A level Biology: Post your doubts here!

[hassam]

please tell anser of how natural selection brings about evolution?

 

[Star-fire]

http://www.xtremepapers.com/CIE/Interna ... _qp_13.pdf
can some1 explain questions no. 38 & 40. PLZ
The answers r:A and B

 

[lychee26]

Copy/paste your question here.
i cant open the papers for some reason :/

 

[sweetiepie]

in question 40

the answer is A cox its according to number of individuals just c it

hope it helps

 

[Star-fire]

in question 40

the answer is A cox its according to number of individuals just c it

hope it helps

Thts wut i thought but the actual answer is B,
anywayz my exam is over :Yahoo!:
and thnx 4 tryin

 

[rz123]

please tell anser of how natural selection brings about evolution?

my try:
if there is no change in environment and it is stable, natural selection is unlikely to bring any evolution, the most common alleles with max advantages will be passed on to the successive generations. However, if there is a change in an environment, alleles which were previously advantageous to some specie may become disadvantageous now. for example in a snowy environment the individuals in a species of mammal may have white fur that camouflages them against the snow and confers an advantage in escaping predators. If the climate changes so that snow no longer lies on the ground, then animals with white fur may be more likely to be killed then the brown fur ones. those with brown fur are now most likely to reproduce and pass on their alleles to the next generation, over time brown may become the most common colour in the population. this is an example of evolutionary selection

 

[rz123]

cn somebody explain me how synapse are involved with memory

here is what i found in a book:
synapses are involved in memory and learning.despite much research, little is yet known about how memory operates. however, there is much evidence that it involves synapses. For example, if your brain frequently receive information about two things at same time, say a sound of a particular voice and a site of particular face, then it is thought that new synapses form in your brain that links the neurones involved in the passing of information along the particular pathways from your ears and eyes. In future, when you hear the voice, information flowing from your ears along this pathway automatically flows into the other pathway too, so that your brain pictures the face which goes with the voice.
hope that helps!!

Very Fascinating! Good Answer. i couldn't find anything about it in the revision guide :x

 

[Dayyanah]

can anyone pls hepl me with resting potential ans action potential
the cambridge text book doesnt make things too clear for me
thnx in advance

 

[sweetiepie]

viewtopic.php?f=26&t=11977

check these 4 notes

 

[rz123]

can anyone pls hepl me with resting potential ans action potential
the cambridge text book doesnt make things too clear for me
thnx in advance

 

[XPFMember]

Assalamoalaikum!!

In June:2010 Paper:41

Q:8 (b) (i) Outline, with reference to CF, what is meant by gene therapy.

Mark scheme says:

1 alters genotype ;
2 insert, dominant/normal, allele ; R gene
3 into, affected/appropriate, cells ;
4 use of vector/named vector ;
5 ref. recombinant DNA ;


In point 2: why does it say 'R gene'
er says: Common errors included references to gene rather than allele.


But the application booklet says: Since it is a recessive condition, such gene therapy does not need to remove or
replace the existing genes in the person’s cells – adding a working copy of the gene
to a cell and having it expressed would be sufficient to permit that cell to transport
chloride ions normally.

The Cambridge Revision guide also refers to inserting the gene. :%)


What's wrong...and whats right????

 

[Dayyanah]

@ sweetiepie thanx aloooooot
@ rviboy once agen, thnx

 

[rz123]

Your welcome

 

[hassam]

whats the meaning of GENETIC DRIFT

 

[sweetiepie]

@ sweetiepie thanx aloooooot

Your Welcome

 

[sweetiepie]

whats the meaning of GENETIC DRIFT

The process of change in the genetic composition of a population due to chance or random events rather than by natural selection, resulting in changes in allele frequencies over time.

OR

Random variation in gene frequency from one generation to another.

BOTH U CAN WRITE

 

[XPFMember]

Assalamoalaikum!!

In June:2010 Paper:41

Q:8 (b) (i) Outline, with reference to CF, what is meant by gene therapy.

Mark scheme says:

1 alters genotype ;
2 insert, dominant/normal, allele ; R gene
3 into, affected/appropriate, cells ;
4 use of vector/named vector ;
5 ref. recombinant DNA ;


In point 2: why does it say 'R gene'
er says: Common errors included references to gene rather than allele.


But the application booklet says: Since it is a recessive condition, such gene therapy does not need to remove or
replace the existing genes in the person’s cells – adding a working copy of the gene
to a cell and having it expressed would be sufficient to permit that cell to transport
chloride ions normally.

The Cambridge Revision guide also refers to inserting the gene. :%)


What's wrong...and whats right????

anybody?

 

[sagystu]

could some one help explain the graph

espicially why and how does the energy level lower again ?

 

[phro5031]

can i request some past papers for A.LEVEL BIOLOGY , I can't find them anywhere , i want paper 2 for A.L. bio. from 1993 to 2002 , i know it's hard , but please try , i also want their mark schemes if possible! , thanks!

 

[Dayyanah]

hey
i have a few qns i need help with

1. explain why a nerve impulse travels faster in a myelinated neurone than in a non-myelinated one? (refer to saltatory conduction) -2 marks

2. explain what happens to the neurotransmitter after it has passed information across a cholinergic synapse -3 marks

3. explain why lateral shoots of a plant increase in lenght when apical buds are removed -3 marks

4.gibberellins is a plant growth regulator that influences stem elongation and seed germination. describe the role of gibberellins in bringing about seed germination. -4 marks

thanx