*Biology Paper 5 tips*

[knowitall10]

I am sorry to be asking this but can someone explain how should we describe Serial Dilution ?
( and the use of microscope to count cells, etc... A lot of questions are like this and I don't know how to write it in the right form :S )

for the microscope thing:
Place the sample on a gridded scale and count the number of cells in one square. don't include the cells which lie out of the square by more than half. then multiply this number by the total number of square the sample takes..and you have your approximate number of cells.
I hope i helped you..

 

[narutogirl]

Please...don't be sorry..this is why you're here

Thank you, that was very helpful

 

[knowitall10]

Thank you, that was very helpful

you're welcome

 

[narutogirl]

for the microscope thing:
Place the sample on a gridded scale and count the number of cells in one square. don't include the cells which lie out of the square by more than half. then multiply this number by the total number of square the sample takes..and you have your approximate number of cells.
I hope i helped you..

Okay that was helpful ( we mention here also the field of view and using the formula pir^2, right? ) okay another microscope question >.<"
When they talk about using a stage micrometer and a graticule and they divide by each other and convert the units, when they want to find the length or diameter this part is ultra confusing :S

 

[LMGD33]

Can I just marvel at your awesomeness from afar? These notes are spectacular and this thread is honestly the most helpful I've ever read! Without you, I doubt I would be handling P5 this easily especially without any lab work this entire year..
knowitall10 I just want to sincerely thank you and hope that God blesses you immensely for all the selfless work you've done for me and many others!
:$ have a great life!

 

[knowitall10]

Can I just marvel at your awesomeness from afar? These notes are spectacular and this thread is honestly the most helpful I've ever read! Without you, I doubt I would be handling P5 this easily especially without any lab work this entire year..
knowitall10 I just want to sincerely thank you and hope that God blesses you immensely for all the selfless work you've done for me and many others!
:$ have a great life!

OMG...so much praise for someone who doesn't deserve...thank you
I'm pleased to help all of u...i wish i could answer narutogirl 's question..bt i gotta go...please help her..

 

[LMGD33]

Okay that was helpful ( we mention here also the field of view and using the formula pir^2, right? ) okay another microscope question >.<"
When they talk about using a stage micrometer and a graticule and they divide by each other and convert the units, when they want to find the length or diameter this part is ultra confusing :S

The formula you mentioned is when you're trying to find the number of cells in a certain area, in that case, you would count the total number of cells in your field of vision, and then calculate the area of your field of vision, say 20 cells in 2.5cm^2 that would be 8 cells per cm^2

As for your other question, If we're talking about a certain length let's say of pollen tubes, then first the sample is placed on a slide and viewed under a microscope of high magnification, around x100. the length of the pollen tube is measured by eyepiece graticule units. Then the eye piece graticule is calibrated using a stage micrometer. The value of each eye piece graticule division is calculated by ( total length in mm of stage micrometer/total divisions of eyepiece graticule). EDIT: If the previous step is not clear, remember: the stage micrometer and the eye piece graticule must be superimposed, and only then do you use the TOTAL length and TOTAL divisions that are superimposed.
This value is in mm and hence must be converted to micrometer by x10^3. Finally the number of units that the length of the pollen tube covered is multiplied by the value of each eyepiece graticule division calculated above, and a final answer is obtained!
Hope this helps

 

[narutogirl]

The formula you mentioned is when you're trying to find the number of cells in a certain area, in that case, you would count the total number of cells in your field of vision, and then calculate the area of your field of vision, say 20 cells in 2.5cm^2 that would be 8 cells per cm^2

As for your other question, If we're talking about a certain length let's say of pollen tubes, then first the sample is placed on a slide and viewed under a microscope of high magnification, around x100. the length of the pollen tube is measured by eyepiece graticule units. Then the eye piece graticule is calibrated using a stage micrometer. The value of each eye piece graticule division is calculated by ( total length in mm of stage micrometer/total divisions of eyepiece graticule). EDIT: If the previous step is not clear, remember: the stage micrometer and the eye piece graticule must be superimposed, and only then do you use the TOTAL length and TOTAL divisions that are superimposed.
This value is in mm and hence must be converted to micrometer by x10^3. Finally the number of units that the length of the pollen tube covered is multiplied by the value of each eyepiece graticule division calculated above, and a final answer is obtained!
Hope this helps

Thank you so much, I just started studying 2 days ago, I am doing my best to at least write SOMETHING in that exam.
Do we calibrate the same way when trying to find the diameter in the field of view, or that won't be necessary?

 

[comrade]

Are these Teaching A2 Biology Practical Skills of any use? I was going through them. I'm not sure. Any suggestions?

Practical 1 - M(b)(c) The effect of light intensity on rate of the Hill reaction
Practical 2 - M(a)/S(b) The effect of nitrate concentration on the production of biomass by algae
Practical 3 - N (d)(m)Urine Analysis –Evaluating and reporting on observations
Practical 4 - Q(a) Systematics and classification
Practical 5 - R(a) Bacterial Transformation
Practical 6 - R(a) Extraction of DNA from Fruit and Vegetables
Practical 7 - R(g) Electrophoresis as a separation process
Practical 8 - S(d) The Effect of Penicillin on Bacterial Growth
Practical 9 - S(e) Producing a model industrial immobilised enzyme column
Practical 10 - T(a)(d) The structure of wind pollinated flowers and fruit.

 

[Amaryllis]

guys , how can i find the (degree of freedom) in paper 5 plzz help in http://papers.xtremepapers.com/CIE/...and AS Level/Biology (9700)/9700_w07_qp_5.pdf q3 table 3.1 how to complete it ..and q3 part b i and ii ...can anyone explain them plz.. and thanks
plzzz i need notes for the part talking about degree of freedom and chi-squared test

 

[NouranAyman]

Guys wat are we suposed to do tomorrow since day after is the exam,, any tips on what shud we do??? Idk i feel the paper is all about common sense
I have a Q also when do we say the result is significant or insignificant when value of x2 is greater than critical value or lower ? *confused* and what about t test is it same??

 

[Marks&Spencers]

Guys wat are we suposed to do tomorrow since day after is the exam,, any tips on what shud we do??? Idk i feel the paper is all about common sense
I have a Q also when do we say the result is significant or insignificant when value of x2 is greater than critical value or lower ? *confused* and what about t test is it same??

True, it is mostly common sense, but you have to practice a lot to get the hang of it and see what the examiners are usually looking for.
You say the difference is significant when the t or x2 values are greater than the critical value, not necessarily double, just greater. This is because, when you want to compare such values, you put in your mind the null hypothesis which is "there is no significant difference", but when you get a value larger than that of the critical one, then the probability of the null hypothesis being correct would be less than 0.05 (the threshold), so the null hypothesis is rejected, hence there is a significant difference.

 

[Marks&Spencers]

guys , how can i find the (degree of freedom) in paper 5 plzz help in http://papers.xtremepapers.com/CIE/...and AS Level/Biology (9700)/9700_w07_qp_5.pdf q3 table 3.1 how to complete it ..and q3 part b i and ii ...can anyone explain them plz.. and thanks
plzzz i need notes for the part talking about degree of freedom and chi-squared test

Regarding table 3.1, if you're wondering about how to complete the expected values, then look at page 8 of this thread. Someone had already asked this question and it was answered. Other than that, the rest of the columns just involve simple calculations.
I agree with you, sometimes that whole degrees of freedom thing can be really annoying, and to be honest I'm not still 100% sure I managed it perfectly or not, but from what I understood from doing past papers, when you're dealing with a x2 test, you look at the number of phenotypes/categories that you look at their expected and observed values, then minus one from that number. In that question, for example, there were 3 categories: grazed for 2 years, ungrazed for 10 years and ungrazed for 30 years. Degrees of freedom would therefore be 3-1=2.
When you're dealing with t tests, you look for the number of samples taken to calculate each mean, minus 1 from each, then add them together. For example, if they tell you that they obtained 10 leaves, measured the surface area of each and obtained a mean for their values, then brought another 10 leaves from a different plant, measured the surface area of each, and obtained a mean for their values. When you compare these 2 means (using a t test), the degrees of freedom would be (10-1) + (10-1) = 18.
Remember, the rule is (n-1). I hope you got it!
(Someone please correct me if I'm wrong, or add information I missed out on.

 

[Just visiting]

guys i need your help
when he asks for variables in experiments
when to put those like temp. and ph. and when to put those like conc. and time

 

[knowitall10]

guys i need your help
when he asks for variables in experiments
when to put those like temp. and ph. and when to put those like conc. and time

It depends on the question, really...like, temperature and pH are usually used for enzyme activity..or sometimes when the experiment is in a living organism in water..
concentration and time are usually for experiments like testing the effect of sucrose or testing permeability of a substance with a chemical...

 

[Just visiting]

Are these Teaching A2 Biology Practical Skills of any use? I was going through them. I'm not sure. Any suggestions?

Practical 1 - M(b)(c) The effect of light intensity on rate of the Hill reaction
Practical 2 - M(a)/S(b) The effect of nitrate concentration on the production of biomass by algae
Practical 3 - N (d)(m)Urine Analysis –Evaluating and reporting on observations
Practical 4 - Q(a) Systematics and classification
Practical 5 - R(a) Bacterial Transformation
Practical 6 - R(a) Extraction of DNA from Fruit and Vegetables
Practical 7 - R(g) Electrophoresis as a separation process
Practical 8 - S(d) The Effect of Penicillin on Bacterial Growth
Practical 9 - S(e) Producing a model industrial immobilised enzyme column
Practical 10 - T(a)(d) The structure of wind pollinated flowers and fruit.

why did u choose those 10 are the others out of syllabus or what

 

[Just visiting]

It depends on the question, really...like, temperature and pH are usually used for enzyme activity..or sometimes when the experiment is in a living organism in water..
concentration and time are usually for experiments like testing the effect of sucrose or testing permeability of a substance with a chemical...

sometimes temp. is invo;ved but its not written in ms

 

[knowitall10]

sometimes temp. is invo;ved but its not written in ms

Then there's probably an alternative or something...can you please give an example of such a question..if you have time?

 

[Just visiting]

Then there's probably an alternative or something...can you please give an example of such a question..if you have time?

now im so tired ill see tomorrow Isa
and thanks for ur efforts

 

[Just visiting]

and can u tell me y did that guy chose only those 10 practical exp. and not others