AQA BIOL4 ~ 11th June 2013 ~ A2 Biology Watch
What exactly do we have to know?
so what is the point in nitrification if the plants can make proteins with ammonia?
Okay slightly weird when I quote you it says something different...I was quoting this:
No, and the mark scheme is specific about this
nitrogen fixing bacteria convert nitrogen gas to ammonia, which is then used by the plant to make amino acids to make proteins.
(they aren't so picky about whether you say ammonium ions or ammonia though!)
But there I was talking about mutualistic nitrogen fixing bacteria, here the bacteria are directly fixed to the roots in nodules so the plants gain the ammonium ions and they are made into amino acids there and then in exchange for carbohydrates to the bacteria.
Plants can only uptake nitrates directly from the soil via active transport.
Also, not all plants are leguminous
(I actually think they can uptake ammonium ions also but prefer nitrates but AQA doesn't say anything about this so it's best to assume they can't)
Mark, release, recapture
Carbon cycle and nitrogen cycle I find confusing, always forget the points but would be okay if it came up
Succession (so hard to word the answers)
Directional/stabilising selection (again, hard to word)
The one thing I don't know. =(
So scared about this exam tomorrow. Desperately need a good A in this to get an A overall, got 72 UMS (B) last time. I've done all the past papers again, getting A*s each time like I did in January... So I'm just going to run through all my notes one last time and hope for the best. This exam is such a lottery when it comes to the mark scheme, I feel I must trust in good luck now.
Feel like I've neglected this one though, was focusing on maths this morning, done nowhere near as much as I did in January so can't see how I can do any better!
AAnyone know why for question jan 2011 2bii, I can't say that because male 7 is rhesus negative so if the allele was present on the X chromosome it would get expressed therefore it cannot be on the X chromosome? Anyone?
Males only get it from their mothers, so if you have 2 a mother who is homozygous recessive, if it was carried on the X chromosome the male would express the recessive allele but 3 is rhesus positive and doesn't express this thus it can't be on the x chromosome
Plants - Pyruvate (lose CO2) > ethanal (NADH-NAD) > ethanol
Animals - pyruvate (NADH to NAD) > lactate - removed by blood to liver, converted to glycogen when oxygen available, causes cramp if it accumulates.
What else do we need to know?
After going through June 2012 paper, it says no NADPH produced during electron transport chain, I thought NAD was reduced, not NADP?
Said Jan 13 by mistake.
6 Sea otters were close to extinction at the start of the 20th century. Following a ban
on hunting sea otters, the sizes of their populations began to increase. Scientists
studied the frequencies of two alleles of a gene in one population of sea otters.
The dominant allele, T, codes for an enzyme. The other allele, t, is recessive and
does not produce a functional enzyme.
In a population of sea otters, the allele frequency for the recessive allele, t, was found
to be 0.2.
6 (a) (i) Use the Hardy-Weinberg equation to calculate the percentage of homozygous
recessive sea otters in this population. Show your working.