VCE Biology Question Thread

[Chang Feng]

Okay thanks. I aren't required to know affinity increased right? I can just state that electrons n hydrogen form water

[alchemy]

Okay thanks. I aren't required to know affinity increased right? I can just state that electrons n hydrogen form water

Don't need to know anything about affinity increasing

[nerdmmb]

Is the wavelength of light and light intensity the same thing?

If not, what's the difference between them?

Thanks.

[eagles]

They differ in that intensity represents the number of photons emitted whereas wavelength gives us the colour of light.

Long wavelengths = reds, oranges
Short wavelengths = violets, blues

[Scooby]

As electrons pass down from one cytochrome to the next, enough energy is released to drive adp and inorganic phosphate into atp. At the same time, its affinity for oxygen molecules are increased so water molecules are formed.

Alright, so, ATP synthesis occurs when H+ is driven from the intermembrane space into the mitochondrial matrix via ATP synthase. This occurs down the H+ concentration gradient (ie. before H+ is moved back into the matrix its concentration in the intermembrane space is much higher). The way that we establish this concentration gradient (sometimes referred to as a pH gradient or proton gradient) in the first place is by pumping H+ from the matrix into the intermembrane space via various membrane transport proteins. Since this is not occurring down a concentration gradient, it's active transport, and energy is needed. This energy comes from those electrons liberated from NADH and FADH₂. After they're liberated from those electron acceptors, the electrons are passed along a series of membrane transport proteins (some but not all of which are cytochromes). Movement of these electrons along those transport proteins provides energy to move H+ into the intermembrane space. And once the H+ concentration gradient is established (with the matrix having the relatively lower concentration compared to the intermembrane space), H+ diffuses back into the matrix via ATP synthase, generating ATP by oxidative phosphorylation.

Oh, and eventually those electrons are gonna reach the end of this "chain" of membrane transport proteins. Once that happens the electrons are "mopped up" by oxygen and combine with H+ to form water.

Hope that made some sense!

[vox nihili]

Alright, so, ATP synthesis occurs when H+ is driven from the intermembrane space into the mitochondrial matrix via ATP synthase. This occurs down the H+ concentration gradient (ie. before H+ is moved back into the matrix its concentration in the intermembrane space is much higher). The way that we establish this concentration gradient (sometimes referred to as a pH gradient or proton gradient) in the first place is by pumping H+ from the matrix into the intermembrane space via various membrane transport proteins. Since this is not occurring down a concentration gradient, it's active transport, and energy is needed. This energy comes from those electrons liberated from NADH and FADH₂. After they're liberated from those electron acceptors, the electrons are passed along a series of membrane transport proteins (some but not all of which are cytochromes). Movement of these electrons along those transport proteins provides energy to move H+ into the intermembrane space. And once the H+ concentration gradient is established (with the matrix having the relatively lower concentration compared to the intermembrane space), H+ diffuses back into the matrix via ATP synthase, generating ATP by oxidative phosphorylation.

Oh, and eventually those electrons are gonna reach the end of this "chain" of membrane transport proteins. Once that happens the electrons are "mopped up" by oxygen and combine with H+ to form water.

Hope that made some sense!

Cytochrome is actually only involved in one part of the ETC, which is moving between complex III and complex IV. That's way too much detail though, don't be thinking about cytochrome, ubiquinol or anything like that guys!

[Scooby]

Cytochrome is actually only involved in one part of the ETC, which is moving between complex III and complex IV. That's way too much detail though, don't be thinking about cytochrome, ubiquinol or anything like that guys!

Yeah, they're never gonna assess this stuff (they did in one of my school's SACs but they did teach us it in class), it's just good to know if you're interested 

[vox nihili]

Yeah, they're never gonna assess this stuff (they did in one of my school's SACs but they did teach us it in class), it's just good to know if you're interested 

It's a bit too much I think.

YOU DO NO NEED TO KNOW THE FOLLOWING, IT'S THERE FOR INTEREST ONLY

For those who are interested though:

Electrons from NADH molecules and stripped off by complex I. Naturally, the biproduct of this reaction is H⁺. These electrons make their way through the complex itself, until they reach the docking site of coenzyme Q. The electrons reaction with coenzyme Q, making QH₂ (ubiquinol). In addition to this, complex I also pumps 4 protons (per NADH) from the matrix of the mitochondria to the intermembrane space. This pumping establishes a concentration gradient across the membrane, which also creates a charge difference across the membrane as well.

Electrons from FADH₂ molecules are stripped off by complex II. Similarly, they make their way through the metal centres in complex II until they reach the Q docking site. They react with Q and protons to make QH₂. Unlike complex I, complex II does not pump protons.

The QH₂ molecules synthesised at complexes I and II dock at complex III, where they are oxidised back to coenzyme Q. Thus, complex II has accepted the electrons from complexes I and II. These electrons pass along the complex, much in the same manner as complex I and II (through metal centres) and make their way to a cytochrome c docking site. Like coenzyme Q, cytochrome c can carry electrons. This is because it contains a haeme group in the centre, with the central ion being reduced from Fe³⁺ to Fe²⁺. The movement of the electrons through complex III drives the pumping of 4 protons for each FADH₂ or NADH molecule. Cytochrome c leaves complex III and sets off for complex IV.

Cytochrome c docks at complex IV, where it the haeme group is oxidised and the electrons donated to the complex. The electrons make their way through the complex's metal centres, driving the pumping of 2 protons per NADH/FADH₂ molecule. Once they have reached the "end" of the complex, they are combined with protons and molecular oxygen to form water, one of the biproducts of respiration (hooray!). This is the only step at which oxygen is required in all of aerobic respiration.

The proton gradient that has been established by the pumping of protons by complexes I, III and IV is used to fuel a process called chemiosmosis. The protons are allowed to diffuse back through the F₀ subunit of an enzyme called ATPase. This diffusion results in the rotation of the γ-subunit, which in a sense, bashes inorganic phosphate and ADP together synthesising ATP.

And that is the story of the ETC. Note as well that NADH produces more ATP than FADH₂. Remember that NADH enters at complex I, which pumps 4 protons. Thus, NADH electrons go through complexes I, III and IV (pumping 4, 4 and 2 protons respectively). FADH₂ electrons, however, bypass complex I and pass through complexes II, III and IV (pumping 0, 4 and 2 protons respectively). Given that NADH results in the pumping of 10 protons and FADH₂ the pumping of 6, it stands to reason that FADH₂ yields 40% less ATP molecules than NADH.

[millie96]

is anybody familiar with the photosynthesis prac involving the leaf discs which are infiltrated with water in one test and sodium bicarbonate in the other? can somebody explain to me why the leaf discs float in the bicarb sol thanks

[howlingwisdom]

is anybody familiar with the photosynthesis prac involving the leaf discs which are infiltrated with water in one test and sodium bicarbonate in the other? can somebody explain to me why the leaf discs float in the bicarb sol thanks

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.

[nerdmmb]

It's a bit too much I think.


For those who are interested though:

Electrons from NADH molecules and stripped off by complex I. Naturally, the biproduct of this reaction is H⁺. These electrons make their way through the complex itself, until they reach the docking site of coenzyme Q. The electrons reaction with coenzyme Q, making QH₂ (ubiquinol). In addition to this, complex I also pumps 4 protons (per NADH) from the matrix of the mitochondria to the intermembrane space. This pumping establishes a concentration gradient across the membrane, which also creates a charge difference across the membrane as well.

Electrons from FADH₂ molecules are stripped off by complex II. Similarly, they make their way through the metal centres in complex II until they reach the Q docking site. They react with Q and protons to make QH₂. Unlike complex I, complex II does not pump protons.

The QH₂ molecules synthesised at complexes I and II dock at complex III, where they are oxidised back to coenzyme Q. Thus, complex II has accepted the electrons from complexes I and II. These electrons pass along the complex, much in the same manner as complex I and II (through metal centres) and make their way to a cytochrome c docking site. Like coenzyme Q, cytochrome c can carry electrons. This is because it contains a haeme group in the centre, with the central ion being reduced from Fe³⁺ to Fe²⁺. The movement of the electrons through complex III drives the pumping of 4 protons for each FADH₂ or NADH molecule. Cytochrome c leaves complex III and sets off for complex IV.

Cytochrome c docks at complex IV, where it the haeme group is oxidised and the electrons donated to the complex. The electrons make their way through the complex's metal centres, driving the pumping of 2 protons per NADH/FADH₂ molecule. Once they have reached the "end" of the complex, they are combined with protons and molecular oxygen to form water, one of the biproducts of respiration (hooray!). This is the only step at which oxygen is required in all of aerobic respiration.

The proton gradient that has been established by the pumping of protons by complexes I, III and IV is used to fuel a process called chemiosmosis. The protons are allowed to diffuse back through the F₀ subunit of an enzyme called ATPase. This diffusion results in the rotation of the γ-subunit, which in a sense, bashes inorganic phosphate and ADP together synthesising ATP.

And that is the story of the ETC. Note as well that NADH produces more ATP than FADH₂. Remember that NADH enters at complex I, which pumps 4 protons. Thus, NADH electrons go through complexes I, III and IV (pumping 4, 4 and 2 protons respectively). FADH₂ electrons, however, bypass complex I and pass through complexes II, III and IV (pumping 0, 4 and 2 protons respectively). Given that NADH results in the pumping of 10 protons and FADH₂ the pumping of 6, it stands to reason that FADH₂ yields 40% less ATP molecules than NADH.

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

[alchemy]

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

I don't think so...
T-Rav said "if you're  interested" it'd be good to know.

[soNasty]

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

[nerdmmb]

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!

[eagles]

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.