation is high then data is unreliable.

Also i was wondering if anyone has any notes (general) and any specific Vitamin C notes, seeing as though that's the expected experiment to come tomorrow.


Didn't overlapping standard deviations decrease validity?
Original post by Ali Bizri
Reliability.
If the standard deviation is low then data is reliable.
If the standard deviation is high then data is unreliable.

Also i was wondering if anyone has any notes (general) and any specific Vitamin C notes, seeing as though that's the expected experiment to come tomorrow.


How do you know vitamin C is gonna come tomorrow?
Reply 38
Original post by Saima Hasnain
I'm not really sure, but when you talk about reliability usually you talk about whether the standard deviations are overlapping or their range.


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No, when SD values are low, that shows reliability. When the error/SD bars overlap, this shows the data isn't valid, and so a conclusion cannot be made.
Original post by OmarKG
No, when SD values are low, that shows reliability. When the error/SD bars overlap, this shows the data isn't valid, and so a conclusion cannot be made.


Why is it then that when questions in the papers come on commenting on the reliability of a set of data, in the ms overlapping standard deviations are discussed?

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