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AQA - BIOL4 - 13th JUNE 2014

There is greater respiratory losses as you go up the trophic level. Why?

My guess would be that the first trophic level is plants which don't respire as much as animals further up the chain. and could also be that the animals get bigger for each trophic level so more respiratory loss? maybe not

Reply 1181

blueberrysro

15

Original post by WavingFLag

Can someone explain respiration to me. In one of the mark schemes it says oxygen is involved in krebs cycle, but from nelson thorne i don't see any oxygen involved. Oxygen is only involved in electron transport chain

Oxygen is the terminal electron acceptor at the end of the ETC. It combines with e- and H+ to make water

Reply 1182

Jaanu

1

Can someone pls explain to me 2bii fpr the jan 11 paper. Thanks!

Reply 1183

Layontheland

1

Original post by Jaanu

For this:Explain how resistance to an antibiotic could become widespread in a bacterial population following a gene mutation conferring resistance in just one bacterium . Can someone explain to me what "frequency of resistant types increases in subsequent generations" means and what actually is a selection pressure. Thanks!

"frequency of resistant types increases in subsequent generations"

This means that the allelic frequency of the resistant gene e.g. resistance to penicillin, increases in the NEXT generations of bacterium. Of course that would occur since bacterium that are resistant will die and leave the resistant bacterium who can thrive in the absence of competition for resources.

A selection pressure is theoretically a 'force' that favours organisms that have a particular characteristic e.g. in this case resistance, these resistant bacterium will be SELECTED FOR by the selection pressure and therefore survive and pass on this allele for resistance.

Hope this makes sense

Reply 1184

walkers38

17

Original post by CakeIsthebest

How do you get those?

500 questions biol4 google it. its a tsr forum with all old spec papers. Or google BYB5 as that is the paper similar to biol4 in old spec papers,

Reply 1185

lllllllllll

13

Original post by walkers38

There is greater respiratory losses as you go up the trophic level. Why?

More energy is lost maintaining a core body temp. and carnivores use more energy in respiration to hunt for prey.

Reply 1186

walkers38

17

Original post by blueberrysro

Oxygen is the terminal electron acceptor at the end of the ETC. It combines with e- and H+ to make water

But that still doesn't explain why the mark scheme said oxygen is used in Krebs cycle.

Reply 1187

Layontheland

1

Original post by walkers38

There is greater respiratory losses as you go up the trophic level. Why?

As you go up the trophic level you get larger organisms e.g. large mammals, who have a smaller surface area to volume ratio. These organisms have to respire MORE in order to maintain a body temperature and thus have a greater metabolism (as these organisms tend to be warm blooded)

Reply 1188

sherbetlily

Original post by WavingFLag

I thought if it was sex linked only the males inherited the disease? As they have no equivalent on y chromosome

Yeah but if a female inherits two recessive alleles (presuming the disease is recessive) then she can also have it :smile:

Reply 1189

visualcocaine

Original post by walkers38

Hahah

Ok help me, what's the difference between natural, stabilising and directional selection.

Directional Selection - results in phenotypes at one extreme of the population being selected for, phenotypes at the other extreme selected against.

Stabilising Selection - results in phenotypes around the mean being selected for and ones at extremes being selected against.

Natural Selection - Variation between members of a population, competition/disease/predation etc results in members with certain adaptations surviving, breeding and passing on their advantageous alleles to next generation. This changes the allelic frequency in gene pool.

Reply 1190

Jaanu

1

Original post by Layontheland

"frequency of resistant types increases in subsequent generations"

This means that the allelic frequency of the resistant gene e.g. resistance to penicillin, increases in the NEXT generations of bacterium. Of course that would occur since bacterium that are resistant will die and leave the resistant bacterium who can thrive in the absence of competition for resources.

A selection pressure is theoretically a 'force' that favours organisms that have a particular characteristic e.g. in this case resistance, these resistant bacterium will be SELECTED FOR by the selection pressure and therefore survive and pass on this allele for resistance.

Hope this makes sense

Thanks for replying! :smile:

Does that mean " frequency of resistant type increases and not types" as one type favours another

Reply 1191

Layontheland

1

Original post by walkers38

But that still doesn't explain why the mark scheme said oxygen is used in Krebs cycle.

There probably saying it in the sense oxygen in INDIRECTLY involved in the kreb cycle.

Assuming oxygen is absent, there is a backlog of electrons in the ECT, this halts the kreb cycle as the electron carriers will still be carrying these excess electrons. So the electrons from the kreb cycles stop moving. Essentially stopping the kreb cycle all together.

Take the mode of action of cyanide as an example. Cyanide inhibits the enzyme that joins oxygen, protons and electrons together to form water. Cyanide STOPS respiration.

Reply 1192

AMELIA-x

7 Mark Question for people! "Explain how the reactions occurring in the mitochondrion generate ATP"

No idea how to word it :frown:

Reply 1193

Layontheland

1

Original post by Jaanu

Thanks for replying! :smile:

Does that mean " frequency of resistant type increases and not types" as one type favours another

Yeah, it depends on the question of course and what example they are talking about. In the mark schemes they always credit, increase in Allele frequency. In this case the allele would be the allele for anti-biotic resistance.

Reply 1194

TheFootyKing19

10

Wish HARDY-WEINBERG LAW + CONDITIONS come up as 5 marker...

Reply 1195

jamesfancourt

2

Original post by AMELIA-x

7 Mark Question for people! "Explain how the reactions occurring in the mitochondrion generate ATP"

No idea how to word it :frown:

ATP is generated in the matrix of the mitochondria in the krebs cycle by substrate level phosphorolyation. Also reduced NAD and FAD are produced. These reduced co-enzymes attatch to cristae of the mitochondria and release electrons which are accepted by electron carrier protiens and go down the electron transport chain in redox reactions loosing energy at each level. Protons are pumped into the inner mitochondrial membrane space where they go down a proton gradient and pass through ATP synthase where ATP is made from Pi+ADP. Oxygen acts as the terminal electron acceptor and combines with protons to form water