VCE Biology Question Thread

[Owlbird83]

Yes, active transport always occurs via a carrier protein (as far as VCE bio goes).

Prokaryotes have no nucleus. Instead, they have a circular chromosome with its genetic material that kind of just floats around in the cytosol. It would be impossible for any cell to have a non-membrane bound nucleus because the contents would just spill out anyway and the nucleus wouldn’t exist anymore.

Also, just to add onto this, bulk transport (endocytosis and exocytosis) is the other form of active transport.

[Chocolatepistachio]

For the question why would cells need to break down old mitochondria? How are they replaced?

Is this correct:
cells need to break down old mitochondria because they become less efficient as they age. They are replaced by the process of mitochondrial biogenesis. Respiration occurs inside the inner membrane of the mitochondria but this surface becomes inefficient as it gets older and the production of energy slows down.

[Erutepa]

For the question why would cells need to break down old mitochondria? How are they replaced?

Is this correct:
cells need to break down old mitochondria because they become less efficient as they age. They are replaced by the process of mitochondrial biogenesis. Respiration occurs inside the inner membrane of the mitochondria but this surface becomes inefficient as it gets older and the production of energy slows down.

While the precise reasons why mitochondria are broken down aren't fully understood, from what I have read it seems that a main reason is detection of mitochondrial damage - something that will likely occur with age due to mutation accumulation and potentially other factors. Saying that the mitochondria become inefficient with age is probably an acceptable answer, but I would personally lean towards stating that mitochondria will become damaged with age and that when they are damaged they will be broken down. The process by which mitochondria are replaced is specifically binary fission (mitochondrial biogenesis involves other processes, although would probably still be an acceptable answer).
This all being said, this level of knowledge isn't really detailed by the study design - so unless your teacher has stressed that you need to know this for something like a SAC  - this is probably irrelevant for VCE biology

[Chocolatepistachio]

Thanks Erutepa!

[Chocolatepistachio]

For this question:
Theoretically what proportion of offspring from a cross between parental genotypes Pp; Qq; Rr; Ss and Pp; qq; Rr; Ss would have the genotype pp; qq; rr ; ss?

How do you work this out and get the answer of 1/128.

[Sine]

For this question:
Theoretically what proportion of offspring from a cross between parental genotypes Pp; Qq; Rr; Ss and Pp; qq; Rr; Ss would have the genotype pp; qq; rr ; ss?

How do you work this out and get the answer of 1/128.

Just to give you a headstart. Consider the first parent. The likelihood of this parent producing a gamete with a p allele is 1/2. That is the same for the q,r and s alleles as well.

[Chocolatepistachio]

How did you get 1/2

For the first one do just cross Pp with Pp and then Qq and qq

[Sine]

How did you get 1/2

For the first one do just cross Pp with Pp and then Qq and qq

You've got heterozygote (two different alleles). Given even chance of both alleles then getting 1 of them is 1/2.

Think about what sort of gametes you can get from the genotype. All the sames principles that you would follow with a simpler question apply. E.g. Aa the possibke gametes are A and a.

[Chocolatepistachio]

I’m so confused
Do you do 1/2 x 8

[-Lilac-]

I’m so confused
Do you do 1/2 x 8

Not quite. If you are not used to doing these problems I suggest working through each cross separately.

Pp; Qq; Rr; Ss X Pp; qq; Rr; Ss

So do each of the four crosses (use a punnet square if you need to visualize it).

Pp and Pp = PP, Pp, Pp, pp
Qq and qq = Qq, qq, qq, Qq
Rr and Rr = RR, Rr, Rr, rr
Ss and Ss = SS, Ss, Ss, ss

Therefore:
 pp; qq; rr ; ss = 1/4 * 1/2 * 1/4 *1/4 = 1/128

Hope this helps

[Chocolatepistachio]

Oh ok thank you!

[Chocolatepistachio]

In humans, colourblindness is a sex linked recessive disease. A woman who is a carrier for the trait marries a man with normal vision. What is the chance that they will have a colourblind son.

Is it 25%?

Are all prokaryotes unicellular or are there some that are multicellular

[Calebark]

In humans, colourblindness is a sex linked recessive disease. A woman who is a carrier for the trait marries a man with normal vision. What is the chance that they will have a colourblind son.

Is it 25%?

Are all prokaryotes unicellular or are there some that are multicellular

25% is correct. 50% chance of any son being colourblind as the allele is on the X-Chromosome, and then a 50% chance of having a son on top of that. Good job

A prokaryote is by definition unicellular

[Chocolatepistachio]

Can photosynthesis occur at all without light or can it just only occur for a short time because I thought it would not occur at all

The outputs of water splitting are oxygen, 2atp and loaded acceptor molecules. What does loaded acceptor molecules mean

[Owlbird83]

Can photosynthesis occur at all without light or can it just only occur for a short time because I thought it would not occur at all

The outputs of water splitting are oxygen, 2atp and loaded acceptor molecules. What does loaded acceptor molecules mean

It wouldn't occur at all without light.

The loaded acceptor molecule is NADPH. When it's unloaded, it's NADP+. In the light dependent stage, when the water is split, the Hydrogen ions and electrons are accepted by the NADP+ to create NADPH. The NADPH then carries the H ions and electrons to the light independent stage, where it unloads them to the calvin cycle, where they are used to build the glucose molecule. Then it goes back to get more again to get more like a taxi sort of haha.
Also, ATP is similar, it gets loaded with energy in the light dependent stage, and then brings it to the light independent stage to be released by breaking the bond and releasing a phosphate, becoming ADP + Pi. ANd then it goes and does it again.
Hope this doesn't sound too confusing haha