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AQA A-Level Biology (7402) Exam Thread - June 12th, June 20th and June 26th

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Reply 1580
do we need to know about density dependent and density independent factors in ecology?
Anyone have a mocked-up version of Paper 2? Any teachers on TSR or anything? I know there's the specimen paper but I'd like to do more than one in prep for the exam!!!
Reply 1582
i reckon there wont be a whole load on succession as this was covered in paper 2 spec... unlikely to be up again straight away
Original post by alaskayounglives
Anyone have a mocked-up version of Paper 2? Any teachers on TSR or anything? I know there's the specimen paper but I'd like to do more than one in prep for the exam!!!


Have you done the Set 2 specimens? Theres loads of threads on here with them on :smile:
what do we need to know about anaerobic respiration?
Reply 1585
Original post by jblogs_8265
what do we need to know about anaerobic respiration?


this is all just from my head, so don't quote me, but basically-

anaerobic = not enough o2
so glycolysis can happen but ONLY glycolysis
glycolysis produces 2x pyruvate molecules and 2x reduced NAD

IN ANIMALS; lactate is produced
so; pyruvate + red NAD ---> lactate + oxi NAD

IN PLANTS/YEAST;
pyruvate + red NAD --> CO2 + ethanol

basically purpose is to still supply ATP but only 2ATP molecules which is very low compared to anaerobic respiration
it is never one or the other, if there is low O2 then anaerobic resp will happen with a bit of aerobic respiration

it is good because it supplies some ATP but lactate builds up in muscles and causes muscle fatigue= bad

redNAD needs to be converted back to oxi NAD so it can be reused in glycolysis in the cytoplasm of cells


hope this makes sense- this is the basics and probably the only stuff you could get asked on it :wink:
Reply 1586
who can help me with genetic tech? i get stuck so badd
Reply 1587
Original post by daniiiiiii
can someone help me please:
1. i know npp = gpp - r and npp is the energy avaliable for growth, reproduction and the next trophic level, but where about would atp energy come in? is it part or npp, as it isnt lost as heat during respiration but is formed..

2. for plant growth, do plants grow by forming atp from respiration and using this for growth, or by making polysacharrides from things like photosynthesis?


plants photosynthesise in the sunlight, use glucose to get energy
at nighttime, no sunlight so can't photosynthesis so they respire to produce ATP which is there immediate energy source :smile:
Original post by eza11
who can help me with genetic tech? i get stuck so badd


You need to ask more specific questions if you want help.

Are you using the specification (ctrl-f "3.8.1"), If you aren't then it's by far the best place to start, I don't know why all teachers don't tell their students to do this.

If you're already using it what part do you get stuck on?
(edited 6 years ago)
Reply 1589
Original post by Lookatmyeggs
You need to ask more specific questions if you want help.

Are you using the specification (ctrl-f "3.8.1":wink:, If you aren't then it's by far the best place to start, I don't know why all teachers don't tell their students to do this.

If you're already using it what part do you get stuck on?




3.8.4.3 Genetic fingerprinting (A-level only) this bit!! gel electrophoresis and i dont get the VNTR's?? :smile:
Reply 1590
Okay so I'm confused, is saprobiotic decomposition and saprobiontic decomposition the same thing ?
Reply 1591
also can anyone summarise phosphorus cycle, and what we need to know- is all that we need to know just the basic cycle? thank you
Original post by H_MO
Okay so I'm confused, is saprobiotic decomposition and saprobiontic decomposition the same thing ?


Yes, saprobiotic nutrition is undertaken by saprobionts.
Has anyone else noticed in the past papers whenever it's a doctor or scientist drawing conclusions they're pretty much right, but whenever it's a student they're wrong af?
Original post by Lookatmyeggs
Every AQA exam I've ever taken, before I've even opened the question paper, I've mentally written off 15-20% of the marks as unattainable due to mark scheme ******** and dependence on blind luck. Like an AQA tax off the top of what you actually know. You just have to concentrate on getting as much as possible out of the other 80%. Everyone is sitting the same paper, so if you've revised enough the ******** should be balanced out for everyone. hopefully...


Agreed! I honestly can't understand how stupid the mark scheme can be sometimes in terms of how precise or rigid the answer must be and you're like "no one is EVER going to think to say this unless you've asked the exact same question before?!"
Like you say its just given that you're going to lost some marks just due to how stupidly pedantic they are, but i just tend to chuck a bunch of answers at them and hope that one of them is what they're looking for :P
Reply 1595
Original post by eza11
also can anyone summarise phosphorus cycle, and what we need to know- is all that we need to know just the basic cycle? thank you

Okay, so here is what I got
- phosphorous present in sedimentary rock as phosphate ions (PO43-)

- when sedimentary rock erodes, leaves soil containing PO43-)

- plants absorb PO43-) to make phospholipid/DNA/ATP

- consumers eat plants to obtain phospholipid/DNA/ATP

- organic material (dead plants, dead animals, animal waste) are broken down by saprobiotic decomposers, this releases Phosphate Ions (PO43-) back into the soil

- (if soil sediments and hardens, over time, it returns to a rock state)

- [mycorrhize are fungi in the roots of plants to support uptake of scarce minerals like phosphate ions]
Reply 1596
Original post by H_MO
Okay, so here is what I got
- phosphorous present in sedimentary rock as phosphate ions (PO43-)

- when sedimentary rock erodes, leaves soil containing PO43-)

- plants absorb PO43-) to make phospholipid/DNA/ATP

- consumers eat plants to obtain phospholipid/DNA/ATP

- organic material (dead plants, dead animals, animal waste) are broken down by saprobiotic decomposers, this releases Phosphate Ions (PO43-) back into the soil

- (if soil sediments and hardens, over time, it returns to a rock state)

- [mycorrhize are fungi in the roots of plants to support uptake of scarce minerals like phosphate ions]



thank you! is that all we need to know x
Reply 1597
Original post by eza11
thank you! is that all we need to know x


yep pretty much :u:
Original post by eza11
3.8.4.3 Genetic fingerprinting (A-level only) this bit!! gel electrophoresis and i dont get the VNTR's?? :smile:


Gel electrophoresis uses the fact that larger DNA fragments move more slowly across a piece of agar, when a voltage is set up across it, than smaller pieces. If you have two different DNA samples which have been fragmented by the same restriction endonucleases, then the fragments in each sample will all be different sizes because the DNA between each cutting point is different, so each sample will form a different pattern when the fragments move across the agar to different distances (and are then separated into single strands and hybridised with something radioactive or fluorescent so we can actually see them).
Therefore, the more similar the patterns, the more similar the DNA, the closer the genetic relationship.

The best bit of the DNA to do this test on are therefore; bits that exist in everyone, have variable length and frequency in all individuals (except identical twins), and are passed down between generations like normal genes. These are VNTRs or variable number tandem repeats. They are introns which, as far as we know, don't do anything. They just exist in different lengths because their length doesn't mean anything. The clue is in the name, variable number, tandem repeats. they're called tandem repeats because they're made up of repeating sequences, like a recurring decimal.
(edited 6 years ago)
Original post by eza11
this is all just from my head, so don't quote me, but basically-

anaerobic = not enough o2
so glycolysis can happen but ONLY glycolysis
glycolysis produces 2x pyruvate molecules and 2x reduced NAD

IN ANIMALS; lactate is produced
so; pyruvate + red NAD ---> lactate + oxi NAD

IN PLANTS/YEAST;
pyruvate + red NAD --> CO2 + ethanol

basically purpose is to still supply ATP but only 2ATP molecules which is very low compared to anaerobic respiration
it is never one or the other, if there is low O2 then anaerobic resp will happen with a bit of aerobic respiration

it is good because it supplies some ATP but lactate builds up in muscles and causes muscle fatigue= bad

redNAD needs to be converted back to oxi NAD so it can be reused in glycolysis in the cytoplasm of cells


hope this makes sense- this is the basics and probably the only stuff you could get asked on it :wink:


Don't forget the ATP that's made via substrate-level phosphorylation during glycolysis - you've only mentioned the NADH + H+ and 2 x pyruvate here.

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