HSC Biology Question Thread

[sidzeman]

Hey could someone explain these 2 questions for me please?
For the punnete square cross, I've forgotten how to draw it up when you have dihybrid crosses

[Opengangs]

Hey could someone explain these 2 questions for me please?
For the punnete square cross, I've forgotten how to draw it up when you have dihybrid crosses

I'm on my phone so I can't give an extensive answer. For the time being, I'll just briefly explain the mc.

Consider the sixth and the seventh couple on generation II. We notice that if it were recessive, then all of the offspring will not be affected; this suggests that the couple must be heterozygous dominant. This means the genetic inheritance being affected carries the recessive gene, which looks to be (C)

[av-angie-er]

Hi! For the genetics elective, can anyone explain the difference between endonuclease/exonuclease enzymes and DNA glycosylase in relation to the repair of damaged DNA? I was taught in class about glycosylase but found that a past HSC paper example response only mentioned endonuclease and exonuclease enzymes, which appear to have a similar function. Thanks

[maddiewainwright]

Hi! For the genetics elective, can anyone explain the difference between endonuclease/exonuclease enzymes and DNA glycosylase in relation to the repair of damaged DNA? I was taught in class about glycosylase but found that a past HSC paper example response only mentioned endonuclease and exonuclease enzymes, which appear to have a similar function. Thanks

Hi av-angie-er,
Basically, endonuclease enzymes are able to cut double stranded DNA anywhere along the molecule, and exonucleases are only able to cleave DNA at the ends of the molecule. Both of types enzymes break the sugar phosphate backbone to cleave DNA strands.
DNA glycosylase does not cleave the sugar phosphate backbone, it only cuts out damaged nitrogenous base pairs, leaving a site for DNA repair.
These different enzymes would perform different functions in repair, depending on the extent of damage (i.e. whether a sequence + its sugar/phosphate backbone need to be removed).
Hope this helps!

[sidzeman]

I'm on my phone so I can't give an extensive answer. For the time being, I'll just briefly explain the mc.

Consider the sixth and the seventh couple on generation II. We notice that if it were recessive, then all of the offspring will not be affected; this suggests that the couple must be heterozygous dominant. This means the genetic inheritance being affected carries the recessive gene, which looks to be (C)

Ahhhh I see that makes sense thank you!

Hi! For the genetics elective, can anyone explain the difference between endonuclease/exonuclease enzymes and DNA glycosylase in relation to the repair of damaged DNA? I was taught in class about glycosylase but found that a past HSC paper example response only mentioned endonuclease and exonuclease enzymes, which appear to have a similar function. Thanks

Is this for the genetics: the code broken elective? I study it as well but I've never heard of these terms (endonuclease and etc) - what syllabus dotpoints is this under?

[inescelic]

Hi,
Can someone please clarify how metabolism changes for homeostasis?
I have read that when temperature is low, metabolism increases as energy is being taken up to generate heat in the body.
Yet when animals experience cold, their metabolism instead drops as they hibernate?
A quick summary of metabolism and temperature change would be nice

[pikachu975]

Hi,
Can someone please clarify how metabolism changes for homeostasis?
I have read that when temperature is low, metabolism increases as energy is being taken up to generate heat in the body.
Yet when animals experience cold, their metabolism instead drops as they hibernate?
A quick summary of metabolism and temperature change would be nice

External temperature increasing causes lower metabolism in ENDOTHERMS as it generates heat so they don't want too much metabolism. It causes higher metabolism in ECTOTHERMS as they are more active when it's hot.

When external temperature decreases, endotherm metabolism increases as cellular respiration generates heat. For ectotherms it decreases as they conserve body heat until it is warm enough to search for food efficiently as searching for food to replenish energy while it is cold would be inefficient.

Note that internal temperature for humans barely varies due to homeostasis so enzymes are always efficient while for ectotherms their internal temperature changes.

[av-angie-er]

Hi av-angie-er,
Basically, endonuclease enzymes are able to cut double stranded DNA anywhere along the molecule, and exonucleases are only able to cleave DNA at the ends of the molecule. Both of types enzymes break the sugar phosphate backbone to cleave DNA strands.
DNA glycosylase does not cleave the sugar phosphate backbone, it only cuts out damaged nitrogenous base pairs, leaving a site for DNA repair.
These different enzymes would perform different functions in repair, depending on the extent of damage (i.e. whether a sequence + its sugar/phosphate backbone need to be removed).
Hope this helps!

Ohh okay, thank you! Super helpful

[inescelic]

External temperature increasing causes lower metabolism in ENDOTHERMS as it generates heat so they don't want too much metabolism. It causes higher metabolism in ENDOTHERMS as they are more active when it's hot.



When external temperature decreases, endotherm metabolism increases as cellular respiration generates heat. For ectotherms it decreases as they conserve body heat until it is warm enough to search for food efficiently as searching for food to replenish energy while it is cold would be inefficient.

Note that internal temperature for humans barely varies due to homeostasis so enzymes are always efficient while for ectotherms their internal temperature changes.

Alright the second bit makes sense so thank you!
But for the second bit:
You're saying temp increase causes higher metabolism in ENDOTHERMS as they are more active when it's hot. But hang on, don't they want to lower metabolism so they don't generate as much heat when its already hot? I thought animals like kangaroos reduced activity and metabolism in hot temperatures so they generated less heat?

[pikachu975]

Alright the second bit makes sense so thank you!
But for the second bit:
You're saying temp increase causes higher metabolism in ENDOTHERMS as they are more active when it's hot. But hang on, don't they want to lower metabolism so they don't generate as much heat when its already hot? I thought animals like kangaroos reduced activity and metabolism in hot temperatures so they generated less heat?

My bad I meant ectotherms it was a typo

[arunasva]

I don't get the concept of threshold potential, can someone clear it out ? Thanks

[pikachu975]

I don't get the concept of threshold potential, can someone clear it out ? Thanks

It's the membrane potential value that must be fulfilled to start an action potential, i.e. -55 mV

[Potatohater]

I don't get the concept of threshold potential, can someone clear it out ? Thanks

Not all stimuli generate a response, if they did we'd probably go crazy! Therefore the membrane potential must reach the -55 threshold (from a resting potential of -70) to stimulate an electrochemical signal, and thus response. It's like a gun, all or nothing, either the trigger is pulled or it doesn't.

When the response is triggered the electrochemical signal is generated by making the normally negative inside, positive. This is done by opening sodium channels. The more sodium that's let in, the easier it is for more sodium to come in, and so the inside becomes positive and the out side negative. (Depolarisation)
Once the signal has been generated and sent along the neurone the negatively charged inside is restored by removing potassium ions. This causes the downward turn of the graph (repolarisation)
When graphing action potential there's also a little dip below the resting membrane potential (hyperpolerisation) which is just to create a break between signals so we aren't constantly buzzing with constant streams of infomation.
I'm hoping that cleared things up

[Potatohater]

No that's good, thank you! I definitely understand what you meant with the different theories of evolution, makes sense Also competition for resources and its role in evolution can be a bit confusing, but do you think what I have said about it in the above response makes sense?
Bio seriously stress me out because I feel like I never know if what I'm writing is going to match the marking criteria. Some questions in bio are open to many different interpretations and that makes it so stressful:( Any tips?

I know right! This where I lose my marks, I know all the content but I'm not sure what to write to make the markers happy. As for tips, I try and deconstruct the question and try and work out how many components there are to it and match that up to the question. So if it says compare and contrast X and Y and its 4 marks I tend to assume I get a mark for 2 simularities and 2 differences. I havnt quite worked out the trick to the longer ones though. When I have the marking guidelines it all makes sense but in the exam I have no idea what they want. As for the competition for recourse section, it made sense to me that without competition from mammals birds are able to occupy environmental niches, but I think it could be explained a tad more clearly and concisely.

[Ciararonq]

Hi there! This might be a silly question but I was wondering if there are any strategies or tips in answering questions along the lines of "Evaluate the reliability/validity of this experiment? How would you go about answering these questions (eg. Q 28a 2016 paper) Thank you !