A level Biology: Post your doubts here!

[darks]

Before mRNA leaves nucleus, the DNA should have replicated and an mRNA strand should have synthesized, i.e. transcription. However, the DNA being replicated is not part of the question because the very first statement says that the events being discussed are from transcription. I made the mistake of ignoring this part (thanks for reminding me with this quesiton btw, tomorrow we have to read the stem of the questions VERY carefully, each word is relevant). First make a mental note of transcription:

- DNA breaks into two strands by bonds between complementary bases breaking, 1 occurs the first time.
- One strand acts as template strand and free RNA nucleotides pair with this template strand's complementary nucleotides, 4 occurs the first time.
- Bonds form between complementary bases, the free RNA nucleotides and the complementary nucleotides to hold the RNA nucleotides in place, 2 occurs the first time.
- RNA polymerase I believe then joins up the RNA nucleotide backbone by forming sugar-phosphate bonds while they are held in place by the previous step, thus, 3 occurs the first time.
- Once this RNA strans is complete (the mRNA has formed), complementary bonds between its nucleotides and the template DNA's nucleotides break, 2 occurs for the second time
- The DNA forms bonds with the complementary bases of the other strand which was broken off in the very first step to make the DNA molecule again, 1 occurs for the second time.
- DNA has been formed again, mRNA has formed, and thus, mRNA is ready to leave and it does so.

So only 1 and 2 occur twice. Hope I helped.

Perfect!

 

[darks]

DNA Unwinds---------->Bonds broken once
Bonds form between complementary bases of the DNA sense strand and mRNA strand being formed ----->Bonds formed once
Once mRNA is formed bonds are broken again --------> Bonds broken twice
DNA strands reform complimentary base pair bonding ------->Bonds formed Twice
3 and 4 happen more than twice ,at an undefined number of times depending on the length of RNA formed.

Thanks!!!

 

[darks]

Metallic9896 are you able to manage time? I tend to complete the paper exactly on time.. And tomorrow we also have to shade, so i am really scared on the time part : p

 

[Thelastmoment]

Good luck tomorrow guys <3 Hope you do well

 

[Metallic9896]

Alright, my turn to ask questions. This question is all over the page so taking two screenshots.


Okay I got rid of A cause I know that capillaries have the highest "total" cross sectional area (for increased diffusion). I got rid of B for the same reason.

Now to C and D. Both have the same cross sectional area graph so that's out of the window. Both also show similar trends in everything else too so it's the actual shapes of the graphs that we need to know, which is insane, at least to me. So how do I know which one is correct?

 

[darks]

What will be the exact order?

 

[Metallic9896]

Metallic9896 are you able to manage time? I tend to complete the paper exactly on time.. And tomorrow we also have to shade, so i am really scared on the time part : p

Don't worry about it it'll be the opposite tomorrow. I never timed myself at home but always manage to do it in time with time left for revision. Only in Chemistry do I finish exactly on time in the paper itself. If you manage exactly on time right now I can assure you you'll be done by 50 minutes max.

 

[darks]

Alright, my turn to ask questions. This question is all over the page so taking two screenshots. View attachment 62462
View attachment 62463

Okay I got rid of A cause I know that capillaries have the highest "total" cross sectional area (for increased diffusion). I got rid of B for the same reason.

Now to C and D. Both have the same cross sectional area graph so that's out of the window. Both also show similar trends in everything else too so it's the actual shapes of the graphs that we need to know, which is insane, at least to me. So how do I know which one is correct?

Is it D..?

 

[Metallic9896]

View attachment 62464
What will be the exact order?

Can't be sure about the exact order but heaviest here I assume is directly related to the relative sizes. The heaviest will probably be the nucleus, followed by chloroplasts (but not here since this is an animal cell), then mitochondrion, and so on. D is a ribosome, and you would know that the smallest (and subsequently, lightest) is the ribosome. A is a lysosome which is small enough, but ribosomes are smaller. B is mitochondrion and C is nucleus, both of which are enormous compared to A and D. So it's A vs D, and you know lysozomes are the packets of hydrolytic enzymes while ribosomes are what make up the enzymes and in all diagrams we see them as much smaller compared to the protein strand that they make. So yeah. XD

 

[Metallic9896]

Is it D..?

Yeah it is, but why?

 

[darks]

Yeah it is, but why?

I looked at "wall thickness".. C shows them to be very similar... while veins are relatively a lot thinner, compared to arteries. I also don't understand the other graphs "Exactly", But C can also be rejected, as it shows arteries/arterioles to have similar pressures, which is totally wrong as pressure decreases as blood travels further from aorta

 

[Thelastmoment]

Alright, my turn to ask questions. This question is all over the page so taking two screenshots. View attachment 62462
View attachment 62463

Okay I got rid of A cause I know that capillaries have the highest "total" cross sectional area (for increased diffusion). I got rid of B for the same reason.

Now to C and D. Both have the same cross sectional area graph so that's out of the window. Both also show similar trends in everything else too so it's the actual shapes of the graphs that we need to know, which is insane, at least to me. So how do I know which one is correct?

Okay, so next comes velocity and it decreases upto capillaries and increases when it comes to veins because of muscle contraction the velocity increases.
So answer should be D

 

[Metallic9896]

Okay, so next comes velocity and it decreases upto capillaries and increases when it comes to veins because of muscle contraction the velocity increases.
So answer should be C

But it's not That's what I thought too but it's D so darks's (darks' .. ? XD where do I put the apostrophe hmm they say Stevens' or Stevens's, I'll go with darks') explanation seems to be correct.

 

[Thelastmoment]

But it's not That's what I thought too but it's D so darks's (darks' .. ? XD where do I put the apostrophe hmm they say Stevens' or Stevens's, I'll go with darks') explanation seems to be correct.

Wrong letter lol

 

[Thelastmoment]

We did kind of the same question it was in an o/n series

 

[Metallic9896]

I looked at "wall thickness".. C shows them to be very similar... while veins are relatively a lot thinner, compared to arteries. I also don't understand the other graphs "Exactly", But C can also be rejected, as it shows arteries/arterioles to have similar pressures, which is totally wrong as pressure decreases as blood travels further from aorta

Nice going man the point about pressure makes great sense.

 

[Metallic9896]

Wrong letter lol

Oh lol okay great then. Thanks a lot guys. Will drop off more if I come across any.

 

[Thelastmoment]

View attachment 62464
What will be the exact order?

As for this question:
At the bottom: Nucleus
Then (upwards) : Chloroplasts ,Mitcohondria
Then: RER and SER
Then Ribosomes at the top

 

[Thelastmoment]

I have a feeling that tomorrow there will be completely new questions considering our paper 4

 

[Metallic9896]

I have a feeling that tomorrow there will be completely new questions considering our paper 4

Shushhhh :'(