VCE Biology Question Thread

[RazzMeTazz]

What would be the exact inputs and outputs for the light dependent reactions, Calvin Cycle, glycolysis, Kreb's cycle and the Electron transport system - for a vce level?

Thanks!

[howlingwisdom]

If more substrate is added (assuming that enzyme, temperature etc is constant) will this increase the amount of product produced or just increase the rate of the reaction up until the enzyme becomes saturated with substrate?

[Chang Feng]

Bio sac Wednesday. My sac was about putting liver (catalase) in test tube and then seeing the height of bubbles produced (due to detergent to see rate of reaction) in 2min. This was under different temp, different size if liver?? So I have 3 independent variables being size of liver, temp, and time?? I have to plot a graph, but it doesn't say how many different functions (as in height bubbles produced VS enzyme size, etc) I have to do. Could anyone help me?

[alchemy]

If more substrate is added (assuming that enzyme, temperature etc is constant) will this increase the amount of product produced or just increase the rate of the reaction up until the enzyme becomes saturated with substrate?

It will increase the rate of the reaction up until the enzyme becomes saturated with substrate. Like I mentioned earlier, enzymes do not affect how much product is formed by a reaction...

[eagles]

Urgent!!

Why do we avoid punching veins of leaf discs and must ensure that leaf discs are punched from leaf blade? This is for a prac involving punched leaf discs immersed in bicarbonate solution and measuring rate of photosynthesis with different coloured lights.

Thanks

[DJA]

Urgent!!

Why do we avoid punching veins of leaf discs and must ensure that leaf discs are punched from leaf blade? This is for a prac involving punched leaf discs immersed in bicarbonate solution and measuring rate of photosynthesis with different coloured lights.

Thanks

I haven't personally done this prac but thinking about it logically I'd think that the reason why you wouldn't want leaf veins in your discs of leaves is because plant veins don't contain chlorophyll. Hence in order to maintain a relatively constant amount of chlorophyll in every leaf disk (for accurate comparison for rate of photosynthesis)  the prac requires you to cut only disks from the green leaf blade and not the veins.

If you have veins in some leaf disks, you WILL have some inaccuracies due to different amounts comparatively of areas on the disk with chorophyll.

[Rishi97]

Quick question,
6) How do enzymes affect activation energy
I know that the answer is basically "Enzymes lower the activation energy" but this doesn't sound like a yr 12 answer. It sounds too simple and unscientific. Could someone tell me how they would explain it.
Thanks

[nerdmmb]

Quick question,
6) How do enzymes affect activation energy
I know that the answer is basically "Enzymes lower the activation energy" but this doesn't sound like a yr 12 answer. It sounds too simple and unscientific. Could someone tell me how they would explain it.
Thanks

Enzymes weaken and break the bonds present in the substrate which in turn speeds up the rate of the reaction by lowering the activation.

Someone please correct me if I'm wrong.

[alchemy]

Enzymes weaken and break the bonds present in the substrate which in turn speeds up the rate of the reaction by lowering the activation.

Someone please correct me if I'm wrong.

Not only that; they can bind more than one substrate molecules together to build a more complex one. Such reactions are termed 'anabolic' or 'synthesis' reactions, requiring energy. What you've described are 'catabolic' reactions.

[nerdmmb]

Not only that; they can bind more than one substrate molecules together to build a more complex one. Such reactions are termed 'anabolic' or 'synthesis' reactions, requiring energy. What you've described are 'catabolic' reactions.

ohhh my bad

How do they reduce activation energy in anabolic reactions then?

[Chang Feng]

Urgent questions for enzyme sac. How does increase product concentration slow down rate of reaction. Do they bind to enzyme like an inhibitor- but aren't they not complementary to substrate so how do they bind

[Chang Feng]

Also how is activation energy reduced by enzyme...ie something with enzyme putting stress one substrate so the bonds break easier and moving the substrate closer together so bind easily in anabolic reactions?? Help clarify please

[Chang Feng]

Do cofactors and coenzymes simply just fill in active site of enzyme and what else do they do (required in VCE biology)

[Vicbelgaus]

hey there i'm not certain of how much we know about coe-enzymes and co-factors

But i do know that they don't simply fill the active site of an enzyme.
Co-enzymes: usually act as carrier molecules and help bring the substrate to the enzyme.
Co-factors: actively participating with the catalysis of the substrate, by attaching to the enzyme itself and helping the substrate or substrates undergo their reaction easier.

hope that helps 

[Tyleralp1]

Chang Feng, I shall attempt to answer your three questions:

From my understanding, I don't believe the concentration of product effects the rate of reaction of an enzyme. Maybe in a confined area, the number of products may increase overtime, thus limiting the space through which enzymes+substrates can travel. Therefore, there are less enzyme-substrate collisions in a given time frame, hence slowing down the rate of reaction. Or maybe even, as the product fills up the area of enzymes, the space is limited for which substrates can come in. Hence, less and less enzymes can catalyse reactions as time goes on. Though I've personally never come across this given situation.

As for enzymes reducing the activation enegy: An enzyme’s selective three dimensional shape, the active site, is complimentary to the substrate it binds to. When in the active site, the chemical bonds are closer, therefore allowing the chemical bonds to weaken and change with less energy. An enzyme therefore lowers the entropy of substrate, freeing them from translational and rotational movements.

Coenzymes are organic molecules that are required by certain enzymes to carry out catalysis. They bind to the active site of the enzyme and participate in catalysis but are not considered substrates of the reaction. Coenzymes often function as intermediate carriers of electrons, specific atoms or functional groups that are transfered in the overall reaction. An example of this would be the role of NAD in the transfer of electrons in certain coupled oxidation reduction reactions.
Cofactors are often classified as inorganic substances that are required for, or increase the rate of, catalysis. This binds to the active side, and still allows for the complimentary pairing of the specific substrate, but provides the necessary inputs for the reaction to take place.