Qualification > Sciences
ALL CIE BIOLOGY DOUBTS HERE !!!
**RoRo**:
--- Quote from: Martin Luther King Jr on December 06, 2010, 10:24:57 am ---1. Mitosis is important in these cases so as to replace dead cells with new identical ones which will carry out the same function as the others preceding it. Hence this is to ensure the survival of this particular species.
Example : (i) The body cells of a child undergoes mitosis for growth so that the child becomes bigger and have more developped organs which will be more efficient in their respective jobs.
2. Identical cells should be produced to ensure the survival of the respective species as well as the genes coding for it. If the cells are not identical the organism is going to be affected as the same genes will not be present and hence will not be able to carry out the wanted function.
3. Meiosis is required to half the number of chromosome in each gamete. This will ensure that upon fertilization the required number of chromosomes will be restored. In other words it prevents the number of chromosome to double each generation.
Example : (i) In man, we have 46 chromosome in each cell. Our body produces gamete with half the number of chromosome(23) such that at fertilization two gametes combine together to form one cell. Hence number of chromosome is restored. (23 + 23 = 46)
--- End quote ---
Finally someone replied!
THANK YOU VERY MUCH!! :D
I have another question:Can you please explain to me the experiment [evidence that DNA replicates by semi-conservative method]? I don't understand what this experiment is about and how is it conducted! :/
Deadly_king:
--- Quote from: The Secret on December 06, 2010, 11:20:37 am ---Finally someone replied!
THANK YOU VERY MUCH!! :D
I have another question:Can you please explain to me the experiment [evidence that DNA replicates by semi-conservative method]? I don't understand what this experiment is about and how is it conducted! :/
--- End quote ---
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.
As you can see only 50% of the original DNA is restored each generation. This is why it is called semi-conservative.
**RoRo**:
--- Quote from: Martin Luther King Jr on December 06, 2010, 11:38:23 am ---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.
As you can see only 50% of the original DNA is restored each generation. This is why it is called semi-conservative.
--- End quote ---
Thank you very very much! ;D
That was really simple, to the point and well-explained!! :)
Deadly_king:
--- Quote from: The Secret on December 06, 2010, 11:44:38 am ---Thank you very very much! ;D
That was really simple, to the point and well-explained!! :)
--- End quote ---
Hehe.................anytime dude :D
mdwael:
Do plant cells have lysosome structure? In wikipedia it says they dont, only animals do. But I came across the Multiple choice question in which the answer says that they infact do have lysosome structure. The past paper is 2010 cie 9700 qp_11 summer question number 4.
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version