안녕하세요!

1) proton concentration forms in the thylakoid because of proton pump proteins (ETC proteins) exist in the thylakoid membrane. They push protons from the stroma into the thylakoid. 

2) which is why there is increased concentration of protons in the thylakoid compared to the stroma. All the protons formed from the creation of NADP+ from the Calvin cycle are ultimately pushed into the thylakoid by these proteins. 

3) you can think of cyclic phosphorylation as analogous to fermentation in animal cells. plant cells that do not have enough NADP+ temporarily refeed electrons back into the ETC proteins to create small amounts of ATP. 

4) cyclic just means "circle" or "loop". anything that continues as a cycle or resembles a circle is referred to as cyclic. you are probably thinking of cyclic AMP (cAMP) which is a AMP molecule that has a ring structure that resembles a circle, making it distinctive compared to normal AMP. 

Thylakoid 배울때 등장하는 ETC proteins 슬라이드를 다시 복습하면 궁금한 부분들이 많이 해결될거 같아요!

열공하시고 혹시 또 질문이 생기면 게시판에서 만나요!