Photosynthesis & Cellular Respiration

[Hinuku]

What should I concentrate on while learning photosynthesis and cellular respiration - I've got about 12 hours left until school starts and I alsso have to write a lab report and an essay so I can't learn everything really

[Mahuta ♥]

It would help if you have the diagrams infront of you now.

Krebs Cycle:

After the link reaction, you have acytelcoA, a 2 Carbon molecule with the coA enzyme.

The Cycle starts with a 4carbon.

The 2carbon is added to it so: 2+4=6 we get a 6 carbon molecule.

The 6 carbon is changed into 5 carbon. Therefore, we must reduce the carbon number by removing CO2, so CO2 is lost. Everytime a CO2 is lost, a H2 is lost as well. So you have the NAD+ + H2----> NADH+ + H+.

The 5 carbon is changed into 4carbon by the exact same process, CO2 and NADH+ + H+ formed.

The 4 carbon formed isnt the same as the one we started with, so to get it back to the first one, we remove 2H2. One is taken by the NAD+ and the other by FAD.

ATP is formed as well in this process.

So to sum up the krebs cylce produces the following: 1 ATP, 1 FADH2, 3NADH+ + H+, 2CO2

Calvin's Cycle:

Calvin Cycle is the independent reaction part of photosynthesis.

We start with a 5 carbon sugar called Ribulose Bisphosphate but you can call it RuBP.

RuBP chnages to 2 molecules of 6 carbon, so a CO2 is added.

The 6 carbon compound(organic acid) is called Glycerate 3-phosphate(a 6 carbon with 3 phosphates).

This is done by RUBISCO ENZYME.

Glycerate 3-phosphate is turned into a carbohydrate called triose phosphate (by reduction = addition of Hydrogen).

This happens by removing 2 phosphates, hence, 2ATP--->2ADP + P.

Also, 2 hydrogens are ADDED, so 2NADPH----> 2NADP+.

You have 6 molecules of triose phosphate formed. 5 of which are regenerated into RuBP. One molecule is used to form glucose phosphate to use for biomass, storage..etc..etc.

The whole purpose of the Calvin's Cycle is to convert CO2 to a carbohydrate. This how we get glucose as a product of photosynthesis. This is also why we say plants generate their own nutrition.

If there's any part you want clarified dont hesitate to ask me, because I dont feel I made it that clear.

More to respiration, but you don't have time..so those are the most important.

Here's the light dependent explained by another member:

"his reaction is also divided into two main processes but the difference is that they take place almost simultaneously. These are: photolysis of H2O and photophosphorylation.

Chlorophyll is located in the thylakoid membranes of the chloroplast in groups of molecules called photosystems (there are two types of photosystem: 1 and 2). When chlorophyll absorbs sunlight energy, an electron within the molecule is raised to a higher energy level (the electron is said to be excited). Once this happens, chlorophyll is photoactivated. Excited electrons pass from molecule to molecule until they reach an e- acceptor at the reaction centre of photosystem II. Once here, the electron will pass along a chain of carriers in the thylakoid membrane. The flow of the electron will cause the pumping of protons into the thylakoid. Soon, a proton gradient is created (there is more protons in the fluid space inside the thylakoid than on the outside). ATP synthase (located in the thylakoid membranes) will then allow the protons to flow across the concentration gradient, using the energy released to synthethize ATP. The production of ATP by means of an excited electron from Photosytem II is non-cyclic photophosphorylation.

The light-dependent reaction is not over yet

Once the electron has released energy to make ATP, it passes onto Photosystem I (from Photosystem II). Photosystem I can now be photoactivated by absorbing light. When this happens, the excited electron will also travel through a short chain of carriers until it reaches NADP+ in the stroma. NADP+ accepts two high-energy electrons from the electron transport chain and one H+ ion from the stroma, forming NADPH + H+. This is good but as you may have noticed, Photosystem II has given away electrons to supply Photosystem I. Hence, PII will need to replace these electrons by means of the photolysis of water molecules. The clorophyll molecule at the reaction centre is positively charged. By means of an enzyme (at the reaction centre), water molecules in the thylakoid space are split (photolysis) into H+ and oxygen ions and electrons(the electrons are given to the positively charged chlorophyll). Both oxygen and H+ are by-products of this breaking down of water molecules. Oxygen is a waste product and is excreted (think of the equation for photosynthesis).

For the light-independent reaction you must have a diagram in order for me to explain. Tell me if you do have one or I'll try to find one to complete my explanation. I hope all of what I've said is useful!"

I know I just gave the whole light dependent process here, but I personally write all this to garuntee that I dont miss any marks.

Phosphorylation:

This follows the same principal as oxidative phosphorylation in respiration.

1)When light is absorbed by the photosystem (2), electrons are excited and released into the electron carrier chain(which consists of proteins).

2) Everytime electrons move from one carrier to another, a Hydrogen ion is pumped across the thylakoid membrane into the thylakoid space.3)So, you will have a high concentration of protons(hydrogen ions), therefore, you have a concentration gradient.

4)Hydrogen ions are pumped out of the thylakoid through the ATP Synthase, causing it to spin, this spinning generates energy.

5)electrons are accepted by the NADP+.

You have to remember that the hydrogen ions come from the photolysis of water that produce protons as well as electrons(which replace the ones accepted by the NADP+).

Chemiosmosis refers to the diffusion of protons, so basically, they wanted you to explain this by mentioningand referring to chemiosmosis.

And.here's the thread for all questions about biology:

Biology HL/SL