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AQA BIOL2~3rd June 2013~AS Biology (Now Closed)

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Reply 2440
Avatar for WheezyT
WheezyT
2
Original post by LiamDaly
Can someone post 6 marker for fish gas exchange? Want to make sure I've got similar points


Posted from TSR Mobilehh


Just some rough bullet points:

Many Gill Filaments with Lamella attached, increases SA

Lamella site of gaseous exchange are single cell thick = short diffusion pathway

Counter current flow so oxygen always diffuses, equilibrium not met

Ability to ventilate to maintain concentration gradients :biggrin:
Reply 2441
Avatar for LiamDaly
LiamDaly
Can someone post jan 2013 paper please. Need to go over mitosis graph and it scribbled out


Posted from TSR Mobilehh
Original post by Manni
Whats independent assortment regarding?


Meiosis it enables chromosomes to split up in anyway. So different alleles are formed resulting in genetic diversity
Original post by LiamDaly
Can someone post 6 marker for fish gas exchange? Want to make sure I've got similar points


Posted from TSR Mobilehh


Alrighty then, here we go:

1. Fish have structures called gills. They consist of a gill rack that hold many flat layers of gill filaments which provide a large surface area for gas exchange.
2. Ech gill filament has multiple lamellae, that also increase the surface area for diffusion.
3. The lamellae have a thin wall, which reduces the diffusion distance.
4. Water flows in the opposite direction to the blood in the lamellae, in a countercurrent flow system. This maintains a diffusion gradient along the length of the lamellae, which increases the amount of O2 into the blood and CO2 out the blood

:smile:
Original post by doctordee
If anybody has any last minute questions or are confused on any topics feel free to private message me.
I'd be more than happy to go through things with you.
Good luck guys!


Can you predict your top 3 choice of what the 6 markers may be on? :smile:
Original post by laithmo96
Does anyone know how much ums each unit holds and how much we need to get an A,B thanks!


unit 1: 100 ums
unit 2: 140 ums (in this exam an A is worth 112 ums which is about 62-63 marks)
ISA: 60 ums

you need 240 ums overall to get and A and 210 to get a B
Could someone post a 6 marker on gas exchange in insects? Thanks
Original post by Bixel
I bet AQA will be nasty and give us it again! Haha, they seem to like giving similar questions, and they just change a few words :P


I don't think they will - it's not a big enough part of the syllabus
Original post by Sumi Prakash
Could someone tell me the purpose of the casparian strip please?



it blocks the apoplast pathway so water has to take the symplast route. This means water has to go through the cell membrane to get to the xylem so what substances in the water go through can be controlled
Original post by laithmo96
Does anyone know how much ums each unit holds and how much we need to get an A,B thanks!



Click on this link and scroll down to Biology :smile: all on there:

http://store.aqa.org.uk/over/stat_pdf/UMS-GRADE-BOUNDARIES.PDF
Original post by Sumi Prakash
Could someone tell me the purpose of the casparian strip please?

To push the water in the apoplastic pathway (cell wall) into the symplastic pathway (cytoplasm) :biggrin:
Original post by laithmo96
Does anyone know how much ums each unit holds and how much we need to get an A,B thanks!


I'll just do this for AS level:

Biology Unit 1:
33.3% of the total AS marks
100 UMS

Biology Unit 2:
46.7% of the total AS marks
140 UMS

Unit 3 (ISA):
20% of total AS marks
60 UMS

Total UMS: 300
You need 240 UMS in total for an A and 210 UMS overall for a B :smile:
Original post by VigneshSB
Could someone post a 6 marker on gas exchange in insects? Thanks


http://www.thestudentroom.co.uk/showthread.php?t=2233709&page=64&p=42893362#post42893362
Does anybody have a link to the AS Nelson Thornes textbook or some useful revision notes???? Pretty desperate :frown:
Reply 2454
Avatar for hali123
hali123
When you're asked how many different genera are shown in the diagram, how do you work it out?
Reply 2455
Avatar for LiamDaly
LiamDaly
Original post by VigneshSB
Could someone post a 6 marker on gas exchange in insects? Thanks


Gas exchange and water loss in sample paper is:

Air diffuses in through the spiracles
Into the tracheae then into the tracheoles
Diffusion gradient is maintained (by ventilation)
Tracheoles associated with cells
Oxygen diffuses into cells
( and muscle movement provides ventilation - replacement of air)

Water loss limited by valves shutting the spiracles
And waxy waterproof cuticle


Posted from TSR Mobilehh
Reply 2456
Avatar for Sorro10
Sorro10
5
This is all the 6-Marker questions from the past papers with Mark Scheme answers, I didn't post this someone posted it, not sure who but I DO NOT TAKE ANY CREDIT FOR THIS!
ALL PAST LONG MARK QUESTIONS AND ANSWERS .docx.doc82.7KB
Original post by hali123
When you're asked how many different genera are shown in the diagram, how do you work it out?


Genera = genus, right? Well, that's the first name of the species so count how many different first names there are... At least I think that's what you do.
Original post by hali123
When you're asked how many different genera are shown in the diagram, how do you work it out?


you count how many different first names there are
Original post by Scienceisgood


Much appreciated! :smile:

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