A level Biology: Post your doubts here!

[rz123]

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

 

[Sagnesia]

1 question plz
explain,using named example,how mutation can affect phenotype?? 7 marks

 

[rz123]

xplain,using named example,how mutation can affect phenotype?? 7 marks hope it helps...

 

[omg]

but the ms asks for continuous , discontinuous, genetic inherited phenotypic variations!!! its q7 from may/june 2005 p4!!

 

[aliya_zad]

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

variations are of 2 types- phenotypic and genotypic.
phenotypic variations are influenced by environmental factors whereas genotypic variations are not influenced by environmental factors.
Variations can also be continous or discontinuous.For example gender of an organism is a discontinuous variation whereas height of an organism is a continuous variation.
Variations can result due to selection pressures as well..For eg..if selection pressures act against small individuals but not larger ones the range of variation shifts towards the larger size..this results in a directional selection and could have occured due to a change in allele frequency..So when pressures are applied on organisms they give rise to variations enabling "survival of the fittest"where the organisms with variations best adapted to the surroundings survive.These organisms are able to pass on their favourable characteristics to their offspring while those who lack such features die.
Genotypic variations can occur as aresult of gene mutation as well.For instance in the disease sickle-cell anaemia the existence of sickle shaped RBC'S is caused due to a gene mutation and this helps people survive better in regions where malaria is endemic.


http://en.wikipedia.org/wiki/Natural_selection
I guess this can help u out as well..

 

[Sagnesia]

Can anyboby describe me this question....Describe the part played by auxins in apical dominance in a plant shoot
ms points...7 max
16. IAA / plant growth regulator ; R plant hormone
17. synthesised in, growing tips / apical buds / meristems ; R root tip
18. moves by diffusion ;
19. moves by active transport ;
20. from cell to cell ;
21. also, mass flow / in phloem ;
22. stimulates cell elongation ; R cell enlargement
23. inhibits, side / lateral, buds / growth ; A inhibits branching
24. plant grows, upwards / taller ; A stem elongates
25. auxin not solely responsible or interaction between auxin and other plant growth regulators ;
26. AVP ; e.g. role of ABA and lateral bud inhibition
27. AVP ; e.g. cytokinins antagonistic to IAA / gibberellins enhance IAA

 

[iceman]

hey everyone plz explain Meselson-Stahl experiment
thanks in advance

 

[rz123]

hey everyone plz explain Meselson-Stahl experiment
thanks in advance

http://en.wikipedia.org/wiki/Meselson–Stahl_experiment

 

[iceman]

http://en.wikipedia.org/wiki/Meselson–Stahl_experiment

thanks but do questions related to this experiment come often??

 

[rz123]

thanks but do questions related to this experiment come often??

no, at-least not in mcq's, i have hardly seen mcq's related to it but don't know about theory. u shud understand the experiment...

 

[omg]

pls can sombody tell me the benfits of maintaining biodiversity??

 

[hassam]

mantains food webs....mantains large gene pool.....ethical reasons e.g some people think that we must protect and preserve this vast array of species for future generations to comE.....some species can serve as a food source for humans.,....plants like herbs can have use in making medicines....some useful products can be obtained from these species e.g (fish oil from fish).....trees can provide wood for construction purposes and also help in preventing soil erosion so reducing chance of floods......rare beautiful species cn also serve as a tourist attraction(.g coral reefs in marine ecosystem or peacocks etc.)

 

[hassam]

http://www.xtremepapers.com/CIE/International A And AS Level/9700 - Biology/9700_w09_qp_52.pdf
q 3 b(ii)

 

[omg]

http://www.xtremepapers.com/CIE/International A And AS Level/9700 - Biology/9700_w09_qp_52.pdf
q 3 b(ii)

thanls
and for ur qs ;
there is not sufficent data to support the hypothesis . comparisons b/w ethanol con and temp is nt a valid one.for reliable results, all ethanol conc shud b tested at all temps.

 

[omg]

pls smbdy explain me the process of oogenesis i find it pretty confusing idk why :/ hekp neededdddddddd

 

[DANGERBP]

umm guyz do u happen to have a level bio note on biodiversity ive been searchin but me no find ! =p
and the bio syllabus plzzz
ide b grateful ! =)

 

[DANGERBP]

pls smbdy explain me the process of oogenesis i find it pretty confusing idk why :/ hekp neededdddddddd

huuh thats the first time i heard of this word ! is it included in the syllabus (a level ) !! ?? =S

 

[princesszahra]

its the process of formation of ova!!
http://www.sparknotes.com/testprep/books/sat2/biology/chapter7section2.rhtml

 

[omg]

huuh thats the first time i heard of this word ! is it included in the syllabus (a level ) !! ?? =S

Yes it is in the applications. Human reproduction

 

[DANGERBP]

Yes it is in the applications. Human reproduction

lol ya i took it but just forgot it i should so start revising =p

heres wat i know about it
<=
the undifferentiated premodial germ cells in the fetal ovaries, the oogonia divide mitotically to give rise to 6 to 7 million oogonia by the 5th month of gestatation . at this time mitotic division starts .
at the end of the fetal stage the oogonia begins the early steps of 1st meotic division (primary oocyte division )
from puberty primary follicle sstarts developing into 2ndary fol. and it completes its 1st meotic division b4 ovulation.
2 daughter cells are produced . most of the cytoplasm is recieved by the secondary oocyte (1 of the 2 daughter cells )
the other daughter cell forms a polar boy
and the 2nd meoticdivision isnot completed until the head of thespermatozoa enters during firtilization

lol guess thats all we need to know ! =p =)