What does this line means?
The cyclic phosphorylation also occurs when light of wavelength beyond 680 nm are available for excitation.
Dear student,
Cyclic photophosphoryation occurs when light of wavelength of 700 nm is available. This line means that the wavelength of light if greater than 680 nm is sufficient to excite electrons from PSI for cyclic photophosphorylation. So, this line is correct because if wavelength is greater than 680 nm then PSII will not be activated and the wavelength may reach 700 nm which is sufficient to excite electrons from PSI for cyclic photophosphorylation.
Regards
Cyclic photophosphoryation occurs when light of wavelength of 700 nm is available. This line means that the wavelength of light if greater than 680 nm is sufficient to excite electrons from PSI for cyclic photophosphorylation. So, this line is correct because if wavelength is greater than 680 nm then PSII will not be activated and the wavelength may reach 700 nm which is sufficient to excite electrons from PSI for cyclic photophosphorylation.
Regards