VCE Biology Question Thread

[Yacoubb]

Sorry for asking so many questions guys.. I had one more..

Basically I was told that organelles do not necessarily require membranes. (e.g. ribosomes are not membrane-bound) Is this true?

This is true. Some organelles (i.e. ALL those found in prokaryotic cells and SOME found in eukaryotic cells) are not membrane bound. The best example of this is the ribosome.

[nerdmmb]

This is true. Some organelles (i.e. ALL those found in prokaryotic cells and SOME found in eukaryotic cells) are not membrane bound. The best example of this is the ribosome.

Thank-you!

[MM1]

Referring to osmosis, what's correct to say: a higher water concentration or higher solute con. when taking about hypo/hypertonic solutions? Or is both correct?

[Stick]

The terms "high water potential" and "low water potential" are probably more favourable. Water is the solvent, not the solute, and hence using the term "concentration" isn't really viable. Alternatively, you can refer to the concentration of the solute in question.

[alchemy]

Referring to osmosis, what's correct to say: a higher water concentration or higher solute con. when taking about hypo/hypertonic solutions? Or is both correct?

When describing or referring to osmosis, it's good to mention relate to the water concentration instead of solute concentration, just like how Stick described it above. However, really both are fine.

[grannysmith]

The terms "high water potential" and "low water potential" are probably more favourable. Water is the solvent, not the solute, and hence using the term "concentration" isn't really viable. Alternatively, you can refer to the concentration of the solute in question.

So it would be: osmosis is the net movement of water molecules from a region of low water potential to a region of high water potential, across a semi permeable membrane. Is it necessary to mention the expenditure of energy?

[Stick]

You can include it if you'd like.

[MM1]

So it would be: osmosis is the net movement of water molecules from a region of low water potential to a region of high water potential, across a semi permeable membrane. Is it necessary to mention the expenditure of energy?

It's probably not necessary but you could refer to it as the passive net movement of ... etc.

Also, I think it would be a good idea to mention the solute concentration perhaps? So 'a region of low water potential (high solute concentration) to a region of high water potential (low solute con.). That's if your comparing solutions.
 

[Yacoubb]

So it would be: osmosis is the net movement of water molecules from a region of low water potential to a region of high water potential, across a semi permeable membrane. Is it necessary to mention the expenditure of energy?

My definition:

Osmosis is the passive, net movement of free water molecules across the semi-permeable plasma membrane, from an area of low solute concentration, to an area of high solute concentration, along the osmotic gradient.

[MM1]

When describing or referring to osmosis, it's good to mention relate to the water concentration instead of solute concentration, just like how Stick described it above. However, really both are fine.

Thanks alchemy! (+1 is not working for some reason)

[nerdmmb]

I had a question regarding DNA.
I know that hair and nails do not contain DNA. But can someone please tell me why. Is it because they do not require DNA and the roots are responsible for their growth?
 
Also, it is somehow related to the fact that both hair and nails are made of keratin? Thank-you

[MM1]

I had a question regarding DNA.
I know that hair and nails do not contain DNA. But can someone please tell me why. Is it because they do not require DNA and the roots are responsible for their growth?
 
Also, it is somehow related to the fact that both hair and nails are made of keratin? Thank-you

The hair strand and nail are made of proteins which were created by the cells lining the hair strand (the follicle) and the nail (the nail bed). I'm guessing they don't exactly require DNA because they aren't performing a function that necessitates 'directions' from DNA. A red blood cell would be a good example of this.
Also I believe, since keratin is a globular protein it's quite large and needs space to occupy. Hair and nails degenerate like RBC so there is no point of having DNA in the actual hair strand or nail.

Someone please correct me if I'm wrong. Cheers.

[nerdmmb]

The hair strand and nail are made of proteins which were created by the cells lining the hair strand (the follicle) and the nail (the nail bed). I'm guessing they don't exactly require DNA because they aren't performing a function that necessitates 'directions' from DNA. A red blood cell would be a good example of this.
Also I believe, since keratin is a globular protein it's quite large and needs space to occupy. Hair and nails degenerate like RBC so there is no point of having DNA in the actual hair strand or nail.

Someone please correct me if I'm wrong. Cheers.

Thanks! So would it be true to say that hair and nails are composed of dead cells that carry no function and thus have no DNA?

[alchemy]

I had a question regarding DNA.
I know that hair and nails do not contain DNA. But can someone please tell me why. Is it because they do not require DNA and the roots are responsible for their growth?
Also, it is somehow related to the fact that both hair and nails are made of keratin? Thank-you

This is an interesting question that I somehow stumbled upon while doing a research task sometime ago. 
Firstly, recall that DNA is contained in the nucleus. Hair, skin and nail cells destroy their nuclei as part of their developmental process. They do this in order to maximize the space in the cell filled with the structural protein keratin. This means that the cell nucleus and other internal parts of the cell are destroyed and their space is filled by keratin. MM1 said pretty much the same, I think.

[MM1]

Thanks! So would it be true to say that hair and nails are composed of dead cells that carry no function and thus have no DNA?

I don't think so. They do carry out a function. I'm thinking of red blood cells here but I'm not 100% sure. I wouldn't term them 'dead cells' because they do contain protein which is an organic molecule that is functioning. In a sense, they are dead but I wouldn't bet on it.