VCE Biology Question Thread

[Jason12]

are we still required to know about tissue rejection in the current study design because it comes up in previous practice exams (2012) I've been doing?

[alchemy]

So just realise that after 1 binary fission, you got 2 genetically identical cells. Hence, after 1 more binary fission, you got 4, and then after the next binary fission, you got 8 => this is an exponential growth (can't believe I bring Methods in -,-)
Hence, after 9 binary fission, you got 2^9, which is 512 cells.

There's more instances when Math comes into Biology in VCE. See Question 3.e. in 2010 VCAA Biology Exam 2.

[Rachelle]

For hormones that are amino acid derivatives, would thyroid hormones,  or perhaps tyrosine kinase be an example of that? And could they pass through the cell membrane directly? Because I know that my textbook says that they can due to their 'small and hydrophobic nature' but in the NOB book it says that amino acid derivatives cannot pass through the plasma membrane.

[nhmn0301]

For hormones that are amino acid derivatives, would thyroid hormones,  or perhaps tyrosine kinase be an example of that? And could they pass through the cell membrane directly? Because I know that my textbook says that they can due to their 'small and hydrophobic nature' but in the NOB book it says that amino acid derivatives cannot pass through the plasma membrane.

Yeah, as far as I'm aware, it is amino acid derivatives.
For your second question, amino acid derivatives won't generally pass through the cell membrane like lipid-based hormones. "Small and hydrophobic" -> amino acid is not really that small, if you look at the structure of an amino acid, it contains carboxyl group, amino group, a hydrogen and a variable group, all of these can make up a fair large amount of molar mass (in the case tyrosine kinase, they are around 181.19 gmol-1, so you can imagine amino acid is actually not that small). About the "hydrophobic" nature, I don't know why your textbook call them hydrophobic but they are generally soluble in water, they can be insoluble when we place them with hydrocarbon (which is a non-polar solvent). The only case that I can think of where amino acid derivatives are not soluble in water are because of their large molar mass or  the nature of the R group (but I guess we don't  really need to over-complicate things for VCE). I don't know if you do Chem 3/4 or not, but if you don't and really want to know why amino acid are soluble, then look up "zwitterions" form, these might help you a bit !
Anw, in brief, I don't generally think amino acid derivatives hormones can easily pass through the cell membrane because they are generally polar and not lipophilic in nature.
Correct me if I'm wrong.

[Rachelle]

Yeah, as far as I'm aware, it is amino acid derivatives.
For your second question, amino acid derivatives won't generally pass through the cell membrane like lipid-based hormones. "Small and hydrophobic" -> amino acid is not really that small, if you look at the structure of an amino acid, it contains carboxyl group, amino group, a hydrogen and a variable group, all of these can make up a fair large amount of molar mass (in the case tyrosine kinase, they are around 181.19 gmol-1, so you can imagine amino acid is actually not that small). About the "hydrophobic" nature, I don't know why your textbook call them hydrophobic but they are generally soluble in water, they can be insoluble when we place them with hydrocarbon (which is a non-polar solvent). The only case that I can think of where amino acid derivatives are not soluble in water are because of their large molar mass or  the nature of the R group (but I guess we don't  really need to over-complicate things for VCE). I don't know if you do Chem 3/4 or not, but if you don't and really want to know why amino acid are soluble, then look up "zwitterions" form, these might help you a bit !
Anw, in brief, I don't generally think amino acid derivatives hormones can easily pass through the cell membrane because they are generally polar and not lipophilic in nature.
Correct me if I'm wrong.

Oh okay. I see. But i know that thyroid hormones do pass through the plasma membrane by diffusion. Would this be excluded from the definition you provided above? applying specifically to thyroid hormones: despite it being an amine based molecule, it may pass htorugh the plasma membrane by diffusion into the cytoplasm and nuclei of its vast array of target cells. Perhaps amine-based cannot pass through as your explanation seems valid, but thyroid hormones is an exception..?

[Rachelle]

What constitutes the internal environment?
(in relation to the external env of the organism which is the environment)

[nhmn0301]

Oh okay. I see. But i know that thyroid hormones do pass through the plasma membrane by diffusion. Would this be excluded from the definition you provided above? applying specifically to thyroid hormones: despite it being an amine based molecule, it may pass htorugh the plasma membrane by diffusion into the cytoplasm and nuclei of its vast array of target cells. Perhaps amine-based cannot pass through as your explanation seems valid, but thyroid hormones is an exception..?

Some information has been updated http://www.ncbi.nlm.nih.gov/m/pubmed/11493579/. Hope that helps!

[nhmn0301]

What constitutes the internal environment?
(in relation to the external env of the organism which is the environment)

I would say temperature, osmotic concentration (water + ions concentration), nutrient level etc.

[Rishi97]

Describe one difference between apoptosis and necrosis

Thanks

[nubs]

Necrosis involves cellular swelling, apoptosis involves shrinkage.

Cellular contents leak out into the extracellular space during necrosis, in apoptosis organelles/contents are released in apoptotic bodies

Necrosis is usually followed by an inflammatory response, apoptosis is not

[Rachelle]

Does anyone know the purpose of Ca2+ ions in the synaptic knob? When they diffuse into it, it causes the secretory vesicles to migrate towards the pre-synpatic membrane, though how?

[nubs]

How exactly it happens depends on the neuron, really. There are a number of possible models explaining how it works but as far as I'm aware not all are agreed on and the mechanisms in general are not entirely understood - so you definitely won't be expected to know them.

You don't need to know how Ca++ influx leads to neurotransmitter release, just that it is able to by causing the vesicles to move towards the synapse etc.

[MM1]

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!

[nhmn0301]

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

I don't know if this would answer your question or not:
but chlorophyll is found in chloroplast as you already know. Chloroplast are actually a type of cynobacteria, which mean they are actually a prokaryotic cells itself (that's why they contain their own DNA and genetic materials). These prokaryotic cells can produce chlorophyll and from evolution, plants probably take up these cells because first, they help them to possess photosynthesis and second, for these cells, plants give them nutrients to survive.
So yeah, chlorophyll are PRODUCED, without them, plants would look red or pale yellow. But keep in mind that not all plants have chlorophyll though (cause they are parasites) !
Correct me if I'm wrong.

[The Usual Student]

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