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A level Biology: Post your doubts here!

confused123

confused123

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shan5674 said:
can someone please explain the experimental evidence for the semi-conservative replication of DNA in genetics. I dont understand the whole heavy DNA and the generations stuff...
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no one does.
Evidence for the semi-conservative replication of DNA.

In an experiment on e.coli(a bacteria) these were used to follow the DNA in the new cells every generation.

NOTE : Bacteria are used in this experiment since they replicate very rapidly causing this experiment not to last too long.(Generation time is about 50 minutes at 36oC)

The bacteria were grown in a nutrient medium containing the heavy isotope of Nitrogen-15. This replaced the normal Nitrogen-14 in the DNA. The bacteria labelled with N-15 contained the original or parental DNA. These bacteria were then transferred in a medium containing N-14 and allowed to grow.

Other similar bacteria were left for their DNA to replicate 2 or 3 times. The DNA was then extracted and centrifuged. The heavier the DNA, the closer to the bottom of the tube it settles. The DNA appeared as bands in the tubes as shown.
 
S

sagystu

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confused123 said:
http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w09_qp_11.pdf
18, 20, 31, 32, and 40. thanks a lot
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32; each cell it passes through it passes through(in and out ) 2 membranes but RBC only 1 membrane ,,so 2 squamous of alveoli 2 sq. of cappillaries and 1 memb of rbc so tatal 5 =D

31; 1 cartillage = present
2 cillia of epithilum
3 iam GEUSSING mucus holding vesicles

20; SORRY I COULDN'T UNDERSTAND IT EITHER

18; a hapliod organism can't produce gametes so no means of sexual reproduction so answer is D
 
xxfarhaxx

xxfarhaxx

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asalamu alaikum....
here r some predicted question fr da AS prctical paper...
1. osmosis on onion cell
2. thy hav provided us wth egg n oil bt no reagents... any gues on wt might cum.???? pls let us knw....
3.cros section of da lungs....

guys if ul knw abt anythn pls let us knw!!!

wasalam!!!!
 
confused123

confused123

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xxfarhaxx said:
asalamu alaikum....
here r some predicted question fr da AS prctical paper...
1. osmosis on onion cell
2. thy hav provided us wth egg n oil bt no reagents... any gues on wt might cum.???? pls let us knw....
3.cros section of da lungs....

guys if ul knw abt anythn pls let us knw!!!

wasalam!!!!
Click to expand...
on what grounds do you make predictions and who exactly made these? plz share. :)
 
xxfarhaxx

xxfarhaxx

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May allah help all of us pass da xam with flying colours...Inshaallah!!!! :)
SOME USEFUL DUA'S!!

DUAS WHILE PREPARING FOR EXAMS

DUA BEFORE STUDYING
Allahumma infa'nii bimaa O Allah! Make useful for me what You
'allamtanii wa'allimnii taught me and teach me knowledge
maa yanfa' unii. that will be useful to me.Allahumma inii as'aluka O Allah! I ask You for the understanding
fahmal-nabiyyen wa hifthal of the prophets and the memory of the
mursaleen al-muqarrabeen. messengers, and those nearest to You.
Allahumma ijal leesanee O Allah! Make my tongue full of
'amiran bi thikrika wa Your remembrance, and my heart
withqalbi bi khashyatika. consciousness of You.

Innaka 'ala ma-tasha'-u (O Allah!) You do whatever You wish,
qadeer wa anta hasbun-allahu and You are my Availer and
wa na'mal wakeel. Protector and the best of aid.
DUA AFTER STUDYING
Allahhumma inni astaodeeuka O Allah! I entrust You with what I
ma qara'tu wama hafaz-tu. have read and I have studied.
Faradduhu 'allaya inda (O Allah!) Bring it back to me whenhagati elayhi. I am in need of it.
Innaka 'ala ma-tasha'-u (O Allah!) You do whatever You wish,
qadeer wa anta hasbeeya and You are my Availer and
wa na'mal wakeel. Protector and the best of aid.
DUA WHILE STUDYING SOMETHING DIFFICULT
Allahumma la sahla illama O Allah! Nothing is easy except what
ja-'altahu sahla wa anta taj You have made easy. If You wish, You
'alu al hazana etha shi'ta sahla can make the difficult easy.
DUA FOR ANXIETY
Allahumma inni a'oodhoo bika O Allah! I seek refuge in You from anxiety
minal-hammi walhuzni, wal-'ajzi and sorrow, weakness and laziness,
wal-kasali wal-bukhli wal-jubni, miserliness and cowardice, the burden of
wa dal'id-dayni wa ghalabatir-rajaal debts and from being oppressed by men.
DUA FOR DISTRESSAllahumma rahmataka arjoo falaa O Allah! It is Your mercy that I hope for
takilnee ilaa nafsee tarfata so do not leave me in charge of my affairs
'aynin wa aslih-lee sha'nee even for a blink of an eye and rectify
kullahu, laa ilaha illa anta for me all of my affairs. None has the right to be worshiped except You.
DUA FOR CONCENTRATION
"Salla-l-laahu alaa Muhammad wa aal-e Muhammad. Allahumma inni as'aluka yaa mudhakkira-l khayr wa faa'ilahu wa-l-aamimira bihi dhakir-ni maa ansaani-hi-shaytan."
"Blessings of ALLAH be upon Muhammad and his progeny. O Allah I ask you, the one who mentions goodness and actualizes it and commands it, remind me of that which the shaytan makes me forget."
 
Idolfanatic95

Idolfanatic95

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xxfarhaxx said:
asalamu alaikum....
here r some predicted question fr da AS prctical paper...
1. osmosis on onion cell
2. thy hav provided us wth egg n oil bt no reagents... any gues on wt might cum.???? pls let us knw....
3.cros section of da lungs....

guys if ul knw abt anythn pls let us knw!!!

wasalam!!!!
Click to expand...
This for real? o_O
 
xxfarhaxx

xxfarhaxx

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wts a stage micrometer n a graticule,, n hw do u use thm to measure???:confused:
plz hlp!!!!!!!!!
 
confused123

confused123

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xxfarhaxx said:
wts a stage micrometer n a graticule,, n hw do u use thm to measure???:confused:
plz hlp!!!!!!!!!
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hey should know this and memorize a lot of times because this question is very common!
if u want to know dat how much does one eye piece graticule represents then simply divide the number of e.p.g divisions covering the width of cell in 0.1 mm. this will give you that how much does 1 eye piece division represents. multiply with thousand to get the width in micrometers. then multipy with the number of ep divisions visible to find the field of view.
 
confused123

confused123

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Idolfanatic95 said:
20) It is possible for any cell in the body to contain mutated DNA. perhaps cancer cells divide rapidly and would have a very short interphase as compared with other normal cells.
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dude can you draw plan diagrams for trachea, vein, capillary.. Thanks
 
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