Light harvesting in photosynthesis employs both classical and quantum mechanical processes with an energy efficiency of almost 100 percent. For light to produce energy in classical processes, photons must reach reaction sites before their energy dissipates in less than one nanosecond. In photosynthetic processes, this is not possible. Because energy can exist in a superposition of states, it can travel all routes within a material at the same time. When a photon finds the correct destination, the superposition collapses, making the energy available. However, no purely quantum process can be wholly responsible, because some quantum processes slow down the movement of quantized objects through networks. Anderson localization prevents the spread of quantum states in random media. Because the state acts like a wave, it is vulnerable to disruptive interference effects. Another issue is the quantum zeno effect, in which an unstable state never changes if it is continuously measured/watched, because watching constantly nudges the state, preventing it from collapsing.
Interactions between quantum states and the environment act like measurements. The classical interaction with the environment changes the wave-like nature of the quantum state just enough to prevent Anderson localisation, while the quantum zeno effect extends the quantum states lifetime, allowing it to reach the reaction centre. The proposed long lifetime of quantum coherence in the FMO influenced many scientists to investigate quantum coherence in the system, with Engels 2007 paper being cited over 1500 times within 5 years of its publication. The proposal of Engel is still debated in literature with the suggestion that the original experiments were interpreted incorrectly assigning the spectral oscillations to electronic coherences instead of ground-state vibrational coherences, which will naturally be expected to live longer due to the narrower spectral width of vibrational transitions.