VCE Biology Question Thread

[Gogo14]

Ok,but how are the marks allocated and what about the method?

[Mishmosh]

Ok,but how are the marks allocated and what about the method?

Check the 2010 VCAA exam 1 Question 2b the question tells you where the marks are and the examiners reports tells you what key words you need.

[vox nihili]

Hello, I just want to clarify a confusion with the study design that I have. The 2013-2016 Study Design eliminates the need for us to cover homeostasis, but we still have to be comfortable with stimulus-response models. So my question is to what extent do stimulus-response models need to be covered?

Thanks

Stimulus-response and homeostasis are two different things. You'd still need to know stimulus-response in complete detail. Just know the steps and be able to apply it to signalling or a physiological system.

[johnhalo]

Stimulus-response and homeostasis are two different things. You'd still need to know stimulus-response in complete detail. Just know the steps and be able to apply it to signalling or a physiological system.

I assumed that stimulus-response models only referred to variables such as a change in internal temperature of an organism, change in blood glucose levels e.t.c. (well that's what N.O.B seems to suggest), and they relate to homeostasis. Could you give an example of a signalling or a physiological system that it could be applied to? I assume the general [Stimulus > Receptor > Control Centre > Effector > Response] is used right?

Thanks heaps T.Rav

[vox nihili]

I assumed that stimulus-response models only referred to variables such as a change in internal temperature of an organism, change in blood glucose levels e.t.c. (well that's what N.O.B seems to suggest), and they relate to homeostasis. Could you give an example of a signalling or a physiological system that it could be applied to? I assume the general [Stimulus > Receptor > Control Centre > Effector > Response] is used right?

Thanks heaps T.Rav

Well the examples you gave are physiological systems to which the model applies. Sure, it plays a key role in homeostasis, but more generally it describes the ways that signals can affect outcomes. IT can also be used on a cellular level though as well.

[TheAspiringDoc]

Would it be correct to say that the enzymes present in chlorophyll are an input for light dep. and the enzymes present in the stroma are an input for light indep.?

Thank you

Expanding on cosine's answer, let us take a look at the simple definition of enzymes:
Biological proteincatalysts
i.e., by definition, the are proteins that increase the rate of biochemical reactions without themselves being used up in the reactions.
So yeah, bcause input only refers to things that are used, they are not an 'input'

[TheAspiringDoc]

Hey guys I wrote a template for explaining how natural selection caused the evolution of some characteristic in a population and was hoping you could critique?

Spoiler

Template: 4 Marks

-Variation exists within the population of ____________, and some of them have alleles that made them/their ______
-_________ provide a selection pressure
**
-Those ________ with the favourable __________________ phenotype will be selected for, while those with the unfavourable _____________ phenotype will be selected against (because __________)
-Those ________  with the/that are  ________ will be more likely to survive long enough to reproduce, so they will contribute more to the next generation's gene pool. Hence, the frequency of the allele(s) for _______ will increase within the population and more ___________ will be/have _______________

Add in as second point if 5 Marks: *overproduction of offspring occurs within the population, and the environment cannot support all of the new offspring. Thus, competition is inevitable.*




Example:
explain how natural selection caused an increase in the length of giraffe necks over time

-Variation exists within the population of giraffes, and some of them have alleles that made their necks longer
-Vertically high sources of food provide a selection pressure
-Those giraffes with the favourable longer-necked phenotype will be selected for, while those with the unfavourable shorter-necked phenotype will be selected against (because the longer-necked giraffes will be able to access food at greater heights)
-Those giraffes with the longer necks will be more likely to survive long enough to reproduce, so they will contribute more to the next generation's gene pool. Hence, the frequency of the alleles for longer necks will increase within the population and more giraffes will have longer necks

[HasibA]

multi cellular and unicellular organisms have both an internal environment and an external environment , right?
textbooks seems unclear

also, a unicellular has an external environment they can do little to control , but what about it's internal environment?

a multi cellular organism has an internal environment it can can regulate , but what about its external environment? do i need to know the specifics for vce biol? 

[Splash-Tackle-Flail]

Quick Q: would someone be able to explain why our sense of taste and smell involves our visceral sensory neurons?

[cosine]

multi cellular and unicellular organisms have both an internal environment and an external environment , right?
textbooks seems unclear

also, a unicellular has an external environment they can do little to control , but what about it's internal environment?

a multi cellular organism has an internal environment it can can regulate , but what about its external environment? do i need to know the specifics for vce biol?

Yes the intracellular environment is the environment inside cells, and the extracellular environment is the environment outside cells, the interstitial fluids etc.

Unicellular organisms, lets consider bacteria, have little control over their extracellular environment, however they are in charge of their intracellular environment, well they have to, otherwise they would not be able to survive and meet their energy requirements. Bacterial cells do this by synthesising proteins from their bacterial chromosome or their plasmids.

There is not much needed to know about how multicellular organisms maintain their extracellular environments, but you should be familiar with some factors. For example, the internal body temperature, this needs to be maintained at optimal to ensure the catalysts (enzymes) of the organism function at their optimal to maximise metabolism rate, hence to keep the organism functioning, the internal pH levels, osmolarity, blood glucose levels etc.. Just know that maintaining a stable external environment (internal relative to the body) is known as homeostasis, and it almost always requires negative feedback loops.

Hey guys I wrote a template for explaining how natural selection caused the evolution of some characteristic in a population and was hoping you could critique?

Spoiler

Template: 4 Marks

-Variation exists within the population of ____________, and some of them have alleles that made them/their ______
-_________ provide a selection pressure
**
-Those ________ with the favourable __________________ phenotype will be selected for, while those with the unfavourable _____________ phenotype will be selected against (because __________)
-Those ________  with the/that are  ________ will be more likely to survive long enough to reproduce, so they will contribute more to the next generation's gene pool. Hence, the frequency of the allele(s) for _______ will increase within the population and more ___________ will be/have _______________

Add in as second point if 5 Marks: *overproduction of offspring occurs within the population, and the environment cannot support all of the new offspring. Thus, competition is inevitable.*




Example:
explain how natural selection caused an increase in the length of giraffe necks over time

-Variation exists within the population of giraffes, and some of them have alleles that made their necks longer
-Vertically high sources of food provide a selection pressure
-Those giraffes with the favourable longer-necked phenotype will be selected for, while those with the unfavourable shorter-necked phenotype will be selected against (because the longer-necked giraffes will be able to access food at greater heights)
-Those giraffes with the longer necks will be more likely to survive long enough to reproduce, so they will contribute more to the next generation's gene pool. Hence, the frequency of the alleles for longer necks will increase within the population and more giraffes will have longer necks

Very, very well written response, seriously, good job. However, you just forgot to mention why shorter necked giraffes are unable to contribute to the next generations gene pool (they obviously can not reach the high trees and hence can not maintain their bodily functions as a lack of energy). Good job though.

[Jaspreet]

can anyone please explain cellular respiration

[cosine]

can anyone please explain cellular respiration

Cellular respiration is the process whereby unicellular and multicellular organisms convert chemical energy (glucose, sugars, more complex carbs) into a form of energy that cells can rapidly and conveniently use, the form known as Adenosine Triphosphate (ATP). Now in VCE biology, glucose is the main sugar that is known to be hydrolyzed for energy harvesting.

Glycolysis:
What happens?
Glucose molecules are broken down via enzymes.

What is released?
- 2 pyruvate molecules
- 2NADH molecules
- 2 ATP molecules (however there are 4 produced in total, but 2 are used up in the same reaction, so net production of 2).

Where does it occur?
Cytosol of cells.

Does it require oxygen?
No. If there is no oxygen available after glycolysis, then the pyruvate molecules will undergo fermentation reactions, in animals lactic acid is produced, and in plants/yeast ethanol and CO2 are produced. However, if there is oxygen available in the cell, then the following reactions will also occur after glycolysis.

Krebs cycle (Citric acid cycle):
What happens?
In the Krebs cycle, the two pyruvate molecules enter the mitochondria to undergo further reactions. There are two minor stages (not formal) in the krebs cycle, an initial stage where the pyruvate molecules react with CoA (coenzyme A) to produce CO2, NADH and Acetyl CoA. The Acetyl CoA then undergoes further reactions and produces another two CO2 molecules, 3 NADH molecules and 1 ATP molecule and 1 molecule of FADH2. Remember that two molecules of pyruvate are yielded from 1 molecule of glucose.

What is released?
- 6CO2
- 8NADH
- 2FADH2
- 2ATP

Where does it occur?
Krebs cycle occurs in the mitochondrial matrix (the fluid substance that is enclosed within the inner membrane of the mitochondria)

Does it require oxygen?
Yes, hence this is the second step of aerobic cellular respiration, and the following process is the final step of the aerobic pathway.

Electron Transport Chain:
What happens?
Remember the 'carrier' molecules from the previous pathways? Well the NADH and FADH2 molecules move along to the cristae of the inner membrane (projections of the inner membrane) and they release their electrons and H ions. The electrons 'flow' along the protein molecules embedded within the cristae (known as cytochromes). As these electrons pass along the cytochromes, the hydrogen ions are also being released from the NADH molecules. This means that a concentration gradient is accumulating of H ions, hence the Hydrogen ions need to diffuse (facilitation, since ions are charged and cannot simply diffuse through the membranes) down their gradient. As this occurs, the transmembrane (a protein that is embedded and protrudes through the membrane) enzymes known as ATP synthase simultaneously synthesise ATP molecules as Hydrogen ions diffuse down. This process synthesises approx. 32-34 molecules of ATP, depending on the need and type of cell (muscle cells require 34 as they are involved in more movement and protein contractions as compared to the cells of the stomach). So what happens with the hydrogen ions and the electrons that are being passed down the various cytochromes? Well, lone oxygen molecules await them and accept them, to produce water (H2O).

What is released?
- 32-34 ATP molecules
- 8NAD+ (no need to list this)
- 2FAD (no need to list this)
- Water molecules (amount not required)

Does it require oxygen?
Yes and it is the last step of aerobic cellular respiration.

[geminii]

Hi everyone,

I looked at my textbook and it says 'beta cells decrease their production of insulin.'
I then searched up on the internet and a website said 'beta cells produce insulin'.

So I guess I have two questions -
1. How does a cell produce insulin? I thought the pancreas did that? Or is it the pancreas cells?
2. Do beta cells increase the production of insulin, or do they decrease it, and do they start it in the first place? What even causes the pancreas to start producing insulin?

The textbook also says 'the hormone glucagon acts on the liver to release more glucose into the blood' and 'alpha cells increase their production of the hormone glucagon, which acts on the liver to convert stored glycogen to glucose' and 'glucose passes from the liver into the bloodstream'. I don't mean for this to be a stupid question, but isn't it the pancreas that does this? Or is the liver involved in this process too? Is the textbook right? And if so, then what does the pancreas do?

Thanks in advance for clearing this up!

[cosine]

Hi everyone,

I looked at my textbook and it says 'beta cells decrease their production of insulin.'
I then searched up on the internet and a website said 'beta cells produce insulin'.

So I guess I have two questions -
1. How does a cell produce insulin? I thought the pancreas did that? Or is it the pancreas cells?
2. Do beta cells increase the production of insulin, or do they decrease it, and do they start it in the first place? What even causes the pancreas to start producing insulin?

The textbook also says 'the hormone glucagon acts on the liver to release more glucose into the blood' and 'alpha cells increase their production of the hormone glucagon, which acts on the liver to convert stored glycogen to glucose' and 'glucose passes from the liver into the bloodstream'. I don't mean for this to be a stupid question, but isn't it the pancreas that does this? Or is the liver involved in this process too? Is the textbook right? And if so, then what does the pancreas do?

Thanks in advance for clearing this up!

Hi AceVCE777

Insulin is a protein, so the cells that are responsible for the production of insulin must have an abundance of the Rough Endoplasmic Reticulum (I say RER instead of just free-roaming ribosomes because the insulin is secreted, and any protein that is secreted for extracellular use is synthesised by the RER, whereas any intracellular-used protein is synthesised by free ribosomes). So these cells produce this protein-based hormone and secrete it. These cells are found in the pancreas, remember, the pancreas is an organ, organs are made up of tissues and tissues are made up of many specialised cells. So the beta cells of the pancreas are responsible for the secretion/production of insulin. The pancreas has two types of cells - alpha cells that produce glucagon and beta cells that produce insulin.

Ever wondered why people with diabetes can not produce insulin? It is partially because they lack the beta cells in their pancreas, so when there is an abundance of glucose in their blood, the beta cells can not produce insulin to ensure a decrease in blood glucose levels. Hence they have to inject insulin right before/after a meal so that the insulin is present to convert glucose into stored glycogen in the liver.

Imagine you ate a sugar block that was made from raw glucose. This glucose now enters your blood stream and there are sensory cells that detect a rapid increase of glucose levels in the blood. Now to maintain homeostasis (stable internal environment), the body must do something to negate the stimulus. So it embarks on a negative feedback loop which involves the beta cells. So how do you trigger beta cells all the way at the pancreas to secrete insulin? Well, signalling molecules (hormones) travel to the beta cells, and if they are protein-based they will bind to transmembrane receptors, and if they are lipid based they will bind to intracellular receptors to initiate signal transduction. This complex signal transduction pathway eventually leads to the production and secretion of an abundance of insulin. Now what does this insulin do to ensure that the blood glucose level decreases to normal? Well, the insulin converts (by some mechanisms/reactions, not important) glucose into glycogen and stores it in the liver. It also allows cells to uptake more glucose from the blood stream, so that they can respire efficiently.

The same goes with the glucagon secretion pathway. However, glucagon is only released by alpha cells of the pancreas. When there are low levels of glucose in the blood stream, then alpha cells receive a signal to produce and secrete glucagon, another hormone, to travel to the liver (remember from before, this is where all the glycogen (stored energy) is kept), and in the liver, glucagon converts glycogen into glucose and releases it into the blood stream, ultimately raising the blood glucose levels and eliminating the initial stimulus - hence the whole process is a negative feedback loop of homeostasis.

[Shax]

Can anyone explain the difference between the functions of the rough endoplasmic reticulum and the Golgi complex?
Does post-translational modification occur in the rough er or the Golgi body?
Where does protein packaging into vesicles occur?
What is the difference between transport and secretory vesicles?
Is it true that the endoplasmic reticulum provides an internal membrane network for the transport of substances to other organelles in the cell (other than the Golgi body)?

Any help is appreciated, guys