A level Biology: Post your doubts here!

[hammadullah]

plz help me
i need to know how to create a thread here
thank you

 

[hammadullah]

An enzyme hydrolyses the two heavy polypeptide chains of an antibody molecule. The hydrolysis occurs at the hinge region and breaks the antibody into three fragments. How many of these fragments are able to bind to antigens?
A=0
B= 1
C= 2
D=3

2

 

[ashcull14]

PLEASE EXPLAIN A REASON FOR EACH OPTION

 

[ashcull14]

2

HOW???????????????

 

[Mahmood Magdy]

Thanku for replying, but i dont understand how the sample number is 12 in Q1c(i) and y multiply 2.5 with 112 in Q12

And plz explain me these too nov 9 p51 Q2c ii, june9 p5 Q3 biii ( here erorr bars overlap but in ms its written no overlap)

The number of samples is simply 4*3=12
If you carefully read the question, they said that
• the cats without tails are always heterozygous
• the ratio of their offspring ‘with tails’ and ‘without tails’ is not as expected for this
type of cross. A normal person will multiply 112 by 0.5 but the second point states that it is not as expected, and so the only choice left is 0.25.
Well for nov 2009, the trick is to realize that every value is in 1dp, so you will calculate the mean first getting 6.18 rounded upto 6.2. Then ((6.2*1000)-3000)/3000 = 107%

June 2009, you miss understood the data, it is mean +- Standard deviation, Error bars is 2*Standard ERROR (+ and -). The MS says the sets of data do not overlap, which could be explained in terms of SD etc.

 

[qwertypoiu]

An enzyme hydrolyses the two heavy polypeptide chains of an antibody molecule. The hydrolysis occurs at the hinge region and breaks the antibody into three fragments. How many of these fragments are able to bind to antigens?
A=0
B= 1
C= 2
D=3

I think 2?
This is how i picture it, it seems two of them can still bind to antigens.

 

[qwertypoiu]

View attachment 52122
PLEASE EXPLAIN A REASON FOR EACH OPTION

A i think

Because yes water moves through membranes everywhere, as a result of random motion.
And yes water moves into cell 1 by osmosis, since it has a low (-7 is lowest number there) water potential.
As for number 3, it is wrong, water DOES move in both directions, just that both rates are same and so overall there is no net movement, but water still moves in both directions.
As for number 4, water does move out but this doesn't necessarily always mean that plasmolysis has occured.

 

[ashcull14]

A i think

Because yes water moves through membranes everywhere, as a result of random motion.
And yes water moves into cell 1 by osmosis, since it has a low (-7 is lowest number there) water potential.
As for number 3, it is wrong, water DOES move in both directions, just that both rates are same and so overall there is no net movement, but water still moves in both directions.
As for number 4, water does move out but this doesn't necessarily always mean that plasmolysis has occured.

THNK U SO MUCH

 

[slisjunknown]

Can someone pls tell me what this answer should be?
Explain why sickle cell anaemia is common in areas where malaria is endemic
p.s.I've checked the marking scheme already and it doesn't make sense to me

 

[ashcull14]

Can someone pls tell me what this answer should be?
Explain why sickle cell anaemia is common in areas where malaria is endemic
p.s.I've checked the marking scheme already and it doesn't make sense to me

Sickle cell anemia is expressed as a recessive disease, meaning that in order to have SSA, you need to inherit two SC gene, one from each of your parents. People with only one SC gene, do not get SSA, but have what is called sickle cell trait. The connection to malaria is that virtually everyone in sub-Sahara Africa suffers from at least one bout with the disease before they reach adulthood. Malaria spends part of its life cycle inside red blood cells. A person with SC trait has blood cells with half normal hemoglobin, and half SC hemoglobin. The malaria parasite doesn't survive as well in these cells, and as a result, the individual with SC trait is more likely to survive and reproduce, passing that protection along to the next generation
sickle hemoglobin might get in the way of the Plasmodium parasite infecting red blood cells, reducing the number of parasites that actually infect the host and thus conferring some protection against the disease:-
1- Malaria is caused by Plasmodium falciparum, a parasite that completes a part of its life cycle in the red blood cells of human beings. It enters the human bloodstream when a female Anopheles mosquito, carrying the parasite, bites a healthy individual. It has been observed that the red blood cells of individuals with sickle cell trait, break down when infected with the malarial parasite. Since the parasite needs to complete a part of its life cycle inside the red blood cells, destruction of the cells does not allow the disease to get established in the individual.
2- The parasite thrives on hemoglobin in order to grow. The mutated Hb S leads to the formation of a polymerized form of hemoglobin that cannot be ingested by the parasite. Hence, the malarial parasite is not able to complete its life cycle, and cause disease in the individual.
3- The red blood cells of people with sickle cell trait, tend to sickle under very low oxygen tension. The parasite reduces the oxygen tension in the blood cells that they infect, because they use up the oxygen carried by the hemoglobin for their own metabolism. This sickles the red blood cells that is destroyed by the phagocytes.
4- In case of low oxygen concentration, the potassium in the red blood cells leak out of the cells that contain the abnormal hemoglobin. The parasite needs high levels of potassium to develop and due to its leakage the parasite fails to grow in a blood cell, that have the abnormal hemoglobin.
More research is required to get a conclusive explanation for the association of sickle cell in areas with high incidence of malaria. However, this association is a remarkable example of heterozygous advantage, in which the carriers of a recessive allele have higher chances of survival than those homozygous for the mutated gene.

 

[ilovepineapples]

Is it the exdexel one?

No its the CIE one

 

[Xaptor16]

its an AS Level question but i really need help:
40 A farmer grows a different crop in a field each year for three years. In the fourth year the farmer plants a leguminous crop and then ploughs this into the soil. The next year the rotation starts again. Which microorganisms will increase by the time the rotation starts again?
1 denitrifying bacteria
2 nitrifying bacteria
3 nitrogen-fixing bacteria
4 decomposing bacteria

A 1, 2 and 3
B 1, 2 and 4
C 1, 3 and 4
D 2, 3 and 4

 

[qwertypoiu]

Sickle cell anemia is expressed as a recessive disease, meaning that in order to have SSA, you need to inherit two SC gene, one from each of your parents. People with only one SC gene, do not get SSA, but have what is called sickle cell trait. The connection to malaria is that virtually everyone in sub-Sahara Africa suffers from at least one bout with the disease before they reach adulthood. Malaria spends part of its life cycle inside red blood cells. A person with SC trait has blood cells with half normal hemoglobin, and half SC hemoglobin. The malaria parasite doesn't survive as well in these cells, and as a result, the individual with SC trait is more likely to survive and reproduce, passing that protection along to the next generation
sickle hemoglobin might get in the way of the Plasmodium parasite infecting red blood cells, reducing the number of parasites that actually infect the host and thus conferring some protection against the disease:-
1- Malaria is caused by Plasmodium falciparum, a parasite that completes a part of its life cycle in the red blood cells of human beings. It enters the human bloodstream when a female Anopheles mosquito, carrying the parasite, bites a healthy individual. It has been observed that the red blood cells of individuals with sickle cell trait, break down when infected with the malarial parasite. Since the parasite needs to complete a part of its life cycle inside the red blood cells, destruction of the cells does not allow the disease to get established in the individual.
2- The parasite thrives on hemoglobin in order to grow. The mutated Hb S leads to the formation of a polymerized form of hemoglobin that cannot be ingested by the parasite. Hence, the malarial parasite is not able to complete its life cycle, and cause disease in the individual.
3- The red blood cells of people with sickle cell trait, tend to sickle under very low oxygen tension. The parasite reduces the oxygen tension in the blood cells that they infect, because they use up the oxygen carried by the hemoglobin for their own metabolism. This sickles the red blood cells that is destroyed by the phagocytes.
4- In case of low oxygen concentration, the potassium in the red blood cells leak out of the cells that contain the abnormal hemoglobin. The parasite needs high levels of potassium to develop and due to its leakage the parasite fails to grow in a blood cell, that have the abnormal hemoglobin.
More research is required to get a conclusive explanation for the association of sickle cell in areas with high incidence of malaria. However, this association is a remarkable example of heterozygous advantage, in which the carriers of a recessive allele have higher chances of survival than those homozygous for the mutated gene.

Could you tell me if you typed all this yourself?
If not please send me the link from where you got it

 

[qwertypoiu]

its an AS Level question but i really need help:
40 A farmer grows a different crop in a field each year for three years. In the fourth year the farmer plants a leguminous crop and then ploughs this into the soil. The next year the rotation starts again. Which microorganisms will increase by the time the rotation starts again?
1 denitrifying bacteria
2 nitrifying bacteria
3 nitrogen-fixing bacteria
4 decomposing bacteria

A 1, 2 and 3
B 1, 2 and 4
C 1, 3 and 4
D 2, 3 and 4

I'm not sure but is it B?

 

[Xaptor16]

I'm not sure but is it B?

its D i dont understand it, i need explanation for the answer

 

[Xaptor16]

another AS question:
14 The fluidity of the cell surface membrane can be changed by a number of factors. As the fluidity of cell surface membranes decreases, which process would be least changed?
A active transport
B diffusion
C endocytosis
D osmosis
the answer is A... why?

 

[qwertypoiu]

another AS question:
14 The fluidity of the cell surface membrane can be changed by a number of factors. As the fluidity of cell surface membranes decreases, which process would be least changed?
A active transport
B diffusion
C endocytosis
D osmosis
the answer is A... why?

Sorry can't help you in either of your questions but please tell me which year/paper you got these questions I'm interested in asking my teacher now.

 

[Mahmood Magdy]

another AS question:
14 The fluidity of the cell surface membrane can be changed by a number of factors. As the fluidity of cell surface membranes decreases, which process would be least changed?
A active transport
B diffusion
C endocytosis
D osmosis
the answer is A... why?

Because simply Active transport mostly depends on the carrier proteins not the fluidity. I mean, whether the phospholipid bilayer is rigid or fluidish etc it won't affect Active transport, because either way the molecules transported are polar and so won't pass through the bilayer.

 

[liptonice]

guys whats may june 2007 paper 4 question 7 c) i and ii ?

i got confused why is is not for offspring genotypes male: CbCw, CbXA and for female; XAXa and XACb
i did not do power to B etc ? C^B
So i hope u will understand better .

 

[liptonice]

and also from May june 2007 paper 4, question 4a : Describe the role of insulin in the regualtion of blood glucose concentration ?

why in the MS its written about K+ ions pump and Ca2+ ions ?????????