A level Biology: Post your doubts here!

[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.

 

[Sadi66]

CT NOV 2011 P11: Q33 why option D wrong.. u did nt checked it,
Question is about inhaling smoke.......pls 3xplain

 

[qwertypoiu]

View attachment 52738

please help !!!

All energy made in the ecosystem comes from photosynthesis. The energy that the plant lost, kept, used, etc. ALL originally came from its photosynthesis. Therefore:
Energy from photosynthesis: 27,000 + 3000 = 30,000
Energy from Sun = 1,000,000
Percentage = 30,000/1,000,000*100%=3%

 

[princess Anu]

Someone plz help with this

 

[qwertypoiu]

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

Answer should be C. Number of bubbles should be rounded off to a whole number, how can you have 9.2 bubbles? Our measuring device (ie our eyes) cannot measure fractions of bubbles. Furthermore, there is no justification for having two, or three significant figures in our calculated result when our raw data did not have as many.
So only student 2 did it correct.

 

[qwertypoiu]

Guys! I need help in this one!

Correct answer is B.

dipeptide will have two amino acids:
0.7nm x 2 = 1.4nm
subtract from this the H2O that is given out:
1.4 nm - 0.110nm - 0.06 x 2 nm = 1.17nm
close enough to 1.2 nm eh?

 

[Farhad221]

CT NOV 2011 P11: Q33 why option D wrong.. u did nt checked it,
Question is about inhaling smoke.......pls 3xplain

Not A as mucus production is inctreased, Ciliated epithelium are destroyed so ciliatry movement is reduced, tobacco smoke does not decrease oxgen transport. so the answer is D

 

[Sadi66]

Not A as mucus production is inctreased, Ciliated epithelium are destroyed so ciliatry movement is reduced, tobacco smoke does not decrease oxgen transport. so the answer is D

Its not its C in MS

 

[Sadi66]

Pls explin may 13 p12, Q12

 

[qwertypoiu]

How do we calculate the maximum number? :/

Firstly since there are 700 nucleotides in the entire DNA molecule, and there are two strands of DNA in the molecule, there must be 700/2 = 350 base pairs.
G-C pairs have 3 hydrogen bonds as opposed to A-T's 2. We assume that all the nucleotides are G-C (which is highly unlikely) to maximize the number of bonds.
3x350=1050 bonds
C.

 

[Farhad221]

Someone plz help with this

Is the answer D

 

[princess Anu]

I haven't checked the ms myself but somebody posted it saying the ans was D so yeah maybe

 

[Farhad221]

I haven't checked the ms myself but somebody posted it saying the ans was D so yeah maybe

So here we go CO does not cause the destruction of epithelium cells, and nicotine only causes blood vessels to dialate and increase blood pressure hence we are left with C which i checked in my book and does confirm that it causes platelets to stick together.
EDIT: MY bad, blood vessels constrict.

 

[princess Anu]

So here we go CO does not cause the destruction of epithelium cells, and nicotine only causes blood vessels to dialate and increase blood pressure hence we are left with C which i checked in my book and does confirm that it causes platelets to stick together.

firstly Co does damage the epithelium by releasing superoxide radicals
secondly nicotine constricts (not dilate)the vessels :s

 

[Farhad221]

firstly Co does damage the epithelium by releasing superoxide radicals
secondly nicotine constricts (not dilate)the vessels :s

I cant find anything on CO damaging the endothelium cells however NO do form free radicals that effect the endothelium cells. however i am not completly certain.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2517732/
ANYONE ELSE CAN HELP US ON THIS REGARD PLEASE

 

[Farhad221]

Sorry i have got no clue either.

Its not its C in MS

 

[Farhad221]

 

[Farhad221]

 

[Farhad221]

 

[Studydayandnight]

Guys! I need help in this one!

Correct answer is B.

HELP! HOW DO WE DO THIS?!