VCE Biology Question Thread

[vox nihili]

Is chlorophyll produced or is it always present in a plant?

Also, does anyone know where I can find STAV 2007 Unit 3 Trail exam paper solutions? Thanks!

Both. There are always low levels, but production goes up when it's sunnier.

[nhmn0301]

1. How do the different structures of starch and cellulose impact their usage in humans and other organisms?
2. Are certain kinds of carbohydrates more efficient at storing and releasing energy than other types of carbohydrates? Why is this

I think I would have to mention a bit of Chemistry here so sorry if you don't do Chem:
Starch and glycogen are used for energy storage and they are made up from Alpha glucose , they tend to make up highly branched structure. However, cellulose are made up from beta glucose and they tend to form long, rigid structure. Due to these differences in the glucose monomer, we have polysaccharides that is specifically to storage and structure.
If you mean the different form of carbohydrates such as monosaccharide, disaccharide and polysaccharides then normally, when plants want to transport glucose in the body, they transport them in the form of sucrose, which is disaccharide. The reason is glucose is soluble in water and reactive so if you transport them in their original form, they might react with different things along the way. Whilst sucrose, they have lower degree of solubility (if you do Chem, you might understand, otherwise, don't worry too much) and therefore might tend to be less reactive then glucose. They don't transport polysaccharide because they do tend to be quite large in size and molar mass, transporting them in the body might take up a lot of energy.
Correct me if I'm wrong.

[RazzMeTazz]

Could someone please explain what the difference between centrioles and centrosomes are?

Also do the spindle fibres develop from the centrioles?

[RazzMeTazz]

What are examples of some cells with a long cell cycle?

[vox nihili]

What are examples of some cells with a long cell cycle?

Neurones, muscle cells.

[RazzMeTazz]

Are histone proteins the only type of proteins associated with DNA ?

Or are there other types too?

[vox nihili]

Are histone proteins the only type of proteins associated with DNA ?

Or are there other types too?

There are heaps of proteins associated with DNA. Histones are the major structural proteins, but there are heaps of enzymes that are involved with DNA. There are also proteins that bind to DNA in order to inhibit its expression. You've encountered some DNA associated proteins such as DNA pol, DNA helicase, DNA ligase. You may also have heard about topoisomerase and telomerase (they're not in the course)

[RazzMeTazz]

In meiosis, at the end of telophase 1 and then cytokinesis, would it be correct to assume that the chromosomes take upon the structure of chromatin once again?

And then during prophase 2, they condense into chromosomes once again?

[Rishi97]

Both autosomes and sex chromosomes carry genes coding for features unrelated to sex

This makes no sense to me. Don't sex chromosomes carry genes that determine sexual characteristics???
Thanks

[RazzMeTazz]

In what phase/s of mitosis and meiosis, do the spindle fibres attach to the kinetochores ?

[simpak]

Both autosomes and sex chromosomes carry genes coding for features unrelated to sex

This makes no sense to me. Don't sex chromosomes carry genes that determine sexual characteristics???
Thanks

Yes, they do, but they also carry genes that determine non-sexual characteristics.  For instance, X and Y chromosomes have 'pseudoautosomal' regions that are relatively identical between either chromosome.  So no matter if you have an X or a Y chromosome (or both), you will have some genes that are 'the same' and that code for things that are unrelated to sex.  There is no difference between males and females for that characteristic, because both different chromosomes happen to carry the same gene.
Similarly, on autosomes, you could have some genes that help determination of sex but that only become active when you have a Y chromosome.  (Beyond VCE course: For one simplified and conceptual explanation for you, many genes on the Y chromosome encode 'transcription factors' which are types of proteins that can associate with DNA and control the switching on or switching off of other genes. So a transcription factor encoded by the Y chromosome could activate or deactivate genes found on autosomal chromosomes.  If you are male, and you have the Y transcription factors, the genes on the autosomal chromosomes will be activated in your cells by the transcription factor --> sex determination.  If you are female, and you do not have these transcription factors, the genes on the autosomal chromosomes will not be active --> sex determination by a lack of gene expression).

[vox nihili]

In what phase/s of mitosis and meiosis, do the spindle fibres attach to the kinetochores ?

So any time that the chromosomes are being pulled anywhere. So they're probably attaching around prometaphase and won't break down until telophase.

[RazzMeTazz]

Does DNA ligase only help in DNA synthesis on the lagging strand, to seal the okazaki fragments together?

Or does it help with DNA synthesis on the leading strand as well?

[vox nihili]

Does DNA ligase only help in DNA synthesis on the lagging strand, to seal the okazaki fragments together?

Or does it help with DNA synthesis on the leading strand as well?

Just the lagging stand. It also fixes any issues, so if there's a strand break or something, DNA ligase may be recruited to come and fix it up.

[ravi2]

hey what is the difference between a reflex action/response and reflex arc?