Biology P5 Doubts, Guess Papers, Important Concepts and Leaks.

[SB29597]

A Level Biology P5 Doubts, Guess Papers, Important Concepts and Leaks. Post them all here!
If you think anything is really important, cant figure something out, have a gut feeling about a concept being asked or have a useful friend- comment!

 

[Gummy Beat]

I still don't fully understand the t test and what to do with error bars (what is overlap)

 

[SB29597]

I still don't fully understand the t test and what to do with error bars (what is overlap)

Basically, an error bar is a graphical representation of the scope of error in the readings or the standard deviation. If you have two or more sets of data, and the error bars that you draw for the values at any point overlap, then it means that the difference between the two groups is not significant and in the even that they do not overlap, the difference is significant and can be attributed to a cause.
Does that make sense?

 

[Gummy Beat]

oh i get it now. But how do you draw the error bars on a graph (bar charts and histograms)
edit: And how do you know whether to use t test or chi squared test for an expirement
thanks in advance

 

[SB29597]

The T test is used to assess whether the means of data with normal distribution ( I really hope you take stat, otherwise you'll need to know a few basics of normal distribution) are significantly different. There is a formula given t= (mean of sample 1- mean of sample 2)/ {(SD of sample 1/ no of measurements in sample 1 ) + (SD of sample 2/ no of measurements in sample 2)} Dont worry they'll give you this formula. You plug the values in it, and you will obtain a number.
Then, you will have to calculate degrees of freedom. This you may have to remember, the formula is v= (number of values in sample 1 - 1) + (ninmber of values in sample 2 -1)
Next, they will ask you for a confidence level- 5%, 10% or something. Check the column in which that value is given, locate the row with the degree of freedom which you have obtained previously. So you will zero down on a single number. Subtract the greater value from the smaller value (the one in the table and your t test value). If the difference is greater than 0.05 for 5%, 0.1 for 10% (and so on) than the difference is not due to chance and can be attributed to another factor.

 

[SB29597]

oh i get it now. But how do you draw the error bars on a graph (bar charts and histograms)
edit: And how do you know whether to use t test or chi squared test for an expirement
thanks in advance

For that, you need to find the standard error, given by standard deviation/ sq root of number of measurements. Plot that value as a bar over the main bar or point- try googling around for images- you'll immediately understand when you read this explanation with a picture.

 

[sam1234]

In the questions for planning an investigation, is there a proper format? Or we can write randomly?

 

[sam1234]

If we need a solid co2 absorbant what do we use?

 

[Oishee Asif]

If we need a solid co2 absorbant what do we use?

Easiest I remember for CO2 absorbent:
KOH (potassium hydroxide) pellets.
Highly corrosive though, so you could write about safety precautions too. You'd have to replace them every time you repeated the experiment.

 

[SB29597]

If we need a solid co2 absorbant what do we use?

NaOH or KOH is good.

 

[SB29597]

In the questions for planning an investigation, is there a proper format? Or we can write randomly?

Write 8- 10 out of these:

Independent variable
Dependent variable
Standardizing variable
Dilution table
Procedure- in detail, at least 4 to 5 points
Control
Precautions/ Safety
Minimizing error

 

[abdul arham]

Write 8- 10 out of these:

Independent variable
Dependent variable
Standardizing variable
Dilution table
Procedure- in detail, at least 4 to 5 points
Control
Precautions/ Safety
Minimizing error

ok 1 guestion is that can i write as : DEPENDENT VARIABLE : 1 rate of photosynthesis ,2 amount of light absorbed ............................................................ or shall i only write 1 rate of photosynthesis , 2amount of light absorbed ......is there any need to write this kind of lines
Independent variable
Dependent variable
Standardizing variable

 

[SB29597]

ok 1 guestion is that can i write as : DEPENDENT VARIABLE : 1 rate of photosynthesis ,2 amount of light absorbed ............................................................ or shall i only write 1 rate of photosynthesis , 2amount of light absorbed ......is there any need to write this kind of lines
Independent variable
Dependent variable
Standardizing variable

There's no need to, if you mention the right stuff, but it's always best to.
CIE marking is crazy, and one really should not take risks.
It also makes more sense to write that.

 

[abdul arham]

okk thnak u sisiter!

 

[R.M2013]

A0A.

Can u please help me, They ask u to make solutions. How do we make simple dillutions from a given volume? (i hope u understand my question)

 

[SB29597]

A0A.

Can u please help me, They ask u to make solutions. How do we make simple dillutions from a given volume? (i hope u understand my question)

I assume you are asking about dilution.

This can be asked in two ways:-

We may be provided with a stock solution, and we have to dilute it.
I'm going to take an example.
Say we have 1% standard solution. And we need appx 10 cm3 of each diluted solution
So,

0.2%- 2 cm3 of sol + 8 cm3 of water
0.5%- 5 cm3 of sol + 5 cm3 of water
0.8%- 8 cm3 of sol + 2 cm3 of water

You get the drift.

Another way is that we need to prepare a solution.
Say we need to make a 1 mol/ dm3 sol of glucose

molecular formula of glucose is C6H12O16
relative atomic masses are: Carbon- 12, Hydrogen: 1 and Oxygen- 16
So relative molecular mass of glucose is (12*6)+(1*12)+(16*6) = 180

So, you take weight out 180g of glucose, mix it in a little water. Add watere to it till it reaches the 1 dm3 mark and viola! It's ready.
You can then use this to do serial dilutions too.

 

[nimzy95]

You can use the formulae c1/m1*v1 = c2/m2*v2 . This Is for proportion dilutions .

 

[nimzy95]

Does anyone know how to draw the error bar using standard error ? According to my book, we have to multiply the standard error by 2 :/ the marking schemes say differently though.

 

[Oishee Asif]

You can use the formulae c1/m1*v1 = c2/m2*v2 . This Is for proportion dilutions .

Could you state what each letter denotes?

 

[JoHN_95]

How to perform the proportional dilution..do we keep the m constant in the formula ?