VCE Biology Question Thread

[eagles]

so i did my bio sac on enzymes.. you know the usual
liver 1cm cube crushed then mixed with sand and water to make a sort of 'stock'
added 1ml stock into 1 test tube and 2ml hydrogen peroxide into it too, measured bubbles, splint tested..
added 1ml distilled water and 2ml h2o2 in another tube and measured bubbles, splint tested...

following to part b of the experiment we placed 1ml of liver stock in 5 different test tubes and placed them in water baths of 0,20,40,60,80 degree heat, let them sit for 25mins and then proceeded to place 2ml of h2o2 in them and record the amount of bubbles and what happens to the splint..

anyway, regarding the controls used in this experiment, are they the fixed amount of h2o2 used, the amount of distilled water used, and the fixed temperature? or am i getting this confused with controlled variables? or are they the same thing? pretty curious

The factors that you have listed are considered as controlled variables. They are defined to be variables of the experiment that would affect the dependent variable but which we keep constant.
(Recall that only 1 variable should be altered at any one time in the experiment - independent variable)

On the other hand, a control group is exposed to all the factors of the experiment except the independent variable. In the liver practical, the control group is the test tube with the distilled water in it as it is not exposed to the stock.

Hope this makes sense

[eagles]

I had a few questions regarding the photosynthesis and cellular respiration pracs.

For cellular respiration, we will most likely be required to carry out the prac on peas in test tubes and measure how much oxygen is sucked into the tube under water - to test the rate of respiration.
Can someone please tell me what's the significance of having a similar test-tube with glass beads in it as a control tube? (Apparently, it's got something to do with temperature but I don't quite understand what)

Also, for the photosynthesis prac, we'll be using punch holes to get circular portions of a leaf and immerse it in water which contain baking soda, then we'll shine light into the water and measure the rate of photosynthesis by measuring the time taken for the leaves to float up.
Why is it that when the leaves produce oxygen, it floats?

Thanks!

I'm not sure about the glass beads question.
However, for the floating discs, have a read of howlingwisdom's explanation:

The leaf discs float in the bicarbonate solution because they have undergone photosynthesis (the bicarbonate solution provides the carbon dioxide necessary for this process to occur. The oxygen produced (the waste product) fills the air spaces within the leaf discs, causing them to rise and float.

[millie96]

could somebody explain the calvin cycle in simple terms?

[nerdmmb]

Hello! I have a couple of questions and would really appreciate your help.

Since simplified word equation for aerobic respiration is:
glucose + oxygen --> carbon dioxide + water + 36 ATP

I was wondering whether these are accepted forms for the word equation for anaerobic respiration:
glucose --> lactic acid + 2 ATP
or glucose --> ethanol + carbon dioxide + 2 ATP

What is the original source of energy for aerobic respiration in plants?
I'm thinking it can be light energy since photosynthesis is required to make the glucose needed for the process or cellular respiration. Or is an answer such as 'glucose' sufficient?

Thank you.

Both of your equations for anaerobic respiration are correct however the first one is applicable to animals only and the second is applicable to plants only. This is because lactic acid is a product of anaerobic respiration in animals however in plants, it is ethanol and carbon dioxide.

I think glucose would be sufficient. In the glycolysis stage, out of the 4 ATP molecules that are produced, 2 are used for active transport of the products of glycolysis into the mitochondria. So this is how it's basically driven.

[soNasty]

The factors that you have listed are considered as controlled variables. They are defined to be variables of the experiment that would affect the dependent variable but which we keep constant.
(Recall that only 1 variable should be altered at any one time in the experiment - independent variable)

On the other hand, a control group is exposed to all the factors of the experiment except the independent variable. In the liver practical, the control group is the test tube with the distilled water in it as it is not exposed to the stock.

Hope this makes sense

thanks!!

[nerdmmb]

could somebody explain the calvin cycle in simple terms?

During the calvin cycle, the NADPH molecules from the light dependent stage of photosynthesis react with 6CO2 to synthesise glucose. At the same time, 6H20 is produced.

This stage which is also known as the light independent stage of photosynthesis is driven by the energy (18 ATP molecules) that is produced in the light dependent stage of photosynthesis.

So basically:
The inputs are: 6CO2 + 18ATP + NADPH
And the outputs are: C6H1206 + 18ADP + 18Pi + 6H20

[grannysmith]

So basically:
The inputs are: 6CO2 + 18ATP + NADPH
And the outputs are: C6H1206 + 18ADP + 18Pi ++ 6H20

Is it really necessary to include 6H2O as a product of photosynthesis?

[nerdmmb]

Is it really necessary to include 6H2O as a product of photosynthesis?

No as long as you don't write 12H2O as a reactant and just stick to 6H2O instead.

[vox nihili]

Should I be worried that I know none of this? As in, what's a complex?

Not at all! You just merely need to know that the ETC exists and that it produces a shitload of ATP.

[slothpomba]

Standard advice is to ask your teachers for exams first. Your classmates may also have them in one form or another. We used to share them here but that is of course illegal and we have (very long) since stopped publicly distributing them and allowed them to be publicly distributed here. If all else fails, buy them. You may be able to get into some kind of pool with your friends and share the ones you buy to help reduce costs (if you do need to wind up buying them).

[Rishi97]

Hi
I am having trouble understanding the processes of photosynthesis and cellular respiration
Any techniques that worked for you? Some tips would be great
Thanks

[millie96]

Could somebody please explain to me the absorption spectrum (photosynthesis) and what we need to know about this?

[katiesaliba]

Do carrier proteins transport glucose across membranes? (Glut-1, right?)

[grannysmith]

Could somebody please explain to me the absorption spectrum (photosynthesis) and what we need to know about this?

You don't really need to know much about it; just know that different pigments (chlorophyll, carotenoids) absorb different wavelengths of light, and the wavelengths which they reflect are the colours which we perceive.

Do carrier proteins transport glucose across membranes? (Glut-1, right?)

Yeah

[soNasty]

if i had a graph of products produced vs time with an obvious saturation point
and i increased the amount of substrate, but still had the same amount of enzyme, would i produce a greater amount of product?
also, if i halved the amount of enzyme, but kept the same amount of substrate, would i produce less product ?