VCE Biology Question Thread

[CarrymetoUni]

I just had a practical investigation on cellular respiration and photosynthesis. We had 4 specimen jars filled with water and bromothymol blue. Two of them had the plant elodea placed inside them and two didn't. One of the elodea jars was covered with aluminum foil to prevent light from getting through and the same thing was done for one of the non-elodea jars as well.
I'm finding it hard to identify the - independent variable, dependent variable and control group in this experiment.
Can anyone help me out with this please?

[geminii]

I just had a practical investigation on cellular respiration and photosynthesis. We had 4 specimen jars filled with water and bromothymol blue. Two of them had the plant elodea placed inside them and two didn't. One of the elodea jars was covered with aluminum foil to prevent light from getting through and the same thing was done for one of the non-elodea jars as well.
I'm finding it hard to identify the - independent variable, dependent variable and control group in this experiment.
Can anyone help me out with this please?

Wait, so did two of the jars just not have any plant or anything in them? What's the point of having those jars then?
Was there anything else in the jars apart from the elodea (for two of them) and the water and bromothymol blue?

[johnhalo]

Yeast is capable of aerobic resp. right?

[CarrymetoUni]

Yeah, the jars had nothing in them except water and bromothymol blue. The only difference was that one of them was covered in aluminum foil, which we later removed during day 2 of the experiment. It was a 3 day experiment, during the second day we removed the aluminum foil from both of the jars. I'm not sure why we did it but I'm guessing we used the jars without elodea as a control group?

[geminii]

Yeah, the jars had nothing in them except water and bromothymol blue. The only difference was that one of them was covered in aluminum foil, which we later removed during day 2 of the experiment. It was a 3 day experiment, during the second day we removed the aluminum foil from both of the jars. I'm not sure why we did it but I'm guessing we used the jars without elodea as a control group?

Ah true.
So I'm guessing since the lack/presence of elodea was the control, perhaps the amount of light the jar was exposed to was the independent variable. And the dependent variable was the growth of the elodea? The dependent variable depends on what you were actually measuring.

[cosine]

Yeast is capable of aerobic resp. right?

Yes, some (not all) prokaryotic cells actually need to photosynthesise or synthesise ATP, but we know that they don't have organelles (mitochondrion and chloroplasts). However, these single-celled organisms have the required machinery embedded in their membranes.

Non-VCE required knowledge, but it will help you understand how exactly yeast and other unicellular organisms can respire aerobically if they don't have the required organelles:

The endosymbiosis theory states that primary eukaryotes engulfed (phagocytosis) alpha proteobacterial cells, which were the ancestral cells that now are thought to be the mitochondrion in almost every eukaryotic organism. So when molecules/structures are engulfed, they are enclosed in a phagosome, which means when this bacteria was engulfed, it had an extra surrounding membrane. Now think carefully about mitochondria, they have an outer membrane and an inner membrane, whose inner projections in the mitochondrial matrix are known as cristae. This means that the outer membrane came from the eukaryotic phagosome, and the inner membrane came from the original plasma membrane of the bacterial cell. SO, this also means that the original bacterial cells were indeed capable of cellular respiration, because they already had the cristae required for ETC. So in other words, they say that alpha proteobacterial cells WERE mitochondria, and hence that is a reason why they can respire aerobically, without organelles.

[sunshine98]

I just had a practical investigation on cellular respiration and photosynthesis. We had 4 specimen jars filled with water and bromothymol blue. Two of them had the plant elodea placed inside them and two didn't. One of the elodea jars was covered with aluminum foil to prevent light from getting through and the same thing was done for one of the non-elodea jars as well.
I'm finding it hard to identify the - independent variable, dependent variable and control group in this experiment.
Can anyone help me out with this please?

Independent variable - what you changed (ie. presence of light)
Dependent variable - what changed as a result of the change in your independent variable/ what your measuring
So I know that bromothymol blue is an indicator. I'm assuming that what it was used for is the fact that as CO2 increases (during respiration) it will react with water to form carbonic acid and hence show a specific colour, cause acidity increased? What did you measure? Colour changes ? or 

[CarrymetoUni]

We recorded the colour given by the Bromothymol blue in the solution. From that we could tell if CO2 had increased or decreased. I'm confused as to whether the dependent variable would be the colour of the pH indicator or the amount of CO2. We didn't specifically measure CO2 but we were able to assume if there were changes in the amount of carbon dioxide based on the colour of the solution.
Sorry for my brief description of the experiment.

[vox nihili]

We recorded the colour given by the Bromothymol blue in the solution. From that we could tell if CO2 had increased or decreased. I'm confused as to whether the dependent variable would be the colour of the pH indicator or the amount of CO2. We didn't specifically measure CO2 but we were able to assume if there were changes in the amount of carbon dioxide based on the colour of the solution.
Sorry for my brief description of the experiment.

Amount of CO₂.

It's what you're actually looking at, the bromothymol blue is just the way that you measure it.

Think of it like this: if you were trying to look at how successful diets were, then your IV would be diet and DV would be weight loss. Your DV is not, however, "change in mass as recorded by Salter scales".

[gameboy99]

We did a prac about photosythesis and cellular respiration on algae.
We had 4 test tubes.
test tube A  - had 10 algae balls, put under light
test tube B - had 10 algae balls, put in dark
test tube C - had no algae balls
test tube D - had no algae balls

I believe that test tubes C and D are controls in this experiment but I'm not sure why. Could someone explain??

[Gogo14]

We did a prac about photosythesis and cellular respiration on algae.
We had 4 test tubes.
test tube A  - had 10 algae balls, put under light
test tube B - had 10 algae balls, put in dark
test tube C - had no algae balls
test tube D - had no algae balls

I believe that test tubes C and D are controls in this experiment but I'm not sure why. Could someone explain??

They are controls because there is no indepedent variable. So, they are a group which you can compare your results to to see if the independent variable changed the dependent variable in other samples.

[blacksanta62]

Is an understanding of photo system 1 &2 required in VCE i.e. will it ever come up in a SAC or exam explicitly? It wasn't in my textbook  but you tube videos from Khan academy and crash course seem to mention it a lot. Thank you.

[Gogo14]

Is an understanding of photo system 1 &2 required in VCE i.e. will it ever come up in a SAC or exam explicitly? It wasn't in my textbook  but you tube videos from Khan academy and crash course seem to mention it a lot. Thank you.

Nah, my teacher said you only need to know where the stages occur and what is produced or taken in.
Also, is ATP synthase a channel protein or enzyme? Or both?

[vox nihili]

Nah, my teacher said you only need to know where the stages occur and what is produced or taken in.
Also, is ATP synthase a channel protein or enzyme? Or both?

Both

[blacksanta62]

Follow up question to your post: Do I need to know what ATP synthase is?