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A level Biology: Post your doubts here!

Mahnoorfatima

Mahnoorfatima

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And.. one other thing, if for instance I get 27/40 and the grade threshold is 29 for A and 26 for B. What grade do i get then? A or B?
 
Mahmood Magdy

Mahmood Magdy

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qwertypoiu said:
View attachment 52531


plz plz help! thank you
Click to expand...
As it is leguminous, the nitrogen fixing bacteria will increase and as he ploughs it into the soil, the decomposing bacteria will increase too. As a result of the increased ammonium compounds in the soil, so will the nitrogen fixing bacteria increase in quantity. Denitrifying bacteria should also increase but they dont becuz the plants are constantly taking away the Nitrate and NH4+ ions.
 
qwertypoiu

qwertypoiu

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Mahnoorfatima said:
Paper 12 question 35 and 36??https://docs.google.com/viewerng/vi.../11/9700_Oct-Nov-2010-All-Question-Papers.pdf
Click to expand...
q35 is about normal breathing. So we should be concerned with tidal volume, not vital capacity.
For every row, multiply tidal volume by number of breaths per minute, to get total volume of air breathed in a minute normally:
A = 14 x 0.6 = 8.4
B = 15 x 0.6 =9.0
C = 16 x 0.5 = 8.0
D = 17 x 0.5 = 8.5

Therefore B is the answer.

For question 36, D is the answer, how can the data from 1997 to 2005 tell us with certainty that we will never get rid of disease from S. aureus?
 
qwertypoiu

qwertypoiu

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Mahmood Magdy said:
As it is leguminous, the nitrogen fixing bacteria will increase and as he ploughs it into the soil, the decomposing bacteria will increase too. As a result of the increased ammonium compounds in the soil, so will the nitrogen fixing bacteria increase in quantity. Denitrifying bacteria should also increase but they dont becuz the plants are constantly taking away the Nitrate and NH4+ ions.
Click to expand...
Thank you :)
 
qwertypoiu

qwertypoiu

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Mahnoorfatima said:
https://docs.google.com/viewerng/vi...11/9700_May-June-2011-All-Question-Papers.pdf
paper 13 question 18 PLEEEASEEEEE!!!!!!!!!!!
Click to expand...

Q13:
Specificity of an enzyme is based on the shape of its active site. The shape of the active site is based upon the shape of the enzyme, which is a protein. The shape of proteins and how their polypeptides associate is based upon quaternary structure, which affects the shape of active site. The perfect 3D shape of each polypeptide chain involved is based upon the tertiary structure (affects shape).
Tertiary structure involves features from the secondary structure as well like alpha helix and beta pleated sheet (affects shape).
All protein molecules have the exact shape they have because of the primary structure, the sequence of amino acids determines how exactly they interact and form a 3-D shape.
Therefore answer is A, the specificity of an enzyme is based on primary, secondary, tertiary, and quaternary structure.

Q18:
Cytokinesis is the process when the cell membrane splits between the two new nuclei after telophase, so:
1. No,new organelles are not made, they were already replicated before this.
2. Yes, cytokinesis will make a split between the cells, so the organelles are separated between the cells.
3. No, nuclear envelope reforms during telophase, cytokinesis is only about membrane splitting.
 
qwertypoiu

qwertypoiu

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Mahnoorfatima said:
http://studyguide.pk/Past Papers/CIE/International A And AS Level/9700 - Biology/9700_w08_qp_1.pdf
Question 4. And in question 12 why cant it be B since the rate of reaction should be 0 at startt when no substrate and Active site are colliding?
and in question 23, How can the lowest H2O potential be in xylem!>?? It only has H2O!
And for 26 why not A?
And in 40, why not D?
PLEASE SOMEONE HELP! :(:(:(:cry::cry:
Click to expand...
Q4:
From the diagram, you should have measured the shortest distance from the alveolar air space to inside a red blood cell. This should be 7.5 mm, convert this to micrometres and divide by 2500.
Q12:
As a general rule, rate of reaction is NEVER zero. Especially at around 25 degrees the graph of B shows, how could the rate be zero? And you're wrong to say no substrate and active site are colliding, yes they ARE colliding, all we are changing is temperature, which affects how frequently and effectively they collide that's all.
Q23:
Xylem does not only have H2O, it has H2O with many ions dissolved inside. You should know that water travels like this:
Soil water ---> root hair cell ---> endodermis ----> xylem
You should also know that water travels DOWN its water potential gradient. Thus, the order from highest to lowest water potential will be in this exact order.
Q26:
It says RBCs are near a resting muscle.
Resting means less CO2 produced, thus it will be graph on the left (non-Bohr Shift one)
Muscle means they have low oxygen partial pressure, so it has to be from the point on left.
It cannot be A, because the cells are near a resting MUSCLE, A is having a HIGH oxygen partial pressure.
Q40:
Why not D? Because it's wrong :)
Basically most of energy lost is through heat from respiration! We're very inefficient energy users. (Which btw is an advantage, we WANT to be warm for homeostasis
 
qwertypoiu

qwertypoiu

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Mahmood Magdy said:
As it is leguminous, the nitrogen fixing bacteria will increase and as he ploughs it into the soil, the decomposing bacteria will increase too. As a result of the increased ammonium compounds in the soil, so will the nitrogen fixing bacteria increase in quantity. Denitrifying bacteria should also increase but they dont becuz the plants are constantly taking away the Nitrate and NH4+ ions.
Click to expand...
Thank you so much you're awesome man
 
Mahnoorfatima

Mahnoorfatima

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qwertypoiu said:
Q4:
From the diagram, you should have measured the shortest distance from the alveolar air space to inside a red blood cell. This should be 7.5 mm, convert this to micrometres and divide by 2500.
Q12:
As a general rule, rate of reaction is NEVER zero. Especially at around 25 degrees the graph of B shows, how could the rate be zero? And you're wrong to say no substrate and active site are colliding, yes they ARE colliding, all we are changing is temperature, which affects how frequently and effectively they collide that's all.
Q23:
Xylem does not only have H2O, it has H2O with many ions dissolved inside. You should know that water travels like this:
Soil water ---> root hair cell ---> endodermis ----> xylem
You should also know that water travels DOWN its water potential gradient. Thus, the order from highest to lowest water potential will be in this exact order.
Q26:
It says RBCs are near a resting muscle.
Resting means less CO2 produced, thus it will be graph on the left (non-Bohr Shift one)
Muscle means they have low oxygen partial pressure, so it has to be from the point on left.
It cannot be A, because the cells are near a resting MUSCLE, A is having a HIGH oxygen partial pressure.
Q40:
Why not D? Because it's wrong :)
Basically most of energy lost is through heat from respiration! We're very inefficient energy users. (Which btw is an advantage, we WANT to be warm for homeostasis
Click to expand...

Thanks a bunch! You almost saved my life. :)
 
MYLORD

MYLORD

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qwertypoiu said:
In addition to what Mahmood said, you should also know that:
  • Adenine and Thymine/Uracil are linked by 2 hydrogen bonds
  • Guanine and Cytosine are linked by 3 hydrogen bonds.
Click to expand...
why cant base A and base G bond ?
whats the scientific reason ?
 
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