biology paper 1 doubts

[Irfan1995]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w10_qp_12.pdf

Does anyone know why the answer to question number 9 is D??

D is the structure of glycerol, not a natural alkyl group or one of its derivatives.

 

[Taci12]

excuse in which exam is this question ??

Nov 11, p11. Sorry for late reply, internet connection got broken

 

[Taci12]

Plants' cell walls are fully permeable. That is, they allow anything to pass through, even water. That is, until the cell is completely turgid then it won't allow any net movement of water in to prevent bursting.

Thanks!

 

[nelly trich]

I deleted my post. Here is exactly what I know:
Stroke volume = end systolic volume - end diastolic volume
End systolic volume = volume of blood after a contraction
So even after the ventricle contracts, there will still be some blood left over (maybe not all the blood made it through past the semilunar valve and went back to the ventricle).[/quote
and we are supposed to know this , It's the first time to know that there's residual blood in the ventrical!

 

[Irfan1995]

To be honest, I'm not exactly sure. I know it because our school teaches us biology much tougher than the AS. So I studied the AS material from my school book, not the Cambridge book. Our teacher just told us which chapters to study for, and that's what I did.

 

[athaan]

To be honest, I'm not exactly sure. I know it because our school teaches us biology much tougher than the AS. So I studied the AS material from my school book, not the Cambridge book. Our teacher just told us which chapters to study for, and that's what I did.

I'd be happy to be taught by your teacher xD

I understand a lot of stuff more after searching it in internet and browsing through wikipedia pages.
although it has more things that would confuse me, at least I understand it a little bit better!

I was quite shocked knowing there would be a residual blood, since the function of atrioventricular valve is to prevent those kind of things happening, right? 0.o

 

[InnocentAngel]

Yes, you're right. A habitat is where an organism lives. But if the tree carries out phtotosynthesis and absorbs water etc..., then it is more than "just a habitat". They're describing for you the role of the tree in the ecosystem which is its niche. ONE of its roles may be that it is a habitat, but that's not all. Makes sense?

Oh yessss!!! Thanks ! U're really intelligent

 

[yashi30]

Every single order of protein structure affects the shape of a protein (including the active site of an enzyme).

Take it this way: with sickle cell anemia, one of the polar amino acids is replaced by a non-polar one. This changed the primary structure. Since the new amino acid is non polar, it can't make any hydrogen bonds, so the secondary structure is ruined. Also, since the new amino acid is non polar, it has to face the centre of the molecule, not outside, so the polypeptide has to refold to do that - tertiary structure ruined. Now the entire beta polypeptide chain cannot interact with the other three in the same way anymore - quaternary structure changed.

hydrogen bonds in secondary structure of protein are actually formed between -C=O and -N-H, so every amino acid contains these groups.
hydrogen bonds in tertiary structure of protein are those formed between R-groups having the appropriate parts.
right?

 

[Irfan1995]

hydrogen bonds in secondary structure of protein are actually formed between -C=O and -N-H, so every amino acid contains these groups.
hydrogen bonds in tertiary structure of protein are those formed between R-groups having the appropriate parts.
right?

No, what you're talking about is a peptide bond.
Hydrogen bond is formed when a partially positive hydrogen atom in one molecule is bounded to a partially negative nitrogen, oxygen, or fluorine atom in another. This happens with a partially positive hydrogen atom in one amino acid binding with an oxygen atom in a fifth amino acid. This makes the structure coil into an alpha helix.

EDIT: The tertiary structure is mainly formed by amino acids with polar (hydrophilic) R groups on the outside and with other amino acids with non-polar (hydrophobic) R groups on the inside. This makes the protein like a ball (polar aa's on the outside surface and non-polar aa's on the inside surface)

 

[railey]

Please help!

 

[ZohaibAsad]

Please help!

Because each chromatid holds a replicated part of a DNA

 

[Irfan1995]

Please help!

There are 46 chromosomes just before prophase.
Every chromosome is made up of 2 chromatids.
So you have a total of 46 x 2 = 92 chromatids just before prophase.

Every chromatid contains one DNA molecule.

There is no spindle present just before prophase. It starts forming by late prophase and continues until the end of metaphase.

 

[nelly trich]

Does trachea contain elastic fibres ?1
!!!

 

[athaan]

Does trachea contain elastic fibres ?1
!!!

Yes, it does.

 

[athaan]

What is the role of epidermis and smooth muscle in respiratory system?

 

[Irfan1995]

What is the role of epidermis and smooth muscle in respiratory system?

Epidermis is a squamous tissue. It's main function is to protect the system.
Smooth muscle is important in the system to stretch (NOT contract) and recoil (NOT relax) during inhalation and exhalation. It's important to allow the maximum amount of oxygen to be transferred.
EDIT: When smooth muscle stretches, it increases the surface area to volume ratio. When it recoils, it helps force out carbon dioxide out of the airways.

 

[athaan]

Epidermis is a squamous tissue. It's main function is to protect the system.
Smooth muscle is important in the system to stretch (NOT contract) and recoil (NOT relax) during inhalation and exhalation. It's important to allow the maximum amount of oxygen to be transferred.

thank you! this clears my confusion when doing problems about respiratory system, so at least I can know where epidermis and the smooth muscle are located.

 

[xtremeforums]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w07_qp_1.pdf

Nov 07 question 34.
Which disease is not likely to pass directly from parent to child?
A. Cholera
B. AIDS
C. malaria
D. tuberculosis.

Why is the correct answer C?
The only sense i could make out of this is that, malaria needs a vector for its transmission (Anopheles mosquito) but malaria can pass directly to the fetus through placenta of the mother too, just like AIDS..

Anyone has an explanation for this?

 

[Irfan1995]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w07_qp_1.pdf

Nov 07 question 34.
Which disease is not likely to pass directly from parent to child?
A. Cholera
B. AIDS
C. malaria
D. tuberculosis.

Why is the correct answer C?
The only sense i could make out of this is that, malaria needs a vector for its transmission (Anopheles mosquito) but malaria can pass directly to the fetus through placenta of the mother too, just like AIDS..

Anyone has an explanation for this?

The question says from parent to child, not from parent to embryo or parent to foetus.

EDIT: cholera can be transmitted through contaminated food
AIDS can be transmitted through breast feeding
TB can be transmitted when a mother coughs/sneezes next to her child.

As you said, malaria needs a vector to pass.

 

[xtremeforums]

The question says from parent to child, not from parent to embryo or parent to foetus.

Hmm makes sense! Thanks!