Edexcel AS Biology Unit 1

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Can you write your answers as bullet points?

yep i think you can but not for the ones with the * by them, on the front of the paper it says they mark those questions depending on how well it's written, etc.

This is taken from the front of a past paper:

Questions labelled with an asterisk (*) are ones where the quality of your written communication will be assessed
– you should take particular care with your spelling, punctuation and grammar, as well as the clarity of expression, on these questions.

Reply 41

LyreBirds

Original post by Qtj987

is this exam wed 21/05?

Yeah! ie, tomorrow morning! :s-smilie:

Reply 42

EggsterminateMe

Original post by Monki1

Same, I am also resitting this unit I HAVE to get an A in this paper. :frown:

Same. My life depends on the A. I just need at least an overall B in AS and them hopefully I can get the A's in 6Bio4 and 6Bio5

Reply 43

Tha Realest

Can someone please explain the following :

How amino acids join together, to form the 3D structure of a protein ???

- Thanks

Reply 44

MartaZiolko

Original post by lucy97

I think so :smile:

just be careful though, make sure you develop your points. Probably best to avoid bullet pointing for the longer answers, so avoid it in 4-6 markers!

You can as long as it's not the QWC question :smile:

Reply 45

EggsterminateMe

Original post by Monki1

Same, I am also resitting this unit I HAVE to get an A in this paper. :frown:

Same. I need a B grade overall for as and then aiming for As on 6bio4 and 6bio5.

Reply 46

EggsterminateMe

I'm seriously going to hate it if they ask too many question on CF. they've asked enough last year.

Reply 47

Me123456789

Can anyone please please explain this question.Not the answer the question. I actually don't understand what is says :confused:

Explain how the primary structure of an enzyme determines its three-dimensional (tertiary) structure and its properties.

Reply 48

lucy97

Original post by Me123456789

Can anyone please please explain this question.Not the answer the question. I actually don't understand what is says :confused:

Explain how the primary structure of an enzyme determines its three-dimensional (tertiary) structure and its properties.

I think this is talking about how the different R groups in the primary structure of a protein (amino acid) bond to form the 3d shape. Also the tertiary structure could be an enzyme so where the bonds form depends on whether the substrate can match..

Kinda answered it but hopefully it helps :smile:

Reply 49

Changing Skies

Original post by EggsterminateMe

I'm seriously going to hate it if they ask too many question on CF. they've asked enough last year.

Agreed

Posted from TSR Mobile

Reply 50

LyreBirds

Original post by Tha Realest

Can someone please explain the following :

How amino acids join together, to form the 3D structure of a protein ???

- Thanks

The amino acids are linked into a polypeptide chain by peptide bonds. Hydrogen bonds form between the amino acids in the chain changing the overall shape (into a beta pleated sheet or an alpha helix for example), further bonds form between the in the amino acid and change the shape further. This may be the final 3D structure of a protein, or it may form bonds between itself and other polypeptide chains to reach it's final 3D structure.

(something like that? may not be quite right, wrote in rush)

Reply 51

EggsterminateMe

Original post by Changing Skies

Agreed

Posted from TSR Mobile

That was a hard paper too. I just hope the grade boundaries are lower this year

Reply 52

Tiam.N

Original post by LyreBirds

Does anyone have a method for answering those questions in the exams about interpreting data/describing a graph? I've always dropped marks on them in the mocks because I always seem to talk about the wrong bit of the graph, or mention completely different things than what's on the mark scheme.

I have the exact same issue. Any advice would be appreciated.

Reply 53

Ripper Phoenix

guys can you explain diff between tunica media tunica intima?

Reply 54

Tha Realest

Please can anyone explain the following ...

How a gene mutation causes a build up of mucus in the respiratory system,
of a person with cystic fibrosis ???

- Cheers

Reply 55

isabelfinn

Original post by LyreBirds

There are also marks awarded for naming the bonds in the 3d structure: sulphur bridges, ionic bonds, hydrogen bonds and hydrophilic/hydrophobic interactions.

A further mark on top of that is awarded for saying that these bonds in the tertiary structure are formed between the R groups of different amino acids

Reply 56

EggsterminateMe

Original post by Tiam.N

I have the exact same issue. Any advice would be appreciated.

What i usually do is describe the trend in the graph backing it with an example. That 2 marks right there.

And then I try and spot the unusal thing about the trend- like an outlier or maybe the line does not start at 0 or something or maybe That should usually get you 3 marks.

Original post by Tha Realest

Please can anyone explain the following ...

How a gene mutation causes a build up of mucus in the respiratory system,
of a person with cystic fibrosis ???

- Cheers

If you have the Edexcel biology book AS, you can use page 74 to answer the question but here's what I would say:

o What happens is that in a person with CF, the CFTR channel protein may not function properly or will be absent.
o This means the Chloride ions in the cell cannot go through the CFTR Channel protein (as they usually do) and into the mucus.
o When the CFTR Channel protein is open, the sodium ion channel closes. But in a person with CF the sodium ion channel is open as the CFTR channel is obviously not working properly.
o This means that Sodium ions will continously flow into the cell.
o As there is a high concentration of sodium and chloride ions in the cell, water will also leave the mucus and enter the cell by omosis to balance the concentration.
o This will leave the mucus sticky and make it harder for the cilia to beat properly

*someone correct me if I'm wrong. Thanks!

Reply 57

isabelfinn

Original post by Tha Realest

Please can anyone explain the following ...

How a gene mutation causes a build up of mucus in the respiratory system,
of a person with cystic fibrosis ???

- Cheers

There should be marks awarded for:

1. Gene mutation changes the sequence of bases
2. Changes in the primary structure (order of amino acids, coded for by the bases)
3. Changes in the folding on the protein (an additional mark is given for stating it is the CFTR protein), so the CFTR protein is faulty/doesn't function properly
4. CFTR protein cannot pump Cl- ions into the mucus via the apical membrane
5. Water does not move out of cell into mucus via osmosis, as there is not a higher water potential in the cell.
6. Na+ ions are continuously pumped out.
7. Lack of water in mucus makes it sticky

That should be all the points :smile:

Reply 58

isabelfinn

Original post by Paras Agarwal

guys can you explain diff between tunica media tunica intima?

The veins and arteries consist of 3 layers. The inner most layer is the tunica intima, the middle layer is called the tunica media (and the outer layer is the tunica externa).

The tunica intima is a single layer of folded squamous epithelial cells.

The tunica media is the thickest layer and is made of elastic tissue and muscle fibres