VCE Biology Question Thread

[The Usual Student]

How would that be different from a phospholipid bilayer? Phospholipids bilayer are practically the same thing except they don't form miscelles because of their shape

i guess they are similar concepts at heart, they both follow the same logic. But the phospholipid bilayer has a few more features such as cholesterol and protein channels that assist its functions.

[The Usual Student]

Can someone explain the following

1) how does temperature effect osmosis? lets say a cell is placed into a lower solute concentration solution ( hypo tonic ), and lets say another cell is also place in a hypotonic solution but at 50 C degrees, I understand that osmosis may occur quicker in the later but I don't understand the logic behind it since a reaction isn't occuring so it is not a case of reaction rates
2) same as above but for simple diffusion
3) Can H202 pass through the phospholipid membrane through simple diffusion? assuming concentration gradient is higher in the solution then in the cell.

[cosine]

Can someone explain the following

1) how does temperature effect osmosis? lets say a cell is placed into a lower solute concentration solution ( hypo tonic ), and lets say another cell is also place in a hypotonic solution but at 50 C degrees, I understand that osmosis may occur quicker in the later but I don't understand the logic behind it since a reaction isn't occuring so it is not a case of reaction rates
2) same as above but for simple diffusion
3) Can H202 pass through the phospholipid membrane through simple diffusion? assuming concentration gradient is higher in the solution then in the cell.

1). Temperature affects the rate of osmosis because higher temperatures will increase the kinetic, molecular energy/movement of molecules, so the water molecules have a more rapid rate of diffusing through the membrane. Likewise with low temperatures, the molecular kinetic energy is reduced, so the water molecules move relatively slower, hence rate of osmosis is reduced too.

2). Same as above xD

3). No idea but you're not required to know. Just know that non-polar, relatively small particles/molecules can only simply diffuse through plasma membranes. And also small polar molecules such as water and oxygen. No need to know further than this.

[cosine]

So I was doing the dishes for my mum, and I read on the detergent bottle: 'Phosphate Free'. And for the duration of the washing I went crazy and tried to form my own hypothesis and reasoning for the detergent being phosphate free. So can anyone doing VCE Bio explain to me why being phosphate free helps the detergent do its job better? (Testing your knowledge on solubility and polarity)

[geminii]

Hey everyone, we did a prac at school for bio where we had four test tubes and put hydrogen peroxide and 1/2 tsp sand in each, and a different type of liver in each of them (fresh, boiled, ground up) and left the fourth test tube without any liver.

I have one main question - what is the purpose of the sand? I know it has something to do with it being a rough surface, but can anyone elaborate? Thanks so much!

[molecular.]

Hey Cosine,

Well, 'phosphate free' detergent does not make the detergent do its job better. Phosphate detergents are great for cleaning as they prevent certain ions from disturbing the cleaning process, making them quite efficient for cleaning dishes. However, recently there has been a change to 'Phosphate free' detergents due to the harmful affects of phosphate on our waterways, which comes from the phosphate detergent that goes down the drain. The high levels of phosphate in our waterways results in increased production of algae, which reduces the health of our waterways - making it harder to swim and drink from such areas.

[Photon]

Hey guys, here are just a few basic questions that I have. I left some space so that if you choose to answer a question you can just place your answer under the question lol. Also, guaranteed up-votes to whoever answers any of the questions for me.

- Can endo/exocytosis happen down as well as against the concentration gradient?



- Can large hydrophobic molecules pass through the membrane?



- How much do I need to know about glycosisdic bonds?



 - Are all mono and disaccharides soluble in water?



- Is it correct to say starch and glycogen are slightly soluble in water but cellulose is hydrophobic?



- Are steroids a type of hormone? If so then aren't hormones generally made of proteins?



- I read somewhere that secretion is not a good way to describe the exocytosis of proteins as it should only be used for the exocytosis of wastes. What would be a more appropriate term to use instead?



- Is the plasmodesmata used only via the phloem pathway in a plant's vascular system?



- Is the following correct answer to a SAC question:
            - Osmosis the net movement of water molecules from an area of high concentration of solute to an are of low concentration of solute.

            - Simple diffusion is the net movement of particles from a region of low concentration to a region of high concentration.
 
            - Active transport is the movement of molecules with the help of ATP. (I tried not to say against the concentration gradient because of bulk transport)


- Is the electron micrograph better (at seeing smaller things) than the light microscope but worse than the electron microscope?


- Are all polypeptides proteins?



- Is it true that all proteins have a teritiary structure?




OMG ITS MY 100th POSTfewjnffjewbfehfbwejfbebvsdjcsFDW3o83232r3frh3dklnkrenqi

[qwertyqwerty]

Hey guys, here are just a few basic questions that I have. I left some space so that if you choose to answer a question you can just place your answer under the question lol. Also, guaranteed up-votes to whoever answers any of the questions for me.

- Can endo/exocytosis happen down as well as against the concentration gradient?
Yes, endo/exocytosis is not limited by the concenteration gradient. It is used whenever bulk transport is needed.


- Can large hydrophobic molecules pass through the membrane?
Probably not, the gaps between the phospholipids are not big enough. It would probably use endo/exocytosis (think of a white blood cell engulfing a pathogen)


- How much do I need to know about glycosisdic bonds?

Don't know what this is, sorry

 - Are all mono and disaccharides soluble in water?



- Is it correct to say starch and glycogen are slightly soluble in water but cellulose is hydrophobic?



- Are steroids a type of hormone? If so then aren't hormones generally made of proteins?
Steroids are lipid based hormones. Generally, but there are lipid-based hormones too.


- I read somewhere that secretion is not a good way to describe the exocytosis of proteins as it should only be used for the exocytosis of wastes. What would be a more appropriate term to use instead?
Intercellular transport? (If the protein moves to another cell)


- Is the plasmodesmata used only via the phloem pathway in a plant's vascular system?



- Is the following correct answer to a SAC question:
            - Osmosis the net movement of water molecules from an area of high concentration of solute to an are of low concentration of solute.

I think you need to mention the term "differentially permeble membrane".

            - Simple diffusion is the net movement of particles from a region of low concentration to a region of high concentration.
yes
 
            - Active transport is the movement of molecules with the help of ATP. (I tried not to say against the concentration gradient because of bulk transport)
I would mention against the concentration gradient with assistance of carrier proteins. Although bulk transport does use energy, I think "active transport" refers to the carrier proteins. Not sure about this.

- Is the electron micrograph better (at seeing smaller things) than the light microscope but worse than the electron microscope?
Don't know

- Are all polypeptides proteins?
A polypeptide is a chain of amino acids. It has a primary and secondary structure. For it to be a protein, a tertiary structure is needed.


- Is it true that all proteins have a teritiary structure?
Yes, otherwise it would just be a polypeptide chain.



OMG ITS MY 100th POSTfewjnffjewbfehfbwejfbebvsdjcsFDW3o83232r3frh3dklnkrenqi

[cosine]

- Can endo/exocytosis happen down as well as against the concentration gradient?
Endocytosis is from high to low. Just think about when pathogens are endocytosed by phagocytes, the pathogens are going from a high to low concentration. Also think about when Amoeba organisms absorbed water in bulk in their watery environment, obviously from high to low concentrations. Also, exocytosis typically occurs from high to low concentrations, such as when production of antibodies from plasma B cells is occurring, the antibodies are being produced at a rapid rate inside the cell and accumulating, and the exocytose outside the cell into the tissue. However, this knowledge is not required for VCE, just know that endo/exo are active transport and require energy (ATP)

- Can large hydrophobic molecules pass through the membrane?
No, not directly through the membrane, they are too large and hence can puncture the plasma membrane. Instead, they can endocytose through the membrane. However, small hydrophobic molecules such as alcohol can indeed pass through via simple diffusion.


- How much do I need to know about glycosisdic bonds?
Just know that glycosidic bonds are the bonds between the monomers of polysaccharides.


 - Are all mono and disaccharides soluble in water?
Yes


- Is it correct to say starch and glycogen are slightly soluble in water but cellulose is hydrophobic?
No, because polysaccharides such as glycogen, cellular and starch are in fact not soluble in water, they are all hydrophobic. This is due to their structure and size.


- Are steroids a type of hormone? If so then aren't hormones generally made of proteins?
Yes, steroids are a type of hormone, also known as lipid-based hormones. No, there are two types of hormones:
1. Lipid-based hormones (hydrophobic hormones)
2. Protein-based hormones (hydrophilic hormones)


- I read somewhere that secretion is not a good way to describe the exocytosis of proteins as it should only be used for the exocytosis of wastes. What would be a more appropriate term to use instead?
Secretion typically refers to the process whereby something is synthesised and released. For example when an endocrine gland produces a hormone and secretes it into the blood stream. So, only if the cell has for example produced a protein via the Rough ER, then you can easily say that the proteins were secreted or exocytosed, either is fine. However, if the cell is 'excreting' wastes, then that is the better term to use.

- Is the following correct answer to a SAC question:
            - Osmosis the net movement of water molecules from an area of high concentration of solute to an are of low concentration of solute. It is correct, but osmosis is ALWAYS the movement of water molecules ACROSS A MEMBRANE. That is a vital part that you have missed, the membrane part.

            - Simple diffusion is the net movement of particles from a region of low concentration to a region of high concentration. Incorrect, a better structured answer would be: Simple diffusion is the net movement of particles from a region of high concentration to a region of low concentration, going along the concentration gradient. Simple diffusion is a passive form of movement. Also, in your definition, you wrote that it goes from low to high, please do not confuse this with active transport, diffusion is always high to low.

            - Active transport is the movement of molecules with the help of ATP. (I tried not to say against the concentration gradient because of bulk transport) I like your thinking about the concentration gradient, but unfortunately in VCE Biology, you must include that active transport is the transport against the concentration gradient. As I said above, you are right in saying bulk transport is indeed from high to low, but for VCE just assume that it is not.


- Are all polypeptides proteins?
For VCE, yes assume that. But in reality, polypeptides are amino acid linkages that are <50 amino acids, whereas proteins are >50 amino acids, so technically, polypeptides are not proteins.

- Is it true that all proteins have a teritiary structure?
Yes, all functional proteins have a tertiary structure, because this level of structure determines the function of the proteins.

[sunshine98]

- Is the following correct answer to a SAC question:
            - Osmosis the net movement of water molecules from an area of high concentration of solute to an are of low concentration of solute.

The other ones seem to be answered, but just wanted to draw attention on this point. This is incorrect. You kinda reversed your definition. It would be correct if you said:
Osmosis the net movement of water molecules from an area of high concentration of solute free water molecule to an area of low concentration of solute free water molecules
Or alternatively , if you wanted to stick with using the 'solute concentration' , your  definition is reversed. So it becomes
 Osmosis the net movement of water molecules from an area of high low concentration of solute to an are of low   high concentration of solute.
Oh and definitely add the membrane to the definition

[CarrymetoUni]

I just had a Biology SAC based on an practical investigation of enzymes.
One of the questions was-
Does an increase in enzyme concentration have an affect on the rate of reaction? Explain how you arrived to your conclusion.
My answer was-
An increase in enzyme concentration does have an effect on the rate of reaction. An increase in enzyme concentration decreases the time taken for a reaction to occur because there are more active sites for the substrates to bind to. The time of the chemical reaction will keep decreasing as the concentration is increased until the point of saturation is reached. I can also link back to my results on the practical investigation, which showed that the time taken for the lipids to hydrolyse in milk decreased as the lipase concentration was increased.

I feel like by quoting the point of saturation part I've potentially got the whole question wrong since it doesn't apply to this question.
If you were marking this SAC would you give me a mark of 0 for this question? 

[sunshine98]

I just had a Biology SAC based on an practical investigation of enzymes.
One of the questions was-
Does an increase in enzyme concentration have an affect on the rate of reaction? Explain how you arrived to your conclusion.
My answer was-
An increase in enzyme concentration does have an effect on the rate of reaction. An increase in enzyme concentration decreases the time taken for a reaction to occur because there are more active sites for the substrates to bind to. The time of the chemical reaction will keep decreasing as the concentration is increased until the point of saturation is reached. I can also link back to my results on the practical investigation, which showed that the time taken for the lipids to hydrolyse in milk decreased as the lipase concentration was increased.

I feel like by quoting the point of saturation part I've potentially got the whole question wrong since it doesn't apply to this question.
If you were marking this SAC would you give me a mark of 0 for this question?

Yh I didn't like that u used 'point of saturation'. From what I know that's most commonly used to describe when there is an excess of substrate and not enough enzymes (and hence active sites). Then you would say that the point of saturation was reached(cause all the active sites are saturated) . But it doesn't apply in your circumstance.  Other than that your answer seems ok , except some parts seem unnecessary. Like your first sentence. If in timed condition that would waste some of your time. You could have just said 'Yes.... blah blah'
I don't think you would get the whole question wrong. But it depends on the number of marks its worth and how harsh  your teacher is.

[johnhalo]

Just some clarification:

Why does a graph showing enzyme concentration plateau?

I know that with substrate concentration, it plateaus since the enzymes are saturated with substrate and the rate can't go faster, but why does enzyme concentration plateau?

[CarrymetoUni]

My teacher is quite lenient when it comes to marking, well that is what I've heard. In terms of marks, we had to do the procedure and aim of the prac and then answer 7 questions. The enzyme concentration was one part of a whole question in which we were given a graph showing enzyme concentration vs reaction rate. To also clarify this prac is worth 1/3 of the actual SAC. We have 3 practicals that we are doing and altogether they are getting marked out of 50 with a criteria that marks you on your knowledge, methodology and interpretation of your results. The thing that has me worried is that since the SACs of are school are extremely easy losing even 1 mark might affect the overall study score I receive because SACs get moderated at the end. I feel like the SACs for my school should be harder because there is no way of differentiating the good students from the bad by asking easy questions such as- What happens to enzymes when they become denatured? Are you guys getting similar questions to these in terms of difficulty? 

[she0071]

Hi! I was just wondering,
What is the difference between Myosin and Myoglobin?
they're both proteins right?