VCE Biology Question Thread

[alondouek]

*Apologies for the potentially longer-than-anticipated answers (which probably cover material beyond the scope of the course), I'm a strong believer in the contextualisation of knowledge as a learning tool! Let me know if there's anything you want me to elaborate on or clarify.

1. A slight rise in heart rate (pulse) may occur just prior to the start of the period of exercise?  Try to explain why this may be the case.
Is this because the adrenal glands are anticipating exercise, and are releasing adrenaline increasing the heart rate?

You've got the gist of it! In situations that require bodily stress (exercise, fight-or-flight-inducing situations), the autonomic nervous system (ANS) will induce the release of a range of chemicals e.g. epinephrine (adrenaline) and norepinephrine (noradrenaline) to stimulate the body into a certain state that better prepares it for a strenuous situation (i.e. one that might require the individual to fight (or face the source of "danger") or perform flight (that is, flee the source of "danger").

This state is due to a part of the ANS called the "sympathetic nervous system" or SNS, which regulates the fight-or-flight response by causing changes to almost all the major body systems in response to a stress stimulus (though it is active at low levels in non-stress situations too). The ANS is also composed of the parasympathetic nervous system (PSNS) which is predominant in regular, everyday situations, as well as the enteric nervous system (ENS) which controls the gastrointestinal system.

Aside from examples like exercise and dangerous situations, the sympathetic nervous system is very prevalent in people who are experiencing anxiety or a panic attack. The brain 'believes' that the body is being threatened (though it isn't), so it releases chemicals such as adrenaline to stimulate the body into a state where it can flee whatever 'danger' might be present. The downside is that it causes the unfortunate effects of irrational panic, such as a stomach ache and nausea, restlessness, strong fear and irritability.

2. Suggest some reasons for the differences in the values of volume of blood pumped during rest and after exercise.
I can only think that during exercise vasodilation occurs, increasing the size of the blood vessels allowing blood to pump through at a greater rate

You're part right, because vasodilation is certainly a factor in increases blood pressure during exercise (i.e. it's one of a number of things that happens in that situation). The SNS - as mentioned above - will stimulate the release of certain chemical messengers such as adrenaline that 'pump up' the body so it can deal with whatever the stimulus to this situation is. There are numerous effector sites that are impacted by these messages, such as the heart, lungs, sweat glands and blood vessels.

The change in blood pressure specifically can be demostrated by a neat mathematical equation:

where Q = Cardiac Output, SV = Stroke Volume and HR = Heart Rate.

Because we are increasing both the heart rate (HR) and stroke volume (SV, the volume of blood removed from a single heart ventricle with each beat), this means that cardiac output (Q) is therefore increased. This cardiac output is the amount of blood pumped by the heart over a time interval, and as shown above it is increased by the actions of the sympathetic nervous system. Vasodilation itself is a response to this, because the blood vessels need to expand to accommodate the increased volume of blood moving through them.

From this, we can understand that while a person is at rest - and the parasympathetic nervous system (PSNS) is dominant - these changes to heart/lung/blood vessel 'behaviour' haven't occurred because the chemical messengers that elicit the above response haven't been released. As such the volume of blood being pumped by the heart (Q) is less than during exercise.

Hope this helps!

[maurlock]

*Apologies for the potentially longer-than-anticipated answers (which probably cover material beyond the scope of the course), I'm a strong believer in the contextualisation of knowledge as a learning tool! Let me know if there's anything you want me to elaborate on or clarify.

You've got the gist of it! In situations that require bodily stress (exercise, fight-or-flight-inducing situations), the autonomic nervous system (ANS) will induce the release of a range of chemicals e.g. epinephrine (adrenaline) and norepinephrine (noradrenaline) to stimulate the body into a certain state that better prepares it for a strenuous situation (i.e. one that might require the individual to fight (or face the source of "danger") or perform flight (that is, flee the source of "danger").

This state is due to a part of the ANS called the "sympathetic nervous system" or SNS, which regulates the fight-or-flight response by causing changes to almost all the major body systems in response to a stress stimulus (though it is active at low levels in non-stress situations too). The ANS is also composed of the parasympathetic nervous system (PSNS) which is predominant in regular, everyday situations, as well as the enteric nervous system (ENS) which controls the gastrointestinal system.

Aside from examples like exercise and dangerous situations, the sympathetic nervous system is very prevalent in people who are experiencing anxiety or a panic attack. The brain 'believes' that the body is being threatened (though it isn't), so it releases chemicals such as adrenaline to stimulate the body into a state where it can flee whatever 'danger' might be present. The downside is that it causes the unfortunate effects of irrational panic, such as a stomach ache and nausea, restlessness, strong fear and irritability.

You're part right, because vasodilation is certainly a factor in increases blood pressure during exercise (i.e. it's one of a number of things that happens in that situation). The SNS - as mentioned above - will stimulate the release of certain chemical messengers such as adrenaline that 'pump up' the body so it can deal with whatever the stimulus to this situation is. There are numerous effector sites that are impacted by these messages, such as the heart, lungs, sweat glands and blood vessels.

The change in blood pressure specifically can be demostrated by a neat mathematical equation:

where Q = Cardiac Output, SV = Stroke Volume and HR = Heart Rate.

Because we are increasing both the heart rate (HR) and stroke volume (SV, the volume of blood removed from a single heart ventricle with each beat), this means that cardiac output (Q) is therefore increased. This cardiac output is the amount of blood pumped by the heart over a time interval, and as shown above it is increased by the actions of the sympathetic nervous system. Vasodilation itself is a response to this, because the blood vessels need to expand to accommodate the increased volume of blood moving through them.

From this, we can understand that while a person is at rest - and the parasympathetic nervous system (PSNS) is dominant - these changes to heart/lung/blood vessel 'behaviour' haven't occurred because the chemical messengers that elicit the above response haven't been released. As such the volume of blood being pumped by the heart (Q) is less than during exercise.

Hope this helps!

Wow, thank you so much for the detailed answer this is amazing!

[katiesaliba]

What's the difference between van der waal forces and hydrophobic forces?
Also, do proteins establish their tertiary/quaternary structures at ribosomes?If so, then what is meant by the modification of proteins in the rough ER?

[KanMan]

If a sample of typsin is added to milk, to catalyse the breakdown of casein- is the reaction regarded as endergonic/anabolic or exergonic/catabolic? I have a suspicion that it is catabolic due to the break down of the protein into amino acids, yet I can't determine whether there is a net surplus or deficit in energy in terms of substrate reacting to form the product. Thanks

[grannysmith]

If a sample of typsin is added to milk, to catalyse the breakdown of casein- is the reaction regarded as endergonic/anabolic or exergonic/catabolic? I have a suspicion that it is catabolic due to the break down of the protein into amino acids, yet I can't determine whether there is a net surplus or deficit in energy in terms of substrate reacting to form the product. Thanks

By definition, catabolic reactions are exergonic as the breakage of bonds releases a net amount of energy. It is exergonic as it is a catabolic reaction.

[Rishi97]

Tomorrow I have a sac on the leaf disc prac. The leaf discs are placed into sodium bicarbonate solution and after a certain amount of time, the disk starts to float
- Why do they start to float?
- What is the point of covering the syringe with your finger? Why do you have to create a vacuum?
- What is the control and control group?

Thanks

[rhinwarr]

- Why do they start to float?

The leaf discs carry out photosynthesis (using carbon from the sodium bicarb solution) so they produce oxygen. This oxygen fills the air spaces in the leaves, decreasing their density so allowing them to float in the solution.

- What is the point of covering the syringe with your finger? Why do you have to create a vacuum?

Yes it is to create a vacuum to get the air out of the air spaces in the leaves so they sink.

- What is the control and control group?

Need more information about what your prac is about.

[Rishi97]

Yes it is to create a vacuum to get the air out of the air spaces in the leaves so they sink.

Why do we want them to sink though? Isn't the whole prac about timing how long it takes for half the leaves to float?

[jessica666]

Could somebody tell me if membrane receptors involved in signal transduction are always glycoproteins? Or can other receptors be involved. Also, what is the chemical nature of receptors in the cytoplasm?

Thanks 

[rhinwarr]

Why do we want them to sink though? Isn't the whole prac about timing how long it takes for half the leaves to float?

Well you wouldn't be able to see it float if it was already floating. You need take all the air out first so all the gas formed can be attributed to photosynthesis and not any pre-existing gases.

[RazzMeTazz]

Is the thylakoid membrane a third membrane system in chloroplasts or an extension of the inner membrane, folding into stacks to form grana?

  thanks!

[rhinwarr]

Is the thylakoid membrane a third membrane system in chloroplasts or an extension of the inner membrane, folding into stacks to form grana?

They are a third membrane system. There are two outer membranes and then the inner membranes are the thylakoid membranes which are separate from the outer membranes.

[alchemy]

Could somebody tell me if membrane receptors involved in signal transduction are always glycoproteins? Or can other receptors be involved. Also, what is the chemical nature of receptors in the cytoplasm?

Thanks 

They're not always glycoproteins. I remember one VCAA question where they asked for the difference between the responses produced by  epinephrine in muscle cells and liver cells. Epinephrine DID attach to membrane receptors in both, but attached to different receptors to cause a different response in each cell.
The receptors in the cytoplasm (steroid hormone receptors) are still proteins; it's just that they aren't located on the membrane.

EDIT: Forgot to answer the second part of the question. Fixed now (:

[RazzMeTazz]

In the photosynthesis equation, why is there water as part of the outputs as well?

I read about the process of photosynthesis but it does not say anything about the formation of water?
o.O

[alchemy]

In the photosynthesis equation, why is there water as part of the outputs as well?

I read about the process of photosynthesis but it does not say anything about the formation of water?
o.O

The full equation for photosynthesis has water as an output (because it actually is). However, there is no net output of water. Hence, the simplified equation omits water as an output.