A level Biology: Post your doubts here!

[magnesium]

Q16- phosphate and hydrophilic head occupies less space. Hydrocarbon chains are large and have a chain structure.
Q29- xylem is dead. heating will not affect it. only phloem will get affected.
Q30- xylem will be affected 1st. water moves through xylem and its the appoplast pathway. so if fungi grow there it gets affected.
Q 38- photosynthesis is needed for growth and respiration as it provides glucose. so 21500*500*1500=23500
Q7- water potential=solute potential+pressure potential. water and solute potential are equal so pressure is 0

XYLEM IS APOPLAST PATHWAY?why did u multiply 21500 ,500,1500 ,,i guess 21500 and 1500 must b added

 

[Mairaxo]

XYLEM IS APOPLAST PATHWAY?why did u multiply 21500 ,500,1500 ,,i guess 21500 and 1500 must b added

sorry typing error! i meant + not * yes xylem is appoplast

 

[Noor Ahmad]

20 x 2 = 40 - 2 = 38

Thank youu!

 

[Irfan1995]

Question 3b (iv) How do we find the number of degrees of freedom?
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s09_qp_5.pdf

degrees of freedom = (number of readings in the 1st set - 1) + (number of readings in the 2nd set - 1)
or, degrees of freedom = TOTAL number of readings - 2
The two formulae are exactly the same thing.

They tell you in the question that the pH was measured at hourly intervals for 20 hours, so each set has 20 readings.
degrees of freedom = (20 - 1) + (20 - 1) = 38
Using the second formula, degrees of freedom = (20 + 20) - 2 = 40 - 2 = 38

 

[Noor Ahmad]

degrees of freedom = (number of readings in the 1st set - 1) + (number of readings in the 2nd set - 1)
or, degrees of freedom = TOTAL number of readings - 2
The two formulae are exactly the same thing.

They tell you in the question that the pH was measured at hourly intervals for 20 hours, so each set has 20 readings.
degrees of freedom = (20 - 1) + (20 - 1) = 38
Using the second formula, degrees of freedom = (20 + 20) - 2 = 40 - 2 = 38

THANK YOUU!

 

[dornam]

Am I right in that the question 1 papers from a year (let's say 2010 May / June, there are the papers 11, 12, 13), are actually the same ones but with another order of the questions?

 

[Noor Ahmad]

When is chi-square test used and when is t-test used?

 

[Twinks05]

Yes can someone explain to me what is T test and when is it used in comparison to the chi square test?

Also any idea as to what may come in paper five this year?

 

[Irfan1995]

When is chi-square test used and when is t-test used?

Chi-squared: comparing one set of data to a 'standard'/'expected'. Used for discontinuous data.

T-test: comparing two sets of data. Used for continuous data that can be normally distributed.

 

[oldfashionedgirl]

Chi-squared: comparing one set of data to a 'standard'/'expected'. Used for discontinuous data.

T-test: comparing two sets of data. Used for continuous data that can be normally distributed.

Could you please explain q3, (b) (ii)......the one about probability.

http://papers.xtremepapers.com/CIE/...and AS Level/Biology (9700)/9700_w07_qp_5.pdf

and one more question i have is regarding the number of degrees of freedom....earlier in this thread you specified a formula which i used in this same question, (b) (i)
but the answer i got wasn't correct ?!
Some help would be appreciated, thanks.

 

[Noor Ahmad]

Chi-squared: comparing one set of data to a 'standard'/'expected'. Used for discontinuous data.

T-test: comparing two sets of data. Used for continuous data that can be normally distributed.[/quote

THANKS AGAIN!

 

[Noor Ahmad]

Chi-squared: comparing one set of data to a 'standard'/'expected'. Used for discontinuous data.

T-test: comparing two sets of data. Used for continuous data that can be normally distributed.

but...how do we know if the data is continous/normal?

 

[ahmed abdulla]

just tell me the way plz ...
h4rriet

 

[Irfan1995]

just tell me the way plz ...
h4rriet

I think the only way is to get a ruler and measure the distance. Convert it to the actual distance using the magnification provided.

 

[Irfan1995]

Could you please explain q3, (b) (ii)......the one about probability.

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w07_qp_5.pdf

and one more question i have is regarding the number of degrees of freedom....earlier in this thread you specified a formula which i used in this same question, (b) (i)
but the answer i got wasn't correct ?!
Some help would be appreciated, thanks.

About the probabilities, they are asking for the probabilities that the value of chi-squared you got is due to chance. If your value was very high, then the probability would be very low. In this example, there's only a 0.001 (=0.1%) chance that a value of chi-squared could occur. The value of chi-squared is 39.9, so the probability of this occurring is much less than 0.001.

The formula I provided earlier was for the t-test only.
For the chi-squared test, the degrees of freedom = number of different types of readings - 1
You have three different types of readings (grazed for 2 years, ungrazed for 10 years, ungrazed for 30 years). The degrees of freedom = 3 - 1 = 2

 

[Irfan1995]

but...how do we know if the data is continous/normal?

Discrete/discontinuous data is data that can only take specific values. For example, your blood type is either A, B, AB, or O. You can't have anything "in between". You only have those 4 possibilities. Another example is the outcomes of a genetic experiment. You can have observed values of 15 green mice and 5 black mice. You can't have 17.4 green mice and 4.39 black mice. Another example could be the number of students in a class,

Continuous data is data that can take a range of values. For example, a person's height could be 160 cm, 180 cm, or anything in between, or even greater than 180 cm or less than 160 cm. Normally distributed means that most of the data is found between 160 cm and 180 cm. But that also means that you can find some samples outside this range. Another examples are a person's weight, quantity of milk produced by a cow, time to complete a race etc...

 

[dornam]

Here is the paper: http://papers.xtremepapers.com/CIE/...nd AS Level/Biology (9700)/9700_s11_qp_11.pdf

Can anyone explain me questions 15, 19 and 36?

For question 15, the examiner report states that the cell surface membrane does not allow intracellular transport but intercellular... I don't understand this.

For question 19, doesn't formation of chromosomes occur in prophase? Or is it a matter of terms, and it would be condensation and not formation?

For question 36... examiner report says that malaria is unlikely to be passed on from parent to child directly. But malaria can be transmitted across placenta, so? How can cholera be transmitted directly from parent to child?

 

[ahmed abdulla]

I think the only way is to get a ruler and measure the distance. Convert it to the actual distance using the magnification provided.

which length do we have to measure ... where is the RBC .. it we dont use ruler to measure to u think we use our hands

 

[Warrior66]

Asalam-o-Alaikum!!
Could anyone please answer this question for me...I never get it and it has been repeated a number of times in the past papers.. :/
http://papers.xtremepapers.com/CIE/...and AS Level/Biology (9700)/9700_w04_qp_1.pdf Question number 30
and a similar one: http://papers.xtremepapers.com/CIE/...nd AS Level/Biology (9700)/9700_s10_qp_11.pdf Question number 27
thanks a bunch!

 

[Mairaxo]

which length do we have to measure ... where is the RBC .. it we dont use ruler to measure to u think we use our hands

2 black shaded cells are the RBC's