Question

Give a general description of

what photosynthesis and cellular respiration each accomplish. Describe and

compare the process of chemiosmosis in photosynthesis and cellular respiration.

Identify the source of the high-energy electrons that drop down the electron transport

chain in photo-phosphorylation versus oxidative phosphorylation. Where is the ATP

produced in each process? What is the proton-motive force?

Answer 1

Photosynthesis is a physicochemical process by which photosynthetic organisms convert light energy into chemical energy in the form of reducing power NADPH and ATP; & use these chemicals to drive carbon dioxide fixation into glucose. Thus anabolism (i.e synthesis) is goal of photosynthesis.

Cellular respiration is an oxidative process, in which free energy released from catabolism (i.e breakdown) of organic compounds (eg. glucose) is used in formation of ATP.

Chemiosmosis is a proton pumping theory involving movement of ions across a semi permeable membrane down their electrochemical gradient generating ATP . It is proposed by Peter Mitchel.

Chemiosmosis in photosynthesis

Begins in stroma.

Protons are pumped into the thylakoids (across the thylakoid membrane), before diffusing back into the stroma

ATP synthase is embedded into thylakoid membrane.

Chemiosmosis in respiration

Begins in mitochondrial matrix.

Protons are pumped out of the matrix (across cristae) into the intermembrane space before diffusing back into the matrix.

ATP synthase is embedded into cristae.

The source of the high energy electrons that drop down the electron transport chain is water in photo-phosphorylation and NADH+H⁺ or FADH₂ in oxidative phosphorylation.

Photo-phosphorylation

ATP is produced in stroma

Oxidative phosphorylation.

ATP is produced in mitochondrial matrix.

Proton- motive force (pmf) is the electrochemical potential difference between protons in aqueous phases on different sides of any membrane.