A level Biology: Post your doubts here!

[mohmed ahmed soliman]

oestrogen inhibits gnrh release from hypothalamus so this have negative feedback ob both FSH/LH release from anterior pituitary gland
why in MS they only write that oestrogen has negative feedback on FSH alone

 

[qwertypoiu]

oestrogen inhibits gnrh release from hypothalamus so this have negative feedback ob both FSH/LH release from anterior pituitary gland
why in MS they only write that oestrogen has negative feedback on FSH alone

Because that much detail is not expected at this level.

 

[pundadesh]

Hi guys, can someone clear my doubt regarding this examiner report comment

'Candidates lost credit by stating that the alveoli have a large surface area to volume ratio'

This relates to the question:
'Describe and explain how the structure of the human gas exchange surface is adapted for maximum efficiency'

 

[mohmed ahmed soliman]

Hi guys, can someone clear my doubt regarding this examiner report comment

'Candidates lost credit by stating that the alveoli have a large surface area to volume ratio'

This relates to the question:
'Describe and explain how the structure of the human gas exchange surface is adapted for maximum efficiency'

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

 

[Shah34]

Hello
I wanted to ask as only a month left how should I be revising biology?

 

[My Name]

Hello
I wanted to ask as only a month left how should I be revising biology?

Are you giving AS only?

 

[Shah34]

Are you giving AS only?

Yes

 

[Shah34]

Significance of Michaelis Menten constant. Plz anyone explain ?

 

[Rizwan Javed]

Significance of Michaelis Menten constant. Plz anyone explain ?

The significance of Vmax and Km values:

■■ It enables scientists to make computerised models of biochemical pathways or even the behaviour of whole cells because it helps to predict how each reaction in a proposed pathway will proceed and therefore how the enzymes will interact. The consequences of changing conditions such as temperature, pH or the presence of inhibitors can be built into the models.

■■ An enzyme’s preference for different substrates can be compared quantitatively.

■■ By understanding what affects enzyme efficiency, scientists may in future be able to design better catalysts, linking this to genetic engineering.

■■ For a commercially important enzyme, the performance of the same enzyme from different organisms can be compared.

■■ The calculations involved can be applied to other fields of biochemistry, such as antibody–antigen binding.

■■ Knowing Km means the proportion of active sites occupied by substrate molecules can be calculated for any substrate concentration.

These are taken from the Biology Coursebook .

 

[mohmed ahmed soliman]

in allopatric speciation qs they always write ref to mutation
what should i write for this qs coming in p4

 

[Eugene99]

How comes photosynthetic prokaryotes do not need chloroplasts to photosynthesize? It's C

 

[princess Anu]

Help (

 

[My Name]

How comes photosynthetic prokaryotes do not need chloroplasts to photosynthesize? It's CView attachment 60065

ER:
Whilst nearly 60% of the more able candidates answered this correctly, over 80% of less able candidates did not realise that prokaryotes do not have a cellulose cell wall or any organelles such as chloroplasts.

 

[My Name]

Help (

Hey sorry I don't think I'll be much help on this.
But I was wondering why have you highlighted 0.5?

 

[Eugene99]

ER:
Whilst nearly 60% of the more able candidates answered this correctly, over 80% of less able candidates did not realise that prokaryotes do not have a cellulose cell wall or any organelles such as chloroplasts.

yep, as per your instructions I do read ERs now, but this one, I was just solving yet and this question was buggin me a lot. But the thing is we didn't learn this in the syllabus! did we? I read both books more than once and not a single word about photosynthesizing prokaryotes was mentioned! This is just not fair! And to think about it, aren't 80% more population in favor of the chloroplasts to be in prokaryotes!, but the 80% 'less able candidates' I come in the category of! Ahh! :/

 

[My Name]

yep, as per your instructions I do read ERs now, but this one, I was just solving yet and this question was buggin me a lot. But the thing is we didn't learn this in the syllabus! did we? I read both books more than once and not a single word about photosynthesizing prokaryotes was mentioned! This is just not fair! And to think about it, aren't 80% more population in favor of the chloroplasts to be in prokaryotes!, but the 80% 'less able candidates' I come in the category of! Ahh! :/

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'.

 

[Rizwan Javed]

yep, as per your instructions I do read ERs now, but this one, I was just solving yet and this question was buggin me a lot. But the thing is we didn't learn this in the syllabus! did we? I read both books more than once and not a single word about photosynthesizing prokaryotes was mentioned! This is just not fair! And to think about it, aren't 80% more population in favor of the chloroplasts to be in prokaryotes!, but the 80% 'less able candidates' I come in the category of! Ahh! :/

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) .

 

[princess Anu]

Hey sorry I don't think I'll be much help on this.
But I was wondering why have you highlighted 0.5?

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

 

[My Name]

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) .

Nice timing.

 

[princess Anu]