VCE Biology Question Thread

[katiesaliba]

Slightly confused about the differences between protein channels and protein carriers in the plasma membrane. What exactly passes through each? Do small particles and ions only pass through protein channels and do larger molecules only pass through protein carriers? Are protein carriers only involved in active transport?

Thanks!

[slothpomba]

hi, just a quick question... or two
I did a biology sac today on photosynthesis and respiration
for part A we had to pour pond water in 4 tests tubes and two containing elodea
which then we had to add drops of phenol red indicator
then bubble CO2 gas through the solution which changed the colour to more of a yellow
we then had to add ammonia and leave 2 test tubes in light, two in dark.
questions I have are:
Complete the following table
Indictor colour                               PINK                     Yellow
Name of process                              ?                             ?
what is the purpose of the tubes with no elodea?
and predict what would happen if you moved the tube in the dark containing elodea into light for two days?
it would be wonderful if anyone could help clarify these questions

We're not a homework service, i think it would be best for your learning (and us, we all volunteer our limited time here) if you attempt it  first and show us your attempt (doesn't matter if it's wrong).

[slothpomba]

Slightly confused about the differences between protein channels and protein carriers in the plasma membrane. What exactly passes through each? Do small particles and ions only pass through protein channels and do larger molecules only pass through protein carriers? Are protein carriers only involved in active transport?

Thanks!

A protein channel is just that, a channel, think of a pipe for instance. There's nothing going on, its basically a hole or a pore through which things can move. Think of those slides they have at maccas as well (the tunnels) there is nothing moving you, it is simply a channel to get from A to B. Now think of a water slide or sitting on someones lap in a slide (like you may have done when you were a kid) something is actively carrying you through this channel.

There are some differences and similarities to be noted. A channel protein still works via simple diffusion, things just simply across this hole/opening in the membrane (much like a slide i guess, you need no push). When they are carried through the channel, it is not simple diffusion, they kind of attach to (or "hug") a carrier molecule and they both kind of go through together.  Please note that both these actions are still with the concentration gradient however, neither are active transportation.

[soNasty]

are we expected to know info regarding ATPase, Rubisco, and other certain enzymes also involved in the calvin benson and light dependent stages of PS?

[Vicbelgaus]

are we expected to know info regarding ATPase, Rubisco, and other certain enzymes also involved in the calvin benson and light dependent stages of PS?

No VCAA doesn't require us to know the certain enzymes involved in the Calvin cycle or the light dependent stages in photosynthesis.
to clear up any confusion here is the key knowledge we need to know ( taken out of the vce biology study design 2013-2016).
It is only required to know ''requirements for photosynthesis- including: the structure and and function of chloroplast; the main inputs and outputs of the light dependent and light independent stages.''(Calvin cycle)

[katie101]

The illustration below shows the molecular structure of a portion of granum membrane.

What is the role of the acceptor molecule?

Picture attached

Any help greatly appreciated

[katie101]

How are the ‘holes’ in a slice of bread formed?

[nhmn0301]

The illustration below shows the molecular structure of a portion of granum membrane.

What is the role of the acceptor molecule?

Picture attached

Any help greatly appreciated

Acceptor molecule is a molecule that has a capacity to accept electrons. Hence, looking at its location, you can be certain that this molecule directly involve in the electron transport chain happens in Light dependent stage during Photosynthesis. Electrons will pass through these molecules and release its energy. These energy will be used to actively pump the H+ ions into the outer space membrane and generate a concentration gradient....etc etc (you know the whole process).
Hope this helps!

[nhmn0301]

How are the ‘holes’ in a slice of bread formed?

Bread are made up from yeast. If you put yeast inside an extreme temperature which is lack of O2(like the oven), it will undergo fermentation, pyruvate during glycolysis is converted into ethanol, carbon dioxide and water. These carbon dioxide molecules are factors that generating the raising effect in dough and "holes" in bread. (think about CO2, it's a gas, then it will try to escape from the dough and hence, generating a force from inside of the dough, forcing the dough to rise).
Hope this helps!

[katie101]

Thanks, i understand it now!!

[Jason12]

how does the light dependent and light independent stage in photosynthesis work? The textbooks seems confusing can someone explain it an easier way?

[nhmn0301]

how does the light dependent and light independent stage in photosynthesis work? The textbooks seems confusing can someone explain it an easier way?

I'll try to explain it in a more detailed way:
Light dependent stage:
Plants contain chlorophyll in their leaves, when they are exposed to sunlight, light energy will excite the electrons in the chlorophyll and these exited electrons are what trigger photosynthesis.
Firstly, photosynthesis can be seen as a reverse of cellular respiration in which light dependent stage occurs in a slightly similar fashion as the Electron transport chain in respiration. What's different is obviously the location of light dependent stage, which is in the thylakoid membrane (grana). Embedded in these thylakoid membrane are protein channels and enzymes that are able to produce ATP. Excited electrons will release the energy that it gains from sunlight to these protein channels and that will be used to actively pump the H+ ion out of the outer space membrane to generate a concentration gradient. When we have a sufficient concentration gradient between the inner cell and outer space membrane, H+ ions will flush back into the ATP syntheses for the production of ATP ( at this stage, you can see that it is exactly like Electron transport chain). However, the H+ ions will be shuttled by the electron carrier called NADP+ ( whilst cellular reparation is NADPH). Moreover, referring back to what happened with the chlorophyll, since it has donate some of its electrons to the protein channels, it is now electron short, and immediately need some source of electron to make up for this. This is why H20 comes into need, water will be split into H+ ion and O2 due to the high electronegativity that chlorophyll proceeds. O2 will be released out of the plant cell through stomata.
Hence, what we end up after the light dependent stage is a lot of ATP, NADPH and O2 (O2 is a by-product).
Light-indenpendent stage (Calvin cycle):
Now that we have produced a lot of ATP and NADPH, let's make some glucose. Cells use the energy from ATP to combine the H+ ion that NADPH brings and CO2 into glucose. This process in called Carbon fixation in which we are changing Inorganic carbon into Organic Carbon. Notice that we adding simple structure molecules into a complex structure, this is called anabolism ( hence it is endergonic and also a condensation process). What we get after joining molecules together? H20. This is when the RHS H20 in the equation comes from. It is worth notice that the LHS H20 and RHS H20 are not the same because one is used and one is newly formed.
Hence, what we end up after the Calvin Cycle is Glucose ( C6H12O6), NADP+, ADP + Pi, H20.
Hope this helps!

[Rishi97]

wow thanks for that nhmn0301..that is sooo helpful

[Jason12]

inputs for stage 1 are just sunlight and water (some things say nadp/atp is an input?)

[Sense]

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 ?