A level Biology: Post your doubts here!

[Gémeaux]

type the question as this ppr is not present in xtremepprz

ikr, but the question has in it a diagram. =/

 

[KurayamiKimmi]

http://www.xtremepapers.com/CIE/International A And AS Level/9700 - Biology/9700_s03_qp_1.pdf
can anyone explain why the answer to q16 is A and not B?

 

[rz123]

http://www.xtremepapers.com/CIE/International A And AS Level/9700 - Biology/9700_s03_qp_1.pdf
can anyone explain why the answer to q16 is A and not B?

because the chromosomes number remains the same after mitosis, i.e 46 in humans. unlike meiosis where the chromosome number halves after the cell replication. it can't be a homologous pair caz mitosis is taking place not meiosis, dre needs to be passing of the same characteristics and features which the parent cell had to the daughter cells hence A is correct..

 

[Nibz]

- Homologous chromosome pairing only occurs during Meiosis. So either A or C is correct.
- In mitosis, the chromosomes replicate and divide equally into new cells. So chromosome number doesn't change.
Hence option A.

 

[rz123]

What are the differences and similarities between the xylem vessels and sieve tubes?
give a brief explanation for the differences in structure.

 

[KurayamiKimmi]

What are the differences and similarities between the xylem vessels and sieve tubes?
give a brief explanation for the differences in structure.

Xylem vessels are dead cells , with lignified walls (except at the plasodesmata) whereas sieve tubes elements are living cells (but devoid of nuclei and ribosomes) and donot have lignified walls
Xylem vessels's end plates are broken down to form a continous tube (like a drainpipe) without any obstruction whereas sieve tube elements hae sieve plats perforated by sieve pores
also, along with sieve tube element elements there are companion cells which contain a lot of mitochondria and are nucleated -to help with the uploading of sucrose into sieve elements

 

[KurayamiKimmi]

http://www.xtremepapers.com/CIE/International A And AS Level/9700 - Biology/9700_s04_qp_1.pdf
explain question 30 anyone ? ^^

 

[rz123]

http://www.xtremepapers.com/CIE/International A And AS Level/9700 - Biology/9700_s04_qp_1.pdf
explain question 30 anyone ? ^^

maybe because larger animals are comparatively less active whereas smaller animals and insects need to efficiently transport oxygen to all part of the body due to their very active living..:/

 

[rz123]

Hi, Need help!
As and Alevel Biology book by Marry Jones. Endorsed By Cambridge..
Chapter 9 ''The Mammalian Heart''
Q.number 9.1 SAQ b and c part

Ch 8 ''The mammalian transport system'' : SAQ Q. 8.13 regarding dissociation curve

Can you give a comparison between arteries veins and capillaries ..? Thank you.

 

[eyamwir]

can anyone please
1.explain the role of NADP in photosynthesis?
2.describe why variation is important in natural selection?
3.explain the role of isolating mechanisms in the evolution of new species
4explain how an action potential is transmitted along a sensory neurone

 

[shan5674]

can someone please tell me what exactly do we need to know from the chapter infectious diseases. Do we need to know how the diseases were spread in the past and the dates and countries and all that? or just an outline of the diseases history? because my text book has so much information about the history of the disease where it originated from the years and the graphs and census done on the diseases world wide its too much info and i dont want to study it all if its not required so plss can someone tell me? this is for As btw


Also if any of youll have notes for that chapter would be really great
please and thank you

 

[rz123]

can someone please tell me what exactly do we need to know from the chapter infectious diseases. Do we need to know how the diseases were spread in the past and the dates and countries and all that? or just an outline of the diseases history? because my text book has so much information about the history of the disease where it originated from the years and the graphs and census done on the diseases world wide its too much info and i dont want to study it all if its not required so plss can someone tell me? this is for As btw


Also if any of youll have notes for that chapter would be really great
please and thank you

the pathogens which cause different diseases, mode of transmition, global pattern of dat disease, how to eradicate or prevent those diseases etc....check the syllabus man...

 

[omg]

can someone please tell me what exactly do we need to know from the chapter infectious diseases. Do we need to know how the diseases were spread in the past and the dates and countries and all that? or just an outline of the diseases history? because my text book has so much information about the history of the disease where it originated from the years and the graphs and census done on the diseases world wide its too much info and i dont want to study it all if its not required so plss can someone tell me? this is for As btw


Also if any of youll have notes for that chapter would be really great
please and thank you

go through the syllabus and past papers!
dats all i did for this chap for my xam!

 

[Ashique]

http://www.xtremepapers.com/CIE/International A And AS Level/9700 - Biology/9700_s03_qp_1.pdf
can anyone explain why the answer to q16 is A and not B?

Answer has to be among A or D, since the number of chromosomes remains the constant. So that eliminates B and C from the options. Now in mitosis, DNA replications occurs for each chromosome, so that after telophase, both the daughter cells have the same genetic code for transcription/translation; so again the need of the chromsome number to stay constant is seen. So would it happen if homologous chromosomes pair instead of the chromatids separate? So we can conclude th answer is A.

 

[larina]

Assalamo Alaikum!

How to find the expected number in a chi-squared test??

 

[Student12]

Hi, Need help!
As and Alevel Biology book by Marry Jones. Endorsed By Cambridge..
Chapter 9 ''The Mammalian Heart''
Q.number 9.1 SAQ b and c part

Ch 8 ''The mammalian transport system'' : SAQ Q. 8.13 regarding dissociation curve

Can you give a comparison between arteries veins and capillaries ..? Thank you.

For the comparison between arteries veins and capillaries :
Artery:
- Thick muscular wall
-Much elastic tissue
-Small lumen relative to diameter
-Capable of constriction
- Not permeable
- Valves in aorta and pulmonary artery only
- transport blood from the heart
-Oxygenated blood expect in pulmonary artery
-Blood under high pressure (10- 16 kPa)
-Blood moves in pulses
-Blood flows rapidly

Vein:
-Thin muscular wall
-Little elastic tissue
-Large lumen relative to diameter
-Not capable of constriction
-Not permeable
-Valves thoughout all veins
-Transport blood to heart
-Deoxygenated blood except in pulmonary vein
-Blood under low pressure (1kPa)
-No pulses
-Blood flows slowly

Capillary:
-No muscles
-No elastic tissue
-Large lumen relative to diameter
-Not capable of constriction
-Permeable
-No valves
-Links arteries to veins
-Blood changes from oxygenated to deoxygenated
-Blood pressure reducing (4-1 kPa)
-No pulses
-Blood flow slowing

Hope it Helps !

 

[rz123]

For the comparison between arteries veins and capillaries :
Artery:
- Thick muscular wall
-Much elastic tissue
-Small lumen relative to diameter
-Capable of constriction
- Not permeable
- Valves in aorta and pulmonary artery only
- transport blood from the heart
-Oxygenated blood expect in pulmonary artery
-Blood under high pressure (10- 16 kPa)
-Blood moves in pulses
-Blood flows rapidly

Vein:
-Thin muscular wall
-Little elastic tissue
-Large lumen relative to diameter
-Not capable of constriction
-Not permeable
-Valves thoughout all veins
-Transport blood to heart
-Deoxygenated blood except in pulmonary vein
-Blood under low pressure (1kPa)
-No pulses
-Blood flows slowly

Capillary:
-No muscles
-No elastic tissue
-Large lumen relative to diameter
-Not capable of constriction
-Permeable
-No valves
-Links arteries to veins
-Blood changes from oxygenated to deoxygenated
-Blood pressure reducing (4-1 kPa)
-No pulses
-Blood flow slowing

Hope it Helps !

Indeed it helps! Thankyou so much!

 

[Gémeaux]

As and Alevel Biology book by Marry Jones. Endorsed By Cambridge..
Chapter 9 ''The Mammalian Heart''
Q.number 9.1 SAQ b and c part

answers are given at the back.
still, 9.1 (b) ventricular systole will be when pressure rise is greatest., dat is from about 0.15 to 0.45 which is the time of closing and opening of atrio-ventricular valves respectively.
when the ventricular systole is over, ventricle relax, i.e. its diastole. this is from about 0.45 to approx 0.7s.
(c) atria contracts after ventricular diastole, and the pressure change will be smaller this tym so both frm 0 to 0.15 and 0.7 to 0.85 are atrial systoles.
i am not sure about (ii) but as far as i've known, ventricular diastole and atrial diastole occur at the same time. this is when atria are filled. so probably this will be same as b(ii).

this also might help.

 

[Gémeaux]

As and Alevel Biology book by Marry Jones. Endorsed By Cambridge..
Ch 8 ''The mammalian transport system'' : SAQ Q. 8.13 regarding dissociation curve

a(i) from the curve ( and also the table given below) 96.5%

(ii)fully saturated means 100%, so by unitary method,
%age : vol. of O2
100 : 1.3
96.5 : x
x = (96.5 * 1.3 )/ 100 = 1.25 cm^3

b(i) 24%
(ii) again the method above, vol. of O2= (24 * 1.3)/100 = 0.312 cm^3

 

[rz123]

answers are given at the back.
still, 9.1 (b) ventricular systole will be when pressure rise is greatest., dat is from about 0.15 to 0.45 which is the time of closing and opening of atrio-ventricular valves respectively.
when the ventricular systole is over, ventricle relax, i.e. its diastole. this is from about 0.45 to approx 0.7s.
(c) atria contracts after ventricular diastole, and the pressure change will be smaller this tym so both frm 0 to 0.15 and 0.7 to 0.85 are atrial systoles.
i am not sure about (ii) but as far as i've known, ventricular diastole and atrial diastole occur at the same time. this is when atria are filled. so probably this will be same as b(ii).

this also might help.

really i never checked end of the book (i have a pirated book so can't get it properly from the image at the back)
Thankyou so much it is clear now. the image helped and for the c part i guess its taking place between .48 seconds to .74 s when the ventricles r done with contraction..