A level Biology: Post your doubts here!

[Eugene99]

It's written in the book. Prokaryotes, no matter they are photosynthesising or not, they don't contain organelles. Cell-wall in prokaryots is made up of peptidogylcan (murein) .

Even I got this question wrong.Because by seeing that the last one is chloroplast and question said photosynthetic I did choose the option that had 5.
I know even I have't about 'photosynthesizing prokaryotes' but we have to know characteristics of prokaryotes and that includes that they do not have 'membrane- bound organelles'.

oh yes you guys are right

 

[My Name]

Don't be sorry
Lol Idk this was long ago
may be because my teacher told us something about 0.5 or 0.05 being the cut off probability idk something like that I don't remember exactly:S

Ohkay I think it shouldn't be highlighted.
It isn't related.

 

[Rizwan Javed]

Nice timing.

 

[My Name]

View attachment 60070

Which year is this?
Did you check the ER?

 

[princess Anu]

J03

Which year is this?
Did you check the ER?

 

[mohmed ahmed soliman]

explain role of synapse in nervous system





adaptation / ACh amount reduces due to overuse of synapse ;
wide range of responses ;
due to interconnection of many nerve pathways ;
inhibitory synapses affect other synapses ;
involved in memory / learning ;
due to new synapses being formed ;
summation / discrimination ;

help these points is always there in MS and i cant write anything for them especially the underlined ms points

 

[mohmed ahmed soliman]

...

 

[princess Anu]

explain role of synapse in nervous system





adaptation / ACh amount reduces due to overuse of synapse ;
wide range of responses ;
due to interconnection of many nerve pathways ;
inhibitory synapses affect other synapses ;
involved in memory / learning ;
due to new synapses being formed ;
summation / discrimination ;

help these points is always there in MS and i cant write anything for them especially the underlined ms points

Do you want the complete answer in paragraph form?
How much marks is it for?

 

[mohmed ahmed soliman]

6 marks it was november 2009 p42
section b
full asnwer answer is better

 

[mohmed ahmed soliman]

complete answer in paragraph form

yes please

 

[funky brat]

View attachment 60070

Since the chromatids are lying at the equator, the phase of division must be metaphase and the question has mentioned meiosis so it can be both meiosis 1 and 2 but as it can be seen one division has already occured so it can only be meiosis 2. And it just can't be telophase because the chromosomes are at the poles not in the centre.

 

[tasneemfawzy98]

October/November 2006 paper 4 question 2

How to get the correct hierarchy of the alleles ??
thank you so much.

 

[pundadesh]

human gas exchange surface I THINK IN such qs u dont need to mention anything about ratio

For the question 'how alveoli are adapted for gaseous exchange',
The mark scheme also said 'I high SA:V ratio/ increase SA'

 

[mohmed ahmed soliman]

explain role of synapse in nervous system





adaptation / ACh amount reduces due to overuse of synapse ;
wide range of responses ;
due to interconnection of many nerve pathways ;
inhibitory synapses affect other synapses ;
involved in memory / learning ;
due to new synapses being formed ;
summation / discrimination ;

help these points is always there in MS and i cant write anything for them especially the underlined ms points

?

 

[princess Anu]

Since the chromatids are lying at the equator, the phase of division must be metaphase and the question has mentioned meiosis so it can be both meiosis 1 and 2 but as it can be seen one division has already occured so it can only be meiosis 2. And it just can't be telophase because the chromosomes are at the poles not in the centre.

How do we know one division has occurred? does the outer line represent the cell membrane of the initial cell/ the germ cell? and the two inner lines are the cell surface membranes of the two daughter cell formed? is that so?

 

[princess Anu]

?

Okay
so first describe synapse as the functional apposition between two neurones where an impulse is transmitted from one neurone to another via chemical means
Synapse helps in uni directional flow of impulses because a) the synpatic vesicles and voltage gated Ca ion channels are present only on the pre synaptic knob b) receptors of ACh are only on post synaptic neurone
Synapses are involved in memory and learning which results due to the formation of new synaptic interconnections
They allow temporal (i.e adding up of 2 or more impulses coming from the same neurone at different times )and spatial summation( i.e adding up of 2 or more impulses arriving from different neurones at the same time) which results in interconnection between nerve pathways and this inturn leads to wider range of responses
Synapses are also involved in a phenomenon of ADAPTATION which reduces the frequency of impulses sent to the CNS due to a constant stimulus, this ensures the CNS is not bombarded with useless information such as the information regarding clothing

 

[mohmed ahmed soliman]

Okay
so first describe synapse as the functional apposition between two neurones where an impulse is transmitted from one neurone to another via chemical means
Synapse helps in uni directional flow of impulses because a) the synpatic vesicles and voltage gated Ca ion channels are present only on the pre synaptic knob b) receptors of ACh are only on post synaptic neurone
Synapses are involved in memory and learning which results due to the formation of new synaptic interconnections
They allow temporal (i.e adding up of 2 or more impulses coming from the same neurone at different times )and spatial summation( i.e adding up of 2 or more impulses arriving from different neurones at the same time) which results in interconnection between nerve pathways and this inturn leads to wider range of responses
Synapses are also involved in a phenomenon of ADAPTATION which reduces the frequency of impulses sent to the CNS due to a constant stimulus, this ensures the CNS is not bombarded with useless information such as the information regarding clothing

thanks but may u clarify this MS point adaptation / ACh amount reduces due to overuse of synapse ;

 

[princess Anu]

thanks but may u clarify this MS point adaptation / ACh amount reduces due to overuse of synapse ;

Basically when a certain stimuli is constantly generating an action potential it is using neurotransmitter ACh constantly for the transmission across a synapse which leads to depletion of ACh
this is how our brain ignores constant 'useless' stimulus

 

[Peaceful]

Salam!
Is the Barron's or the Princeton Review a better book for SAT Biology subject test?

 

[My Name]

Salam!
Is the Barron's or the Princeton Review a better book for SAT Biology subject test?

This is the AL forum btw. :3 Anyway I will tag someone who can maybe help.
Midnight dream ??
Rizwan Javed