Explain the basic steps in the first half of photosynthesis (light-dependent reactions). Describe the movement of electrons and the importance of hydrogen ions in developing a proton gradient that allows for ATP production.

Photosynthesis is the process by which plants make their own food in the presence of sunlight by utilizing carbon-dioxide and water and produces oxygen and energy.

The process of photosynthesis has two types of reactions: light-dependent reactions and light-independent reactions.

The light-dependent reactions occur in the thylakoid membranes of chloroplasts in which plants use light energy to form ATP and the reduced electron carrier NADPH.

In this reaction, photosystem II (P700) absorbs lights energy and passed it to reaction center. this energy is then is transferred to photosystem I (P680), that pump an electron to a high energy level. The high-energy electron then travel to an electron transport chain and releases energy. this released energy pump H+  ions into the thylakoid interior from the stroma and build a gradient  H+ ions move through gradient and they pass through ATP synthase resulting in the formation of ATP.

The higher energy electron as moves into an electron transport chain, the electron is passed to NADP+ to form NADPH.

in 1859, charles darwin set out his theory of evolution by natural selection as an explanation for adaptation and speciation. he defined natural selection as the "principle by which each slight variation [of a trait], if useful, is preserved".