A level Biology: Post your doubts here!

[dornam]

Can someone help with 1. a) iii) from here http://papers.xtremepapers.com/CIE/...nd AS Level/Biology (9700)/9700_w12_qp_33.pdf

I'm trying for an hour already to make those solutions and I don't know how to complete the table... in the mark scheme it states that the volumes of R are 0.375, 0.25, 0.125. where did those come from?

 

[Irfan1995]

Can someone help with 1. a) iii) from here http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w12_qp_33.pdf

I'm trying for an hour already to make those solutions and I don't know how to complete the table... in the mark scheme it states that the volumes of R are 0.375, 0.25, 0.125. where did those come from?

According to the question:
"You will need to make dilutions of the 0.4% solution of R, so that the concentration of R is reduced by 0.1% between each successive dilution. You will need 10 cm^3
of each concentration."
So you will need to prepare 5 solutions of the following concentrations: 0.4% (the original), 0.3%, 0.2%, 0.1%, 0.0% (control)
To prepare the original, just take 10 ml of R and put it in a test tube.
To prepare the following concentrations, use the following formula: volume of solute solution = (required concentration/initial concentration) * total volume required
The initial concentration is 0.4, and the total volume required is 10.
To prepare 0.3% solution:
volume of R = (0.3/0.4) * 10 = 7.5 ml. Since the total solution must be 10 ml, you need to add 2.5 ml of water (since 2.5 + 7.5 = 10)
To prepare 0.2% solution:
volume of R = (0.2/0.4) * 10 = 5.0 ml. You must also add 5 ml of water to make the total volume of the liquid in the test tube 10 ml.
To prepare 0.1% solution:
volume of R = (0.1/0.4) * 10 = 2.5 ml. Add 7.5 ml of water
To prepare 0% solution: obviously, just add 10 ml of water.

I'm pretty sure that my answer is correct, so I really don't know how the mark scheme got 0.375, 0.25, and 0.125.

 

[dornam]

Yes, I did it in the same way. But the mark scheme says that volumes of R (in cm^3) and 0.375, 0.25, 0.125...

 

[Irfan1995]

Yes, I did it in the same way. But the mark scheme says that volumes of R (in cm^3) and 0.375, 0.25, 0.125...

I just had a look at the mark scheme. Quoting:
"(0.3)7.5 and (0.2) 5 and (0.1)2.5"
So I guess this means that 0.3% corresponds to 7.5 ml of R, and 0.2 --> 5, and 0.1--->2.5

 

[dornam]

Thanks a lot!!

 

[knowitall10]

knowitall10
JAzakAllah khair for that! Thanx a lot! It really did help
May Allah bless you

Ameen Wa Iyyaki Ukhtee

 

[dornam]

Can someone check my drawing? I know it has a lot of mistakes, but I have no one to check it.

It is the exercise 2. c) from this paper: http://papers.xtremepapers.com/CIE/...nd AS Level/Biology (9700)/9700_w12_qp_35.pdf

Here's my drawing: http://i41.tinypic.com/3089ytu.jpg

Also, what does a large plan diagram suppose exactly? For example, if I have to make a large plan diagram of this: http://www.wesapiens.org/file/2878028/General+structure+of+the+stomach+wall

Should I draw the foldings of the mucosa?

 

[Irfan1995]

Can someone check my drawing? I know it has a lot of mistakes, but I have no one to check it.

It is the exercise 2. c) from this paper: http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w12_qp_35.pdf

Here's my drawing: http://i41.tinypic.com/3089ytu.jpg

Also, what does a large plan diagram suppose exactly? For example, if I have to make a large plan diagram of this: http://www.wesapiens.org/file/2878028/General structure of the stomach wall

Should I draw the foldings of the mucosa?

I would say that this is a very good drawing. The lines are generally drawn in an accurate way, but there is one striking error:
Don't draw one line for two cell membranes. That is, each cell must have its own cell membrane border; don't use the same border and 'build up' on it to draw the second cell. You have to draw another line that touches it (and that's not easy).

EDIT: Concerning the plan diagram:
Yes, you're supposed to draw the foldings of the villi, but that should be the outermost line you draw. The purple areas around it come from the stain hence should not be drawn (or even shown).

 

[dornam]

Those are the cells that must be drawn, right? And it the mark scheme says that do not give points if mitochondria are drawn... which are the mitochondria? dark blue? and the nucleus light blue?

 

[strangerss]

I have a pretty silly question if we encounter a question for say, 5 marks, and the marking scheme gives 10 seperate points which are relevant to the question, does that mean we need to tell them all 10 separate points?

Naah you pick five , because each point is for one mark

 

[strangerss]

I would say that this is a very good drawing. The lines are generally drawn in an accurate way, but there is one striking error:
Don't draw one line for two cell membranes. That is, each cell must have its own cell membrane border; don't use the same border and 'build up' on it to draw the second cell. You have to draw another line that touches it (and that's not easy).

EDIT: Concerning the plan diagram:
Yes, you're supposed to draw the foldings of the villi, but that should be the outermost line you draw. The purple areas around it come from the stain hence should not be drawn (or even shown).

What purple areas?

 

[knowitall10]

What purple areas?

probably the ones you see on the slide when placed under the microscope.
And for the plan diagram, my friend, it only requires the outline of the drawing, so the inner folding and the number of layers or membranes you see. Never ever draw the components of the cell, like organelles. dornam this is especially regarding your drawing: you drew the nucleus. that's not supposed to be included in your diagram ever. Yes, label what you can (i.e the outline of whatever you're seeing on the slide) and don't ever label the cell organelles. I only saw the diagram and not the question. So i'm telling you how to draw the plan digram in general. however, if the question requires you to label the nucleus than i guess you should draw it and label it... i'm in A2, but i cannot forget the stern instructions my teacher had given me last year Wow, i still shake at my memories. I used to hate plan diagrams! Aahh.. i'll never want to repeat AS bio in my life!

 

[Atiqa asl]

Can sum one plz tell me whats cuming in bio paper31 and what r the sources of error and improvement

 

[knowitall10]

Can sum one plz tell me whats cuming in bio paper31 and what r the sources of error and improvement

Assalamu Alaykum!!
I don't think you should find out what's coming in the paper beforehand, my friend this exam is to test your capability of succeeding...not your capability of memorizing answers. Pray well, inshAllah Allah Will Help you even if you don't know a single thing

And considering the sources of error, post the question again, without asking what's coming in the exam, and inshAllah someone will help you out
Asslamu Alaykum!

 

[dornam]

Thanks for your advices!

Can someone show me how should I draw 2 adjacent plant cells? Especially the area where the plant cell walls are and the middle lamella...

 

[knowitall10]

Thanks for your advices!

Can someone show me how should I draw 2 adjacent plant cells? Especially the area where the plant cell walls are and the middle lamella...

It obviously depends on what you see, but here:

 

[dornam]

Thanks!

Regarding foldings, for example if I would have this micrograph: http://www.wesapiens.org/file/5817009/Lung,+Masson+trichrome

The foldings of the inner layer on the drawing must have exactly the same shape as those on the micrograph? Or the idea is to be folded, no matter if it matches the micrograph or not?

 

[knowitall10]

Thanks!

Regarding foldings, for example if I would have this micrograph: http://www.wesapiens.org/file/5817009/Lung, Masson trichrome

The foldings of the inner layer on the drawing must have exactly the same shape as those on the micrograph? Or the idea is to be folded, no matter if it matches the micrograph or not?

It must match what you see... because they now what they give, so the idea of folding must be according to the diagram. But yes of coarse if by any chance you are unable to focus your microscope, and you know what it must be looking like, then draw your assumption. like last year, I had to draw a turgid plant cell, although i'm a pro at focusing microscopes(Alhamdulillah), out of panic i couldnt focus it, but then i drew a plant cell that was turgid because i know what they look like...

 

[dornam]

when I draw table for comparisons or for showing results, can I draw them using a pencil? Do I have to draw them using a ruler or can I draw them freely, only with hand?

 

[Atiqa asl]

As u wish they only need to see ur answer but yes heading on each coloum must be there