A level Biology: Post your doubts here!

[Farhad221]

Can someone explain to me the effect of carbon dioxide on haemoglobin?

it decreases the haemoglobin(HB) affinity for oxygen, This is known as the BOHR EFFECT. Why does this happen well in water CO2 molecules from carbonic acid H2CO3 which dissociates to form H+ and HCO3 - ions. This is catalysed by the enzyme carbonic anhydrase. H+ ions then react with HB to form HHB hence releasing the oxygen molecules HB was bidden to. This helps to release more oxygen in active muscles. I

 

[princess Anu]

then how do we decide which molecule is a macromolecule :/

 

[princess Anu]

guys can anyone tell me where can I find 2006-2003 past papers?

 

[Farhad221]

then how do we decide which molecule is a macromolecule :/

I think in bio the poly molecules are considered macro the rest are not macro , However you should confirm this first.

 

[Farhad221]

guys can anyone tell me where can I find 2006-2003 past papers?

Student bounty

 

[qwertypoiu]

then how do we decide which molecule is a macromolecule :/

Macromolecules have THOUSANDS of atoms joined together.
Glucose has mere 24 atoms only...
Polymers like starch (polysaccharide) , protein (polypeptide) and nucleic acids (polynucleotide) are macromolecules...
Note that lipids are also simple molecules...

 

[princess Anu]

MS mentions this as Anaphase/ Early telophase.


I thought cytokinesis is occurring here or maybe its late telophase because the cell seems to be pinched at the centre

How are we supposed to realise its Anaphase?

 

[princess Anu]

and this too, how do we know if B is the alveoli

 

[qwertypoiu]

Aoa
Can someone PLEASEE explain to me the process of semi-conservative replication of DNA through the N14/N15 experiment like I know how replication occurs but Im not able to do the mcqs with this stuff.. I need to know the list of outcomes after each generation so if someone could please list out the results after each generation.. thankss guyss!

Let's consider DNA made of only N14 to have mass of 14 units and those made of N15 completely to have a mass of 15 units.

If DNA made of N14 atoms is placed in a solution containing N15 atoms only:

At first mass of all DNA molecules is 14 units.

After first division, mass of all DNA molecules is 14.5 units.

After second division, 50% of DNA molecules have a mass of 14.5 units, the other 50% have a mass of 15 units.

After third division, 25% of DNA molecules have a mass of 14.5 units., the other 75% have a mass of 15 units.

After fourth division, 12.5% of DNA molecules have a mass of 14.5 units., the other 87.5% have a mass of 15 units.

I could go on but I think you see a pattern. I love math so there:

After nth division, [ 200/(2^n) ]% of DNA molecules have a mass of 14.5 units, the other [ 100 - 200/(2^n) ]% have a mass of 15 units.

 

[qwertypoiu]

MS mentions this as Anaphase/ Early telophase.


I thought cytokinesis is occurring here or maybe its late telophase because the cell seems to be pinched at the centre

How are we supposed to realise its Anaphase? View attachment 52919

I'm not sure 100% but I think,

During telophase, nucleolus should be reforming, and nuclear envelope should also be reforming.
In the picture, this is not occurring, so we would call this anaphase or early telophase.
It cannot be late telophase because by then the two features I mentioned should be visible.

 

[Farhad221]

Correct me if i am wrong also in anaphase we are able to see cleavege between two cells which is shown here whereas in telophase cytokenesis is more obvious

I'm not sure 100% but I think,

During telophase, nucleolus should be reforming, and nuclear envelope should also be reforming.
In the picture, this is not occurring, so we would call this anaphase or early telophase.
It cannot be late telophase because by then the two features I mentioned should be visible.

 

[qwertypoiu]

Correct me if i am wrong also in anaphase we are able to see cleavege between two cells which is shown here whereas in telophase cytokenesis is more obvious

I'm not sure but yeah maybe cytokinesis can begin slightly earlier and complete separation occurs after telophase.

 

[princess Anu]

no! its usually during late telophase or cytokinesis we can see cleavage furrow and cytokenesis occurs after telophase

 

[princess Anu]

Let's consider DNA made of only N14 to have mass of 14 units and those made of N15 completely to have a mass of 15 units.

If DNA made of N14 atoms is placed in a solution containing N15 atoms only:

At first mass of all DNA molecules is 14 units.

After first division, mass of all DNA molecules is 14.5 units.

After second division, 50% of DNA molecules have a mass of 14.5 units, the other 50% have a mass of 15 units.

After third division, 25% of DNA molecules have a mass of 14.5 units., the other 75% have a mass of 15 units.

After fourth division, 12.5% of DNA molecules have a mass of 14.5 units., the other 87.5% have a mass of 15 units.

I could go on but I think you see a pattern. I love math so there:

After nth division, [ 200/(2^n) ]% of DNA molecules have a mass of 14.5 units, the other [ 100 - 200/(2^n) ]% have a mass of 15 units.

can u explain why is the % getting halved every generation?

 

[fantastic girl]

yes as they are growing they require energy for replication of dna and protien synthesis.
23 is D because lingin strengthen the xylem vessels so they wont collapse under hydrostatic pressure which in this case is due to high rate of transpiration.

so that means sucrose shud be moving into the roots eh ?
thanks bro

 

[Farhad221]

yes

so that means sucrose shud be moving into the roots eh ?
thanks bro

 

[MYLORD]

somebody explain why is the option B not correct ?

 

[MYLORD]

how do the plant cells multiply and grow ? by mitosis ? and plant cells do not have centrioles so how do they divide in the first place ????

 

[qwertypoiu]

how do the plant cells multiply and grow ? by mitosis ? and plant cells do not have centrioles so how do they divide in the first place ????

Plant cells duplicate by mitosis. However, there are many mechanisms by which duplication may occur in various organisms. We are not required to know how a plant cell does mitosis.

 

[MYLORD]

Plant cells duplicate by mitosis. However, there are many mechanisms by which duplication may occur in various organisms. We are not required to know how a plant cell does mitosis.

alright gud