Question

This essential skill asks you to compare and contrast energy conversions in mitochondria with those in chloroplasts. To highlight the similarities and differences in these processes, enter answers to this questions series in the answer field.

1) Both processes involve a hydrogen ion electrochemical gradient. State the location (specific membrane location) and the direction of this electrochemical gradient in mitochondria and in chloroplasts.

2) Both processes involve electrons at a high energy state early in the processes. In the two separate processes, where does the energy carried in these electron states come from?

3) Once some of the energy is extracted from the high-energy electron states, the electrons have to be deposited on some acceptor molecule. Identify this acceptor molecule in both processes (oxidative phosphorylation vs photosynthesis).

(Each of these questions can be answered with a sentence or two.)

Answer 1

Electrochemical gradient: Electrochemical gradient is an active transport usually for ions which moves across the membrane and also it determines the movement of ions which actively transports or diffuses across the membrane.

S.No.	Mitochondria	Chloroplast
1.	The electrons produced moves from mitochondrial matrix-inner mitochondrial membrane (less electron-hungry state) to inter membrane state (more electron-hungry state).	The electrochemical gradient in chloroplast, enables the movement of electrons along electron transport chain in the thylakoid membrane and during this process the ions are pumped across the thylakoid membrane.
2.	The process takes place inside the matrix of the mitochondria.	The process takes place inside the stroma of the chloroplast.
3.	The electron transport within mitochondria takes place during cellular respiration process.	The electron transport in chloroplast takes place during photosynthesis process.
4.	The energy source for the process is glucose.	The energy source for photophosphorylation in chloroplast is from sunlight.
5.	The oxidative phosphorylation process involves reduction of O2 to H2O with electrons donated by NADH and FADH2. The process occurs equally during light or dark period.	The photophosphorylation method takes place by the oxidation of H2O to O2 with NADP+ as electron acceptor which occurs only during sunlight.
6.	Pigment systems are not involved in the process.	Pigment systems such as PS I and PS II are involved.
7.	In oxidative phosphorylation the final acceptor molecule is molecular oxygen.	In photophosphorylation the final electron acceptor molecule is NADP+

Similarities:

1. Both the process involves flow of electrons, which is tranferred through series of membrane bound carriers like quinones, iron-sulphur proteins and cytochromes.

2. The free-energy obtained by the down-hill (exergonic) process is coupled to the uphill tranport of the protons across the membranes, thus conserving the energy.

3. The electrons (free-energy obtained) provides energy to pump (H+) ions to other side of the membranes and the protons flow back is controlled by a special enzyme called ATP-synthase which helps to synthesize ATP molecules.