VCE Biology Question Thread

[Chocolatepistachio]

What is the difference between a phylogenetic tree and a cladogram

[PhoenixxFire]

What is the difference between a phylogenetic tree and a cladogram

Cladograms have lines the same length whereas phylogenetic trees have lines of different lengths roughly proportionate to the amount of evolutionary change between the linked groups. The study design only refers to phylogenetic trees, don't worry about it too much.

[SmartWorker]

What is the difference between a phylogenetic tree and a cladogram

Also phylogenetic trees show which species are extant (living) and which are extinct, whereas cladograms do not. Cladograms are formed based upon shared characteristics, whereas phylogenetic trees are formed based upon ancestral relationships.

[Chocolatepistachio]

How does the positioning of stomata towards the ground assist in cooling plants

is it to avoid sunlight but then aren’t they present on the underside of the leaf to avoid sunlight

[homeworkisapotato]

They're sometimes under the leaf of plants which are usually in windy conditions so that the absorption rate of water is increased/ stable and is not hindered by the wind turning the leaf everywhere. Another way to cool down, like you said, is to reduce exposure to solar radiation.

[Chocolatepistachio]

How does the positioning of stomata towards the ground assist in cooling plants

Is it because the water goes back into the soil if they are facing down

[homeworkisapotato]

The stomata also absorb water so it would be counterproductive right? I think that if there are stomata on both the surface and the bottom of the leaf, that's more surface area to absorb water and cool the plant.

[Chocolatepistachio]

I don’t think stomata absorb water they release water

[homeworkisapotato]

Oh my god, they do release water! Sorry about that! Then yes, I think you should be right! Sorry!

[SmartWorker]

Hey,

For this question (Qu25 MC from 2017 NHT) the answer is D, but I choose B. Can someone explain this please.

My line of thinking was:
1. Complementary sequence: opposite of given DNA sequence
2. mRNA of complementary sequence would be the opposite of the complementary
(the same as DNA sequence except for the mutation and T is replaced with U)?

Thank you!

[whys]

Hey,

For this question (Qu25 MC from 2017 NHT) the answer is D, but I choose B. Can someone explain this please.

My line of thinking was:
1. Complementary sequence: opposite of given DNA sequence
2. mRNA of complementary sequence would be the opposite of the complementary
(the same as DNA sequence except for the mutation and T is replaced with U)?

Thank you!

The strand they have given you is the template strand, but mRNA makes a complementary copy to the template strand, swapping T with U (so its sequence of bases is identical to the coding strand). This means mRNA will carry the complementary copy of the DNA sequence given, making D the correct answer. I think you've gotten a little confused with the transcription process - if you go back and revise the steps from your textbook/notes it'll make sense.

1. DNA unwinds to expose the template strand
2. RNA polymerase attaches to a promotor in the upstream flanking region of the gene
3. RNA Polymerase catalyses joining of RNA nucleotides that are complementary to DNA template
4. Template strand of DNA is copied (transcribed) to form a pre-mRNA strand (complementary copy), primary mRNA transcript has
 been formed

These are the first few steps of transcription, and as you can see mRNA forms a copy that is complementary to the sequence on the template strand, which is the strand we start off with.

[SmartWorker]

The strand they have given you is the template strand, but mRNA makes a complementary copy to the template strand, swapping T with U (so its sequence of bases is identical to the coding strand). This means mRNA will carry the complementary copy of the DNA sequence given, making D the correct answer. I think you've gotten a little confused with the transcription process - if you go back and revise the steps from your textbook/notes it'll make sense.

1. DNA unwinds to expose the template strand
2. RNA polymerase attaches to a promotor in the upstream flanking region of the gene
3. RNA Polymerase catalyses joining of RNA nucleotides that are complementary to DNA template
4. Template strand of DNA is copied (transcribed) to form a pre-mRNA strand (complementary copy), primary mRNA transcript has
 been formed

These are the first few steps of transcription, and as you can see mRNA forms a copy that is complementary to the sequence on the template strand, which is the strand we start off with.

But then the question says "This mutation was then passed on to the mRNA when transcription of the complementary strand occurred" ? and how can I assume that the given DNA strand is the template strand? In the question it implies that the complementary strand is the template strand ---> the one that is being transcribed.

EDIT: For Transcription process I think the RNA polymerase binds to promoter region of DNA first and then causes DNA to unwind to expose the template strand

[Coolgalbornin03Lo]

But then the question says "This mutation was then passed on to the mRNA when transcription of the complementary strand occurred" ? and how can I assume that the given DNA strand is the template strand? In the question it implies that the complementary strand is the template strand ---> the one that is being transcribed.

I get why your getting confused this wording of complimentary is making it seem like the coding strand of DNA which is complimentary to the templa strand they’ve already given you. However I think they just used the word “complimentary” because the synthesis of mRNA Is catalysed off the template strand of DNA and therefore is “complimentary” to it. These questions sometimes get me as well but I just tend to assume it’s the template strand unless they explicitly star this is the CODING strand. hope that helped!

P.S I’m just a year 12 doing 3/4 bio and far from the best so please take this with a grain of salt )

[Chocolatepistachio]

Why does the high specific heat capacity of water make it efficient for cooling organisms down

[SmartWorker]

Why does the high specific heat capacity of water make it efficient for cooling organisms down

Specific heat capacity refers to the amount of heat that 1gram of a substance is required to absorb in order to increase the temperature by 1ºC. Therefore, a high specific heat capacity means that water can absorb a lot of heat energy.

Hence, the reason why we sweat is that the water released can absorb the heat energy from our body in order to lower the core temperature of our body.

You can elaborate describing the chemical nature of water to explain the strength of its bonds. But you don't need this much detail since it is a Bio question and not a chemistry question