A2 Biology | Post your doubts here

[Idris]

explain the role of natural selection in EVOLUTION?
ms mentions that individuals can potentially overproduce but do not do so cos most die b4 reaching maturity due to disease hunting etc......so as a result population size remains roughly constant.....now WTH has this to do with evolution

Natural selection is the tool for evolution, and the tool for natural selection is :crossing over, independent assortment and most importantly MUTATION, thus species having selective advantage multiply and eventually a new specie which can not inter breed with other species is evolved. evolution is the process where species emerge from existing ones

 

[hassam]

bioleaching can be done in situ>>what does it mean?
ooh i got it.....weel somebody myt find this useful http://wiki.biomine.skelleftea.se/wiki/index.php/In-situ_leaching

 

[omair tahir]

AoA
I need help wid 2 questions plx help.. I knw the answers but i cNt explain it properly so please help
Question ) describe the part played by the proximal convoluted tubules in the functioning of the kidneys [8]

And 2nd is
Explain how the collecting ducts in the kidneys may reduce the loss of water from the body.[7]

 

[Toby Dawson]

Hi, does anyone know what percentage (on average) I need to get in the A2 structured paper and the planning and analysis paper to get an A* considering I got 97% in AS bio? Thanks

 

[ousamah112]

what is the total number of ATPs produced during aerobic cycle??? I am confused.. is it 38,36 or 32??

 

[Toby Dawson]

what is the total number of ATPs produced during aerobic cycle??? I am confused.. is it 38,36 or 32??

Depends whether the 2 reduced NAD's from glycolysis in the cytoplasm are included or not.

 

[omair tahir]

38 if u r counting whle cycle...

 

[Idris]

wwell cn somebody tell em what happens in sympatric speciation.........>???
and i cant get the idea of forming hybrid between two inbred lines.......why are they genetically identical??(is it because the all have parents with same genetic makeup).....what is the purpose of inbreeding ........why new seeds need to be produced every year????

Sympatric speciation is the way in which new species arise without the original species being separated by a geographical barrier. The most common way this occurs is polyploidy that’s how wheat was made.

​

The use of hybrid seed requires the production of new seed each year; the use of seed from farmers' fields of a hybrid would result in a loss of 15 to 20 percent in yield in the succeeding crop because of the reduction of hybrid vigor from inbreeding

ifoI ​

iaIa djdhddh​

To achieve hetrozygosity and uniformity in maize plants, the specialists use inbreeding to produce homozygous plants which can then be crossed to form hybrid.​

rm ​

The seeds from hybrid plants are ​

The seeds from hybrid plants are usually not saved because the resulting progeny are less uniform and lack the productive and vigorous qualities of the original hybrid seeds​

usually not saved because the resulting progeny are less uniform and lack the productive and vigorous qualities of the original hybrid seeds​

and lack the productive and vigorous qualities of the original hybrid seeds​

 

[omair tahir]

Need help wid my questions please

 

[Idris]

AoA
I need help wid 2 questions plx help.. I knw the answers but i cNt explain it properly so please help
Question ) describe the part played by the proximal convoluted tubules in the functioning of the kidneys [8]

And 2nd is
Explain how the collecting ducts in the kidneys may reduce the loss of water from the body.[7]

As the globular filtrate moves through pct, the cell lining of lumen actively secretes sodium ions into blood capillary using energy from ATP. This lowers the concentration of solute in the epithelial cells, hence sodium ions diffuse passively from filtrate into cell , however the diffusion of sodium ions from filtrate takes place through special protein channels(carriers) which co-transport glucose. Thereby glucose moves down its concentration gradient in blood plasma. This increases the solute concentration of capillary fluid, which makes the water move from globular filtrate into blood plasma . Thus there is no overall change in the concentration of filtrate but the volume decreases considerably, about 65 percent of water is reabsorbed in this way and almost all glucose is reabsorbed here. This process is known is selective absorption , as only certain substances are reabsorbed.

Collecting duct runs down into the the medulla where solute concentration of the tissue fluid is very high, with a very low water potential. Water therefore moves out the collecting duct, by osmosis, until the water potential of urine is same as the water potential of the tissue fluid in the medulla, which may be much greater than the water potential of the blood. The degree to which this happens is controlled by ADH. It acts on the plasma membrane of the cells making up the walls of the CT in kidneys, this increases the permeability of membrane to water by increasing number the water permeable channels in the membrane.
I hope this covers the ms points, if not please do inform me.

 

[Executor]

Ok i dont mean to do spam or anything but please go to the following thread and make dua for all of us :
http://www.xtremepapers.com/community/threads/dua-for-all-candidates.14272/

Dont forget to share and Remember every share makes a difference

 

[cwswishy]

i have tried making notes for biology based on past papers mark scheme ( which i also include some main concept from textbook in my notes)....im not sure whether this method of studying is effective...what do you guys think?

 

[saudha]

i have tried making notes for biology based on past papers mark scheme ( which i also include some main concept from textbook in my notes)....im not sure whether this method of studying is effective...what do you guys think?

ITS A SHORTCUT.... BUT PRETTY MUCH AFFECTIVE.... BUT KEEP AN EYE ON THE DETAILED EXP

 

[cwswishy]

ITS A SHORTCUT.... BUT PRETTY MUCH AFFECTIVE.... BUT KEEP AN EYE ON THE DETAILED EXP

thx for ur opinion!hopefully it works for my A2 bio exam =)

 

[cwswishy]

can anyone give a complete explaination on why is mRNA of insulin insolated instead of DNA when forming genetic modified bacteria?? tqvm

 

[sanjeev khadka]

Natural selection is the tool for evolution, and the tool for natural selection is :crossing over, independent assortment and most importantly MUTATION, thus species having selective advantage multiply and eventually a new specie which can not inter breed with other species is evolved. evolution is the process where species emerge from existing ones

I wrote p3 practicals all with pencil..what will happen now..??will my paper be rejected..??Totally worried and scared!!

 

[hassam]

well dna contains all the genes so we ll have to cut the gene using restriction enzymes.....that wud be a very difficult task.....frthermore if we cut the gene..........the mRNA made from it Normally undergoes post transcriptional modification in which introns are spliced out....this cnt be done in bacteria as it has not got the enzymes to perform this task...

 

[hassam]

well....guyxxx.......m worried beacuse of time duration for exam....what do u think....is two hours enuf....especially when u have lots of suggest questions

 

[hassam]

Suggest an advantage of having photosystems, the electron transport chain and ATP
synthase as part of the thylakoid membrane?
i find bio papers quite tough bt GT ARE high compared to phy and chem which seems more easy.........do u guys also find bio papers hard(esp markingschemes)
one important point
DESCRIBE HOW RESTING MEMBRANE POTENTIAL IS mantained?
k there is na+/k+ pump.....everbody knws that ....bt one more thing that k+ voltage gated channels are leaky so some k+ also moves out passively....this also makes inside more -ve compared to outside

 

[user]

well....guyxxx.......m worried beacuse of time duration for exam....what do u think....is two hours enuf....especially when u have lots of suggest questions

aoa wr wb!

inshaAllah they'll be..
make sure u leave out all the questions u feel u dont know or u'll have to think a bit...and do the rest..do mark them or smthng so that u dont miss them in the end...this helps a lot..