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can some one please explain to me how antibiotic resistance is an example of directional selection? i am failing to understand!!! :frown:
Reply 21
piece-of-me
can some one please explain to me how antibiotic resistance is an example of directional selection? i am failing to understand!!! :frown:



directional selection is when the alleles on either side of the mean are favoured. so say for example 80% of the population of spideres have short legs between 10cm to 20cm and the other 20% have a range of leg sizes either being less than 10cm or more than 20 cm.

so if say a predator came that was fast at catching the spiders and only the spiders with longer than 20cm legs could run away than all the rest would die meaning the ones with longer than 20cm legs would reproduce and pass on the allele causing the shift of the mean leg length to be more than 10-20cm.

with antibiotics, non resistant bacteria would die and resisitant bacteria will survive. resistant bacteria is in the minority compared to the non resistant so its a directional selection because the non-common allele is prefered and passed on

make sense? :s-smilie:
916-CALL-TURK
DW - it'll be like 10% for an A anyways :rolleyes:

Yeah it was like that in Jan and I still did rubbish :P
Vamp1reWeekend
Yeah it was like that in Jan and I still did rubbish :P
Apart from the shrew question it wasn't as bad as everyone was making it out to be - I managed 50/75 on my first go which by the LOL-tastic UMS means I would've got 100 :o:
kween21
directional selection is when the alleles on either side of the mean are favoured. so say for example 80% of the population of spideres have short legs between 10cm to 20cm and the other 20% have a range of leg sizes either being less than 10cm or more than 20 cm.

so if say a predator came that was fast at catching the spiders and only the spiders with longer than 20cm legs could run away than all the rest would die meaning the ones with longer than 20cm legs would reproduce and pass on the allele causing the shift of the mean leg length to be more than 10-20cm.

with antibiotics, non resistant bacteria would die and resisitant bacteria will survive. resistant bacteria is in the minority compared to the non resistant so its a directional selection because the non-common allele is prefered and passed on

make sense? :s-smilie:


so like it causes the characteristics of the population to change..thats why its directional selection........

i get it now !!! Thank you so much:biggrin: :biggrin:
Reply 25
piece-of-me
so like it causes the characteristics of the population to change..thats why its directional selection........

i get it now !!! Thank you so much:biggrin: :biggrin:



yep and stabalising selection is when it remains the same characteristic, reducing the allele frequency of the other alleles :smile:
916-CALL-TURK
Apart from the shrew question it wasn't as bad as everyone was making it out to be - I managed 50/75 on my first go which by the LOL-tastic UMS means I would've got 100 :o:


Uhm well I found it hard still, I literally panicked and forgot everything. Which is my fault, I know :smile:
I still think having so much application/hsw does not bode well for me.
Vamp1reWeekend
Uhm well I found it hard still, I literally panicked and forgot everything. Which is my fault, I know :smile:
I still think having so much application/hsw does not bode well for me.
Yeah, I still don't like it much :frown:

BIOL5 is going to rape us with Synopticity/HSW/Application, though :s-smilie:
Reply 28
With energy transfer...abt 10% is passed onto producers to primary consumers right? How comes secondary consumers are able to transfer about 20% energy from primary consumers bodies... Why are secondary consumers more efficient at taking in more energy then primary consumers?

Could someone give me the points to learn about the pyramids of biomass and energy.

How does lightening turn gaseous nitrogen into ammonia?

Are NADP, NADH and FAD considered to be enzymes?

Could someone please explain to me the ETC in respiration? I understand the co-enzymes release the hydrogen atoms and e- then what happens?

Thanks
gcseangel
With energy transfer...abt 10% is passed onto producers to primary consumers right? How comes secondary consumers are able to transfer about 20% energy from primary consumers bodies... Why are secondary consumers more efficient at taking in more energy then primary consumers?
- Some bits are not eaten / can't be digested
- Lost in excretory products
- Lost as heat by respiration

Also, I reckon primary consumers have to eat alot more things to get the energy they need (moreso than consumers higher up the chain), and plants are fairly widely dispersed so they have to move around quite a bit.


How does lightening turn gaseous nitrogen into ammonia?
It just says that it happens in the book, doesn't explain it, so I'm assuming we don't need to know the exact reaction

Are NADP, NADH and FAD considered to be enzymes?
Coenzymes. They work with 'dehydrogenase' enzymes to remove hydrogen and transport it everywhere.

Could someone please explain to me the ETC in respiration? I understand the co-enzymes release the hydrogen atoms and e- then what happens?
- Hydrogen ions from Glycolysis and the Krebs cycle combine w/ NAD and FAD on the cristae
Reduced NAD and FAD donate electrongs of the Hydrogens they'e carring to the first molecule of the ETC
- This causes the Hydrogen to be released as H+. These ions are actively transported across to the inner mitochondrial layer
- Electrons pass along the chain of electron carriers by many redox reactions. Each successive electron carrier is at a lower energy level than the previous so as they pass down they release energy.
- This energy is used to combine inorganic phospate and ADP to make ATP (and heat).
- H+ ions accumiliate in the space between the mitochondrial membranes before they diffuse in the mitochondrial matrix by certain protein channels.
- At the end of the ETC, O2 combines with the H+ ions and the electrons to give water - acts as the final electron acceptor.


Thanks


Do you not have the book?
Reply 30
916-CALL-TURK
Do you not have the book?



I do but not with me i left it in my locker. Is some energy lost as movement from respiration?


Thanks
gcseangel
I do but not with me i left it in my locker. Is some energy lost as movement from respiration?


Thanks
Movement would require energy which would come from respiration, if thats what you mean:smile:
Reply 32
916-CALL-TURK
Movement would require energy which would come from respiration, if thats what you mean:smile:



yeah but how would you put it? Is it acceptable to write something like that?
gcseangel
yeah but how would you put it? Is it acceptable to write something like that?
It's similar to one of the answers to the end of topic questions in the book. Can't remember it exactly, though. You should talk about muscles, ATP (being involved in the contraction) and other things. I tend to go all out on 2 markers just ot make sure I get all the marks.
Reply 34
what sort of how science works stuff are we meant to know?
Reply 35
Can someone please just go through hardy weinberg principle with me?

I dont know when it starts with p2/q2 or p or q.
Reply 36
gcseangel
Can someone please just go through hardy weinberg principle with me?

I dont know when it starts with p2/q2 or p or q.


p^2 + q^2 + 2pq = 1

P^2 stands for the homozogousdominant allele frequency
Q^2 stands for the homozygous recessive allele frequency
2pq is the heteorzygous allele frequency

Q + p = 1

usually they would give you a question such as for every 1 in 450 births there is a recessive condition. so 1/450 = q^2 etc
Has anyone found any Hardy-Weinberg questions in past papers? I can't seem to find any!
Reply 38
I'm resitting this :frown:

Does anyone think the paper will be far more reasonable as AQA have to cover their backs given the last exam? Or is this just wishful thinking? :rolleyes:
Lit2010
I'm resitting this :frown:

Does anyone think the paper will be far more reasonable as AQA have to cover their backs given the last exam? Or is this just wishful thinking? :rolleyes:


Doubt it :frown: They write the exams months in advance...and they don't think they were wrong :rolleyes:

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