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A level Biology: Post your doubts here!

Noor Ahmad

Noor Ahmad

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Irfan1995 said:
21) I'm just as confused as you are. I believe the answer should be D as well.

34) You're right. But that's not what the question's asking.
They asked for the disease which is least likely to be passed from parent to child.
A: you already mentioned it
B: HIV can be passed through the placenta (the connection between the mother and the baby in the womb)
C: Malaria must pass through a vector (the female Anopheles mosquito)
D: Sickle-cell anaemia is a genetic disease, so it can definitely pass from parent to child.
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OH MY, i din't recognize the least likely part.Thanks alot :)
 
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raamish

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in which soil nitrogen fixation bacteria found. Are they found in both boggy(wet soil of denitrifying) and well aerated soil(nitrifying)? can u also confirm if my sentence is correct?
 
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Irfan1995

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ShootingStar said:
and also q34
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w12_qp_12.pdf
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100 ml of arterial blood carries 19 ml of oxygen while the same amount of venous blood carries only 12.5 ml of oxygen.
When the blood passes through the lungs, (19 - 12.5) = 6.5 ml of oxygen is absorbed.
In one minute, 5L of blood passes through the lungs. 5L = 5,000 ml.
If 100 ml of blood absorbs 6.5 ml of oxygen, then 5,000 ml (100 x 50) of blood should absorb (6.5 x 50) = 325 ml of oxygen per minute
 
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Irfan1995

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Noor Ahmad said:
Question 27
http://papers.xtremepapers.com/CIE/...nd AS Level/Biology (9700)/9700_w10_qp_12.pdf
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I'll try to prove (or refute) all options:
Option 1: If you have two isotonic solution (with the same water potential) that are separated by a partially permeable membrane, water will definitely move both ways, but the NET water movement is zero. Also, when you have to solutions of different water potentials (separated by a membrane), water will still move both ways, but the rate of water movement outside the solution with higher water potential will be greater than the other rate. This creates a net movement of water down a potential gradient. Conclusion: no matter what case you have, when there are two solutions separated by a membrane, water will always move both ways.

Option 2: Cell 1 has the lowest water potential, so water will move into it.

Option 3: Just like in option 1, there is water movement, but no NET water movement

Option 4: Water does move out of cell 3, but it will not be plasmolysed. Water will continue to move until all three cells have the exact same water potential as the environment (and themselves). Cell 3's water potential will be lower than -4kPa, but higher than -6kPa. Since cell 1 has a lower water potential than that (and it's not mentioned that it's plasmolysed), then you can't assume that cell 3 will plasmolyse.
 
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Irfan1995

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raamish said:
in which soil nitrogen fixation bacteria found. Are they found in both boggy(wet soil of denitrifying) and well aerated soil(nitrifying)? can u also confirm if my sentence is correct?
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Nitrogen fixation is a reduction reaction, so no oxygen is required. This means that they can live well in boggy and clogged soils.

As far as I know, diazotrophs are facultative anaerobes. This means that they can grow without oxygen. But they cannot fix nitrogen under aerobic conditions (when oxygen is present). However, diazotrophs can form symbiotic relationships (especially with legumes) that allow them to live in nodules which prevent them from excess oxygen exposure.
 
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raamish

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Irfan1995 said:
Nitrogen fixation is a reduction reaction, so no oxygen is required. This means that they can live well in boggy and clogged soils.

As far as I know, diazotrophs are facultative anaerobes. This means that they can grow without oxygen. But they cannot fix nitrogen under aerobic conditions (when oxygen is present). However, diazotrophs can form symbiotic relationships (especially with legumes) that allow them to live in nodules which prevent them from excess oxygen exposure.
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can denitrifying bacteria live in boggy soils. they live in wet soils but arent boggy soils the same. And nitrifying present in well aerated soils right?
 
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kingos3111

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The stage micrometer is replaced by a slide of a plant cell.
0 10 20 30 40 50 60 70 80 90 100
What is the width of a chloroplast?
A 5 μm B 10 μm C 50 μm D 100 μm
 
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raamish

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kingos3111 said:
oct nov 2006 q1 please
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0.1-40
x-4

the answer will be 10um. 0.1 is the diff between 2 points on stage micrometer.then for those 2 points 40 points for graticule scale. just use the diagram and the formula and calculate the answer.
 
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