A level Biology: Post your doubts here!

[hela]

where can I find old past papers MCQ PAPER 1

 

[Irfan1995]

Is it possible to take an A overall if you take a B in paper 3 and paper 5?

I think it's still possible to get an A*

EDIT: Let's take a look at the most recent session available (Oct/Nov 2012):
During that session, the minimum score for a B was 32/60, and the minimum score for a B in paper 5 was 18/30. The A* threshold was 194/260.
Subtracting the scores you already got implies that you have to score a total of 144 marks in the other 3 components (papers).
If you get a 30/40 in Paper 1, and a 45/60 in Paper 2, and a 70/100 in Paper 4 (all of which, I believe, is possible), then you would have scored 145 marks which is enough for an A*
The marks you have to get are slightly above the threshold of an A in those components, so you really don't have to worry too much

 

[Irfan1995]

Can someone explain me this "food containing expressed products of antibiotic resistance marker genes could be consumed at the same time as treatment with the antibiotic was occuring which would potentially reduce the effectiveness of the treatment" ?

This isn't easy to explain, so I'll try to provide an example:
Remember when you're trying to mass-produce insulin, you had to use 2 different types of antibiotics to see which bacteria took up the plasmids? If you just happen to be sick at the same time (while being diabetic and taking insulin), then the antibiotics you're going to use is useless because the insulin you're taking also has an allele which gives resistance to the antibiotic you're taking. Does that make sense? If it doesn't I'll try to clarify it even further.

 

[dornam]

I think it's still possible to get an A*

EDIT: Let's take a look at the most recent session available (Oct/Nov 2012):
During that session, the minimum score for a B was 32/60, and the minimum score for a B in paper 5 was 18/30. The A* threshold was 194/260.
Subtracting the scores you already got implies that you have to score a total of 144 marks in the other 3 components (papers).
If you get a 30/40 in Paper 1, and a 45/60 in Paper 2, and a 70/100 in Paper 4 (all of which, I believe, is possible), then you would have scored 145 marks which is enough for an A*
The marks you have to get are slightly above the threshold of an A in those components, so you really don't have to worry too much

Minimum score for a B was 32/60...which paper is that one?

 

[knowitall10]

Guys..can we start discussing some biology here? I am thirsty for Bio...i hate chem, and i had to explain it :/ Now i love bio..no one has a question....

 

[sashaleon]

What does it mean by "photorespiration is avoided"?

sorta elaborate on these point
How sorghum avoid photorespiration?

1. ref. bundle sheath cells;
2. light independent stage occurs / RuBP found (in bundle sheath cells) ;
3. RuBP / rubisco, kept away from, air / oxygen ;
4. by mesophyll cells ;
5. limits uptake of O2 / maintains high CO2 concentration (in bundle sheath cells) ;
6. enzymes / PEP carboxylase, have high optimum temperature ;
7. approx 45*C ;
not denatured ;

 

[Noor Ahmad]

This isn't easy to explain, so I'll try to provide an example:
Remember when you're trying to mass-produce insulin, you had to use 2 different types of antibiotics to see which bacteria took up the plasmids? If you just happen to be sick at the same time (while being diabetic and taking insulin), then the antibiotics you're going to use is useless because the insulin you're taking also has an allele which gives resistance to the antibiotic you're taking. Does that make sense? If it doesn't I'll try to clarify it even further.

I don't really get it.Could you explain it?
thankyou!

 

[knowitall10]

sorta elaborate on these point
How sorghum avoid photorespiration?

1.ref. bundle sheath cells;
2.light independent stage occurs / RuBP found (in bundle sheath cells) ;
3.RuBP / rubisco, kept away from, air / oxygen ;
4.by mesophyll cells ;
5.limits uptake of O2 / maintains high CO2 concentration (in bundle sheath cells) ;
6.enzymes / PEP carboxylase, have high optimum temperature ;
7.approx 45*C ;
not denatured ;

Photorespiraton happens because the enzyme Rubisco catalyses the combination of O2 with RuBP. It happens especially at hight temperatures and high light intensities.The bundle sheath cells contain RuBP and Rubisco. So in a C4 plant, they are in no direct contact iwth the air outside the cells to keep the enzyme well away from combining with oxygen. Around the bundle sheath cells, is a ring of tightly packed mesophyll cells. the cytoplasm fixes the CO2,a nd the light energy is trapped by the chloroplasts to carry out the light dependent reactions. These cells contain an enzyme called PEP Carboxylase, which catalysses the combination of CO2 with PEP. The compound formed as a result is called oxaloacetate, which is converted to malate, and this is what's passed to the bundle sheath cells.
The light independent reaction (Calvin Cycle), is carried out in the bundle sheath cells. The CO2 is removed from the malate and delivered to RuBP in the normal manner.
Regarding optimum temperature, then the C4 plants, such as sorghum, have high optimum temperatures for their enzymes. (An adaptation for growig in hot climates). So the optimum temp for the activity of PEP carboxylase is around 45'C, and according to what i studied, if the temp drops to 15'C, then this enzyme loses about 70% of its activity.

The same enzyme in C3 plants has a lower optimum temp (of about 30'C) but it loses it's activity at a much much lower temperature compared to the enzyme in C4 plants..

 

[knowitall10]

Can someone explain me this "food containing expressed products of antibiotic resistance marker genes could be consumed at the same time as treatment with the antibiotic was occuring which would potentially reduce the effectiveness of the treatment" ?

Can u please send the link to which paper you found this in? Or where u had read it?
Thank you

 

[Irfan1995]

Minimum score for a B was 32/60...which paper is that one?

Sorry, I made a mistake right there. I meant to say that the minimum score for a B in paper 3 was a 22/40, and for paper 5 was an 18/20. So that means you're supposed to get 154 in the remaining components.
So if you get a 30/40 in Paper 1, 50/60 in Paper 2, and 75/100 in Paper 4, then you should get an A*.

Once again, sorry for the miscalculation

 

[knowitall10]

Sorry, I made a mistake right there. I meant to say that the minimum score for a B in paper 3 was a 22/40, and for paper 5 was an 18/20. So that means you're supposed to get 154 in the remaining components.
So if you get a 30/40 in Paper 1, 50/60 in Paper 2, and 75/100 in Paper 4, then you should get an A*.

Once again, sorry for the miscalculation

Brother...are you in A Levels...can u please do some of that wacky calculation for the scores i need to get to get an A*?
Sorry to take your time..

 

[Irfan1995]

Can someone explain me this "food containing expressed products of antibiotic resistance marker genes could be consumed at the same time as treatment with the antibiotic was occuring which would potentially reduce the effectiveness of the treatment" ?

Okay, let's say you're sick, so you need to take an antibiotic. We know that antibiotics are useless if bacteria are resistant to it.
During the process of genetic engineering, we made plasmids that have an antibiotic-resistant allele.
If you take insulin that's made from these plasmids, then the insulin you're taking has the antibiotic-resistant allele.
When the antibiotic-resistant allele is expressed, it will give a protein that counteracts the antibiotic you're taking.
So the antibiotic you're taking is useless.

 

[Irfan1995]

Brother...are you in A Levels...can u please do some of that wacky calculation for the scores i need to get to get an A*?
Sorry to take your time..

I don't mind, do you have an A in your AS already?

 

[knowitall10]

Okay, let's say you're sick, so you need to take an antibiotic. We know that antibiotics are useless if bacteria are resistant to it.
During the process of genetic engineering, we made plasmids that have an antibiotic-resistant allele.
If you take insulin that's made from these plasmids, then the insulin you're taking has the antibiotic-resistant allele.
When the antibiotic-resistant allele is expressed, it will give a protein that counteracts the antibiotic you're taking.
So the antibiotic you're taking is useless.

Hmmm....Ok ok...I get it....

 

[knowitall10]

I don't mind, do you have an A in your AS already?

LOL!!



No i don't

 

[Irfan1995]

LOL!!



No i don't

Seriously, I don't mind doing some math right here. You can inbox me your scores if you prefer some privacy

 

[knowitall10]

MaxStudentALevel
I'm so happy you're here!!!!

 

[Amy Bloom]

Is it possible to take an A overall if you take a B in paper 3 and paper 5?

YES

 

[dornam]

How can oxygen debt be defined properly?

 

[Irfan1995]

How can oxygen debt be defined properly?

The oxygen required to metabolize/use up the lactic acid produced (or respire it completely)