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A level Biology: Post your doubts here!

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Irfan1995

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Noor Ahmad said:
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
Click to expand...

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

Noor Ahmad

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Irfan1995 said:
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
Click to expand...



THANK YOUU!
 
D

dornam

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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?
 
T

Twinks05

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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?
 
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Irfan1995

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Noor Ahmad said:
When is chi-square test used and when is t-test used?
Click to expand...

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

oldfashionedgirl

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Irfan1995 said:
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.
Click to expand...


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

Noor Ahmad

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Irfan1995 said:
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.
Click to expand...



but...how do we know if the data is continous/normal?
 
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Irfan1995

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oldfashionedgirl said:
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.
Click to expand...

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
 
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Irfan1995

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Noor Ahmad said:
but...how do we know if the data is continous/normal?
Click to expand...

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...
 
D

dornam

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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

ahmed abdulla

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Irfan1995 said:
I think the only way is to get a ruler and measure the distance. Convert it to the actual distance using the magnification provided.
Click to expand...

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 :p
 
Mairaxo

Mairaxo

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Warrior66 said:
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/Cambridge International A and AS Level/Biology (9700)/9700_w04_qp_1.pdf Question number 30
and a similar one: http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s10_qp_11.pdf Question number 27
thanks a bunch! :)
Click to expand...
Q30- fungi grows in the xyelm so water transport in xylem will be less efficient. Transport of water through xylem is appoplast pathway so appoplast pathway gets affected
Q27- water transport in xylem depends on the force of cohesion which keeps the water molecules together and maintains a stream or column of water. Interruption in xylem interrupts the cohesive forces
 
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