VCE Biology Question Thread

[StupidProdigy]

Has anyone done the enzyme SAC yet?
We mixed starch and water together (which was our control) then added iodine later.
The colour was blue black in the end, can someone explain why? 

And does anyone have any practise questions I good do that have done the SAC?
What things should I study?

Thank you so much to whoever answers in advance! 

Look up 'bozeman science' on YouTube. There is a video by this channel that is the same as what you described basically!

[Jay.C]

Hey guys is it still achievable to get a 40+ SS with a unit 3 Sac average of a B+?

[Sine]

I got my Photosynthesis and Cellular Respiration prac and SAC tomorrow. What are possible experiments? Can  someone post what they would write down if they were asked to explain the three stages of Aerobic Respiration and the two stages of Photosynthesis?

[heids]

Hey guys is it still achievable to get a 40+ SS with a unit 3 Sac average of a B+?

Yes, don't stress, just focus on studying and killing Unit 4 and the exam.  Believe the quote in your signature!!!  Your previous SACs are past, you can't change them, but the future is still entirely change-able.  You haven't killed all your chances, promise.

[cosine]

I got my Photosynthesis and Cellular Respiration prac and SAC tomorrow. What are possible experiments? Can  someone post what they would write down if they were asked to explain the three stages of Aerobic Respiration and the two stages of Photosynthesis?

Light-dependent:
Chlorophyll in the thylakoid membranes captures light energy, and the electrons become energised. These electrons are responsible for the splitting of H2O molecules, into 2H+ ions, 2 electrons and an O molecule. The oxygen combines with another oxygen to produce oxygen gas, and is released as a waste product. The electrons go through the electron transfer chain, causing H+ ions to pump inside the membrane, therefore creating a ionic gradient. Because of this, H+ ions will naturally diffuse down their concentration gradient into the stroma, and as they do this through ATP synthase, ATP is formed from ADP + Pi. The H+ ions are now occupied by a NAPD+ molecule, and NADPH is formed.

Inputs: H2O, Light, NADP+, ADP + Pi
Outputs: O2, NADPH, ATP

Light-independent:
The first step is the attachment of a CO2 molecule to a 5C molecule (RuBP), more known as carbon fixation. As this happens, the enzyme Rubisco is responsible for catalysing the reaction to produce an intermediate 6C molecule. This is unstable, so immediately it splits into two separate 3C (PGA) molecules. The NADPH now comes and accommodates these two molecules and donates H+ ions to them, formating PGAL. One of the PGAL molecules is release into the cytoplasm, where it will endure more reactions to eventually produce sugar (glucose). But one of the molecules remains in the stroma and is reused for the next Calvin-Benson cylce set of reactions.

Inputs: ATP, NADPH, CO2
Outputs: ADP + Pi, NADP, Glucose

Let me know what you think of my interpretation of the two stages, and if I have missed anything also, let me know.

[Sine]

Light-dependent:
Chlorophyll in the thylakoid membranes captures light energy, and the electrons become energised. These electrons are responsible for the splitting of H2O molecules, into 2H+ ions, 2 electrons and an O molecule. The oxygen combines with another oxygen to produce oxygen gas, and is released as a waste product. The electrons go through the electron transfer chain, causing H+ ions to pump inside the membrane, therefore creating a ionic gradient. Because of this, H+ ions will naturally diffuse down their concentration gradient into the stroma, and as they do this through ATP synthase, ATP is formed from ADP + Pi. The H+ ions are now occupied by a NAPD+ molecule, and NADPH is formed.

Inputs: H2O, Light, NADP+, ADP + Pi
Outputs: O2, NADPH, ATP

Light-independent:
The first step is the attachment of a CO2 molecule to a 5C molecule (RuBP), more known as carbon fixation. As this happens, the enzyme Rubisco is responsible for catalysing the reaction to produce an intermediate 6C molecule. This is unstable, so immediately it splits into two separate 3C (PGA) molecules. The NADPH now comes and accommodates these two molecules and donates H+ ions to them, formating PGAL. One of the PGAL molecules is release into the cytoplasm, where it will endure more reactions to eventually produce sugar (glucose). But one of the molecules remains in the stroma and is reused for the next Calvin-Benson cylce set of reactions.

Inputs: ATP, NADPH, CO2
Outputs: ADP + Pi, NADP, Glucose

Let me know what you think of my interpretation of the two stages, and if I have missed anything also, let me know.

Thanks for the explanation and is in a lot of detail.

Can you have a look at my Electron transport chain explanation?: Electrons are transferred across cytochromes, oxygen accepts the electrons then reacts with Hydrogen ions producing water. There is a production of 32-34 ATP.

Also can someone post a answer for the question, What is the role of the loaded acceptor NADPH?

[cosine]

Thanks for the explanation and is in a lot of detail.

Can you have a look at my Electron transport chain explanation?: Hydrogen ions combine with oxygen to produce water via a series of electron carriers. There is a production of 32-34 ATP.

Also can someone post a answer for the question, What is the role of the loaded acceptor NADPH?

The role of the NADPH carrier donates the H+ ions to the Calvin-Cycle, so that glucose can be made. Basically it is the source of Hydrogen for the light-independent reactions.

As for the electron transport chain explanation, I'm not sure if it is correct or not, I haven't heard anything like that before so best to find out from someone else.

[cosine]

Today we did a prac on photosynthesis but there are some things that are unclear to me..

We had to create 20 discs of ivy leaves, and place them in a bicarbonate solution (why?), we then sucked out all the oxygen of the leaves by pulling on the syringe. This caused the leaf discs to sink (why?), after that the discs were seperated by 10 in two different cups. One of the cups was placed in the dark, and the other cup was placed under a spotlight.

We had to observe how long it takes for the leaf discs to float.

Why do we suck out the oxygen in the first place?
The discs in the spotlight floated, what does this indicate?

Thank you.

[vanessa14]

I did this prac last year for year 12 orientation and im currently studying for my enzyme sac  but ill tell you what I remember if that helps

We had to create 20 discs of ivy leaves, and place them in a bicarbonate solution (why?)
i think because it contains a tiny amount of detergent to break down the waxy leaf coating

we then sucked out all the oxygen of the leaves by pulling on the syringe. This caused the leaf discs to sink (why?)
because all the oxygen is sucked out

after that the discs were seperated by 10 in two different cups. One of the cups was placed in the dark, and the other cup was placed under a spotlight.
perhaps one was the control and the other was tested under the light to see the rate of photosynthesis(i.e. if the discs had bubbles forming around it, that meant that there is oxygen available pulling the disc up

We had to observe how long it takes for the leaf discs to float.
the rate of photosynthesis

Why do we suck out the oxygen in the first place?
so when it is placed under light, you could see the rate of photosynthesis?

The discs in the spotlight floated, what does this indicate?
that photosynthesis occured

i answered it in the quote
I tried by best answering from memory, do check with other person to make sure and check on google theres a lot of stuff on there! I did the exact same sac and just thought id list the things i did of by memory for you! i hope it helped!

[cosine]

I did this prac last year for year 12 orientation and im currently studying for my enzyme sac  but ill tell you what I remember if that helps

i answered it in the quote
I tried by best answering from memory, do check with other person to make sure and check on google theres a lot of stuff on there! I did the exact same sac and just thought id list the things i did of by memory for you! i hope it helped!

Thanks vanessa14, really helpful!

[vanessa14]

Thanks vanessa14, really helpful!

welcome good luck!

[cosine]

Would using carrot discs instead of leaf discs be more effective?

[Jay.C]

Would using carrot discs instead of leaf discs be more effective?

No due to carrots being orange and being underground they would not photosynthesize. 

[cosine]

No due to carrots being orange and being underground they would not photosynthesize.

I didn't think of that in my sac.... wow....

I said they are much thicker and denser than leaf discs, hence the suction of oxygen would not be as effective - which would vary our experimental results

[Jay.C]

I didn't think of that in my sac.... wow....

I said they are much thicker and denser than leaf discs, hence the suction of oxygen would not be as effective - which would vary our experimental results

It just depends on how harsh of a marker your teacher is. I mentioned that they would not contain chlorophyll and thus it would change the results but because I didn't write, It would prevent them from photosynthesising I lost all marks. :/