A level Biology: Post your doubts here!

[Student12]

explain translocation as an energy-requiring process transporting assimilates, especially sucrose,
between the leaves (sources) and other parts of the plant (sinks) -- its a very important question! I need the detailed answer in good language.
AND
explain the translocation of sucrose using the mass flow hypothesis.

 

[Student12]

describe and explain the significance of the dissociation curves of adult oxyhaemoglobin at different
carbon dioxide levels (the Bohr effect);

state and explain the differences between blood, tissue fluid and lymph;

 

[Gogo]

hi all, please tell me that what happens to a chromosome between the end of anaphase and the start of the next mitosis.

they become chromatinin the nucleus

 

[Gogo]

Role of capillaries in forming tissue fluid?

they release the plasma from the blood which becomes tissue fluid when it enters the tissues.

hope it helps

 

[Student12]

Role of capillaries in forming tissue fluid?

http://www.s-cool.co.uk/a-level/biology/transport/revise-it/transport-in-mammals -- this would help.

 

[confused123]

Role of capillaries in forming tissue fluid?

the blood pressure is lowering from 4 to 1 kp in capillaries. oxygen is being moved out cappilary to tissue fluid via high blood pressure, thru pores and from tranport channels and oxygen moves out of capillary to tissue fluid via difusion.
it allows quite a lot time for gases, nutrients, waste products to be diffused out of the capillaries into tissue fluid

 

[Idolfanatic95]

explain translocation as an energy-requiring process transporting assimilates, especially sucrose,
between the leaves (sources) and other parts of the plant (sinks) -- its a very important question! I need the detailed answer in good language.
AND
explain the translocation of sucrose using the mass flow hypothesis.

http://www.biologyreference.com/Ta-Va/Translocation.html#b
This might help you

 

[confused123]

oct/nov 2003, q.6 , 16 mcq
http://www.xtremepapers.com/CIE/International A And AS Level/9700 - Biology/9700_w03_qp_1.pdf

m/j 2011 , q.6 mcq.
http://www.xtremepapers.com/CIE/International A And AS Level/9700 - Biology/9700_s11_qp_11.pdf

 

[sagystu]

hi every one i can't seem to anderstand the answer to 1 a ii in this exam here is the markcheme ,, i wrote % 0 40 60 80 100 http://www.xtremepapers.com/papers/...nd AS Level/Biology (9700)/9700_s09_ms_31.pdf please help and thanks

 

[Mubasher96]

oct/nov 2003, q.6 , 16 mcq
http://www.xtremepapers.com/CIE/International A And AS Level/9700 - Biology/9700_w03_qp_1.pdf

m/j 2011 , q.6 mcq.
http://www.xtremepapers.com/CIE/International A And AS Level/9700 - Biology/9700_s11_qp_11.pdf

O/N 03 q. 6) the answer is A. the length given beside the cell's drawing, written 35µm, when measured with a ruler gives approximately 10.4 cm. measuring the length of any of the mitochondria, we get about 1.5
Use unitary method,
1.5 : x
10.2 : 35
x= 5.14 which lies in the range of A i.e. 5 to 6µm

16) the answer's B. the graph is of rate of reaction and substrate conc. It shows that between W and X the rate increases with increased conc. of sbstrate. between X and Y, the *rate* stays conc which means that the reaction may still be going on but the rate at which product is made is constt.
A is rejected bcause here substrate conc. can be said to b limiting not enzyme molecules because increase in substr. increases rate of reaction frm which we can deduce that sum enzyme mlecules were still *unoccupied*.
B shows no matter how much of subst. is added rate is same which means no more enzyme molecules are *free* i.e. they're limiting.
C- wrong cuz the graph shows that substrate conc. is still being increased.
D- rejected because product conc. increases bcuz the reation continues to take place even at that same rate.

Hope it helps. =)

 

[Mubasher96]

hi every one i can't seem to anderstand the answer to 1 a ii in this exam here is the markcheme ,, i wrote % 0 40 60 80 100 http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s09_ms_31.pdf please help and thanks

according to the ms, ur answer shouldn't be wrong because ur %ages are evenly spaced, n u must have written correct volumes respectively. but it is a suggestion not to leave such a huge *gap* there. like u used 0 and then directly 40 and then so on with a difference of 20.
the third mark is for writing in an order the percentages, either ascending or descending.

 

[sagystu]

according to the ms, ur answer shouldn't be wrong because ur %ages are evenly spaced, n u must have written correct volumes respectively. but it is a suggestion not to leave such a huge *gap* there. like u used 0 and then directly 40 and then so on with a difference of 20.
the third mark is for writing in an order the percentages, either ascending or descending.

thank u verrrrryyyyyyy much

 

[confused123]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s09_qp_31.pdf
2 a) can someone draw the low power plan diagram for this ..
2 c)

 

[Idolfanatic95]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s09_qp_31.pdf
2 a) can someone draw the low power plan diagram for this ..
2 c)

Im not so sure about the one i drew for part 2 (a)
so just uploading 2 (c)

 

[shan5674]

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...

 

[Idolfanatic95]

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...

http://www.dnaftb.org/20/animation.html
Check this out!

 

[confused123]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w09_qp_11.pdf
11, 12

 

[Idolfanatic95]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w09_qp_11.pdf
11, 12

11) Disulphide bonds are the strongest among all. hydrogen and even ionic bonds lag behind are are comparatively weaker. Both can be broken down by slight PH changes. so the option wud be D.
12) In collagen, having covalent bonds between adjacent molecules and each three-stranded molecule being held together by hydrogen bonds, helps to give great tensile strength to the molecule as a whole And also without having every third amino acid(usually glycine) being small, the three-stranded molecule would not be close enough to form hydrogen bonds and tighter coil so the option is B. peptide bond formation is perhaps not as imp to give tensile strength to the molecule.

 

[confused123]

http://www.xtremepapers.com/papers/...nd AS Level/Biology (9700)/9700_w09_qp_11.pdf
18, 20, 31, 32, and 40. thanks a lot

 

[confused123]

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...

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.