A level Biology: Post your doubts here!

[Saad (سعد)]

Check the 'Glossary' in Mary Jones Biology Book. Do the ones that are in AS syllabus.

Oh yeah, thanks a lot.

Bio last-minute revision notes, anyone? o.o

 

[Saad (سعد)]

FROM SOURCE TO CELL C-
consider the companion cell first,where there is active loading of sucrose taking place.
H+ ions are pumped from the companion cells to mesophyll cells containing sucrose by active transport using ATP as an energy source.
As a result the H+ conc builds up in the mesophyll cells generating a potential difference across the membrane.
The H+ ions then move back into the companion cell down a conc. gradient through carrier proteins co-transporting sucrose molecules.
The sucrose molecules then move through the plasmodesmata into the sieve tube element(cell C)

FROM CELL C TO SINK-
When the sugar enters the cell C, due to low water potential being set up water enters by osmosis.
This builds up hydrostatic pressure.
At sink sugar is being used up( for respiration, conversion of sucrose into glucose and fructose)
This creates a pressure gradient between the source and the sink, causing mass flow of solution in phloem sieve tubes from source to sink.

What does mass flow of solution mean?

 

[Saad (سعد)]

Someone explain to me the Ecology Cycles which are in our syllabus (Nitrogen Cycle, and I think we have Carbon Cycle too).

 

[pearl angel]

http://www.sparknotes.com/
http://revision-notes.co.uk/A_Level/
http://www.mrothery.co.uk/

Cambridge revision guide is also handy.

thanku

 

[Jaf]

s05: 14th) you can see that at B the graph is not steepest. the gradient is low. its not the optimum temperature. k.e of enzyme and substrate will get low at this point. whereas A its not far from the start of reaction so at this pooint bonds will be formed for enzyme substrate complex to be build upon...

LOL wth man.

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s05_qp_1.pdf
Q (14): Why not pick B as the correct one?

The real reason it's not B is because Q is not the highest temperature! The question is trolling you. Look where the highest temperature is, and this is where the KE will be highest.

 

[geek101]

I know the difference between Anaphase and Telophase, but when it comes to real diagrams I can't tell them apart, for example page 6, Fig3.1
http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w09_qp_21.pdf
The markscheme says the diagram is anaphase instead of telophase, can someone explain why

true...but in teleophase the chromosomes usually appear decondensed (or not aligned), and a nuclear envelope reforms....in this picture the chromosomes are still sort of aligned and no nuclear envelope has yet formed, which means it is anaphase..it could also be early telophase, and the mark scheme accepts that.

 

[haroon740]

Cna anyone explain the meselson and stahl dna experiment ...and also about the tidal volume calculations ?
thnks

 

[rogue94]

can someone please explain why triglycerides release more energy on respiration than carbohydrates. This question has been repeated more than once, but i don't understand the points in the mark schemes, what is the chemistry behind it???

 

[confused123]

LOL wth man.

The real reason it's not B is because Q is not the highest temperature! The question is trolling you. Look where the highest temperature is, and this is where the KE will be highest.

bite me!

ok so if the temperature will be highest at the end then enzyme will be denatured till then. i think that the enzyme activity increases twice for every 10 degree rise in temperature until optimum temp is reached. explain.

 

[confused123]

What does mass flow of solution mean?

it means the total fluid moves at once. whole of it moving..

 

[littlecloud11]

can someone please explain why triglycerides release more energy on respiration than carbohydrates. This question has been repeated more than once, but i don't understand the points in the mark schemes, what is the chemistry behind it???

In triglycerides the C-H bond are more abundant than in carbohydrates. consider this, triglycerides- C18H38O6 , carbohydrate - C12H24O12
you can see that the ratio of C-H bonds is greater in triglycerides, when these are broken to form C-O and H-O bonds in CO2 and H2O respectively, more energy is released.

 

[shaadhir]

Someone explain to me the Ecology Cycles which are in our syllabus (Nitrogen Cycle, and I think we have Carbon Cycle too).

only Nitrogen Cycle

 

[user]

Oh yeah, thanks a lot.

Bio last-minute revision notes, anyone? o.o

AsSalamoAlaikum Wr Wb!

check the thread in my signature...the first post..
they're just a few...not the complete thing though...! might be helpful...

 

[Jaf]

bite me!

ok so if the temperature will be highest at the end then enzyme will be denatured till then. i think that the enzyme activity increases twice for every 10 degree rise in temperature until optimum temp is reached. explain.

Uh... KE would increase regardless of the activity of the enzyme. Even if the enzyme is completely denatured and we continue to increase the temperature the KE would also continue to increase. KE only plays a role in the enzyme activity before the optimum temperature is reached in giving the molecules enough (activation) energy to form ES complexes.

 

[Jaf]

Does anyone know if we have to remember the types of immunoglobulins (A, G, M and E) and their functions? Also the 6 different ways antibodies help aid defense?

 

[Amaryllis]

hi
why is the antibiotics non effective on viruses?
and is the co2 transport included in the syllabus or i should only know the bohr's effect?

 

[Soldier313]

Does anyone know if we have to remember the types of immunoglobulins (A, G, M and E) and their functions? Also the 6 different ways antibodies help aid defense?

Type of immunoglobulins...i don't think so (not sure though)
and the 6 diff ways antibodies aid defense....could you please put em up?

 

[Soldier313]

hi
why is the antibiotics non effective on viruses?
and is the co2 transport included in the syllabus or i should only know the bohr's effect?

As far as I know, antibiotics affect the synthesis of the bacterial cell wall and bind to bacterial ribosome, thus because viruses do not have cell walls, the antibiotics can't act on them!
hope that helps!

 

[Soldier313]

hi
why is the antibiotics non effective on viruses?
and is the co2 transport included in the syllabus or i should only know the bohr's effect?

for the issue of CO2 transport, this is what it says in the syllabus:
(q) describe the role of haemoglobin in carrying oxygen and carbon dioxide;
(r)describe and explain the significance of the dissociation curves of adult oxyhaemoglobin at different carbon dioxide levels (the Bohr effect);

 

[Saad (سعد)]

hi
why is the antibiotics non effective on viruses?
and is the co2 transport included in the syllabus or i should only know the bohr's effect?

CO2 transport is in the syllabus. They've asked about it in the past papers, I'm sure.

Antibiotics are ineffective against viruses because viruses are entirely different from other life forms in many different ways (there's even a debate about whether viruses are actually living things to begin with). Antibiotics (Greek 'anti-' against and 'bio' life) only affect proper life forms, such as bacteria and fungi, which have internal machinery, can move around, eat, reproduce, grow, etc. Viruses on the other hand are practically dead - they do not reproduce themselves and cannot metabolize - until and unless they come into contact with a living cell. When they infect the cell, they 'hijack' the internal machinery of that cell and use it to carry out their dirty work.