11a) not going to give you the direct answer here but consider the sites for gaseous exchange in a leaf. Need to also compare the underside and upperside.

11b) there are no gases collected because there is substance X in (the set-up on the right). Substance X absorbs CO2 in the water thus preventing the plant from __________ as _________ is needed for ___________. The plant can only _________, taking in __________ dissolved in the water and giving out CO2 which is also absorbed by Substance X. (need to mention the gases involved for both photosynthesis and respiration)