Biology; Chemistry; Physics: Post your doubts here!

[chocolate_girl]

iyt it is used as a stain to make cell features easier to see...

Is it always necessary to use iodine when preparing slide???

 

[chocolate_girl]

http://papers.xtremepapers.com/CIE/Cambridge International O Level/Biology (5090)/5090_s08_qp_6.pdf please someone tell me how to calculate surface area of given cubes in question no.1 part a.

 

[passion hunter]

Is it always necessary to use iodine when preparing slide???

it is preferred to use a stain when viewing CELLS...even microorganisms..thats all i know

 

[passion hunter]

http://papers.xtremepapers.com/CIE/Cambridge International O Level/Biology (5090)/5090_s08_qp_6.pdf please someone tell me how to calculate surface area of given cubes in question no.1 part a.

use math surface area of cube and cuboid etc

 

[HDIWAN]

okay so why do we multiply it I am so dumb I don't understand how did you do it Please could you answer more clearly
and then how do we change 0.15 to 10 ??
R=3.3+X is it not??
and 3.3+x=0.3*0.5 ?? I know this is not correct but should it not be right
and what about 2*3.3 will give us 0.5 as current
Please help please

when something is written like this 0.5I0 this mean the two things are to multiplied so
0.5*0.3=0.15 A
now this the current when the total resistance in the circuit is twice the resistance of X.
from the table we can see that current in the circuit is 0.15 when we added 6.8+3.3=10.1 ohms
now this is not the total resistance..the total will be (10.1+X)ohms now as the question say the resistance when current is o.15 is twice that of X so this means X=10.1 so that the total resistance becomes TWICE. this is because 10.1 is the resistance between point A and B so X must have this same resistance (10.1) to make THE TOTAL RESISTANCE twice its own value

 

[chocolate_girl]

use math surface area of cube and cuboid etc

Could you please solve it for me, my answers dont resemble to mark scheme

 

[chocolate_girl]

http://papers.xtremepapers.com/CIE/Cambridge International O Level/Biology (5090)/5090_w08_qp_6.pdf
Can someone just have a look at this papers question no.2 -ii) n tell me colour of starch in A-2 i think it will be brown but mark scheme says it is blue-black. Cancsomeone explain me why it is so

 

[Al-Anoud]

http://www.bbc.co.uk/schools/gcsebitesize/science/aqa_pre_2011/radiation/radioactiverev1.shtml..... hope this helps

thanku soo much. it helped alot.

 

[fatima0000]

http://papers.xtremepapers.com/CIE/Cambridge International O Level/Biology (5090)/5090_w08_qp_6.pdf
Can someone just have a look at this papers question no.2 -ii) n tell me colour of starch in A-2 i think it will be brown but mark scheme says it is blue-black. Cancsomeone explain me why it is so

im not getting your point..
observation says that colour is blue black so it tells that starch is present

 

[Khadija_1234]

http://papers.xtremepapers.com/CIE/Cambridge International O Level/Biology (5090)/5090_s10_qp_62.pdf
Please help with Q1 part (d)

 

[Isha Atiq]

Is it always important to use a few drops of iodine when preparing a slide to view under microscope??

Yess, whenever you prepare a slide you always need to add a few drops of iodine after few drops of water, it makes the contents clear.

 

[Isha Atiq]

http://papers.xtremepapers.com/CIE/Cambridge International O Level/Biology (5090)/5090_s10_qp_62.pdf
Please help with Q1 part (d)

take two equal masses of food
mount them tightly on needles
ignite the food items
keep it under the test tube
check the temperature increased in a particular time period
repeat it with other sample too.
the one with most temperature increase has more energy. its advisable to wear gloves and hold the test tube by a testtube holder.

 

[Khadija_1234]

take two equal masses of food
mount them tightly on needles
ignite the food items
keep it under the test tube
check the temperature increased in a particular time period
repeat it with other sample too.
the one with most temperature increase has more energy. its advisable to wear gloves and hold the test tube by a testtube holder.

thank you so much!

 

[tweetie]

Yea just half of the answer : Use a microscope to observe the Yest cells using a high magnification, place yeast cells on a cell counter and stain them to make them visible. ( well i guess that answers almost more than half of the question) what is missing now is to know how to estimate their total population! Any helpful suggestions ?

ahan but thn what abt total poppulation any idea
"

 

[Amaany689]

hey guys!! can any one explain me the practical preperation of media and plate pouring briefly?? um litlle confused

 

[ijlalm]

http://papers.xtremepapers.com/CIE/Cambridge International O Level/Physics (5054)/5054_w11_qp_41.pdf...... how can the answer to the Q2 (a) be '' goes down''......i'm baffled.. can somebody explain?...​

If we decrease the distance on the left side by moving the screw in, the perpendicular distance on that side will be decreased..Now as may know that moment is directly proportional to the perpendicular distance the moment on the left side is lesser so left side goes up and the flattened end goes down..
Hope u got it..

 

[Kamihus]

http://papers.xtremepapers.com/CIE/Cambridge International O Level/Biology (5090)/5090_w08_qp_6.pdf
Can someone just have a look at this papers question no.2 -ii) n tell me colour of starch in A-2 i think it will be brown but mark scheme says it is blue-black. Cancsomeone explain me why it is so

Iodine has a very quick reaction so colour will immediately change to black. Orange will also be correct. Read the Examiner Report for more clarification.

 

[ZaqZainab]

http://papers.xtremepapers.com/CIE/Cambridge International O Level/Biology (5090)/5090_w08_qp_6.pdf
Can someone just have a look at this papers question no.2 -ii) n tell me colour of starch in A-2 i think it will be brown but mark scheme says it is blue-black. Cancsomeone explain me why it is so

for question 2 ii you have to learn the tests which are -starch: add a few drops of iodine solution, a positive result (i.e. starch is present) is a deep blue-black colour, a negative result is orange.
-reducing sugars (e.g. glucose): Benedict’s reagent, then the mixture is heated for 2 to 3 minutes. Positive result is an orange/brick-red colour, negative result is blue (the colour of the Benedict’s reagent).
-proteins: add a few drops of Biuret reagent, a positive result is a mauve/purple colour.
-fats: the emulsion test: ethanol is added to the mixture, this is poured into a test tube with an equal number of distilled water, a positive result a milky-white emulsion forms.

 

[irfan.kheerdali]

what r the type of biology ATP questions often asked ? and its answer. plzzzz help

 

[chocolate_girl]

for question 2 ii you have to learn the tests which are -starch: add a few drops of iodine solution, a positive result (i.e. starch is present) is a deep blue-black colour, a negative result is orange.
-reducing sugars (e.g. glucose): Benedict’s reagent, then the mixture is heated for 2 to 3 minutes. Positive result is an orange/brick-red colour, negative result is blue (the colour of the Benedict’s reagent).
-proteins: add a few drops of Biuret reagent, a positive result is a mauve/purple colour.
-fats: the emulsion test: ethanol is added to the mixture, this is poured into a test tube with an equal number of distilled water, a positive result a milky-white emulsion forms.

No but it says that at very start. Wont iodine b brown wen we have just added it or it quickly turns blue black?