A level Biology: Post your doubts here!

[farhan143]

Can anyone provide me link for online biology practical tutorials??
i found the maths online tutorial very interesting....

 

[hassam]

Explain, using examples, how the environment may affect the phenotype of an organism.
[8]
please anyone answer this question........i never seem to understand this question answer in the marking schemes......
also Describe the maturation of a spermatid into spermatozoan?
regards this question nothing is found in application booklet or revision guide or book...........apart from the very words that spermatids differentiates into spermatozoan

 

[hassam]

what will happen to the mitochondrion if it is placed in a concentrated solution........k exoosmosis will iooccur bt cn smone explain what effect the membranes in particular the crista experience.......

 

[omg]

anybody having papers of 2000 and 2001?????? even older 1999 or 1998?????? pls if u do give me the linkkk !!!! p4!!

 

[aliya_zad]

Explain, using examples, how the environment may affect the phenotype of an organism.
[8]
please anyone answer this question........i never seem to understand this question answer in the marking schemes......
also Describe the maturation of a spermatid into spermatozoan?
regards this question nothing is found in application booklet or revision guide or book...........apart from the very words that spermatids differentiates into spermatozoan

I guess i can help with the first one..
Variations are of two types-phenotypic and genotypic..
Genotypic variations are influenced by genes only whereas phenotypic variations are influenced by both environment and their genes.
Simple examples include eating habits which are responsible for a person's growth..Lets say the person has a gene for tallness but only if the person acquires the required protein will he able to grow tall..Similarly obesity can also result this way as we choose it for us- by eating fatty foods..( i mean the environment is wat has an effect on the phenotype)
Phenotypic variations can also be due to selection pressures..
Here we can take the peppered moth biston betularia as an example..(given in bio text book)
Initial stages all people cud find was moths with pale wings and dark markings giving a speckled appearance.
In the 19th century once industrialisation started growing rapidly in certain areas the numbers of black moths started appearing..
The selection pressure here was the predation of birds coz in areas of industrialization there was polluted air which often covered the tree branches with soot and black moths seem to be better camouflaged than the speckled ones. These selection pressures gives rise to variations enabling "survival of fittest" where organisms with best adapted variations suited to that environment survive.Overtime this causes a genetic drift and change in allele frequency resulting in the ''birth'' of black peppered moths..(This is like an elaborated example)..
So u can go on with more examples as given in the text...
Hope this helped!!

 

[Sagnesia]

i have sum questions related to selection and pressure......can somebody plz give me da answer....
1. eplain da role of isolating mechanisms in da evolution of new species
2.describe da example of artifical selection
3.explain,wid example,how environmental factors can act as stabilising or evolutionary forces of natural selection

 

[Asad]

MCQ 30 http://www.xtremepapers.com/CIE/International A And AS Level/9700 - Biology/9700_s06_qp_1.pdf
Examiner report is wrong definitely?

 

[hassam]

i have sum questions related to selection and pressure......can somebody plz give me da answer....
1. eplain da role of isolating mechanisms in da evolution of new species
2.describe da example of artifical selection
3.explain,wid example,how environmental factors can act as stabilising or evolutionary forces of natural selection

q1.here u ll describe both the allopatric and sympatric speciation......for allopatric u can say that a population gets isolated due to a geographical barrier so hence they cn not breed together and no gene flow occurs.....different selection pressures operate on the two separate populations now(which were once the same population)only those alleles conferring a selective advantage will be passed on since those organsims will have a greater reproductive potential......over time allele frequency changes .....when this occurs we say evolution has occured.....overtime the two populations will no longer be able to interbreed to produce fertile offspring ..when this occurs we say speciation has occured.......example (A large lake evaporates slowly over time, leaving many small ponds. The large lake had
inhabited by one species of fish, but over time, each small pond is inhabited by a different species of fish, each species a descendant of the species which inhabited the large lake. This is an example of allopatric speciation.)
Sympatric speciation......this is where reproductive isolation occurs.......say for example a mutation occurs during meiosis which results in one organism gaining all of the chromosomes and one gaining none.........so the gamete will be diploid in this case......if two such gametes come and fuse together .....the resulting tetraploid organism will be a new species different from the original diploid organism in which the meiosis went wrong.......tetraploid organism's gametes will be diploid and if these gametes fuse with a haploid organism......they will produce a sterile hybrid (i.e infertile) so reproductive isolation occured without any geographical isolation due to a mutation........mutation in which meiosis goes wrong like i mentioned above is called non-disjunction

 

[hassam]

EXAMPLE OF ARTIFICIAL SELECTION:

 

[hassam]

explain,wid example,how environmental factors can act as stabilising or evolutionary forces of natural selection
CHEK mary jones book.......there is an example in which rabbits are plunged into ice age...........in this case white rabbits will be slected for by the environment not the more common agouti rabbits as before.....so environment is selcting for a phenotypic extreme.......thats why its a directional selection

 

[omg]

i have sum questions related to selection and pressure......can somebody plz give me da answer....
1. eplain da role of isolating mechanisms in da evolution of new species
2.describe da example of artifical selection
3.explain,wid example,how environmental factors can act as stabilising or evolutionary forces of natural selection

i wantt help in dese qsss tooooooo!!!

 

[Ahmed Ali Akbar]

MCQ 30 http://www.xtremepapers.com/CIE/International A And AS Level/9700 - Biology/9700_s06_qp_1.pdf
Examiner report is wrong definitely?

No ...it's not.

 

[JD REBORN]

Hey can somebody explain to me how to carry out serial dilution in Q1)ai.

 

[soumayya]

since u need to halve the conc. of enzyme solution, the conc. of the three additional beakers would be: 2.5%, 1.25% and 0.625%.
2.5% enzyme solution: take 10 cm^3 of 5 % enzyme solution + 10 cm^3 of distilled water W
1.25 % enzyme solution: take 10 cm^3 of 2.5 % enzyme solution + 10 cm^3 of distilled water W
0.625 % enzyme solution: take 10 cm^3 of 1.25 % enzyme solution + 10 cm^3 of distilled water W

Hpe zat hlps...

 

[JD REBORN]

since u need to halve the conc. of enzyme solution, the conc. of the three additional beakers would be: 2.5%, 1.25% and 0.625%.
2.5% enzyme solution: take 10 cm^3 of 5 % enzyme solution + 10 cm^3 of distilled water W
1.25 % enzyme solution: take 10 cm^3 of 2.5 % enzyme solution + 10 cm^3 of distilled water W
0.625 % enzyme solution: take 10 cm^3 of 1.25 % enzyme solution + 10 cm^3 of distilled water W

Hpe zat hlps...

Wouldn't this make the last beaker with 20 cm3 while the others are all 10 cm3

 

[soumayya]

for ur exp. u would hve to use constant volumes, thus using only half of it and discarding the rest...

 

[Sagnesia]

stuck in a huge enigma........plz can somebody give me da ans of
1.describe one example of artifical selection
2.eplain da role of isolating mechanisms in da evolution of new species
i hav lots of confusion regarding dis chapter nd esp those 2 question...

 

[JD REBORN]

for ur exp. u would hve to use constant volumes, thus using only half of it and discarding the rest...

So we will discard 10cm3 from last beaker?

 

[soumayya]

during the exp. u'll use only 10 cm^3 to keep vol constant..so obviously u'll hve to discard it..

 

[omg]

can i get a note on the qs: 'describe why variation is important in natural selection'???? PLEASE!!!!