VCE Biology Question Thread

[nhmn0301]

I recently did the enzyme SAC with liver and hydrogen peroxide. There were 3 test tubes each filled 2cm high with hydrogen peroxide and 3 test tubes with pieces of livers boiled for a different amount of time (not boiled, 20 seconds and 2 minutes). Which test tube is the control ? It specifically says in the question which test tube... I thought it was the hydrogen peroxide but they are in 3 separate test tubes? Or is it one of the livers ?

Firstly, it's good to have a proper definition of a control set up. It's basically a comparison set up where all variables in that sample are kept constant (controlled). Whilst in the other samples, 1 factor is varied. Hence, in your experiment, the test tube which contains the liver that is not boiled is definitely the controlled, because in here, you have not altered any of its variable, i.e temperature, pH etc etc. It will be used to compare the enzyme action of other samples where you have deliberately altered.
Hope this helps!

[grannysmith]

I recently did the enzyme SAC with liver and hydrogen peroxide. There were 3 test tubes each filled 2cm high with hydrogen peroxide and 3 test tubes with pieces of livers boiled for a different amount of time (not boiled, 20 seconds and 2 minutes). Which test tube is the control ? It specifically says in the question which test tube... I thought it was the hydrogen peroxide but they are in 3 separate test tubes? Or is it one of the livers ?

The control would be the non boiled liver, as it is unaffected by the independent variable, which is duration of time boiled.

Edit: beaten

[grannysmith]

How can one chemical signal trigger different effects in different target cells?
i. they have different receptors
ii. they involve different proteins in the signal transduction pathway?

Also, does signal transduction only occur when a chemical signal binds to a cell surface receptor?

[nhmn0301]

How can one chemical signal trigger different effects in different target cells?
i. they have different receptors
ii. they involve different proteins in the signal transduction pathway?

Also, does signal transduction only occur when a chemical signal binds to a cell surface receptor?

Yeah, I think your answer is right. I can only think of 2 factors: the involvement of different receptors that receive the signal from hormones and the involment of different enzymes in the signal transduction cascade in different cell.

[Jason12]

in E.T.C is 34 ATP molecules always produced + 4 (from krebs/glycolysis) to make a total of 38 ATP in ALL cells then somehow it is only 36 for other cells and 38 for all heart/liver/kidney cells. Explain please?

[Rishi97]

30.7 kJ is released for work when ATP is hydrolysed. Is more energy or less energy required to regenerate this ATP? Why?
Cheers

[grannysmith]

in E.T.C is 34 ATP molecules always produced + 4 (from krebs/glycolysis) to make a total of 38 ATP in ALL cells then somehow it is only 36 for other cells and 38 for all heart/liver/kidney cells. Explain please?

The Electron Transport Chain does not always produce 34 ATP, it's 32-34 depending on the cell.

30.7 kJ is released for work when ATP is hydrolysed. Is more energy or less energy required to regenerate this ATP? Why?
Cheers

More energy is required, as you can't get out more than you put in

[Rishi97]

More energy is required, as you can't get out more than you put in

Thanks. That makes sense but how would I put it into scientific terms?

[nerdmmb]

Thanks. That makes sense but how would I put it into scientific terms?

There needs to be a net input of energy?

[nerdmmb]

Also, I've actually got a photosynthesis SAC coming up.. Does anyone know what kinds of pracs are done for this particular topic?

[nhmn0301]

Thanks. That makes sense but how would I put it into scientific terms?

Conservation of energy law. You can't produce or make energy, it can only be conserved or change to another state. Hence, the amount of energy requirement is exactly the same.

[MM1]

What's the purpose of avoiding major veins when cutting leaf discs? Thanks!
Also just wondering; why don't cells use lipids instead of glucose as the prime reactant in cellular respiration, since it yields more energy?

[nerdmmb]

What's the purpose of avoiding major veins when cutting leaf discs? Thanks!
Also just wondering; why don't cells use lipids instead of glucose as the prime reactant in cellular respiration, since it yields more energy?

Glucose is an intermediate source of energy which is accepted in cellular respiration. When glucose levels are above normal, they are converted to fats (lipids). Before the body breaks down these fats, it uses what is readily available, glucose instead of giving off energy to convert lipids back into glucose,etc.

Also would like to add that cells do not break down glucose or other organic compounds including lipids solely to yield energy, there are a number of reasons behind these cellular processes including growth, repair,etc.

[vox nihili]

What's the purpose of avoiding major veins when cutting leaf discs? Thanks!
Also just wondering; why don't cells use lipids instead of glucose as the prime reactant in cellular respiration, since it yields more energy?

Cellular respiration is just one energy generating process. There are a host of different energy sources that are actually used by body cells. Sugars are certainly one, but they're not the only, as you know. Indeed, there are cells that don't use glucose (or any sugar) at all to generate energy. Glucose is just a handy energy source because it can be involved pretty well with a lot of biochemical pathways. It's just sort of convenient, easy to obtain in the environment, easy to break down and transport. One particular disadvantage of having lipids as the prime energy source would be that they can't really be transported via blood that well, they're not soluble. That's probably the big issue with them really.

[MM1]

Cellular respiration is just one energy generating process. There are a host of different energy sources that are actually used by body cells. Sugars are certainly one, but they're not the only, as you know. Indeed, there are cells that don't use glucose (or any sugar) at all to generate energy. Glucose is just a handy energy source because it can be involved pretty well with a lot of biochemical pathways. It's just sort of convenient, easy to obtain in the environment, easy to break down and transport. One particular disadvantage of having lipids as the prime energy source would be that they can't really be transported via blood that well, they're not soluble. That's probably the big issue with them really.

That was makes so much sense now; thanks Mr.T-Rav!
Any idea about what's the purpose behind avoiding major veins when cutting leaf discs? This is for the photosynthesis prac. Thanks!