Biology; Chemistry; Physics: Post your doubts here!

[uclesstudnt]

Hi, can i get the marking scheme papers for biology?

You can check the marking schemes for Biology in the Papers section on the homepage. Is it Cambridge O Level Biology (5090)?

 

[scouserlfc]

ok

peop



Hi could just guide me through as how to attempt the physics theory paper in CIE examination?

because it is a lot difficult to figure out which question should I attempt first

Just go in the order no need to fret during paper and dont waste time above all.
In order to do this all u need to practice atleast 5 years of papers (both june and November) but 10 years is more useful.If u do this and you know all concepts and you can apply them in new situations like in those past paper questions you will most prolly succeed in the paper if you cant just practice more and understand what you dont by reading it on websites or in a different book than you use. Nothing more you can do than this except for pray for the best paper you could ever do !

 

[Asad.Babur]

I lost CD of Book by David Sang,

Someone send me Content or LInk for that, it still have book!
Please huurry

 

[Neil Shah]

why should we not use whole seeds and seedlings for experiments? Give 2 reasons....

 

[Neil Shah]

why is a crucible heated thrice in the reaction of calcium and oxygen? Give 2 reasons...
Could someone tell me the answers to these questions?

 

[princess Anu]

Please answer!!!
how do we figure out that in a redox reaction who losses and who gains electrons?
for example:
chlorine+ potassium bromide = Potassium chloride + bromide
who is reducing agent
who is oxidising agent
who reduces
who oxidises?

 

[funky brat]

Please answer!!!
how do we figure out that in a redox reaction who losses and who gains electrons?
for example:
chlorine+ potassium bromide = Potassium chloride + bromide
who is reducing agent
who is oxidising agent
who reduces
who oxidises?

for this you must know the definitions. See, oxidation can be discussed in three diffrent ways, like gain in oxidation state/ gain of oxygen, loss of electron and loss of hydrogen. Similarly reduction is loss of oxygen, gain of electron or gain of hydrogen.
A reducing agent is one which oxidises itself which means it gain electrons while it reduces the other hence reducing agent and an oxidising agent is one which reduces itslef while oxidising the other.

 

[R.M2013]

A0A.
http://papers.xtremepapers.com/CIE/Cambridge International O Level/Biology (5090)/5090_s12_qp_22.pdf
Q-4???

 

[Al-Anoud]

^^Does anyone have the CD for this?

 

[princess Anu]

for this you must know the definitions. See, oxidation can be discussed in three diffrent ways, like gain in oxidation state/ gain of oxygen, loss of electron and loss of hydrogen. Similarly reduction is loss of oxygen, gain of electron or gain of hydrogen.
A reducing agent is one which oxidises itself which means it gain electrons while it reduces the other hence reducing agent and an oxidising agent is one which reduces itslef while oxidising the other.

Yes i agree but how to solve such equations ? like the one i gave above. solve it as an example!

 

[Ram97]

Please answer!!!
how do we figure out that in a redox reaction who losses and who gains electrons?
for example:
chlorine+ potassium bromide = Potassium chloride + bromide
who is reducing agent
who is oxidising agent
who reduces
who oxidises?

Here chlorine reduces as its oxidation no. deceases from '0' in Cl2 to '-1' in KCl
Bromide oxidises as its oxidation no. increases from '-1' in KBr to '0' in Br2.
Reducing Agent is one which oxidises so BROMINE
Oxidising Agent is one which reduces so POTASSIUM CHLORIDE

I think I am correct

 

[Yazka Shathir]

If a strip of magnesium is dropped into excess hydrochloric acid an exothermic reaction occurs.
The rate of this reaction increases during the first few seconds because

A the amount of magnesium is decreasing.
B the magnesium is acting as a catalyst.
C the solution is becoming hotter.
D the surface area of the magnesium is increasing.


Can someone please please explain the answers of this question , SOON |:

 

[SeraphicXynex]

I have a question relating to biology. Is it important to learn about complemental air, tidal air, residual and supplemental air ? Cuxz my notes have given elaborate descriptions and i am getting a bit confused.
Also, any tips for drawing a specimen for P6 Magnification question? Thanks. I have read a lot of these questions and they have really helped me alot. I hope I can get an answer quickly cuz my exam is tomorrow! HELP! Help!

 

[SeraphicXynex]

Please answer!!!
how do we figure out that in a redox reaction who losses and who gains electrons?
for example:
chlorine+ potassium bromide = Potassium chloride + bromide
who is reducing agent
who is oxidising agent
who reduces
who oxidises?

Okay, so if the equation doesnt involve oxygen, remember that it must involve electrons.
OIL RIG = Oxidation Is Loss of electrons and Reduction is Gain of electrons. So:
Cl has valency of -1 which changes to 0 and Potassium bromide is a compound so the valency of bromine is 0 which changes to -1. Since Cl is losing the 1 electron to become neutral, Cl is Oxidising! OIL = Oxidation Is Loss of electrons! AND since Br in KBr is GAINING 1 electron to become Br -1, Br is REDUCING! RIG= Reduction Is Gain of electrons.
Reducing agent = Cl since it itself is oxidising: It helps Br to reduce.
Oxidising agent= KBr since it itself is reducing: It helps Cl to oxidise.
HOPE THIS HELPED !

 

[SeraphicXynex]

Hey guys. Any one know where i can learn about anion reactivity series? I tried using Google but i couldn't find anything useful. Help me please?! Thanks a ton!

Sahana

Hey! I think the correct term for the "anion reactivity serires" is the " anion electrochemical series" You should try Googling that !

 

[Sahana :)]

Wow it worked! Thanks a ton!

 

[princess Anu]

Thanks a lot i understood it at last! D

 

[***amd***]

A0A.
http://papers.xtremepapers.com/CIE/Cambridge International O Level/Biology (5090)/5090_s12_qp_22.pdf
Q-4???

a) by the animal eating.... animals eat it and when the seeds pass through the alimentary canal they are not digested and are egested out intact. The seeds will be discarded along with the feaces anywhere away from the mother plant.
b) i) plants will have no specific sex and gemetes formation will be almost impossible. ii) because asexual reproduction is possible in plants but not in animals... plus, the survival fr such plants s possible but for animals the case is not the same.
c) there are 23 pairs of chromosomes in human cells, in the pair numbered "21" there ma be 1 extra strand of chromosome. OR during the mieosis division in the formation of gemetes, the division of chromosomes between the 2 forming cells may be not appropriate causing unequal number of chromosomes in the 2 cells formed.
hope you understand

 

[SeraphicXynex]

Thanks a lot i understood it at last! D

No Prob

 

[princess Anu]

What are the similarities between nervous system and hormonal system?
Before the start of a race why glucagon is not released but adrenaline is? :/