A level Biology: Post your doubts here!

[strangerss]

What do they mean when they say 70S for ribosomes? what's the meaning of the "S"?

 

[PANDA-]

70s and 80s are two types of ribosomes, 70s are smaller and are present in bacteria ( i think ) and 80s are larger and present in animals.

 

[strangerss]

How is carbon dioxide found in tissues fluid?

 

[strangerss]

Y

70s and 80s are two types of ribosomes, 70s are smaller and are present in bacteria ( i think ) and 80s are larger and present in animals.

yeah you're right hehe , but what does the S mean 0.o?

 

[strangerss]

Can some one please explain question 30 p1 Maj/June variant 2 ?

 

[qffdhruba]

Can some one please explain question 30 p1 Maj/June variant 2 ?

which year?? :/

 

[strangerss]

which year?? :/

Oh I forgot that , it's 2012

 

[megamind]

describe the processes that affect allele frequencies in populations with reference to the global distribution of malaria and sickle cell anaemia;

Use sickle cell anaemia as an example to illustrate and discuss how one genotype may be fitter than another when a particular environmental factor (infection with Plasmodium) is exerting a strong selection pressure

anyone please? im reposting again

 

[qffdhruba]

Oh I forgot that , it's 2012

The confusion may arise between C and D....
The stroke volume depends on the contraction of the cardiac muscles....
So the muscles cannot exert a infinite amount of pressure....
Cause their strength of contraction is limited by the ATP formed in the muscle tissues....
Therefore the volume pumped out by the muscles of the heart increases initially as ventricular end-diastolic volume increases....
But after reaching a maximum point it, does not increase anymore, as the muscles do not have the strength to pump out more blood out of the ventricles...
therefore, answer is D

 

[strangerss]

The confusion may arise between C and D....
The stroke volume depends on the contraction of the cardiac muscles....
So the muscles cannot exert a infinite amount of pressure....
Cause their strength of contraction is limited by the ATP formed in the muscle tissues....
Therefore the volume pumped out by the muscles of the heart increases initially as ventricular end-diastolic volume increases....
But after reaching a maximum point it, does not increase anymore, as the muscles do not have the strength to pump out more blood out of the ventricles...
therefore, answer is D

So the stroke volume is not directly proportional to the ventricular end-diastolic volume , okay I got it , thanks a lot for the help

 

[strangerss]

can someone please explain how the features of this blood vessel make a capillary ?? It's in question paper Maj/June 2012 variant 3 paper 2 question 1

 

[HorsePower]

can someone please explain how the features of this blood vessel make a capillary ?? It's in question paper Maj/June 2012 variant 3 paper 2 question 1

well, the key is to figure out that A is an RBC and we know that the lumen of a cappilary very comparable to the diameter of an RBC, therefore the vessel is a cappilary.

 

[MÁťT PŭמҚ]

Y

yeah you're right hehe , but what does the S mean 0.o?

S is Sediments rate...

 

[Irfan1995]

So w

so what you mean is the volume of air exchanged is the also the volume of air inhaled? but how can the air inhaled be equal to the air exhaled shouldn't it be less ? X_X

If the air inhaled is less than the air exhaled, then you will exhale more than you inhale, so eventually, you should completely run out of air, right?
In order to maintain a constant lung volume, the air inhaled must equal the air exhaled.

 

[Irfan1995]

What do they mean when they say 70S for ribosomes? what's the meaning of the "S"?

S is the Svedberg unit. It refers to the rate of sedimentation during centrifugion. In a 70S ribosome, there is a small ribosomal unit (30S) and a large unit (50S). If you add them up, you get 80S. If you take a little bit of physics, you will know that the size is not proportional to the centripetal force, so if you add up all the components, you won't get the total "size".

 

[Irfan1995]

describe the processes that affect allele frequencies in populations with reference to the global distribution of malaria and sickle cell anaemia;

Use sickle cell anaemia as an example to illustrate and discuss how one genotype may be fitter than another when a particular environmental factor (infection with Plasmodium) is exerting a strong selection pressure

anyone please? im reposting again

Introductory notes:

• Sickle-cell anaemia (SCA) is a recessive genetic disease which causes haemoglobin (hence the RBC) to be shaped like a 'sickle' (crescent/moon-shaped)
• Since RBCs are deformed, they cannot carry oxygen as efficiently as normal RBCs can.
• People with SCA are immune to malaria. This is because (sickle-celled) RBCs rupture shortly after the Plasmodium starts to grow. When the RBC is ruptured, Plasmodium cannot reproduce.

Explanation:
In Africa, malaria is a disease that kills many people. So the advantegous traits would be those that confer resistance to malaria.
Having SCA is an advantage, since sufferers can't contract malaria.
However, being homozygous for SCA is a disadvantage, because they will die from anaemia (their bodies can't receive enough oxygen)
Therefore, the best genotype to have is the heterozygous one. This is because they are immune to malaria, and they don't suffer the severe side effects from anaemia.
But if you look at an European society, no one has SCA, because malaria is not present, so there is no selection pressure favouring the SCA allele. So the allele frequency for SCA is almost zero.

 

[Alice123]

Outline the ways in which the endocrine and nervous systems carryout teir roles in control and co ordination in animals..
Can anyone write the full answer? the marks scheme is given below..
endocrine
1. hormones ;
2. chemical messengers ; A chemicals that transfer information
3. ductless glands / (released) into blood ;
4. target, organs / cells ;
5. ref. receptors on cell membranes ;
6. example of named hormone and effect ;
nervous
7. impulses/ action potentials ; R electrical, signals / current
8. along, axon / neurones / nerve fibres ; R nerves R across
9. synapse (with target) / neuromuscular junction ;
10. ref. receptor / sensory neurones ;
11. ref. effector / motor neurones ;
differences – endocrine
12. slow effect / ora ;
13. long lasting effect / ora ;
14. widespread effect / ora ;
15. AVP ; e.g. extra detail of synapse / hormone changes triggered within cells [8 max]

 

[goodluckayesha]

how the structure of DNA enables it to replicate semi-conservatively?? can sm1 give a detailed proper answer for this question its for 4 marks

 

[strangerss]

well, the key is to figure out that A is an RBC and we know that the lumen of a cappilary very comparable to the diameter of an RBC, therefore the vessel is a cappilary.

Thanks for the help , I didn't even figure out it's a RBC , I know a rbc is biconcave , but it looks to me like a triangle more than anything XS

 

[strangerss]

S is the Svedberg unit. It refers to the rate of sedimentation during centrifugion. In a 70S ribosome, there is a small ribosomal unit (30S) and a large unit (50S). If you add them up, you get 80S. If you take a little bit of physics, you will know that the size is not proportional to the centripetal force, so if you add up all the components, you won't get the total "size".

Thanks a lot for the info.