A level Biology: Post your doubts here!

[Mahmood Magdy]

But what exactly should we know? We just apply stain to color it right?

Uumm yeah I think so, try checking Mary Jones Revision Guide textbook. She summarized everything we need to know for the practicals plus some tips and hints.

 

[Mahmood Magdy]

why not A?

Simply, Amino acids are taken into the cell by symporters(co-transporters), which move Na+ or H+ ions into the cell in the thermodynamically downhill direction and cotransport amino acids with them, even though that is in the amino acids' uphill direction, not by endocytosis. Actually A represents exocytosis not endocytosis.

 

[Mahmood Magdy]

can someone explain to me this question Scribd q1 part b (ii)
P.S i didnt take chem AS

Well I'm not taking Chem but I found this way, it is the easiest according to me. So basically if you dissolve the Molar Mass in 1dm3 of water you get a 1 mol solution. The calculation is as follows in the image attached. So if the question asked for other values, you will just plug them in into the working etc

 

[Physux]

http://maxpapers.com/wp-content/uploads/2012/11/9700_w14_qp_11.pdf
MCQ 16 please explain.

 

[princess Anu]

Simply, Amino acids are taken into the cell by symporters(co-transporters), which move Na+ or H+ ions into the cell in the thermodynamically downhill direction and cotransport amino acids with them, even though that is in the amino acids' uphill direction, not by endocytosis. Actually A represents exocytosis not endocytosis.

But how are we supposed to know that haven't we been taught about bulk transport of larger substances??
+ isn't it endocytosis

 

[qwertypoiu]

http://maxpapers.com/wp-content/uploads/2012/11/9700_w14_qp_11.pdf
MCQ 16 please explain.

The answer is B. Mitotic cell division does NOT allow a cell to get repaired, but rather a damaged TISSUE may be repaired, by replacement of damaged cells with new cells. A damaged cell cannot be repaired, it would just die or if it manages to divide and produce new cells then its gone as well. No cell is getting repaired, just old cells getting replaced by new ones.

 

[qwertypoiu]

I have a question, amongst these:

• trachea
• broncus
• terminal bronchiole
• respiratory bronchiole
• alveolar duct
• alveolus

which of these have elastic fibres? thanks

 

[Mahmood Magdy]

But how are we supposed to know that haven't we been taught about bulk transport of larger substances??
+ isn't it endocytosis

Actually you get to learn that in A2 syllabus. It is exocytosis, if you are going to consider Protein Synthesis. So after the whole process, the golgi apparatus starts pinching into shuttle vesicles that move on the cell surface membrane and fuse with and secrete the enzymes, proteins etc. So in this specific motion, those vesicles will be moving towards the CSM not the other way round. The question also mentioned 'concentrated', this probably means that when taking in large molecules, the conc is low and it starts building up at the RER... Besides, that co-transporter thing is sometimes known as Indirect Active transport. Moreover,after further research, Amino Acids are taken in by Endocytosis, Active transport(both forms), Facilitated diffusion. There isn't a specific way

 

[Lola_sweet]

I have a question, amongst these:

• trachea
• broncus
• terminal bronchiole
• respiratory bronchiole
• alveolar duct
• alveolus

which of these have elastic fibres? thanks

Alveolus has elastic fibres

 

[My Name]

Alveolus has elastic fibres

Even trachea does :3 right?

 

[Lola_sweet]

Even trachea does :3 right?

doesnt the trachea have cartilage in c-shaped
this prevents the trachea frm collapsing
bronchi also ve cartilage in irregular blocks

 

[qwertypoiu]

doesnt the trachea have cartilage in c-shaped
this prevents the trachea frm collapsing
bronchi also ve cartilage in irregular blocks

I was doing end of chapter questions in my book and in the answers it said trachea and respiratory bronchioles also have elastic fibre...

 

[Mahmood Magdy]

Hi, I have a question about tertiary structures of proteins. Their shapes are affected by:

• hydrogen bonds
• ionic bonds
• disulphide bonds
• hydrophobic interactions

between the different amino acids.

Somebody please explain which of these bonds are the strongest and which are the weak ones. (please order them from strongest to weakest)
Also, please explain, for each of them, how they can be broken? I mean which onees are broken by pH changes, which ones by temperature changes, etc.
Thank you!

Ok so the order is as follows :-
- Disulphide
- Ionic
- Hydrophobic Int
- Hydrogen

Broken by temperature :- Mostly hydrogen and hydrophobic
Broken by pH :- Hydrogen and Ionic

Disulphide are the strongest and they are covalent bonds. To break them, you have to add special reducing agents. Moreover, hydrogen are the weakest and literally anything could break them.

 

[Lola_sweet]

I was doing end of chapter questions in my book and in the answers it said trachea and respiratory bronchioles also have elastic fibre...

which book is this?

i dnt remember reading tht trachea had elastic fibres or the respiratory bronchioles

 

[My Name]

which book is this?

i dnt remember reading tht trachea had elastic fibres or the respiratory bronchioles

Probably the one mentioned here:

Read the book online here

 

[Lola_sweet]

Probably the one mentioned here:

but why would trachea and bronchiole need elastic fibres
the alveolus stretches and recoils due to the air flow but i dnt see why trachea or bronchiole need it

could be wrong :/ anyone else knw?

 

[nehaoscar]

Why are sugars moved out of the roots?
The answer is B

 

[My Name]

but why would trachea and bronchiole need elastic fibres
the alveolus stretches and recoils due to the air flow but i dnt see why trachea or bronchiole need it

could be wrong :/ anyone else knw?

I will try to revise this topic.

 

[nehaoscar]

Why is it A?
Why and how will cohesion be affected?

 

[nehaoscar]

http://maxpapers.com/wp-content/uploads/2012/11/9700_w14_qp_11.pdf
MCQ 16 please explain.

It's B because a cell cannot repair any cell. It can form new cells to replace it but it can't repair it.