Question

1) what determines color? what wavelength it light color is least effective in photosynthesis? most effective? why?

2) a)where do the light reactions of photosynthesis occur?

b) which pigment is directly involved in the light reactions of photosynthesis?

c) what role does the pigment place in the light reactions?

Answer 1

1. Wavelength determine the color of object. Color is the wavelength of light it reflects. Plants use wavelength between 300 to 800 nm. Red and blue light are most efficiently used. Green light is less effectively used.

2. a. The light-dependent reactions take place on the thylakoid membranes in photosynthesis.

b. Chlorophyll plays an important role in light reaction of photosynthesis.

c. Photosystems absorb light energy through proteins containing pigments, such as chlorophyll. The light-dependent reactions begin in photosystem II. In PSII, energy from sunlight is used to split water, which releases two electrons, two hydrogen atoms, and one oxygen atom. When a chlorophyll a molecule within the reaction center of PSII absorbs a photon, the electron in this molecule attains a higher energy level. Because this state of an electron is very unstable, the electron is transferred to another molecule creating a chain of redox reactions called an electron transport chain (ETC). The electron flow goes from PSII to cytochrome b6f to PSI; as electrons move between these two photosystems, they lose energy. Because the electrons have lost energy prior to their arrival at PSI, they must be re-energized by PSI. Therefore, another photon is absorbed by the PSI antenna. That energy is transmitted to the PSI reaction center. This reaction center, known as P700, is oxidized and sends a high-energy electron to reduce NADP+ to NADPH. This process is oxygenic photosynthesis.