A level Biology: Post your doubts here!

[hard_worker]

can somebody tell me how do the staggered ends of tropocollagen molecule contribute to tensile strength of collagen??

It aviods presence of weak spot

 

[nehaoscar]

http://freeexampapers.com/A-Level/Biology/CIE/2012-Nov/9700_w12_qp_21.pdf

Question 3 - b - ii

It shows 3 divisions taking place in that time by mitosis
In mitosis, after every division, 2 daughter cells (in this case blood cells) are produced
So shouldn't it be 6 cells produced and not 3...?

 

[Farhad221]

well good luck every one for the paper tomorrow

 

[princess Anu]

Albumin is the most abundant plasma protein.
Suggest why it is important that capillary walls should not be permeable to albumin?

i think should mention that it will affect the osmoregularity, will create low wp in the interstitial space leading to oedema...
what does the ms say?

 

[Abdul Hanan]

http://freeexampapers.com/A-Level/Biology/CIE/2012-Nov/9700_w12_qp_21.pdf

Question 3 - b - ii

It shows 3 divisions taking place in that time by mitosis
In mitosis, after every division, 2 daughter cells (in this case blood cells) are produced
So shouldn't it be 6 cells produced and not 3...?

You meant Q3 a]ii] ?
each time a stem cell divides, it forms one stem cell and one cell that develops into a blood cell (written in start of the question)
The questions asks "how many blood cells?" so out of the 6 cells produced, 3 will be blood cells.

 

[princess Anu]

marking scheme often mentions about natural disasters & lack of rehydration therapy causing the spread of cholera.. can somebody explain how?

 

[nehaoscar]

You meant Q3 a]ii] ?
each time a stem cell divides, it forms one stem cell and one cell that develops into a blood cell (written in start of the question)
The questions asks "how many blood cells?" so out of the 6 cells produced, 3 will be blood cells.

Oh haha okay thanks! That tells me to read and highlight the key points tomorrow!

 

[nehaoscar]

i think should mention that it will affect the osmoregularity, will create low wp in the interstitial space leading to oedema...
what does the ms say?

Oh good! That seems logical! Thanks!
Actually it was a question from a worksheet i had so it doesn't have any answers :/

 

[Laila39]

Anyone got any ideas which chapters will be coming for sure this time? :/ Anyways good luck everyone!

 

[nehaoscar]

In the nitrogen cycle what is the nitrification process with the bacterial enzymes?

NH4+ ---(nitrosomonas)---> NO3- ------(nitrobacter)-----> NO2-

Is this correct?

 

[nehaoscar]

Anyone got any ideas which chapters will be coming for sure this time? :/ Anyways good luck everyone!

https://www.xtremepapers.com/commun...st-your-doubts-here.9858/page-252#post-911780

 

[Abdul Hanan]

In the nitrogen cycle what is the nitrification process with the bacterial enzymes?

NH4+ ---(nitrosomonas)---> NO3- ------(nitrobacter)-----> NO2-

Is this correct?

no not correct switch places of NO3- and NO2-

 

[qwertypoiu]

so what can never be seen on a light micro? and no antigenic variation is when it changes its antigen! during mutation to develop resistance it doesn't change its antigen! but it actually changes the target sites for antibiotics. for example the shape of active site of an enzyme the antibiotic used to inhibit etc.

Endoplasmic Reticulum cannot be seen under a light microscope.
Ribosomes cannot be seen
Nucleolus cannot be seen
Can't think of anything else...

 

[qwertypoiu]

Why do people who have a deficiency of iron in their diet are often lacking in energy and feel tired?

Without iron, the body cannot produce haemoglobin.
Without haemoglobin, oxygen cannot be transported.

 

[qwertypoiu]

Why is there a greater resistance in the systemic circulation than pulmonary?

Systemic circulation is a much longer distance so resistance is to be expected.

 

[qwertypoiu]

https://docs.google.com/viewerng/vi...wp-content/uploads/2012/11/9700_s14_qp_21.pdf

Can someone please explain Qs 4D)

At W, the mass is decreasing. Thus replication by mitosis must have occured. Each new cell gets half the DNA.
At Z, the mass is increasing. Duplication of DNA during S phase of the cell cycle must have happened.

 

[nehaoscar]

no not correct switch places of NO3- and NO2-

Ok thanks! but the nitrosomonas and nitrobacter are in correct place right?

 

[nehaoscar]

http://freeexampapers.com/A-Level/Biology/CIE/2011-Jun/9700_s11_qp_21.pdf
Question 3 - a
How do you know D is uracil and not cytosine?

 

[Awesome12]

http://freeexampapers.com/A-Level/Biology/CIE/2011-Jun/9700_s11_qp_21.pdf
Question 3 - a
How do you know D is uracil and not cytosine?

They have mentioned in the question

"Part of the template sequence of DNA was ATGC"

We also know that the last base given (the one at the bottom) is Guanine. This is the complementary base for Cytosine. Thus D will be the complementary base for Adenine

 

[Abdul Hanan]

Ok thanks! but the nitrosomonas and nitrobacter are in correct place right?

NH4+ ---(nitrosomonas)---> NO2- ------(nitrobacter)-----> NO3-
YES they are on the correct spot.