how many types of cytochromes are involved in the thylakoid electron transport chain

1. five
2. two
3. six
4. four

Energy obtained through the transfer of electrons (blue arrows) down the ETC is used to pump protons (red arrows) from themitochondrial matrixinto the intermembrane space, creating an electrochemical proton gradient across the mitochondrial inner membrane (IMM) called ΔΨ. This electrochemical proton gradient allows ATP synthase (ATP-ase) to use the flow of H+through the enzyme back into the matrix to generate ATP fromadenosine diphosphate(ADP) andinorganic phosphate. Complex I (NADH coenzyme Q reductase; labeled I) accepts electrons from theKrebs cycleelectron carrier nicotinamide adenine dinucleotide (NADH), and passes them to coenzyme Q (ubiquinone; labeled Q), which also receives electrons from complex II (succinate dehydrogenase; labeled II). UQ passes electrons to complex III (cytochrome bc1complex; labeled III), which passes them tocytochromec(cytc). Cytcpasses electrons to Complex IV (cytochromecoxidase; labeled IV), which uses the electrons and hydrogen ions to reduce molecular oxygen to water. So two types of cytochromes are involved.