Biology; Chemistry; Physics: Post your doubts here!

[Mahnoorfatima]

The blood pressure in capillaries is less than the b.p in arteries. As a result, the flow of blood in capillaries is slower than in arteries. Hence, mosquitos can suck more blood in a unit time in capillaries. Plus capillaries are one celled thick which allows easy penetration of the proboscis. Also capillaries are located close to the skin, whereas arteries are more deeper in the body; the proboscis is short and can easily reach the capillaries

And btw right now I'm facing problems in past papers so should I consult book for that as I'm done with my syllabus and Im doing past papers and the mark scheme stuff ?

 

[exploded diper]

Can any one please list all the topics that are not present in biology maater but are part of the cie biolgy syllabus

i know three..... vitamins.... parasitism....microorganism....

 

[exploded diper]

And there is a bio ATP question in which we have to confirm the presence of a substrate that is starch. Well I know the test for it. But the next part is like How could you confirm if amylase has acted on it.? cant we use the same iodine test? In 1st part it would give a positive test while in the second a negative one since amylase has acted on it??

use benedidcts solution ... reducing solution test.....colour will change from blue to red brown/ brick red

 

[exploded diper]

You would need to apply the formula for finding the concentration. If you can't get the right answer then wait I'll solve the whole question and then let you know because the answers from previous parts are needed.

wht is a rectifying diode? can u explain with a circuit..
wht is the relationship in rsistance and voltage in a thermistor and normal circuit?

 

[exploded diper]

I know but can't we use the same repeated test. Now that the enzyme has acted on it and digested it, iodine test would give us a negative result as opposed to the previous part? No?

but this wont show tht there is reducing sugar present ....iodine test will only show tht startch is not present........and the only way to know tht if amylase has acted upon it is tht reducing sugar has been made.....which is shown by beneduct solution

 

[Awesome12]

wht is a rectifying diode? can u explain with a circuit..
wht is the relationship in rsistance and voltage in a thermistor and normal circuit?

A rectifying diode is used to convert AC current in to DC. Its forward biasing (lets assume it flows from left to right in a circuit) allows current to flow, and offers very less resistance, thereby lighting up a lamp. Its reverse biasing (flows from right to left as per my assumption) does not allow current to flow, and offers greater resistance; the lamp will not light. You can imagine it as an indicator light. It is also used in indicator circuits
A thermistor offers less resistance as the temp rises, and vice versa

 

[asadalam]

If amylase has acted on it the starch must have been converted to sucrose (reducing sugar) so you can perform the benedict's test to confirm.

Sucrose is not a reducing sugar

 

[Awesome12]

Sucrose is not a reducing sugar but Maltose and Lactose are

 

[funky brat]

Sucrose is not a reducing sugar

Sucrose is not a reducing sugar but Maltose and Lactose are

Ops sorry.

 

[asadalam]

Ops sorry.

And isnt starch converted to maltose and then glucose?

 

[funky brat]

And isnt starch converted to maltose and then glucose?

Yes, you're right. Amylase can only convert starch to matlose and then maltase converts maltose to glucose.

 

[exploded diper]

A rectifying diode is used to convert AC current in to DC. Its forward biasing (lets assume it flows from left to right in a circuit) allows current to flow, and offers very less resistance, thereby lighting up a lamp. Its reverse biasing (flows from right to left as per my assumption) does not allow current to flow, and offers greater resistance; the lamp will not light. You can imagine it as an indicator light. It is also used in indicator circuits
A thermistor offers less resistance as the temp rises, and vice versa

what is an indicator light?
and thx

 

[asadalam]

what is an indicator light?
and thx

Lights that light up momentarily i believe.AC current flows so lights up when current is in one direction and turns off when it changes.Like the lights in cars that blink...

 

[syeda salka hashmi]

Descibe a named reflex action that is carried by your nervous system?

 

[syeda salka hashmi]

h

Re: Biology,Chemistry & Physics Help Available Here !



Your question is wrong. Barometer measures liquid pressure. Manometer measures gas pressure. You should learn it. It's confusing , and would cost you later on , so get it straight. Manometer measures gas pressure and barometer measures liquid pressure.

Barometer :
Refer to the book for the diagram. Uses the relation :
Pressure in liquid = Density of liquid x gravitational field strength x height of liquid coloumn.

So in other words if any one of the the three varies , the liquid pressure would vary accordingly. For example if a denser liquid is used , the pressure will increase. If the length is increased the pressure increases. But the gravitational field strength will not change as it is the same everywhere on the planet , but if it were to change , yes the pressure would increase.


Manometer :
Refer to book for diagram. ( it is advised you keep the diagram with you while reading this)
Now as you can see a manometer is a U shaped tube. If you pour liquid into it , the liquid levels reach the same height of both sides. Now to measure the gas pressure , you attach a gas supply to one end. If the gas pressure is more then atmospheric pressure ,then the liquid level will fall in the attached tube. Accordingly the level will rise in the other tube. The level that falls and the level that rises are equal. i.e if the level that has fallen is 2 cm , then the level that rose is also 2 cm. The gas pressure is calculated by adding both levels.

Pressure of gas = Level of liquid that falls + Level of liquid that rises.


Hope this helped.

height of the mercury will not be the same hence it'll be changed due to its density !! u can use chemistry experimental key points guide book or physics presseure chapter from POPLE !!

 

[syeda salka hashmi]

k

Re: Biology,Chemistry & Physics Help Available Here !


Never Change the Formula! Only Valencies are cross multiplyed so the formula will be as Ghalya stated !!

K2SO4

 

[syeda salka hashmi]

Re: Biology,Chemistry & Physics Help Available Here !

Can some one explain to me what is the difference between these and the define them
1)Potential Difference
2)E.M.F
3)Current
4)Volts
If Currents and Volts are same then please Pardon me, Actually my teacher doesn't explain us anything and just gives us questions which are totally out of my mind. Worst in Physics

POTENTIAL DIFFERENCE is the conversion of enerrgy hence EMF is the supply of energy to one coulumb of charge
Current is the flow of electrons that are positive and we have different types of current one ov them is conventional current which flows from positive to negative ..

 

[syeda salka hashmi]

Re: Biology,Chemistry & Physics Help Available Here !

Here is my question:
If a mass-less box travels at 7.293 x 10^0 microdoodles, what time will it be in Karachi when Altaf Hussain next sings the song 'Parday main rehney doh'?

well that is a TRADE MARK question

 

[Abeha Malik]

can anyone plz explain me the mcq no. 18. ans is B but how?
http://papers.xtremepapers.com/CIE/Cambridge International O Level/Biology (5090)/5090_s11_qp_11.pdf

 

[syeda salka hashmi]

ma

can anyone plz explain me the mcq no. 18. ans is B but how?
http://papers.xtremepapers.com/CIE/Cambridge International O Level/Biology (5090)/5090_s11_qp_11.pdf

maybe due to the presence of KOH in the beaker and cotinious respiration :?