A level Biology: Post your doubts here!

[ZîîHana Kawaîî]

Best of luck for tomorrow. I hope today's paper was manageable

 

[ZîîHana Kawaîî]

I don't get how are we supposed to calculate the percentage concentrations, like forexample we have to do simple dilution and in the first thing we take 20cm^3 of sucrose solution and 0cm3 of H2O and at the beginning it';s mentioned that the sucrose provided is 4 % so we'll say this 20cm3 is 4% right?
But when we, say, take 10cm3 of sucrose and 10cm3 of h2o what wll be the %age conc? Is there is a specific formula for doing so? Our teacher once told us but I forgot. :/

Use proportion. It becomes 2% sucrose solution then (10cm sucrose of 4% and 10 cm water)

 

[qwertypoiu]

I don't get how are we supposed to calculate the percentage concentrations, like forexample we have to do simple dilution and in the first thing we take 20cm^3 of sucrose solution and 0cm3 of H2O and at the beginning it';s mentioned that the sucrose provided is 4 % so we'll say this 20cm3 is 4% right?
But when we, say, take 10cm3 of sucrose and 10cm3 of h2o what wll be the %age conc? Is there is a specific formula for doing so? Our teacher once told us but I forgot. :/

Let's say you were given an 80% sucrose solution. Now you have to make 10% sucrose solution from it. First thing you ask yourself is, how much volume of this 10% solution do I need to make? Let's say you wanna make 40 cm^3 of it.
Now you divide the volume needed (40cm^3) by the dilution factor. Dilution factor means the factor by which you're diluting something. In our case, we're diluting by a factor of 8, since we're going from 80% to 10%. Note that normally the dilution factor is 10 (from 80% to 8%) or 2 (from 80% to 40%).
So let's divide: 40cm^3 / 8 = 5cm^3
What does this answer represent? It means you're gonna add, to an empty test tube or beaker or whatever, this much of the original solution. So you add 5cm^3 of this 80% solution to the container.
Next you take distilled water, and add exactly the amount required to make up to the volume decided on originally. In our case we decided on 40cm^3. Since we already added 5cm^3 of the other thing now we add 35cm^3 of H2O to make total 40. And there you have it, your 40 Cm^3 of 8% solution. Make sure you stir very well.
I'd also like to note that in food test your dilution factor will almost certainly be 2.

 

[FranticAmaze]

Hey I don't exactly have notes for this but I think some videos might help you.

And if you want you can try Paper 3 2011 O/N ( if I remember correctly) it has some part about Serial Dilution.
Btw there is also this formula which you can use (when sometimes in the question they give you some values and you need to CALCULATE some concentration)
C1V1=C2V2
(C=concentration
V=volume)

a_wiserME!! NotYourType buckle_crackk
these were the links teacher gav us??

 

[Mahnoorfatima]

There's this question where we have to investigate the solution surrounding the seeds(which conntains enzymes) if they hydrolysed thhe sucrose solution or not. We perform benedicts on it. The second part,which i dont get, says describe hpw u could modify this procedure to investigate the effect of temp on the release of the enzyme from the seeds. What do we write here? That the seeds should be soaked in the same sucrose conc and volume but in different temperatures and then after 20 minutes tested for R.S? It's for 3 marks.

 

[Mahnoorfatima]

https://docs.google.com/viewerng/vi...wp-content/uploads/2012/11/9700_w12_qp_33.pdf
qs 2 bi ANYONE!? PLEASE!

 

[hizirofaki]

a_wiserME!! NotYourType buckle_crackk
these were the links teacher gav us??

plz help
c1 is the first conc
c2 concu want constant secrease
v1 volume of sol
v2 vol of water
we can now c1 and c2
but wht abt v1 nd v2
like how can we find them
and can u plz draw an example for me

 

[FranticAmaze]

c1v1=c2v2
c1 is the given concentration
v1 we hav to find out
c2 is the concentration we'r gonna make
v2 is the make up volume which they are asking us to make in the qs

 

[FranticAmaze]

c1v1=c2v2
c1 is the given concentration
v1 we hav to find out
c2 is the concentration we'r gonna make
v2 is the make up volume which they are asking us to make in the qs

this will vary according to the qs

 

[hizirofaki]

thx

c1v1=c2v2
c1 is the given concentration
v1 we hav to find out
c2 is the concentration we'r gonna make
v2 is the make up volume which they are asking us to make in the qs

thxx i got it

 

[qwertypoiu]

https://docs.google.com/viewerng/vi...wp-content/uploads/2012/11/9700_w12_qp_33.pdf
qs 2 bi ANYONE!? PLEASE!

Whenever there is a question like this, the small width lines are the eye piece graticule. The bigger lines are the stage micrometer.
Step 1: 1 eyepiece graticule unit = 0.01 divided by 4 = 0.0025mm
(this is because I know one width of stage micrometer is 0.01mm. I can SEE that there are around FOUR eyepiece graticule units that fit into one of these stage micrometer line gaps)

Step 2: 0.0025mm multiplied by 1000 = 2.5 micrometer.
(just conversion piece of cake )

 

[Mahnoorfatima]

Whenever there is a question like this, the small width lines are the eye piece graticule. The bigger lines are the stage micrometer.
Step 1: 1 eyepiece graticule unit = 0.01 divided by 4 = 0.0025mm
(this is because I know one width of stage micrometer is 0.01mm. I can SEE that there are around FOUR eyepiece graticule units that fit into one of these stage micrometer line gaps)

Step 2: 0.0025mm multiplied by 1000 = 2.5 micrometer.
(just conversion piece of cake )

Thank you!

 

[Mahnoorfatima]

If the vol of the smallest division on a syringe is 0.5(right?) then the degree of uncertainty should be 0.5/2?

 

[saturn21]

Hey I don't exactly have notes for this but I think some videos might help you.

And if you want you can try Paper 3 2011 O/N ( if I remember correctly) it has some part about Serial Dilution.
Btw there is also this formula which you can use (when sometimes in the question they give you some values and you need to CALCULATE some concentration)
C1V1=C2V2
(C=concentration
V=volume)

Thanks loads!

I found an excellent site here.
Look at the first two only, the rest are not required.

Thank you!

 

[MYLORD]

Whenever there is a question like this, the small width lines are the eye piece graticule. The bigger lines are the stage micrometer.
Step 1: 1 eyepiece graticule unit = 0.01 divided by 4 = 0.0025mm
(this is because I know one width of stage micrometer is 0.01mm. I can SEE that there are around FOUR eyepiece graticule units that fit into one of these stage micrometer line gaps)

Step 2: 0.0025mm multiplied by 1000 = 2.5 micrometer.
(just conversion piece of cake )

can u help me with this question which is of year oct/nov 2012 v34 q1)a

 

[qwertypoiu]

can u help me with this question which is of year oct/nov 2012 v34 q1)a

 

[MYLORD]

View attachment 53608

thnx
but can u elaborate that how did u calculate them (volumes of E and W ) by using C1V1=C2V2 ?

 

[madzil]

how was bio p41?

 

[qwertypoiu]

thnx
but can u elaborate that how did u calculate them (volumes of E and W ) by using C1V1=C2V2 ?

Sorry forgot to explain
I'll do the first row the rest can be done in a similar manner.
C1 = 1% <-----what we already have
V1 = unknown <----- volume of E we'll have to add
C2 = 0.8% <-----concentration we wish to make
V2 = 5ml <----- total volume we wanna make
Shuffle formula:
V1=C2*V2/C1 = (0.8%)*(5ml)/(1%)=4ml Of E
We then add 1ml of H2O to make up the solution to 5ml

Note that ml and cm^3 are same thing.

 

[madzil]

Plz plz discuss p41 (