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Edexcel 6BIO1 ~ 9th January 2013 ~ AS Biology

Reply 380

mynameisntbobk

18

Original post by Rubyturner94

@mynameisntbobk
Is that in the revision guide?

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It's going alright :smile:

yourself?

And I'm not sure whether its in the revision guide, this was just something I remembered from GCSE.

Actually, checking the CGP revision guide, they do mention them on page 42, but they don't actually explain what they mean.

Reply 381

NilFBosh

3

I saw a this question in a paper

"Why do you measure the initial rate of reaction?"

Reply 382

CoolRunner

9

Original post by NilFBosh

I saw a this question in a paper

"Why do you measure the initial rate of reaction?"

1) The rate of reaction is at the peak
2) This is beacuse initially there are more substrates to enzyme active sites, so the reaction goes faster and there is no limiting factor.

I hope this is correct, btw what question paper was this on.

Reply 383

The Assassin

OP

18

Original post by NilFBosh

I saw a this question in a paper

"Why do you measure the initial rate of reaction?"

I hated this question and didn't understand the mark scheme, but I kind of do now... I suppose, the rate decreases as the reactants are used up, so it will be highest at the start. Also, the initial rate is measured as this is the fastest rate and the only time that you actually KNOW the concentrations of the reactants.

Reply 384

NilFBosh

3

My pastpapers are with my teacher for corrections, I'll get it on tuesday

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Reply 385

Rubyturner94

I didnt get that question too :frown:

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Reply 386

NilFBosh

3

What are the differences between social and ethical issues?

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Reply 387

gimme those exams

why is the cell membrane described as a fluid mosaic. I don't really get this, what does "mosaic" mean?
Why is a membrane fluid, is it because of properties of water orientation (phosphate head, fatty acid tails?

Reply 388

gimme those exams

Original post by NilFBosh

What are the differences between social and ethical issues?

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I think Social Issues are these where there are effects on our societ - eg. the cost of carrying out amniocentesis...

Ethical Issues are those "Fetus has rights" , "Fetus is living" , "Fetus has rights to live"

Reply 389

CoolRunner

9

Whats going on everyone :biggrin:

few days left til exam. Can anyone give me the full steps for the practicals so i can get full marks so i can memorise it :P

Reply 390

CoolRunner

9

Original post by gimme those exams

why is the cell membrane described as a fluid mosaic. I don't really get this, what does "mosaic" mean?
Why is a membrane fluid, is it because of properties of water orientation (phosphate head, fatty acid tails?

Mosiac means that cell membrane looks dotted like a mosaic when you look down on it from above:

Get it?

Reply 391

gimme those exams

Original post by CoolRunner

Mosiac means that cell membrane looks dotted like a mosaic when you look down on it from above:

Get it?

yeah, but what causes the fluidity of the mosaic?

Reply 392

bubblegummer

Original post by gimme those exams

why is the cell membrane described as a fluid mosaic. I don't really get this, what does "mosaic" mean?
Why is a membrane fluid, is it because of properties of water orientation (phosphate head, fatty acid tails?

Mosaic means the presence of proteins in the membrane whereas fluid means when the phospholipids move within the membrane, they are the reason why the membrane shows its fluidity pattern. also, a membrane is fluid so that proteins can move within the membrane and fuse together to form a new arrangement of proteins :smile:

Reply 393

bubblegummer

Original post by CoolRunner

Always include them. its less risky and guarantees all marks for those monohybrid things

thank you

do you have any examples of dihybrid crosses?

Reply 394

gimme those exams

Original post by bubblegummer

thank you

do you have any examples of dihybrid crosses?

thanks for your both of your answers.
What is a dihybrid cross?

Reply 395

nukethemaly

11

Original post by NilFBosh

I saw a this question in a paper

"Why do you measure the initial rate of reaction?"

It's measured to ensure that substrate is not a limiting factor as it gets used up by the enzyme as the reaction proceeds. Thus if the concentration of substrate is a limiting factor, not all active sites are occupied and rate of reaction is slower than expected.

Reply 396

gimme those exams

There is a Question on June, 2011, which i have some difficulty understanding.
It's Question 4b) where you have to draw tubes and where DNA lies in these(light, heavy)

Neither the markscheme nor the Examiners Report explain the results really.
My theory at the moment is:

Stage 1) Heavy strand, so tube is going to be at the bottom of the solution (how big the width of the band though and why?)

Stage 2) Two strands with one heavy, one light - also called Hybrid?! - So there is going to be one band in the middle as its medium weight (between heavy and light). Is that correct? And how big width of that band?

Stage 3) Drawing the strands i had no problem with. Now is it going to be two bands? One Hybrid in the middle and one light at the top?

Is this understanding and explanation of me correct? I kind of guessed it, had most wrong when i did the paper, but now this kind of seems to make sense...

Reply 397

nukethemaly

11

Original post by gimme those exams

There is a Question on June, 2011, which i have some difficulty understanding.
It's Question 4b) where you have to draw tubes and where DNA lies in these(light, heavy)

Neither the markscheme nor the Examiners Report explain the results really.
My theory at the moment is:

Stage 1) Heavy strand, so tube is going to be at the bottom of the solution (how big the width of the band though and why?)

Stage 2) Two strands with one heavy, one light - also called Hybrid?! - So there is going to be one band in the middle as its medium weight (between heavy and light). Is that correct? And how big width of that band?

Stage 3) Drawing the strands i had no problem with. Now is it going to be two bands? One Hybrid in the middle and one light at the top?

Is this understanding and explanation of me correct? I kind of guessed it, had most wrong when i did the paper, but now this kind of seems to make sense...

If it talks about a particular section being a semi conservative model then that strands would be in the middle with one heavy and one light. Since that's the fundamental principal of the semi conservative model, that it contains an original strand and one new strand.

If it talks about a conservative model then heavy would be at the bottom, both strands would be heavy, and light would be at the top and both would be light strands.

I would assume you'd draw the heavy strands in a bit darker but just to ensure your marks, I'd suggest you obviously label them.