A level Biology: Post your doubts here!

[raamish]

hey can any1 explain the meselsohn dna experiment. I cant understand it

 

[raamish]

are u guys studying gross productivity and primary prodcutivity?

 

[Dukeofwin]

Can anyone post here notes for Diseases caused by Smoking? Please....

 

[MÁťT PŭמҚ]

Can anyone post here notes for Diseases caused by Smoking? Please....

here yew go..!!

 

[strangerss]

Can some one please clear my doubts?
Why does the mosquito have to secrete an anticoagulant the second time into an uninfected person but not the first?
Why there is an increase in the resistance in the blood vessels surrounding the lungs of an emphysema patient?
What is the difference between open and closed circulation?

 

[PANDA-]

Can some one please clear my doubts?
Why does the mosquito have to secrete an anticoagulant the second time into an uninfected person but not the first?
Why there is an increase in the resistance in the blood vessels surrounding the lungs of an emphysema patient?
What is the difference between open and closed circulation?

1. It does secrete an anticoagulant both times. But the anticoagulant does not contribute to the transmission of Malaria in the first bite of the infected person. It is only significant when the infected mosquito, with the pathogen now having infected it and reached its salivary glands, bites an uninfected person. The anticoagulant the mosquito secretes contains the pathogen, so the pathogen enters the person's bloodstream.
2. I don't really know.
3. I don't think an open circulation exists, because closed circulation means blood does not leave the blood vessels.

 

[MÁťT PŭמҚ]

How golgi apparatus packages protiens into lysosomes?? :/

 

[Irfan1995]

Can some one please clear my doubts?
Why does the mosquito have to secrete an anticoagulant the second time into an uninfected person but not the first?
Why there is an increase in the resistance in the blood vessels surrounding the lungs of an emphysema patient?
What is the difference between open and closed circulation?

So that the blood won't clot immediately which kills the host instantly. Plasmodium needs a host to survive.
In emphysema patients, most of the elastic fibres are digested by white blood cells, so there is much greater resistance when the alveoli are trying to expand.
A closed circulation system is one in which all the blood is contained in blood vessels (arteries, veins, and capillaries). An open circulation system is where there are no blood vessels. The blood-like liquid is just pumped by the heart all around the body.

 

[strangerss]

So that the blood won't clot immediately which kills the host instantly. Plasmodium needs a host to survive.
In emphysema patients, most of the elastic fibres are digested by white blood cells, so there is much greater resistance when the alveoli are trying to expand.
A closed circulation system is one in which all the blood is contained in blood vessels (arteries, veins, and capillaries). An open circulation system is where there are no blood vessels. The blood-like liquid is just pumped by the heart all around the body.

So it's not like what panda said above? that it does secret both the times , but it only matters the second?there is a great resistance when the alveoli expand, but what does that have to do with the blood vessels?.. thanks a lot for the help

 

[strangerss]

How golgi apparatus packages protiens into lysosomes?? :/

The proteins to be processed or exported to the cells , their growing chain of amino acids made at the ribsomes on the RER is moved to the cristae of the RER . The cristae then breaks off , forming small vesicles that are transported to the Golgi apparatus , where the protein is modified , by adding a carbohydrate chain for example , then the vesicle containing the modified protein breaks away from the Golgi body and is transported to the cell membrane for secretion by exocytosis. Hope this helped. Btw I don't think proteins are packaged into lysosomes , because the hydrolytic enzymes probably digest it , so I think it's wrong to say that , because they're transported in secretory vesicles

 

[Irfan1995]

So it's not like what panda said above? that it does secret both the times , but it only matters the second?there is a great resistance when the alveoli expand, but what does that have to do with the blood vessels?.. thanks a lot for the help

It secretes both times, and both matter (not only the second).

Capillaries are destroyed in a patient with emphysema, so this is probably the reason why there is a greater 'resistance'.

 

[strangerss]

I read in my book that amino acids are transported in the root nodules to the xylem , how is that? and I thought the xylem only transports mineral ions and water

 

[Wanderer]

What chaps of AS BIO shall we revise for A2 P4 ?? Immunity?? What else?

 

[Soldier313]

Aoa wr wb,
Can someone please look at qn 6 d i) of this paper and elaborate on conjugation and transduction and all that please?

http://papers.xtremepapers.com/CIE/...and AS Level/Biology (9700)/9700_s09_qp_4.pdf
http://papers.xtremepapers.com/CIE/...and AS Level/Biology (9700)/9700_s09_ms_4.pdf

Thanx a lot

 

[knowitall10]

Aoa wr wb,
Can someone please look at qn 6 d i) of this paper and elaborate on conjugation and transduction and all that please?

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s09_qp_4.pdf
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s09_ms_4.pdf

Thanx a lot

Wa3alaikumussalam wa Ra7matullahi wa Barakatuhu!
Explain why genes are rarely used as markers in gene technology?
Conjugation refers to horizontal transmission of the resistant gene my friend. You see, the reason why the plasmid is used is because it is small enough to diffuse into any cell. So this plasmid can basically be transferred from cell to cell and make all of the bacterial colony resistant to antibiotics. This is called horizontal transmission and is often the examiner's favorite word in the exam. According to my teacher, it's what they're looking for in such questions.
Regarding Transduction, this is the vertical transmission of the plasmid, basically from the parent to the offspring. Atleast that's what i've been tought. I searched vertical transmission on the net and it has something to do with viruses...as in the transmission of the plasmid vector from the bacterial DNA to the Viral DNA. I'm not sure of which one is right though. But what i am sure of is that transduction is a method of vertical transmission or is Vertical transmission.
Hope i cleared your doubt.... although i don't think i did really (

 

[knowitall10]

But Soldier313 Either way, both vertical and horizontal transmission are dangerous because if the bacteria are released into the wild, they can bring rise to furthur incurable diseases and add to the problem of antibiotic resistance.

 

[Soldier313]

But Soldier313 Either way, both vertical and horizontal transmission are dangerous because if the bacteria are released into the wild, they can bring rise to furthur incurable diseases and add to the problem of antibiotic resistance.

knowitall10
JAzakAllah khair for that! Thanx a lot! It really did help
May Allah bless you

 

[Jinkglex]

I have a pretty silly question if we encounter a question for say, 5 marks, and the marking scheme gives 10 seperate points which are relevant to the question, does that mean we need to tell them all 10 separate points?

 

[geek101]

hey can any1 explain the meselsohn dna experiment. I cant understand it

heres the experiment, the pictures are from the mary jones book.
so Meselson and this other person decided to prove SEMI CONSERVATIVE REPLICATION.
they used E coli (you dont need to know what they grew and what nitrogen source was provided to the organism)....just know there are two isotopes of Nitrogen a heavy one, N-15 and a light one N-15 which can be given via a nitrogenous source.

1) they grew the bacteria in N-15. so the e cloi used the nitrogen - 15 and incorporated it into their DNA. Now the DNA was entirely N-15. They centrifuged it and a band on the lower level of the test tube formed, because N -15 is heavy
(pic 1 on page 70)

2) Then they placed the e cloi in a medium of N -14. because semi conservative replication occurs.....
currently DNA has 2 N-15 strands
when they put it in N-14
The N-15 strand each serves as a template
so a new N-14 strand comes and attaches to it
and 2 DNA molecules are formed each with one N-15 and one N-14 strand.
When this mixture is centrifuged a band is formed in the middle, since theres light and heavy nitrogen.
(pic 2 page 70)

3) Now when the e cloi are left for more generations...in N-14
now....
there are DNA with one N-14 and one N-15 strand.
when this is left for more time in N-14....
each N-15 and N-14 strand serves as a template....
so to the N-15 a N-14 attaches and to the N-14 another N-14 attaches....
this produces a DNA molecule with N-14 and 15 and another molecule with both N-14...
when this is centrifuged There is a band in the middle, and a band of only N14 which is on the top level of the test tube, because its light.
(pic 3 page 70)

4) as the e coli are left for longer in the N14 the band with purely N14 gets wider. because more and more templates of N14 are there to which more N14 strands attaches....
(pic 4 page 70)

the percentage of hybrid DNA becomes half each time....

 

[Irfan1995]

I have a pretty silly question if we encounter a question for say, 5 marks, and the marking scheme gives 10 seperate points which are relevant to the question, does that mean we need to tell them all 10 separate points?

As far as I know, if you mention 5 points out of 10, you'll get the full mark. But you have to make sure that all the points you mention are in a clear and logical order.