A2 Biology | Post your doubts here

[histephenson007]

Can anyone tell me all the important definition required in the genetics chapter??! gene mutation, codominance...etc

 

[smartangel]

please explain how are the daughter cells different from each other..i dont get independent assortment of chromosomes. there are 2 which are same..the top one and the one right below it are same yeah?

 

[histephenson007]

please explain how are the daughter cells different from each other..i dont get independent assortment of chromosomes. there are 2 which are same..the top one and the one right below it are same yeah?

This is the main part of the picture. When the chromosome line up along the equator, they do it randomly. The white and dark chromosomes can align as in the first picture or not align as shown in the second picture.

 

[angelgirl:)]

can anyone explain to me about recombinant DNA technology in synthesis of human insulin by bacteria. i am a bit confused with the concept. thank you in advance.

rDNA is formed wen the gene for specific character is inserted in the plasmid vector...

 

[aliya_zad]

bt how does all this tauuf relates to size of vessel.....i cnt make a connection

U see if u had to produce large amounts of something...using Batch culture u would need larger vessels coz u harvest a batch at a time..whereas in continuous culture small vessels would suffice coz u know products can be removed as they are produced and reactants are kept adding continuously..

 

[smartangel]

people homozygous for normal Beta polypeptide allele are less likely to have malaria..why?

 

[smartangel]

This is the main part of the picture. When the chromosome line up along the equator, they do it randomly. The white and dark chromosomes can align as in the first picture or not align as shown in the second picture.

thankss!

 

[angelgirl:)]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w11_qp_43.pdf
http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w11_ms_43.pdf
Q 9a

myelin sheath insulate axon so the action potential passes only through the nodes of Ranvier by saltatory conduction...

(saltatory conduction means action potential jumps from 1 nodes of Ranvier to the next witout leaking from the surface of axon membrane so the transmission is very fast)

 

[hassam]

well explain the role of synapses.....
what is adaptation......spatial summation.......

 

[angelgirl:)]

people homozygous for normal Beta polypeptide allele are less likely to have malaria..why?

where did u get this Question from?

 

[histephenson007]

people homozygous for normal Beta polypeptide allele are less likely to have malaria..why?

Isn't it supposed to be homozygous for sickle cell anaemia B-polypeptide??

 

[smartangel]

where did u get this Question from?

i read it in ocr but they havent given an explanation for it..if you have the book its selection n evolution.pg 251-2. its there in the revision guide too!

 

[smartangel]

Isn't it supposed to be homozygous for sickle cell anaemia B-polypeptide??

people homozygous for sickle cell allele die because of it. those heterzygous are less likely to suffer frm an attack of malaria than those homozygous for the normal allele. thats whats the book says. are we supposed to know why?

 

[smartangel]

Explain how natural selection may bring about evolution;

1. individuals in population have great reproductive potential / AW ;
2. numbers in population remain roughly constant ;
3. variation in members of population ;
4. environmental factors / named factor (biotic or abiotic) ; linked to the next 2
5. (cause) many, fail to survive / die / do not reproduce ;
6. those best adapted survive / survival of the fittest ;
7. (reproduce to) pass on alleles ; R genes
8. genetic variation leads to change in phenotype ;
9. ref: changes in, gene pool / allele frequency ;
10. over time produces evolutionary change ;
11. new species arise from existing ones / speciation ;
12. directional / stabilising, selection
are we supposed to link point 4 to 12..or is there any other way to explain point 12??

 

[histephenson007]

i read it in ocr but they havent given an explanation for it..if you have the book its selection n evolution.pg 251-2. its there in the revision guide too!

then, as the book suggests,
(N - normal allele, S- sickle cell anaemia allele)

NN - Safe from sickle cell anaemia, but prone to malaria infection because the red blood cells are in good shape. So, easy for plasmodium pathogens to travel through the red blood cells.

NS - Safe from sickle cell anaemia because there are still many normal red blood cells to carry oxygen. Safe from malaria because the sickle red blood cells do not allow plasmodium pathogens to travel through them.

SS- Fatal for sickle cell anaemia. The person will die at a young age due to severe sickle cell anaemia. This person might theoretically be immune to malaria.

 

[smartangel]

Explain why variation is important in selection;

1. ref. continuous / discontinuous variation ;
2. genetic / inherited variation ;
3. variation in phenotype / characteristics / AW ;
4. (can be due to) interaction of genotype and environment ;
5. e.g. of characteristic that influences survival ;
6. ref. intraspecific competition / struggle for existence ;
7. those with favourable characteristics survive / AW ;
8. pass on favourable characteristics to offspring ;
9. those with disadvantageous characteristics die ;

plz explain continous And disacontinuous variation!?

 

[smartangel]

then, as the book suggests,
(N - normal allele, S- sickle cell anaemia allele)

NN - Safe from sickle cell anaemia, but prone to malaria infection because the red blood cells are in good shape. So, easy for plasmodium pathogens to travel through the red blood cells.

NS - Safe from sickle cell anaemia because there are still many normal red blood cells to carry oxygen. Safe from malaria because the sickle red blood cells do not allow plasmodium pathogens to travel through them.

SS- Fatal for sickle cell anaemia. The person will die at a young age due to severe sickle cell anaemia. This person might theoretically be immune to malaria.

got it!thanks

 

[angelgirl:)]

well explain the role of synapses.....
what is adaptation......spatial summation.......

adaptaion-the amount of neurotransmitter released at the synapse steadly falls off in response to constant stimulation of neurotranmitter chemicals so it gets exhausted and the synapse is described us fatigue.The significane of fatigue is that it prevents damage to an effector through over stimulation...
spatial summation - a post synaptic neuron may recieve impulse from a large no. of impulse excitatry and inhibitory presynaptic neurone , this is known as convergence. The post synaptic neurone is able to summate the stimuli from all the presynaptic neurones. This enables the synaps to act as a centre for the integration of stimuli from a variety of sources and the production of co-ordenate response.that is it collects all the information and decides wat to do next--wether to repond to this stimuli or not...

 

[angelgirl:)]

i read it in ocr but they havent given an explanation for it..if you have the book its selection n evolution.pg 251-2. its there in the revision guide too!

i dont have the revision guide...
ya wat i know very well about this is...
---the homozygous people for sickle cell allel will die becouse of sickle cell anaemia so no effect of malaria as they already die from sickle cell anaemia
---the homozygous normal people will die from malaria
---but the heterozygous carrier of this sickle cell deisease will survive as they neither die from malaria nor from sickle cell anaemia..coz thay have 50% normal blood and 50% sickle cell blood...

 

[smartangel]

crossing over occurs between non sister chromatids of homologous chromosomes yeah?