A level Biology: Post your doubts here!

[backtodev]

Can someone explain how to find the independent and dependent variable ? For paper5

Independant = variable that YOU are changing
Dependant = variable that changes as a result of what you changed

e.g. experiment on finding optimum temperature for an enzyme's rate of reaction
What are you changing? Temperature. So it's the independent variable.
When you change the temperature, the rate changes i.e. the time taken for the enzyme reaction changes. So the dependant variable is the time taken for the reaction to occur/rate.

 

[hela]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s10_qp_11.pdf Q2 Q11 Q30 Q39
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s10_ms_11.pdf Q2 C 11 A 39 C 30 D

http://papers.xtremepapers.com/CIE/...and AS Level/Biology (9700)/9700_s06_qp_1.pdf Q12 D Q13 A Q22 C Q26 D
http://papers.xtremepapers.com/CIE/...and AS Level/Biology (9700)/9700_s06_ms_1.pdf

http://papers.xtremepapers.com/CIE/...and AS Level/Biology (9700)/9700_w06_qp_1.pdf Q13 C
http://papers.xtremepapers.com/CIE/...and AS Level/Biology (9700)/9700_w06_ms_1.pdf

http://papers.xtremepapers.com/CIE/...and AS Level/Biology (9700)/9700_s05_qp_1.pdf Q38 A

 

[backtodev]

hey are there any notes for biology paper 5. im finding it quite hard

check out the first two posts on this thread- they're really useful!
https://www.xtremepapers.com/community/threads/biology-paper-5-tips.27105/

 

[Alice123]

Irfan1995
I have an 84 in AS bio
in p4 i wnt get less dan 85
How much do i av to get in p5??? to get an A*???
honestly speaking i never knew b4, there was a syllabus fr p5
i'm really bad at diagrams...

 

[raamish]

check out the first two posts on this thread- they're really useful!
https://www.xtremepapers.com/community/threads/biology-paper-5-tips.27105/

thanku they are helpful

 

[Soldier313]

Aoa wr wb!
I wanted to know when is it appropriate to use the chi squared test, and when do we have to use the t-test?
If someone could please elaborate with examples?
JazakAllah khair

 

[Irfan1995]

Aoa wr wb!
I wanted to know when is it appropriate to use the chi squared test, and when do we have to use the t-test?
If someone could please elaborate with examples?
JazakAllah khair

When you are dealing with only one set of date: use chi-squared test
When you're comparing between two sets of data: use the t-test

Also, according to what I know, the chi-squared test is used for discontinuous data while the t-test is used for continuous data.

 

[Irfan1995]

Irfan1995
I have an 84 in AS bio
in p4 i wnt get less dan 85
How much do i av to get in p5??? to get an A*???
honestly speaking i never knew b4, there was a syllabus fr p5
i'm really bad at diagrams...

Using the Oct/Nov 2012 curve, to get an A*, you have to get 194/260
If you already got an 84 in AS, then you will need to get a total of 110/130 in your A2.
If you get an 85/100 in P4, then you must get 25/30 in P5 to score an A*
Good luck!

 

[raamish]

When you are dealing with only one set of date: use chi-squared test
When you're comparing between two sets of data: use the t-test

Also, according to what I know, the chi-squared test is used for discontinuous data while the t-test is used for continuous data.

qp: papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s10_qp_51.pdf
i wanted to know the answer to 1c(iii) and (iv) that if we are comparing two means like we are comparing two means of stomata number then we will use t test to compare the two means, so is the t test able to tell if difference between the two means is significant or not and rejects the null hypothesis?
and to state the null hypothesis do we always write that there is no difference in the two sets of data? just want to confirm

 

[raamish]

can anybody give an example of discontinous data and continous data where the chi squared test and t test is applied respectively?

 

[raamish]

how do we write in a sentence that for reliability we write that we are replicating the values at least 3 times and calculate mean. Can somebdy tell me the proper sentence we should use in all questions of outlining procedures that tells about this statement. Plzz help

 

[Soldier313]

When you are dealing with only one set of date: use chi-squared test
When you're comparing between two sets of data: use the t-test

Also, according to what I know, the chi-squared test is used for discontinuous data while the t-test is used for continuous data.

Thank you.
But if you could just clarify,
For qn 2 of this paper, we have two sets of data here, and yet we are using the chi-squared test, why is that?
And besides, isn't light absorbance continuous rather than discrete?


http://papers.xtremepapers.com/CIE/...nd AS Level/Biology (9700)/9700_w09_qp_52.pdf
http://papers.xtremepapers.com/CIE/...nd AS Level/Biology (9700)/9700_w09_ms_52.pdf

Thank you, and sorry for the trouble.

 

[raamish]

Thank you.
But if you could just clarify,
For qn 2 of this paper, we have two sets of data here, and yet we are using the chi-squared test, why is that?
And besides, isn't light absorbance continuous rather than discrete?


http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w09_qp_52.pdf
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w09_ms_52.pdf

Thank you, and sorry for the trouble.

maybe becuase pollen collected from same plant not two different plants. and its discontinous because its collected after the day is over not continously during the day. So thats why maybe its discontinous data. I need confirmation though.

 

[Soldier313]

maybe becuase pollen collected from same plant not two different plants. and its discontinous because its collected after the day is over not continously during the day. So thats why maybe its discontinous data. I need confirmation though.

Thank you for that, and yeah i hope someone can clarify.

 

[kingos3111]

HOW A LEVEL BIO GRADE IS CALCULATED SAY I GOT A D IN AS HOW CAN I GET IN A2

 

[Mairaxo]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s10_qp_11.pdf Q2 Q11 Q30 Q39
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s10_ms_11.pdf Q2 C 11 A 39 C 30 D

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s06_qp_1.pdf Q12 D Q13 A Q22 C Q26 D
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s06_ms_1.pdf

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w06_qp_1.pdf Q13 C
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w06_ms_1.pdf

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s05_qp_1.pdf Q38 A

may 2010- Q2- x400 is a very low magnification. U cannot see organelles. Try using the formula magnification= size of drawing/actual size. U will know that its hard to view cells less than 1mm in size at this mag.
Q11- its not c or d as we dont know anything about the heat capacity. Even i have the confusion and my teachers werent able to answer ehy its a and not b. sorry!
Q30 - its not a as blood never flows back through valves. its not b as theres no relation with the thinning and valve. its not c as blood enters the atrium still. so its d and it makes more sense
Q39 - nitrate turns in nitrogen gas only by denitrifyng bacteria. so it can be either b or c. Then NH4 turns into NO2 and NO3 by nitrifying bacteria so its c. nitrogen to NH4 is done by nitrogen fixing bacteria so it cannot be b.

May 2006 - Q12 - water moves in xylem by capillary action. the forces are transpiration pull, adhesive and cohesive forces. Cohesive force is force between water molecules. This helps rise water in a column.
Q13- temperature is rising from 37 to 80. It cannot be b or d because the concentration of products does not fall to zero. there wil be some products present. The answer is not c as wel because at 80 it wil denature so product concentration will be less and not maximum. so its A beacuse some products will form when temperature rises but when enzyme danatures no more products form and concentration remains the same and is constant.
Q22 - Its not A or B as both 14 and 15 should be present. The DNA replicates only one time. So it should have one parent strand of N15 and other strand is of N14. So it is C as it has both strands in one DNA. Its not D because D suggests that there are 2 DNA and 1 DNA has both N14 strands while the other 1 has N15 strands.
Q26 - Look in the book. Its just a diagram! Xylem has that structure and everyone knows xylem has vessels.
Oct 2006 - Q13 - its not D because it is affected. Its not a or b as the reaction does not decrease. its C. this is because increasing the concentration of substrate increases its chance to fit in enzyme so more products form and rate increases.
May 2005 - Q38 - from C and D it can be obtained. In B beans are used. They are leguminous plants so they have bacteria to produce NH4. But cereals and wheat dont so its A.

 

[Irfan1995]

Thank you.
But if you could just clarify,
For qn 2 of this paper, we have two sets of data here, and yet we are using the chi-squared test, why is that?
And besides, isn't light absorbance continuous rather than discrete?


http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w09_qp_52.pdf
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w09_ms_52.pdf

Thank you, and sorry for the trouble.

Hmm, maybe my previous explanation was a too simplistic one.
With a chi-squared test, you have expected values and observed values. The value of chi-squared just tells you how much the observed values deviate from the expected ones. You don't actually have two sets of data. You have one set of data (the observed values), and you're comparing it to a standard (the expected values).

In a t-test, you have two different sets of data. Neither one of them is "correct" or can be used as a "standard". You just have two different sets of values and you're trying to see how significant is the difference between them.

As for light absorbance, it's definitely discrete. The explanation that follows might be a bit difficult to understand if you don't take Physics (more specifically, quantum physics):
Electrons can only move within certain 'energy shells'. If a photon (whose energy is equal to the difference in energies between two shells) is provided, then an electron will be promoted to the next shell by absorbing the photon. This photon has a specific frequency/wavelength. The electron does not absorb a range of frequencies, only specific ones. This is why the frequency of light absorbed is discrete.

 

[Soldier313]

Hmm, maybe my previous explanation was a too simplistic one.
With a chi-squared test, you have expected values and observed values. The value of chi-squared just tells you how much the observed values deviate from the expected ones. You don't actually have two sets of data. You have one set of data (the observed values), and you're comparing it to a standard (the expected values).

In a t-test, you have two different sets of data. Neither one of them is "correct" or can be used as a "standard". You just have two different sets of values and you're trying to see how significant is the difference between them.

As for light absorbance, it's definitely discrete. The explanation that follows might be a bit difficult to understand if you don't take Physics (more specifically, quantum physics):
Electrons can only move within certain 'energy shells'. If a photon (whose energy is equal to the difference in energies between two shells) is provided, then an electron will be promoted to the next shell by absorbing the photon. This photon has a specific frequency/wavelength. The electron does not absorb a range of frequencies, only specific ones. This is why the frequency of light absorbed is discrete.

Thank you so much bro!
That helped a lot.
And yes, i do take physics (just didn't relate the bio to physics :/ )
Thanx again and sorry for the trouble.

 

[Soldier313]

For question 2 b ii of this paper, why does the ms state that the answer only has to be to 2 decimal places. And the er goes on to state that the answer should have been to 3 significant figures rather than 4. Isn't 0.66 2 sgf or am i confusing stuff here?


And for the same year, qn 3 b iii, how can we know that I (ma) is the smallest allele or the most negatively charged one? I mean we aren't provided with the direction of movement of the fragments.

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w08_qp_5.pdf
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w08_ms_5.pdf

Thank you

Irfan1995 and anyone else taking p5

 

[Alice123]

For w08
From Fig 3.1, we have 2 categories of alleles of the gene

1. membrane protein allele
2. muscle protein allele

Now for membrane protein alleles, IA and Ia(look at the fig)

• IA and Ia have equal frequency (you can easily count them)
• Ia is smaller and negatively charged. This is because, according to the technique of electrophoresis, the smaller fragments move faster towards they anode. (DNA is negatively charged phosphate backbone which are attracted towards the anode ie downwards) The smaller they are, they move faster and the more negatively charged they are.

For muscle protein allele:

• Ima is the smallest
• Imb is the largest among muscle protein allele

Overall notice that muscle protein alleles are smaller (more negatively charged) than muscle protein allele
hope i could help Soldier313