A2 Biology | Post your doubts here

[Nibz]

And this one also..plz..


Explain the role of isolating mechanisms in the evolution of new species;

AOA!

Species are evolved by allopatric as well as sypatric speciation. Isolating mechanisms play very imp. role in separation of different groups of species which may later on develop into new species. In allopatric speciation, geographical isolation occurs in which groups of species move to new places and separate by geographicsal barriers, i.e a mountain range or large forest etc.
Some organisms may move to a distant island surrounded by vast ocean around. In sympatric speciation (examples include evolution of wheat) when two parents from different species breed, the chromosomes are not the same, so meiosis becomes a problem. A hybrid species, if successful, is generally a polypoid with many sets of chromosomes. Many species are isolated by behavioral, temporal, ecological & structural isolation mechanisms. Isolated groups or populations cannot interbreed because their members cannot breed among themselves; hence no gene flow occurs and genes cannot mix b/w populations. Different selection pressures operate in specific environment,. Natural selection occurs and organisms with best adapted traits survive. It brings about change in allele frequencies and gene pool of population becomes different. Over a long period of time, such differences, due to isolating mechanisms, prevent interbreeding and species are reproductively isolated. Once reproductively isolated, the new species emerge are different from ancestral species.

A bit too long, I guess. But you can 'filter out' the best points.

 

[XPFMember]

AOA!

Species are evolved by allopatric as well as sypatric speciation. Isolating mechanisms play very imp. role in separation of different groups of species which may later on develop into new species. In allopatric speciation, geographical isolation occurs in which groups of species move to new places and separate by geographicsal barriers, i.e a mountain range or large forest etc.
Some organisms may move to a distant island surrounded by vast ocean around. In sympatric speciation (examples include evolution of wheat) when two parents from different species breed, the chromosomes are not the same, so meiosis becomes a problem. A hybrid species, if successful, is generally a polypoid with many sets of chromosomes. Many species are isolated by behavioral, temporal, ecological & structural isolation mechanisms. Isolated groups or populations cannot because their members cannot breed among themselves; hence no gene flow occurs and genes cannot mix b/w populations. Different selection pressures operate in specific environment,. Natural selection occurs and organisms with best adapted traits survive. It brings about change in allele frequencies and gene pool of population becomes different. Over a long period of time, such differences, due to isolating mechanisms, prevent interbreeding and species are reproductively isolated. Once reproductively isolated, the new species emerge are different from ancestral species.

A bit too long, I guess. But you can 'filter out' the best points.

Waalaikumassalam wr wb!

That was very helpful...jazakAllahu khairen!!!

 

[Nibz]

Assalamoalaikum wr wb!

Can someone plz help me frame the answer to this question...plz

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 ;

Variation means the presence of different characteristics or traits. It results in different survival rates of organism, which ultimately leads to reproductive success or failure. Organisms with most suitable traits and those that are best adapted to a stable environment have a survival advantage. Those surviving better get more chances of reproduction. They pass on their favourable characteristics to their offsprings and their number further increases. Whereas, those with disadvantageous characteristics cannot survive and die.

Not too good. But may help you somehow.

 

[XPFMember]

Variation means the presence of different characteristics or traits. It results in different survival rates of organism, which ultimately leads to reproductive success or failure. Organisms with most suitable traits and those that are best adapted to a stable environment have a survival advantage. Those surviving better get more chances of reproduction. They pass on their favourable characteristics to their offsprings and their number further increases. Whereas, those with disadvantageous characteristics cannot survive and die.

Not too good. But may help you somehow.

yup..did help...though i have no clue about the first 3-4 points in ms

 

[Nibz]

Doesn't matter. Usually, a '6 marks (MAXIMUM)' question comes on the importance of natural selection. And explaining briefly 3-4 mark scheme points will easily get you those marks.

 

[XPFMember]

Doesn't matter. Usually, a '6 marks (MAXIMUM)' question comes on the importance of natural selection. And explaining briefly 3-4 mark scheme points will easily get you those marks.

Variation means the presence of different characteristics or traits. There will be genetic variation within the population. The interaction of the genotype and environment results in phenotypic variation. Variation results in different survival rates of organism, which ultimately leads to reproductive success or failure. Organisms with most suitable traits and those that are best adapted to a stable environment have a survival advantage. Those surviving better get more chances of reproduction. They pass on their favourable characteristics to their offsprings and their number further increases. Whereas, those with disadvantageous characteristics, cannot survive, and die.
^I think this includes those points too..does this seem ok?
Please, if anyone else can suggest something...make sure you do that

 

[XPFMember]

Assalamoalaikum wr wb!

Explain why promoters need to be transferred into the recipient bacteria together with the genes.

Only the better candidates were able to show that promoters were needed to ensure that the genes
were “switched on” in order to produce the correct protein. It was rare, however, to see a reference
to the fact that a eukaryotic gene had been placed in a prokaryotic cell.
I don't understand the last part..

 

[smartangel]

okay i just have a small confusion regarding Section B. my answers are really short. they do cover all the points in the marking scheme but are hardly half a page. specially the 8 mark question. is it okay? also.. the ms has short points. are they sufficient enough to gain full marks or do we have to elaborate on them?

 

[smartangel]

also in the question, Describe the process of oxidative phosphorylation in the mitochondrion. [9] from June 08..
i dont understand how to connect the chemiosmotic theory that is concerned with production of ATP to the electron being transferred to oxygen and being reduced to water when hydorgen is added. please explain!!

 

[smartangel]

could someone please explain lac operon?

 

[XPFMember]

also in the question, Describe the process of oxidative phosphorylation in the mitochondrion. [9] from June 08..
i dont understand how to connect the chemiosmotic theory that is concerned with production of ATP to the electron being transferred to oxygen and being reduced to water when hydorgen is added. please explain!!

Assalamoalaikum wr wb!
Describe the process of oxidative phosphorylation in the mitochondria.
1. reduced, NAD / FAD ;
2. passed to ETC ;
3. inner membrane / cristae ;
4. hydrogen released (from reduced, NAD / FAD) ; R H2
5. split into electrons and protons ;
6. protons in matrix ;
7. electrons pass along, carriers / cytochromes ;
8. ref. redox reactions ;
9. ref. energy gradient ;
10. energy released ; R produced
11. protons (pumped) into intermembrane space ;
12. proton gradient ;
13. protons pass through (protein) channels ;
14. ATP synthase / stalked particles ;
15. ATP produced ;
16. chemiosmosis ;
17. electron transferred to oxygen ;
18. addition of proton (to oxygen) to form water / (oxygen) reduced to water ;
Reduced NAD and reduced FAD are passed to the electron transport chain. Here, hydrogens are removed from the two carriers and each is split into proton and electron. The electron is transferred to the electron carriers, whilst the protons remain is solution in the mitochondrial matrix.
The hydrogens, picked up by the NAD and FAD, are now split into electrons and protons. The electrons are passed along the electron transport chain, on the inner membrane of the mitochondrion. As they move along the chain, they lose energy which is then used to actively transport the hydrogen ions from the matrix of the mitochondrion, across the inner membrane and into the inter-membrane space. This builds up a high concentration of hydrogen ions in this space. They are allowed to diffuse back into the matrix through special channel proteins that work as ATPases. Associated with each channel is the enzyme ATPsynthase. The movement of hydrogen ions through the ATPases provide enough energy to make ADP combine with the inorganic phosphate to produce ATP. At the end of the chain, the electrons reunite with the protons from which they were originally split. They combine with oxygen to produce water.

 

[XPFMember]

^that was my answer..
my notes compiled for respiration:

 

[smartangel]

Assalamoalaikum wr wb!
Describe the process of oxidative phosphorylation in the mitochondria.
1. reduced, NAD / FAD ;
2. passed to ETC ;
3. inner membrane / cristae ;
4. hydrogen released (from reduced, NAD / FAD) ; R H2
5. split into electrons and protons ;
6. protons in matrix ;
7. electrons pass along, carriers / cytochromes ;
8. ref. redox reactions ;
9. ref. energy gradient ;
10. energy released ; R produced
11. protons (pumped) into intermembrane space ;
12. proton gradient ;
13. protons pass through (protein) channels ;
14. ATP synthase / stalked particles ;
15. ATP produced ;
16. chemiosmosis ;
17. electron transferred to oxygen ;
18. addition of proton (to oxygen) to form water / (oxygen) reduced to water ;
Reduced NAD and reduced FAD are passed to the electron transport chain. Here, hydrogens are removed from the two carriers and each is split into proton and electron. The electron is transferred to the electron carriers, whilst the protons remain is solution in the mitochondrial matrix.
The hydrogens, picked up by the NAD and FAD, are now split into electrons and protons. The electrons are passed along the electron transport chain, on the inner membrane of the mitochondrion. As they move along the chain, they lose energy which is then used to actively transport the hydrogen ions from the matrix of the mitochondrion, across the inner membrane and into the inter-membrane space. This builds up a high concentration of hydrogen ions in this space. They are allowed to diffuse back into the matrix through special channel proteins that work as ATPases. Associated with each channel is the enzyme ATPsynthase. The movement of hydrogen ions through the ATPases provide enough energy to make ADP combine with the inorganic phosphate to produce ATP. At the end of the chain, the electrons reunite with the protons from which they were originally split. They combine with oxygen to produce water.

THANKS A LOT!

 

[Idris]

Assalamoalaikum wr wb!
wanted to share this, I've written it myself with the help of ms. If you think there's any mistake, do let me know. Hope it helps. InshaAllah

Explain how a change in the nucleotide sequence in DNA may affect the amino acid sequence in a protein and hence the phenotype of the organism. (J’09 Q:9a)

1. code is three, bases / nucleotides ; A triplet code
2. (gene) mutation ; R chromosome mutation
3. base, substitution / addition / deletion ;
4. addition / deletion, large effect (on amino acid sequence) ;
5. frame shift ;
6. completely new code after mutation / alters every 3 base sequence which follows ;
7. (substitution) often has no effect / silent mutation ;
8. different triplet but same amino acid / new amino acid in non-functional part of protein ;
9. (substitution) may have big effect (on amino acid sequence) ;
10.could produce ‘stop’ codon ;
11.sickle cell anaemia / PKU / cystic fibrosis ;
12.reference to transcription or translation in correct context ; A description
13.AVP ; e.g. protein produced, is non-functional / not produced / incomplete

A triplet of bases is what which codes for an amino acid. Gene mutation may alter this code by a base addition or deletion and even by a base substitution. Base addition or deletions have large effects as they cause a frame shift, because they alter each 3 base sequence which follows and hence a completely new code after mutation. Substitution, on the other hand, often has no effect and it’s often called the silent mutation. This is because there are more than one triplets coding for the same amino acid, so even after substitution, if it codes for the same amino acid, it won’t have any effect. Though at times, it does produces big effects. For example, if it produces a stop codon, the polypeptide would never be completely formed. Similarly, it may result in a different amino acid, for example, in the case of sickle cell anaemia, a substitution results in the amino acid valine at the sixth position in the B chain instead of Glutamic acid.

(Didn't include point no.12...dunno how to add )

Change in the base sequence cause the tRNA to bring different amino acid as the codon read is different. This leads to different amino acid sequence of a protein, as a result different primary structure of protein is made which ultimately affects the phenotype. (Just explanation)

 

[Idris]

ITS NOT REALLY A CIE QUESTION BT.....a doubt in my mind.....how FSH can cause superovulation when it normally leads to one oocyte per cycle only ,......any idea

I am not sure but maybe during IVF, which involves the administration of hormones which have similar action to Fsh stimulate development of multiple follicle in ovaries due to its different concentration. (hormonal dis balance)

 

[Idris]

Explain how the structure of the leaves of maize plants enables them to
photosynthesise more effectively at high temperatures than wheat plants.
ms of this question says
plasmodesmata between bundle sheath cells and mesophyll cells
relevant comment on stomata
what these two points have to do wid the question

The bundle sheath is surrounded by mesophyll cells which doesn't have any air spaces, so that the rubisco enzyme( which has high affinity for o2) present in the sheath doesn't have any direct contact with oxygen in the intra cellular space and any exchange of air is through plasmodesmata in mesopyll. This arrangement only allows the oxaloacetate to enter sheath where it releases co2 .This refers to the maize ability to minimize photo respiration by this arrangement so that they can photosynthesis at high temperature, at which the stomata close to reduce the water loss by transpiration so that there is high conc. of oxygen in the intra cellular space. Sorry the previous explanation was very vague.

 

[Idris]

okay i just have a small confusion regarding Section B. my answers are really short. they do cover all the points in the marking scheme but are hardly half a page. specially the 8 mark question. is it okay? also.. the ms has short points. are they sufficient enough to gain full marks or do we have to elaborate on them?

I think a explanation would help because often you need to show the connection between points.

 

[Mekal]

I downloaded the syllabus of 2011 & 2012 of A-Level Biology and compared them, and i found nothing to be changed.

My teacher says that it did change !

Is that true ?

 

[hassam]

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

 

[hassam]

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????