AQA Biology A2 Unit 4 Revision Thread

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raceforthefishman

Surely, yield is an advantage of a monoculture (if we're talking about farming)
For instance, all the energy put into that particular ecosystem is focused entirely on that one species and therefore giving the highest yield. If you were growing a crop perhaps...(as there is no comptetition etc.)

When would it be appropriate to use a transect in a study?

i'm pretty sure its when you want to look at stages of succession that are fairly evidently one after the other, say on a beach or something, when it starts as rocks, and then little plants and then bushes etc...

so basically when you want to look a succession in a linear fashion, and then you can see the changes that are taking place :smile:

Reply 81

klgyal

juuu :)

I'm guessing the advantages of a monoculture would be that no nutrients in the soil get wasted on weeds and plants you don't want present?

and maybe that there's maximum productivity if there is no competition for any resources?

not sure if i'm right :hmmmm:

um does anyone know how to define an ecosystem? my textbook says something about interacting abiotic and biotic factors? but my teacher said it was " a community of organisms together with its associated physical environment".... :s-smilie:

thank you guys :smile:

looking at a markscheme to the definition of an ecosystem is says:
An ecosystem is a habitat and community made up of all the interacting abiotic and biotic factors.

Reply 82

klgyal

I am getting so confused with the link reaction in respiration. When the pyruvate loses a hydrogen atom does it become an acetyl group and then combines with coenzyme A to form acetylcoenzyme A ? or does the acetyl group come from some where else??

Explain 3 ways in which farming practices prevent the formation of woodland?

Reply 83

raceforthefishman

klgyal

*For the top bit*
The pyruvate has 3 carbon atoms...
It becomes reduced so loses hydrogen and carbon

2 of the carbon atoms make an acetyl group (you may have heard of acetic acid...being ethanoic acid...having two carbon atoms, thats what the acetyl means -- 2 carbon)
and yes, this then bonds with CoA to give acetylCoA

the remaining carbon is left as carbon dioxide along with NADH

(thats a veyr rough and ready explanation)

Reply 84

klgyal

raceforthefishman

thank you

Reply 85

jimmy303

Another advantage of monoculture is that there's really few niches, therefore there are fewer types of pest, and so it is easier to control the pest population with pesticides or biological control etc. This technically goes for weeds too, if you've got too many types of plant growing for harvest, it's difficult to find a herbicide that doesn't harm the yield of the crop, wheras a monoculture means you can find one that doesn't harm the plant you are growing.
A line transect is useful when you're determining the distribution of a species i would have thought, e.g. whether a plant is present in the first 10 metres from the road and present 50 metres away.

Explain 3 ways in which farming practices prevent the formation of woodland? These are random stabs. Correct me if im wrong. :p:

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Monoculture would reduce the species diveristy of plants, reducing niches and so reducing species diversity of animals, in effect stopping the process of succession.

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Monoculture would also prevent the formation of complex food webs, which would make the environment stable enough to support woodland.

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Regular cropping would remove any compounds from the soil that would have otherwise been replaced when the plant dies. This means the environmental resources cannot sustain such a development.

What does P = C-(R+U+F) or else P = C-R-U-F stand for? Using this and own knowledge, outline four principles of intensive farming practices.

Reply 86

Mahia

jimmy303

•

Monoculture would reduce the species diveristy of plants, reducing niches and so reducing species diversity of animals, in effect stopping the process of succession.

•

Monoculture would also prevent the formation of complex food webs, which would make the environment stable enough to support woodland.

•

Regular cropping would remove any compounds from the soil that would have otherwise been replaced when the plant dies. This means the environmental resources cannot sustain such a development.

What does P = C-(R+U+F) or else P = C-R-U-F stand for? Using this and own knowledge, outline four principles of intensive farming practices.

A large number of livestock in a small space
A lot of waste in a small area
Produces low cost food
Often uses a lot of fossil fuels

Describe the difference in stabilising and directional selection

Reply 87

raceforthefishman

Mahia

A large number of livestock in a small space
A lot of waste in a small area
Produces low cost food
Often uses a lot of fossil fuels

Describe the difference in stabilising and directional selection

Directional selection favours individuals at the extreme ends of a normal distribution...eventually the mean characteristic will have shifted to be this extreme

*what a poor explanation*

Stabilising selection favours average individuals so reduces the number of organisms with 'extreme' characteristics.

How is everyone's revision going? :s-smilie:

Have we had
Why is the climax community the most stable?

Reply 88

VoodooCharles

raceforthefishman

Why is the climax community the most stable?

Because there is very little interspecific competition, and so the populations stay the same.

What is Cultivation, and how does it control populations?

Reply 89

Sammie20

Has anyone done EMPA A2?

Reply 90

Nerdwannabe

Original post by *MJ*

Like I told you yesterday...

Biology is best done with practicals, let's experiment. :hump2:

OP, there is already a big massive thread going with some resource materials and useful links, have a look for it or I can post you a link if you Quote/PM me. :smile:

Good luck. :biggrin:

Hi, would you be able to send me the link please! And if you have the link to the Unit 5 resource thread if there is one! I've spent weeks trying to find it! Thanks :smile:

Reply 91

Fearsmoker

I'm okay with it so far.

Except for one thing: genes.

If it's possible, can somebody go over what the whole section on 'genes' is about in unit 4 (in here/pm whatever)? As in, explain everything to me? Everything from what dominant/recessive/codominant/sex-linked alleles are, what genotype/phenotype means, to how you can tell from an inheritance diagram which person is going to contract a disease etc.

Words will not be able to describe how much it would mean to me if someone explained this to me lol - but i'll try my best. Thanks!

Reply 92

Zetsubeau

Original post by Fearsmoker

I know this thread is kind of dead but for the benefit of all including me I'm gonna see how much gene knowledge I can spurt out.

Genes are a section of DNA that is responsible for a characteristic. This is by coding for a protein such as an enzyme, etc. Genes are carried on chromosomes. They can be expressed (exons) or not expressed (introns).
An organisms genetic code is given during reproduction. When the reproduction is asexual: simple! The genetics of the parent are identical to the child/daughter. When it's sexual, the gametes carry half the genetics each and form a zygote which contains a split of genes. This is where expression is slightly more complex.
When a gene (genotype) is expressed, it creates a phenotype (a characteristic, e.g. blue eyes, brown hair, formation of proto-oncogenes, etc.). When a genotype causes a phenotype, it is dominant. Other genes are often carried which also have a phenotype, but may be dominant or recessive. If it is recessive, the dominant gene is expressed and the recessive is not. When a gene is present but not expressed, it's being carried. The organism is a carrier. Sometimes both are expressed, however, causing a co-dominance (such as AB bloodtype). When a gene is sex-linked, it's carried on the Y chromosome, as that's the chromosome that varies between sexes. This means it's only present in one sex.
I dunno how to explain an inheritance diagram very easily. Just learn the above and the diagram should become clear to you.

Reply 93

Melissa.S.

This unit is really annoying me at the moment, I know the content, have revised sooo much but I just can't seem to get any higher then a D in the practice papers!! Don't know what to do! It's all application questions, they're awful! Has anyone got any tips on how I can improve please!!

Reply 94

F1's Finest

Photosynthesis and Respiration are the easier topics in unit 4, not much application in comparison to the other topics.

My goal is to get between 80-90ums for this paper. Hopefully.

Anyone wanna go through some questions?

I'll kick start.

Why is it important for NAD to be regenerated under anaerobic conditions, e.g. during an endurance race? 2 marks.

(edited 11 years ago)

Reply 95

petethepiratearr

Original post by James A

To allow glycolysis to continue producing a net gain of 2 ATP to use for energy release for muscle contraction

basically without anaerobic or aerobic respiration you wouldn't get any ATP at all :tongue:

this thread is pretty dead yo

Reply 96

tree123

hi does anyone have any useful notes made from the textbbok?

Reply 97

lorobolorolo

Hi I get the first mark point about how at night there is no photosynthesis.
But then the next mark point says that no CO2 is being taken up, so shouldn't the CO2 concentration at night be higher?
Am I missing something here or am I just being stupid -__-