A level Biology: Post your doubts here!

[thats_me]

Thanks A lot ! but I don't understand how 15 is A ??
and ab Q26 I dont get it aslo ...could u explain ?

15-The piece of stalk is placed in sucrose solution with the highest water potential so, water will enter in the stalk. The side through which water will enter will expand/bend so the ans is either A or D & I thick the thick wall is lignified so it is impermeable to water. Thus it will not allow the entry of water & water will enter through the thin wall causing it to expand.
26-Substances such as amino acids & sucrose have to be moved from leaves I.e where they are formed to the parts of the plant where they are needed, so they can be transported in either directions ( eg: if needed in roots or stem) so they can move by mass flow in different directions in different phloem seive tubes.

 

[Snowysangel]

Can someone also please explain these questions to me View attachment 40539View attachment 40540

Water has moved out of the cell in diagram 1 so solution W is more negative than X, but solution Y is less negative than X since water has moved in...so I'll have to go with A

 

[joanna omar]

when we keep increasing the substrate conc
What Does it mean .......At a certain point Enzymes are working at its maximum possible rate ?

 

[mehria]

when we keep increasing the substrate conc
What Does it mean .......At a certain point Enzymes are working at its maximum possible rate ?

when we keep increasing substrate conc. the enzymes rate of reaction increases upto a certain limit n then reaction remain constant as enzymes will then become a limiting factor... 1 substrate will bind with 1 enzyme so if we even increase the conc. of substrates the enzymes won't be able to bind with all of them at a time as enzymes r less than substrates

 

[Mohammed salik]

But we're using an accurate measuring instrument which can measure up till 2 decimal places! It's for a similar reason that using a buttered is more accurate than using a measuring cylinder

Bro.. You are comparing two Diffrent things (Volume and Time).. For time measurement You also have to take account of your Human reaction time which is About 0.3-0.5s .. so We always round our values to nearest Second.

 

[princeali97]

q39..pls explain..http://papers.xtremepapers.com/CIE/...nd AS Level/Biology (9700)/9700_s12_qp_11.pdf

 

[mehria]

q39..pls explain..http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s12_qp_11.pdf

multiply the number of individuals with the biomass of each individual... the one with more biomass will be the producer (e.g. grass)...n the one with less biomass will be the tertiary consumer (e.g. fox)

 

[princeali97]

multiply the number of individuals with the biomass of each individual... the one with more biomass will be the producer (e.g. grass)...n the one with less biomass will be the tertiary consumer (e.g. fox)

what if we multiply all three of them? We'll get the correct answer in this way too
its always from highest energy to lowest.

 

[mehria]

what if we multiply all three of them? We'll get the correct answer in this way too
its always from highest energy to lowest.

ya ryt... n it's askng abt the energy so we have to multiply them all to find how much energy is present in the given biomass of all the individuals.... thnx

 

[princeali97]

ya ryt... n it's askng abt the energy so we have to multiply them all to find how much energy is present in the given biomass of all the individuals.... thnx

Actually i shud thank u

 

[mehria]

Actually i shud thank u

lol u're welcum

 

[Mohammed salik]

is the ans A for Q16 n Q39?

Yes.. This is From W09_11!!

 

[mehria]

Yes.. This is From W09_11!!

Can someone also please explain these questions to me View attachment 40539View attachment 40540

for 16=> we know that in high negative solutions ( conc. / hypertonic) the cells are flaccid where as in less negative solution (dilute / hypotonc) the cells are turgid
so in Solution Y the cells r turgid n r less negative as more water has moved inside the cells by osmosis because solution Y is a hypotonic solution that has more water potential so Solution Y is less negative as well...

 

[mehria]

Can someone also please explain these questions to me View attachment 40539View attachment 40540

Q 39=> if there were present small creatures then no leaf would be left... frm the table we cn see that small areas of leaves that r about 0.03mm r left so it shows that no microorganism or small vertebrates r present in the soil as if they were present then not a single part of the leaves wud have left behind
earthworms n beetles r of average size n they feed on small areas of the leaf without eating the whole leaf...
(u cn refer ths to the caterpillars that eat the green-leafed vegetables, they don't eat the entire leaf !)...

so the ans is A

 

[sidbloom1995]

the ventrical systole starts 0.1 s after atrial systole and last for 0.3 s
i want to know the timing for atrial systole and the ventrical distole!
does anyone know? if so then please help me out

 

[Javiiiii]

Could someone kindly solve a few Biology paper 5s? I need to know how to properly answer the planning question. Any sort of help will be much appreciated.

 

[meh1234]

http://papers.xtremepapers.com/CIE/...and AS Level/Biology (9700)/9700_w07_qp_4.pdf
Question 10 (a) and (b)
The answer points are in the marking scheme, but I can't really put it together.

 

[thats_me]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w07_qp_4.pdf
Question 10 (a) and (b)
The answer points are in the marking scheme, but I can't really put it together.

10a. Chloroplasts are present on the leaf, on which there are fluid filled sacs called thylakoid membrane
On this membrane photo systems are present which consist of clusters of pigments
There are 2 types of pigments, primary( chlorophyll a) & accessory pigments( chlorophyll a, chlorophyll b & carotenoids )
Photo systems consist of 2 regions, light harvesting region & reaction centre
Light harvesting region consists of the accessory pigments & the reaction centre has the primary pigments
There are 2 photo system, photo system1 (p1) & photo system2 (p2)
P1 absorbs a wavelength of 700nm p2 absorbs a wavelength of 680nm
When light falls on p1 the electron will be raised to a higher energy level
This electron will be carried by electron acceptors & It will be replacing the same electron that was lost
Energy in the form of ATP is released when it is raised to a higher level

10b. In light dependent stage both p1 & p2 are involved
When light falls on both the photosytems it causes loss of an electron from p1 which is accepted by electron acceptors
The electron is carried from higher energy level to lower energy level, releasing energy, This energy is used to synthesis ATP
Near p2 photolysis of water occurs which is the splitting of water in presence of light
2H2O-->2H+ + 2e- + O2
The electron lost from p1 are replaced by the electron formed by photolysis of water
& the H+ ions are taken up by NADP to form reduced NADP
This reduced NADP gets reoxidised in the Calvin cycle
This helps to reduce glycerate phosphate to triose phosphate
Triose phosphate is then used to regenerate RUBP & to form other useful products(glucose, cellulose etc)

 

[BeBeskii108]

What was ur question :/?

My question was " What are features, advantages, drawbacks of chi-squared test, standard error and t-test? '

 

[kitkat <3 :P]

My question was " What are features, advantages, drawbacks of chi-squared test, standard error and t-test? '

I believe Its A2 :/