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A level Biology: Post your doubts here!

M

Mohammed salik

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mehria said:
first we have to find the value for the smallest division in eyepiece graticule...
for that :_ 0.1/40= 2.5 x 10^-3 mm
cnge mm into micrometer by multiplying 1000 with ur value
(2.5 x 10^-3) x 1000 = 2.5 micrometer <------- ths is the value for the smallest division in eyepiece graticule

frm the second diagram choose any chloroplast , measure its diameter
in the diagram one of the chloroplast's diameter is 3
so:- 3 x 2.5 = 7.5 micrometer
it is closer to 8 then our ans will b B
Click to expand...
Look 40 division = 0.1mm=100 Micrometers
Now if u see On Diagram Nucleus is the biggest circle which is almost 10 Units.
Now use Ratio

40 : 100
10 : X
X=1000/40=25 Micrometer ans is C
:)
 
joanna omar

joanna omar

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kitkat <3 :p said:
Someone help me with the dissociation curve n bohr effect I dont underdtand it :(
Click to expand...


dissociation curve --->The affinity of HB for Oxygen is measured experimentally by determining the % saturation of oxygen of samples of blood after exposure to air mixture containing different partial pressure of oxygen ...the results,called an oxygen dissociation curve

Bohr effect (shift) ....> It is when HB has a higher affinity for Co2 and hydrogen ions
Its mainly the presence of high partial pressure of Co2 causes the HB to release more Oxygen than in the absence of Co2 ...the is call bohr effect.
 
K

kitkat <3 :P

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joanna omar said:
dissociation curve --->The affinity of HB for Oxygen is measured experimentally by determining the % saturation of oxygen of samples of blood after exposure to air mixture containing different partial pressure of oxygen ...the results,called an oxygen dissociation curve

Bohr effect (shift) ....> It is when HB has a higher affinity for Co2 and hydrogen ions
Its mainly the presence of high partial pressure of Co2 causes the HB to release more Oxygen than in the absence of Co2 ...the is call bohr effect.
Click to expand...
Thanks alot ^_^
 
thats_me

thats_me

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S

Snowysangel

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joanna omar said:
Anyone help me out with .........> Q6 (C)
http://papers.xtremepapers.com/CIE/...and AS Level/Biology (9700)/9700_s09_qp_2.pdf
Click to expand...
A) you can still see remains of the nuclear membrane, the chromosomes/sister chromatids are still lined up at the equator & the sister chromatids haven't separated yet
B) smoke contains a lot of carcinogens which change the sequence of bases is the DNA and hence create mutated genes...and u basically elaborate on thus point by giving examples etc
 
thats_me

thats_me

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Snowysangel said:
Could someone please describe the effects of nicotine on our bodies? Give at least 4 points.
Click to expand...
It is readily absorbed by blood & travels to the brain, there it imitates as acetyl choline which is a neurotransmitter
it stimulates the nervous system to reduce the diameter of the arterioles & to release the hormone adrenaline which causes smooth muscles to contract so blood pressure & heart rate increases
Due to this there is a decrease in blood supply to extremeties of the body such as hands or feet, reducing their supply of oxygen
It also increases the stickiness of blood platelets so there is an increase in risk of blood clotting
 
princeali97

princeali97

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joanna omar said:
can you help me with this http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w13_qp_12.pdf q40
and this http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s13_qp_13.pdf q39
Click to expand...
q40-statementA is valid since in ecosystem Y the dominant producer is large and woody, so would not be easily consumed. StatementB is valid since there is a smaller fluctuation of temperature in marine aquatic ecosystems and also there is less oxygen. Statement C is also valid, since with lower energy losses between trophic levels the ecosystem X can support more trophiclevels. Therefore the answer is statement D.
Q39-same.So it will be B.
 
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