A level Biology: Post your doubts here!

[ahmedgamal986]

please help !!!

 

[Studydayandnight]

Guys! I need help in this one!

Correct answer is B.

 

[Studydayandnight]

What? How can this be C? The average to that is 9.2, not 9. :s

 

[Studydayandnight]

How do we calculate the maximum number? :/

 

[qwertypoiu]

View attachment 52721
I AM WRITING IN BLOCK LETTERS SO THT NO ONE SKIPS THE QUESTION BY MISTAKE..............PLZ HELP!!!!!!!!!

Light intensity is one of the factors that affect the rate of transpiration in a plant. The higher the intensity of light, the more transpiration that occurs, since the plant opens more stomata in order to photosynthesise, since opening stomata allows diffusion of CO2.
However at extremely high light intensities, rate of transpiration drops suddenly, because the plant is losing too much water.
Even if photosynthesis stops for a while, some plants choose to save their water for some time. Therefore, as the graph clearly shows, beyond 30au the transpiration rate falls.

 

[qwertypoiu]

View attachment 52722

Not 100% sure but should be A.
The curve is made because the thin cell wall stretches longer than the thick one, so the difference in length produces the curvature.
Now, as for why the thin walled cells became longer, probably because thin walls are not able to produce as much pressure potential as compared to the thick ones, in order to counter the water potential outside.
Or, another way to think about it is that the thick walled cells are better able to resist change in length due to osmosis.

 

[Sadi66]

Plssxss explain
OCT NOV 2011 P11: Q33 why option D wrong
Oct nov 2011 p12 : Explain Q32
OCT NOV 2010 P11: Q39
MAY 2011: P11 Q36 WHY ANSWER MALARIA ? <malaria also passes from mother to fetus via placenta ref, Marry Jones>

 

[Sadi66]

View attachment 52721
I AM WRITING IN BLOCK LETTERS SO THT NO ONE SKIPS THE QUESTION BY MISTAKE..............PLZ HELP!!!!!!!!!

A?

 

[Farhad221]

Q1:
I don't know if you've used microscopes before (you must actually it's really important for practical) but eyepiece graticule is just something you put in front of the lens. It overlaps a ruler in front of your image. Imagine taking a picture and placing a ruler on top of it. Like this:
View attachment 52719

Does it mean anything? Not at all! It has no units, you can't tell what exactly one line width represents... Is it 1m? 1km? 10km?? (Yes, the ruler line width is 1 cm, but what that represents on the picture, which has been taken at a distance or enlarged, is impossible to tell)
Now imagine zooming into this picture, and placing the same ruler:
View attachment 52720
Did this change the size of this ruler? No! The ruler remains fixed. The scale has changed now, each centimetre of this ruler represents a shorter length (say, instead of representing 1km before, now it does 100m only), because the magnification has changed.

So to the questions:
1. Does this ruler allow you to measure actual distances depicted in this picture? Definitely NOT! You don't know what exactly each centimeter on the ruler means.
2. Does it help you in judging relative proportions in a picture. Yeah!! By moving the picture (specimen), you can measure different parts of the mountain in centimeters and get an idea of what is big and small, etc. It will help you draw this mountain!

Q1:
I don't know if you've used microscopes before (you must actually it's really important for practical) but eyepiece graticule is just something you put in front of the lens. It overlaps a ruler in front of your image. Imagine taking a picture and placing a ruler on top of it. Like this:
View attachment 52719

Does it mean anything? Not at all! It has no units, you can't tell what exactly one line width represents... Is it 1m? 1km? 10km?? (Yes, the ruler line width is 1 cm, but what that represents on the picture, which has been taken at a distance or enlarged, is impossible to tell)
Now imagine zooming into this picture, and placing the same ruler:
View attachment 52720
Did this change the size of this ruler? No! The ruler remains fixed. The scale has changed now, each centimetre of this ruler represents a shorter length (say, instead of representing 1km before, now it does 100m only), because the magnification has changed.

So to the questions:
1. Does this ruler allow you to measure actual distances depicted in this picture? Definitely NOT! You don't know what exactly each centimeter on the ruler means.
2. Does it help you in judging relative proportions in a picture. Yeah!! By moving the picture (specimen), you can measure different parts of the mountain in centimeters and get an idea of what is big and small, etc. It will help you draw this mountain!
3. Did zooming into the pic make our ruler somehow bigger as well? Certainly NOT

3. Did zooming into the pic make our ruler somehow bigger as well? Certainly NOT

I will have to say such great explanation and thank you for it.

 

[Sadi66]

Which statement concerning events occurring in the nitrogen cycle is not correct?
A Free-living nitrogen-fixing bacteria release organic nitrogen compounds into the soil where bacteria convert these to nitrites and nitrates.
B Nitrifying bacteria cause an increase in nitrate ions which are used by plants to make proteins.
C Nitrogen-fixing bacteria use atmospheric nitrogen which is replaced by the action of denitrifying bacteria in waterlogged soil.
D Saprophytic bacteria and fungi decompose organic nitrogen compounds excreted and egested by producers and consumers.

................hows the correct ans D?


Q2How does sucrose move from chloroplasts to the phloem?
1 mass flow
2 apoplast pathway
3 symplast pathway
A 1, 2 and 3
B 1 and 2 only
C 1 and 3 only
D 2 and 3 only
...............hows the ans D?

See is Egested right?
And mass flow occurs in xylem or phloem frm source to sink not from mesophyl to phloem,
Now pls help me in these:
CT NOV 2011 P11: Q33 why option D wrong
Oct nov 2011 p12 : Explain Q32
OCT NOV 2010 P11: Q39
MAY 2011: P11 Q36 WHY ANSWER MALARIA ? <malaria also passes from mother to fetus via placenta ref, Marry Jones>

 

[Farhad221]

View attachment 52721
I AM WRITING IN BLOCK LETTERS SO THT NO ONE SKIPS THE QUESTION BY MISTAKE..............PLZ HELP!!!!!!!!!

At high light intensities stomata usually clos as too much water is lost.
It is not B as the graph shows otherwise and it is not D as it does not explain the sudden change in Transpiratrion rate.
Now C it is true that some stomata are always open but again it does not explain the sudden change in graph.

 

[Sadi66]

View attachment 52729

B?

 

[Farhad221]

View attachment 52722[/QUOTE
Is the answer A. If so then the inner thin walled cells will gain more water than the outer thick walled cells

View attachment 52729

View attachment 52729

The answer is B as 1 only happens at lungs as haem combines with oxygen. 3 also occurs at lungs when H+ ion are dissociated from HHB , which then comibe with HCO3 ions

 

[ashcull14]

The answer is B as 1 only happens at lungs as haem combines with oxygen. 3 also occurs at lungs when H+ ion are dissociated from HHB , which then comibe with HCO3 ions

ryt....thnks

 

[ashcull14]

Not 100% sure but should be A.
The curve is made because the thin cell wall stretches longer than the thick one, so the difference in length produces the curvature.
Now, as for why the thin walled cells became longer, probably because thin walls are not able to produce as much pressure potential as compared to the thick ones, in order to counter the water potential outside.
Or, another way to think about it is that the thick walled cells are better able to resist change in length due to osmosis.

thnk u so muchhhhhhhhhh

 

[ashcull14]

See is Egested right?
And mass flow occurs in xylem or phloem frm source to sink not from mesophyl to phloem,
Now pls help me in these:
CT NOV 2011 P11: Q33 why option D wrong
Oct nov 2011 p12 : Explain Q32
OCT NOV 2010 P11: Q39
MAY 2011: P11 Q36 WHY ANSWER MALARIA ? <malaria also passes from mother to fetus via placenta ref, Marry Jones>

CT NOV 2011 P11: Q33 why option D wrong........smooth muscle is only present in trachea, ronchus and terminal bronchiole...not respiratory bronchiole
Oct nov 2011 p12 : Explain Q32.....i think this chapter has been excluded from 2015 paper syllabus
nov 2010 p11 q39.....the base sequence for normal haemoglobin (Hb^A) has a base CTT...which as a result of mutation is replaced by CAT in (Hb^s) the sickle cell allele ...so a small diference in amino acid sequence results in genetic sickle cell anaemia....since minimum substitution required is 1 the ans is A
May 2011 ,......this que is very tricky ...i had the same prob ...but if u look at the words carefully hes talking about DIRECTLY ,,,
so if u look at cholera it can through unwashed hands
TB can through air
sickle cell anaemia is transmitted right in the genetic coding
for malaria the transmission is not exactly DIRECT as To be transmitted by blood transfusion, parasites must circulate in the blood stream of donors... to generate infection in the blood receiver, such parasites must retain infectivity and follow a series of other SUITABLE conditions like first crossing the mothers blood and then entering the fetal blood for transmission....so u see the transmission is not EXACTLY DIRECT
hop u get it

 

[qwertypoiu]

View attachment 52729

1. Haemoglobin gaining oxygen happens at the lungs, not at active tissues, so this does not occur.
2. H+ ions attach to haemoglobin to form haemoglobinic acid, which changes the shape of haemoglobin molecule and makes it lose oxygen; yes this reaction does occur near respiring tissues (H+ ions come from H2CO3 dissociating, H2CO3 forms near respiring tissues by catalysis of carbonic anhydrase in red blood cells)
3. Joining of HCO3- with H+ to form H2CO3 is something that happens near the lungs, not respiring tissues.
4. Yes this does occur, as explained in no.2's brackets.

So what does not occur is 1 and 3 only (B)

 

[princess Anu]

Q1:
I don't know if you've used microscopes before (you must actually it's really important for practical) but eyepiece graticule is just something you put in front of the lens. It overlaps a ruler in front of your image. Imagine taking a picture and placing a ruler on top of it. Like this:
View attachment 52719

Does it mean anything? Not at all! It has no units, you can't tell what exactly one line width represents... Is it 1m? 1km? 10km?? (Yes, the ruler line width is 1 cm, but what that represents on the picture, which has been taken at a distance or enlarged, is impossible to tell)
Now imagine zooming into this picture, and placing the same ruler:
View attachment 52720
Did this change the size of this ruler? No! The ruler remains fixed. The scale has changed now, each centimetre of this ruler represents a shorter length (say, instead of representing 1km before, now it does 100m only), because the magnification has changed.

So to the questions:
1. Does this ruler allow you to measure actual distances depicted in this picture? Definitely NOT! You don't know what exactly each centimeter on the ruler means.
2. Does it help you in judging relative proportions in a picture. Yeah!! By moving the picture (specimen), you can measure different parts of the mountain in centimeters and get an idea of what is big and small, etc. It will help you draw this mountain!
3. Did zooming into the pic make our ruler somehow bigger as well? Certainly NOT

I'm confused about the 1st.. If we use it together with stage micrometer, we can actually measure cells, no? :/

 

[qwertypoiu]

Which statement concerning events occurring in the nitrogen cycle is not correct?
A Free-living nitrogen-fixing bacteria release organic nitrogen compounds into the soil where bacteria convert these to nitrites and nitrates.
B Nitrifying bacteria cause an increase in nitrate ions which are used by plants to make proteins.
C Nitrogen-fixing bacteria use atmospheric nitrogen which is replaced by the action of denitrifying bacteria in waterlogged soil.
D Saprophytic bacteria and fungi decompose organic nitrogen compounds excreted and egested by producers and consumers.

................hows the correct ans D?


Q2How does sucrose move from chloroplasts to the phloem?
1 mass flow
2 apoplast pathway
3 symplast pathway
A 1, 2 and 3
B 1 and 2 only
C 1 and 3 only
D 2 and 3 only
...............hows the ans D?

As explained before can't do first question
Q2:
Movement of sucrose from chloroplast to phloem does NOT include mass flow.
Mass flow happens when sucrose is translocated from source to sink.
The sucrose moving from source (chloroplast in this case) to the phloem is just the initial step to this, and only involves the companion cell pumping H+ ions using ATP to bind sucrose to H+ ions and make them travel together against sucrose concentration gradient through a co-transporter molecule.
If 1 is wrong, obviously the only option left is D. Once inside the companion cell, H+ ions are detached and sucrose molecules naturally move down their concentration gradient into the phloem elements, this probably involves both the symplast and apoplast transport.

 

[qwertypoiu]

I'm confused about the 1st.. If we use it together with stage micrometer, we can actually measure cells, no? :/

Yes, you're right, by calibration using a stage micrometer we can find out what exactly each division of the eyepiece graticule represents. We can do this because we know the real length of the divisions on stage micrometer, so we can equate the divisions of eyepiece graticule with the divisions of the stage micrometer. Note that a stage micrometer does get magnified and changes size if we change magnification. (so calibration must be done at every magnification)
However, in this question, stage micrometers are not mentioned. Eyepiece graticules alone cannot measure the real size of the specimen.