Physics, Chemistry and Biology: Post your doubts here!

[joulie]

Jolie if u have any other questions plz ask I'm kind of bored LOL

i'll have a rest this night maybe tomorrow i'll hav some questions

 

[Ritter]

Hi, could you please help me with 3 questions (Biology paper1)

1) November 1994

Mark Scheme: D

Why isn't the answer A or B.
___________________________________________________________________________________________________
2) November 1994

Mark Scheme : D

Doesn't the plant respire producing CO2
So answer should be , in my opinion, water and carbon cycle (which is not found in the choices)

___________________________________________________________________________________________________
3) November 1999

Mark Scheme: D

Could you explain it for me


Thanks in Advance.

 

[Abu mota]

Hi, could you please help me with 3 questions (Biology paper1)

1) November 1994

Mark Scheme: D

Why isn't the answer A or B.
___________________________________________________________________________________________________
2) November 1994

Mark Scheme : D

Doesn't the plant respire producing CO2
So answer should be , in my opinion, water and carbon cycle (which is not found in the choices)

___________________________________________________________________________________________________
3) November 1999

Mark Scheme: D

Could you explain it for me


Thanks in Advance.

i cant see any of the questions, all i see is a frog :/

 

[Abu mota]

i've found the second question in Nov 1994, it is only water cycle because in the question if u looked carefully u will find an arrow pointing from the xylem vessels, this means it must be water and so the answer is water cycle only as CO2 comes from the air not from the xylem vessels

 

[JOEJOE]

28) Increase in drymass(mass without water) actually increases when the seedling has produced leaves and able to photosynthesise so able to make sugar which increases the drymass.

For 36) it shows an arrow leaving a leave so water leaves the leaves usually by transpiration so its a part of the water cyle

37) usually when u add a limiting factor the population either increases or decreases so B and C are completely wrong... the population should have its 4 stages

lag
log
stationary
and death phase
(when theres NO limiting factors)
Which are clearly shown on D

Hope thats good expl

 

[122]

Does anyone have the markscheme for igcse paper 1 from 1994-2000 chemistry? Please if anyone does can you post it i need it urgently

 

[AAnsarii]

w09_qp11 q4 http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_w09_qp_11.pdf
if u c d periodic tbl, atomic no goes(4 noble gases): 2,8,18,36.... 18 & 36 have a diff of 18 n not 8, so it could b ne option
same grp should b ticked, but i dnt think unreactive ... plz help

sm ppr q20

 

[AAnsarii]

http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_w08_qp_1.pdf q15, why 20 deg. C?

 

[kainat husain]

PLEASE HELP
http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_w07_qp_1.pdf
q11 how can we find that the answer is B :/ please explain
q18 the answer is C but no idea how to find :/
q20 the answer is B :/
q23 if rubidium is below potassium so how can it react with water faster :/ the answer is C

 

[AAnsarii]

y magnesium cloride does not react wid sulfuric acid?

 

[AAnsarii]

PLEASE HELP
http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_w07_qp_1.pdf
q11 how can we find that the answer is B :/ please explain
q18 the answer is C but no idea how to find :/
q20 the answer is B :/
q23 if rubidium is below potassium so how can it react with water faster :/ the answer is C

q11- try evy 1: C5H11OH + 8O2 = __CO2 + __H2O
C5H11OH + 8O2 = 5CO2 + 6H2O----u can c dat dis isnt balanced, so go 2 d nxt
C6H9OH + 8O2 = _CO2 + _H2O
C6H9OH + 8O2 = 6CO2 + 5H2O---dis is balanced, so if u still want 2 chk wid others do d sm way or tick dis n go ahead

q18- i think reactivitey series sys dat Zn & Mg will react, n Cu is v unereactive, so it won't dat gives u C

q20- C reacts wid O2 in air 2 4m CO2, gas, which leaves 4m d open end, Cu + O2 is coppre oxide, which is a solid, n stays, due 2 d xtra oxygen, d copper thing will have more mass, n as CO2 hs left 4m d C tube, it'll have lesser mass

q23-reactivity 4 metals increases as u go down d grp, it decreases 4 non metals as u go down. so it'll b more reactive if its lower.


sorry if im not clr

 

[AAnsarii]

http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_w08_qp_1.pdf
q29--how do u noe dat no of shells is 2 n not 6?

 

[kainat husain]

q11- try evy 1: C5H11OH + 8O2 = __CO2 + __H2O
C5H11OH + 8O2 = 5CO2 + 6H2O----u can c dat dis isnt balanced, so go 2 d nxt
C6H9OH + 8O2 = _CO2 + _H2O
C6H9OH + 8O2 = 6CO2 + 5H2O---dis is balanced, so if u still want 2 chk wid others do d sm way or tick dis n go ahead

q18- i think reactivitey series sys dat Zn & Mg will react, n Cu is v unereactive, so it won't dat gives u C

q20- C reacts wid O2 in air 2 4m CO2, gas, which leaves 4m d open end, Cu + O2 is coppre oxide, which is a solid, n stays, due 2 d xtra oxygen, d copper thing will have more mass, n as CO2 hs left 4m d C tube, it'll have lesser mass

q23-reactivity 4 metals increases as u go down d grp, it decreases 4 non metals as u go down. so it'll b more reactive if its lower.


sorry if im not clr

thank u soooooooo very much

 

[Ritter]

i've found the second question in Nov 1994, it is only water cycle because in the question if u looked carefully u will find an arrow pointing from the xylem vessels, this means it must be water and so the answer is water cycle only as CO2 comes from the air not from the xylem vessels

Thanks

 

[Ritter]

28) Increase in drymass(mass without water) actually increases when the seedling has produced leaves and able to photosynthesise so able to make sugar which increases the drymass.

For 36) it shows an arrow leaving a leave so water leaves the leaves usually by transpiration so its a part of the water cyle

37) usually when u add a limiting factor the population either increases or decreases so B and C are completely wrong... the population should have its 4 stages

lag
log
stationary
and death phase
(when theres NO limiting factors)
Which are clearly shown on D

Hope thats good expl

thanks for expl. I understood 36

28) doesn't the dry mass increase when number of cells increase?

37) if there are no limiting factors so why is there a death phase. The population should increase continuously.
And could you explain what are limiting factors and their effects.

Thanks again for your help

 

[122]

And also for the question about the apparatus needed in the exothermic and the endothermic question ur rite..Can u believe i didn't read the part which says "mixing equal volumes of the 2 solutions"!!!!

Hey! Do u have the markscheme for chemistry paper 1 from 1994-2000?

 

[Rahma Abdelrahman]

thanks for expl. I understood 36

28) doesn't the dry mass increase when number of cells increase?

37) if there are no limiting factors so why is there a death phase. The population should increase continuously.
And could you explain what are limiting factors and their effects.

Thanks again for your help

Are you sure of the mark scheme answer for 37??!
I believe it should be B.
For 28, Yes, photosynthesis increases cell no. but when still under the soil, the seed is using the available food store in the cotyledon and is not getting extra nutrients from the soil so DRY mass remains constant!

 

[Rahma Abdelrahman]

28) Increase in drymass(mass without water) actually increases when the seedling has produced leaves and able to photosynthesise so able to make sugar which increases the drymass.

For 36) it shows an arrow leaving a leave so water leaves the leaves usually by transpiration so its a part of the water cyle

37) usually when u add a limiting factor the population either increases or decreases so B and C are completely wrong... the population should have its 4 stages

lag
log
stationary
and death phase
(when theres NO limiting factors)
Which are clearly shown on D

Hope thats good expl

Stationary and death phases only appear because of the incidence of a limiting factor !

 

[AAnsarii]

do v need 2 learn d reactivity series 4 metals? plz say no

 

[AAnsarii]

Stationary and death phases only appear because of the incidence of a limiting factor !

otherwise they dont?