A level Biology: Post your doubts here!

[qwertypoiu]

P12 may 2012 q1 explain

C.
D is too large, a thousand micrometer is 1mm!
That would mean we would be able to see cells with naked eyes!
10 to 100 micrometer range is correct, seeing as one of the largest cells in humans is the egg cell, which may have diameter of 0.1mm. (which is 100 micrometer. It is important to learn the sizes!)
You'd not choose B and definitely not A, because you know mitochondria have size of one micrometer.

 

[qwertypoiu]

P12 may 2012 q32 pls explain

COPD cannot be reversed. Once you have emphysema and your alveoli have exploded, how will they come back? These are delicate tissue, important for gas exchange, there is currently no way of growing more alveoli by treatment.
Or at least I've never heard of it... So I'd go for A.

 

[qwertypoiu]

q23 q24 may 2012 p12

23:
Casparian strip is located on endodermis. The material deposited there are suberin. Which blocks water from entry, so they're forced to move by symplast pathway. Even symplast pathway may be blocked as the plant grows, to leave only a few passage cells.
So obviously B, just have to learn this from Transport chapter.

24:
1. apoplast pathway does not include any living components. Molecules only travel through walls.
2. So obviously no crossing of vacuole membrane... That happens in symplast pathway.
3. It includes cell wall as I just mentioned.
4. Nope. Travel through xylem is by mass flow.
So A.

 

[Sadi66]

xylem is made of cell wall?

 

[Sadi66]

Pls explain
MAY 2012 P12 ;
WHY FATTY ACIDS CONSIDERED SAME AS FATS, ITS HYDROLYSED
Q21 EXPLAIN
Q27 EXPLAIN
___________________
OCT NOV 2012 P11:"
Q33 EXPLAIN
_____________
may june 2011 p12:
Q28 : osmosis in xylem?

 

[qwertypoiu]

xylem is made of cell wall?

Xylem has lignified cell wall. However, water does not travel through the walls, but through the lumen, so this cannot be considered apolplast pathway.

 

[Sadi66]

Xylem has lignified cell wall. However, water does not travel through the walls, but through the lumen, so this cannot be considered apolplast pathway.

Pls explain
MAY 2012 P12 ;
WHY FATTY ACIDS CONSIDERED SAME AS FATS, ITS HYDROLYSED
Q21 EXPLAIN
Q27 EXPLAIN
___________________
OCT NOV 2012 P11:"
Q33 EXPLAIN
_____________
may june 2011 p12:
Q28 : osmosis in xylem?

 

[qwertypoiu]

Pls explain
MAY 2012 P12 ;
WHY FATTY ACIDS CONSIDERED SAME AS FATS, ITS HYDROLYSED
Q21 EXPLAIN
Q27 EXPLAIN
___________________
OCT NOV 2012 P11:"
Q33 EXPLAIN
_____________
may june 2011 p12:
Q28 : osmosis in xylem?

If a plant contains fat, it must have fatty acid as well. Fatty acids are a part of lipids.

Q21:
1. True
2. True
3. False. tRNA anticodons will be very similar to that of DNA strand used as a template for transcription, but cannot possibly be the same, as the Thymine nucleotides on DNA will be Uracil on RNA.

Q27. All of them will be found in blood, tissue fluid, and lymph. Carbon dioxide is a small molecule, it can obviously pass through capillary walls to be part of tissue fluid, and also lymph. Glucose is dissolved in blood plasma and is needed by respiring cells, it also has to be in tissue fluid. And therefore lymph as well. Glucose is also small enough to move through wall of capillary. And Yes, white blood cells also are small enough to move through capillaries. Antibodies are found especially concentrated in lymph I think, because WBCs are found in large numbers there.

Q33: D. The graph shows percentage of smokers every year. However, every year population is also OK increasing. So if at beginning around 80% are smokers then later 32% are smokers it might seem okay to conclude that the number of men who were smokers decreased by 60%, but this cannot be true, since population has changed, option D actually states "number of men" so it cannot be true.

Q28: yes, when water has to travel through xylem it will go from root hair to endodermis by symplast or apoplast pathway, symplast pathway is movement by osmosis.

 

[Sadi66]

If a plant contains fat, it must have fatty acid as well. Fatty acids are a part of lipids.

Q21:
1. True
2. True
3. False. tRNA anticodons will be very similar to that of DNA strand used as a template for transcription, but cannot possibly be the same, as the Thymine nucleotides on DNA will be Uracil on RNA.

Q27. All of them will be found in blood, tissue fluid, and lymph. Carbon dioxide is a small molecule, it can obviously pass through capillary walls to be part of tissue fluid, and also lymph. Glucose is dissolved in blood plasma and is needed by respiring cells, it also has to be in tissue fluid. And therefore lymph as well. Glucose is also small enough to move through wall of capillary. And Yes, white blood cells also are small enough to move through capillaries. Antibodies are found especially concentrated in lymph I think, because WBCs are found in large numbers there.

Q33: D. The graph shows percentage of smokers every year. However, every year population is also OK increasing. So if at beginning around 80% are smokers then later 32% are smokers it might seem okay to conclude that the number of men who were smokers decreased by 60%, but this cannot be true, since population has changed, option D actually states "number of men" so it cannot be true.

Q28: yes, when water has to travel through xylem it will go from root hair to endodermis by symplast or apoplast pathway, symplast pathway is movement by osmosis.

can you explain this point 2 in q21:

 

[Sadi66]

qwertypoiu and everyone pls help in these also:: I
OCT 2012 P13:
Q39
______________________________
MAY 2013 P11
Q15: WHY OPTION A WRONG'
Q31
Q39 THE NITROGEN FIXING REQUIRE ANAEROBIC CONDITION FOR N FIXING?

________________________________
MAY 2013 P12:
Q31 EXPLAIN ALL OPTIONS PLS
Q29
Q32
Q35 : PLS EXPLAIN THIS IN DETAIL LIKE WHATS INFLAMMATION AND SCARRED ?
Q40
______________________________
MAY 2013 P13:
Q10; WHY D NOT
Q12
Q15
Q39
________________________
OCT 2013 P12
Q29
Q35
Q39 WHATS INORGANIC NITROGEN ?
Q40
_________________________
OCT 2013 P13;
Q22 WHY C WRONG
_________________________
JUNE 2008 Q27?

 

[qwertypoiu]

can you explain this point 2 in q21:

tRNA are strands of RNA. So obviously they have a sugar phosphate backbone, like how DNA nucleotides join up. They have a long length, and so will twist and coil (much like protein I guess) to form hydrogen bonds with its own nucleotide bases...

As you can see, the section on top is for amino acid to bond.
The bottom parts become the anticodons.
And the rest have twisted in a way to allow for this overall shape, we haven't learnt this far but I'm gonna make a guess that the "primary structure"(unofficial wording here), the sequence of nucleotides, affects which ones become anticodon and which exact amino acid will be able to attach, etc.

 

[Sadi66]

tRNA are strands of RNA. So obviously they have a sugar phosphate backbone, like how DNA nucleotides join up. They have a long length, and so will twist and coil (much like protein I guess) to form hydrogen bonds with its own nucleotide bases...

As you can see, the section on top is for amino acid to bond.
The bottom parts become the anticodons.
And the rest have twisted in a way to allow for this overall shape, we haven't learnt this far but I'm gonna make a guess that the "primary structure"(unofficial wording here), the sequence of nucleotides, affects which ones become anticodon and which exact amino acid will be able to attach, etc.

OCT 2012 P13:
Q39
______________________________
MAY 2013 P11
Q15: WHY OPTION A WRONG'
Q31
Q39 THE NITROGEN FIXING REQUIRE ANAEROBIC CONDITION FOR N FIXING?

________________________________
MAY 2013 P12:
Q31 EXPLAIN ALL OPTIONS PLS
Q29
Q32
Q35 : PLS EXPLAIN THIS IN DETAIL LIKE WHATS INFLAMMATION AND SCARRED ?
Q40
______________________________
MAY 2013 P13:
Q10; WHY D NOT
Q12
Q15
Q39
________________________
OCT 2013 P12
Q29
Q35
Q39 WHATS INORGANIC NITROGEN ?
Q40
_________________________
OCT 2013 P13;
Q22 WHY C WRONG
_________________________
JUNE 2008 Q27?
)))))))))))))))))))))))))))))))
june 2005 q32 why not D?
-------------------------------
oct 2004 p1 q32

 

[AishaPoday]

Can anyone please explain these two magnification related MCQs? Got any notes, regarding this?

 

[Sadi66]

Can anyone please explain these two magnification related MCQs? Got any notes, regarding this?
View attachment 53186

its easy most no. cell when mag is low
and the other one is graticule use search Cambridge graticule calculation teacher guide on google u will get a pdf that explains all
NOW EXPLAIN Q31 OF NOV 2006 P1

 

[qwertypoiu]

Can anyone please explain these two magnification related MCQs? Got any notes, regarding this?
View attachment 53186

Welcome to xpc
1. For highest magnification, you need the greatest magnification in BOTH the objective lens and the eyepiece lens. So your answer should be D.
2. This one is slightly tricky, but you must realise that no.2 cannot be correct. This is because the calibration of eyepiece graticule using a stage micrometer has to be done at every different magnification. In 2 it says the calibration would be done at x4 magnification, but this calibration is not useful for x10 magnification of xylem vessel mentioned in the beginning. Therefore your answer automatically becomes D. Conversion of units is helpful but not essential in finding sizes of anything, I can tell you the distance to the Sun in nanometers and it would be technically correct.

Unfortunately I don't have notes on this topic, but I once answered a question about calibration of eyepiece graticules in detail, you may wish to have a look at it here.

 

[lara dalal]

Can someone please explain to me why the answer is C. Why is number 1 mean wrong? whats the right way to calculate and on what basses do i pick out the anomalous number. Does number 1 even have any anomalies

 

[qwertypoiu]

Can someone please explain to me why the answer is C. Why is number 1 mean wrong? whats the right way to calculate and on what basses do i pick out the anomalous number. Does number 1 even have any anomalies
View attachment 53188

This has more to do with the precision of recording devices used. The devices of measurement used were our eyes in this experiment. Can an eye measure 9.2 bubbles per minute? Nope! When you take average you get many decimal places, for number of bubbles it must be rounded to a whole number. One may also say the number of significant figures in our raw data were too few to justify ourselves with 9.2. Similarly third and fourth one used decimales and three significant figures.

 

[Abdul Hanan]

http://onlineexamhelp.com/wp-content/uploads/2015/02/9700_w14_qp_12.pdf
MCQ 5,26,29
any help please? thanks

 

[fantastic girl]

Replication implies copying something. However the nucleotides that form mRNA are different to those that formed the DNA, so it wasn't exactly a replication.
What I mean is that the mRNA are not copies of the DNA stand, but rather have the complementary bases.
When we talk of DNA replication it's the final double helix molecule that is the exact copy of original - which is true.

As for ecological question perhaps it's because many organisms live in the tree.

Thanks alot
yea for that ecology question there were two diff answers in two years...so which one do we go wid ? :/

 

[Lola_sweet]

http://onlineexamhelp.com/wp-content/uploads/2015/02/9700_w14_qp_12.pdf
MCQ 5,26,29
any help please? thanks

for 26 if u see both 2 and 4 r going thru plasmolysis
which means they ve less water potential thus water moves frm cell 1 into cell 2 and 4