A level Biology: Post your doubts here!

[knowitall10]

dude this wont help
no one can guess it's a THEORY PAPER!

 

[knowitall10]

Where'd the post go? dornam I was just going to reply..where's your post?

 

[dornam]

I found them

 

[knowitall10]

I found them

Oh ok

 

[Oceanic]

Where'd the post go? dornam I was just going to reply..where's your post?

On page 86 if you're asking me

 

[Oceanic]

The whole syllabus is important...the past papers are basically not very important if you are thorough with the whole course.. And have Faith, don't get nervous..inshAllah you'll do awesome. Read the duas posted on the "chat" forum...they're pretty helpful

Thanks for the wishes

 

[knowitall10]

Thanks for the wishes

No problem!

 

[Irfan1995]

Describe a reflex arc and explain why reflex arcs are important...

some1 pls write the answer: markscheme given below

Irfan1995 knowitall10


strong stimulus in receptor / AW ;
action potential / impulses, along sensory neurone ;
dorsal root of spinal nerve ;
into spinal cord ;
synapse with intermediate neurone ;
(then) motor neurone ;
action potential / impulses, to effector ;
action potential / impulses, to brain ;
response ; e.g. knee jerk 5 max can be on diagram
fast / immediate ;
stops / limits, damage / danger ;
automatic / no conscious thought ;
innate / stereotyped / instinctive

If a stimulus is strong enough to exceed a certain threshold, it will stimulate the formation of an action potential in the sensory neurones. It will travel along the axon through the dorsal root of the spinal nerve where it will synapse with an intermediate/relay neurone. Rather than allowing the signal to pass through the brain (as in normal impulses), the reflex will synapse once again to a motor neurone, transferring the action potential there. The motor neurone will send the action potential to the effector to act immediately.
This route is much shorter than the normal route, hence the response will be immediate. This is necessary to remove the source of danger as soon as possible to prevent further damage. As the route skips the brain completely, we are not aware of the action until after a while, hence a reflex action might be termed as "innate".

 

[Irfan1995]

thanks a lot very helpful
can you explain
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w11_qp_11.pdf Q39
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w11_qp_12.pdf Q16
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w10_qp_12.pdf Q2

1) The food web only contains organisms, not abiotic factors such as sunlight, nutrient levels, and oxygen concentrations.

2) If the substrate concentration is high, then there will be a much higher chance that the enzyme would bind to the substrate rather than the (competitive) inhibitor.
If the inhibitor is non-competitive, then it would perform its inhibiting functions regardless of the concentration of the substrate.
So to maximize the initial rate of reaction, the substrate concentration must be high, and the inhibitor must be competitive.

3) The magnification depends on the lens only. If the same microscope is used, then the magnification will not change regardless of the light used.
The maximum resolution is related to the wavelength. From physics, we know that two points could be resolved (in a microscope) if the image is larger than half the wavelength.
Using green light, the minimum length of a specimen to be just resolved is 510/2 = 260 nm
Using red light, the minimum length of a specimen to be just resolved is 650/2 = 325 nm
The specimen has to be bigger in order to be resolved (seen clearly) using red light. So by definition, resolution decreases with red light.

Hope that made sense!

 

[nelly trich]

is it true that section B this sestion is including application ?

 

[nelly trich]

can please anyone of you check june 06 Q3 (A) label B ?

 

[pearl angel]

The whole syllabus is important...the past papers are basically not very important if you are thorough with the whole course.. And have Faith, don't get nervous..inshAllah you'll do awesome. Read the duas posted on the "chat" forum...they're pretty helpful

Hey could u post the link to the duas in the chat forum please?

 

[knowitall10]

Hey could u post the link to the duas in the chat forum please?

They have been made sticky...

 

[pearl angel]

They have been made sticky...

Oh sorry i hadnt checked

 

[nelly trich]

A level community can you please answer my poor questions !!

 

[knowitall10]

A level community can you please answer my poor questions !!

Yes it includes application...and can u please post the link to that p4 question u asked?

 

[Irfan1995]

can please anyone of you check june 06 Q3 (A) label B ?

As far as I know, foot = podocyte

Also, it's really rare to find 2006 questions in the new syllabus; there's a completely different form of questions now.

 

[nelly trich]

the po

As far as I know, foot = podocyte

Also, it's really rare to find 2006 questions in the new syllabus; there's a completely different form of questions now.

check the question again the podocyte is labled in the digram this is not podocyte ! thank you so much for your reply for paper 4 past papers before 07 it contains the core syllabus only having some repeated questions in the new exams

 

[nelly trich]

Yes it includes application...and can u please post the link to that p4 question u asked?

http://papers.xtremepapers.com/CIE/...and AS Level/Biology (9700)/9700_s06_qp_4.pdf

 

[knowitall10]

http://papers.xtremepapers.com/CIE/...and AS Level/Biology (9700)/9700_s06_qp_4.pdf

If it's 3(a) B, then it's foot processes