A level Biology: Post your doubts here!

[nehaoscar]

I will try to revise this topic.

Please can you look at question above and below your comment you just posted on here and see if you know (since i think you are online right now )

 

[Midnight dream]

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?

actually yes, Trachea and bronchioles do have elastic fibres. They allow the lumen to dilate.

You can actually check this from SUMMER 2010/22 Question 5.

 

[My Name]

View attachment 52412
Why are sugars moved out of the roots?
The answer is B

https://www.xtremepapers.com/community/threads/bio-mcqs.7391/#post-96170
Hope that helps

Please can you look at question above and below your comment you just posted on here and see if you know (since i think you are online right now )

I did and I yes I am

 

[Midnight dream]

View attachment 52413
Why is it A?
Why and how will cohesion be affected?

The question refer to XYLEM VESSELS .so the only logical answer is A.

 

[nehaoscar]

The question refer to XYLEM VESSELS .so the only logical answer is A.

Please can you explain because cohesion is a property of water right? so how can it be affected... I thought it would be C as it block the mass flow of water...

 

[nehaoscar]

https://www.xtremepapers.com/community/threads/bio-mcqs.7391/#post-96170
Hope that helps

I did and I yes I am

Haha thanks a lot! it helped to clear the doubt!

 

[nehaoscar]

Can someone give me a list of HIV, TB and Measles having what of the column headings given in the table ?
The answer is D
... So what doesn't have a cell membrane etc...?

 

[salma_69]

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

i don't get why when i add te 85g to 1 dm^3 i get 1 mole, like is it fixed with any other molar mass. What's the use of that step anyway

 

[My Name]

Haha thanks a lot! it helped to clear the doubt!

Welcome

 

[qwertypoiu]

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.

Thanks a lot

 

[qwertypoiu]

Probably the one mentioned here:

The book is actually Biology Coursebook Third Edition:

On page 180, question 7, there's a table which compares the structure of trachea and respiratory bronchiole, and the answer is like this:



So yeah, I was expecting the bottom row to be both crosses, but found out otherwise

 

[qwertypoiu]

View attachment 52413
Why is it A?
Why and how will cohesion be affected?

"Mass flow during translocation" refers to movement inside a phloem, not xylem. So it can't be C!

 

[Lola_sweet]

The book is actually Biology Coursebook Third Edition:

On page 180, question 7, there's a table which compares the structure of trachea and respiratory bronchiole, and the answer is like this:View attachment 52418

View attachment 52418

So yeah, I was expecting the bottom row to be both crosses, but found out otherwise

but why do they ve elastic fibres

 

[qwertypoiu]

View attachment 52414
Can someone give me a list of HIV, TB and Measles having what of the column headings given in the table ?
The answer is D
... So what doesn't have a cell membrane etc...?

Cell membrane:

• HIV does not have a cell membrane, it is a virus, when it enters a T-helper lymphocyte it can replicate and viruses will bud out from it, with membranes from the host cell, but the virus originally never had a membrane.
• TB is caused by Mycobacterium tuberculosis or Mycobacterium bovis, both of which are bacteria. Therefore, they have cell surface membranes.
• Measles is caused by a species of genus Morbillivirus, which is a virus. Again like HIV it doesn't originally have a membrane.

Genes:

• They all have genes, the bacteria have circular DNA, the viruses have either RNA or DNA.

Ribosomes:

• Ribosomes are found in all living cells, bacteria have them (Remember 70S ribosomes?)
• Viruses are not living things (although some scientists say otherwise), just infective agents, they don't contain ribosomes. In fact, all viruses have is 1. DNA/RNA 2. protein coating to protect DNA/RNA 3. Sometimes a lipid coating around this protein coating to protect it while outside (when it is not in a host cell yet)

Respiration:

• All living things respire, but like above, viruses are usually not considered living. So bacteria respire but viruses do not.

Cool stuff about virus:

• viruses do not respire,
• nor do they display irritability;
• they do not move
• and nor do they grow,
• however, they do most certainly reproduce, and may adapt to new hosts.
• Viruses may be defined as acellular organisms whose genomes consist of nucleic acid, and which obligately replicate inside host cells using host metabolic machinery and ribosomes to form a pool of components which assemble into particles called VIRIONS, which serve to protect the genome and to transfer it to other cells. (basically they use organelles of living host cells, they don't have anything of their own)

 

[qwertypoiu]

but why do they ve elastic fibres

No idea

 

[Lola_sweet]

No idea

its nt in the book is it?

 

[qwertypoiu]

its nt in the book is it?

Which one? My book? in that case not in the text, but this answer to End Of Chapter question implies this

 

[Lola_sweet]

Which one? My book? in that case not in the text, but this answer to End Of Chapter question implies this

same here

http://alevelnotes.com/The-Lungs/169?tree=

they said this

• The smooth muscle allows the Lumen (the inside space) to constrict, by contracting. This is useful if there are harmful substances in the air, as is minimises the amount of the substances that can be breathed in.

• The elastic fibres allow the lumen to Dilate (widen) after the smooth muscle has contracted and then relaxed

 

[Mahmood Magdy]

i don't get why when i add te 85g to 1 dm^3 i get 1 mole, like is it fixed with any other molar mass. What's the use of that step anyway

It depends on the solution. You see if they wanted NaCl solution, you will find the Molar Mass(normally given) + 1 dm3 of water to give 1 mol solution.
If they asked you for a specific value of lets say 2 mol solution, then Molar mass * 2
Same way with 0.5 mol, Molar Mass* 0.5
The only reason we divided by 1000 was because they asked us to get the solution in m mol not mol

 

[qwertypoiu]

same here

http://alevelnotes.com/The-Lungs/169?tree=

they said this

• The smooth muscle allows the Lumen (the inside space) to constrict, by contracting. This is useful if there are harmful substances in the air, as is minimises the amount of the substances that can be breathed in.

• The elastic fibres allow the lumen to Dilate (widen) after the smooth muscle has contracted and then relaxed

Hmm not sure about anything

 

[Lola_sweet]

Hmm not sure about anything

Ikr if only the book said something :/

 

[qwertypoiu]

Ikr if only the book said something :/

Actually I think any thing that has smooth muscle must have elastic fiber, according to the information you gave.