turn-based movement

Hey all,

I'm making a sort of cellular automata / artificial life simulation (rather than a game) — so I don't need to worry about the player's movement; just the multitude of gameobjects that are on the grid at any one point.

The only gameobjects I have at the moment are 'cells' (the stationary creatures) and 'photons'. For every tile at the top of my grid ('game board', whatever) there is a 0.1% chance that it will spawn a photon. The photon will then move downwards across the grid at 1 unit per second until it either crashes into the bottom-most border of the grid or hits a cell (which imparts an amount of energy to the cell). My thinking is that once the cell reaches 100 energy, it will spawn a new cell in an empty neighbouring tile.

The problem being that everything moves at once. If two photons are spawned in the same second they will move in sync with each other. All photons move at the same time. And once the cells are able to spawn new cells; they will do so at the same time (if they both reach 100 energy at the same time).

What I want is for every object (whether it be a photon or a cell, or anything else on the board) to take it's 'turn' in a order; rather than everything moving all at once each second. The actual ordering of turns isn't that important (could be random, or predefined by which object was instantiated first).

The way i envision things is that if there are only three photons (photon 1, photon 2, and photon 3) they will move in order (photon 1 moves one unit down; then photon 2 moves one unit down; then photon 3 until every object in the game has 'done its "stuff"' and then the cycle will continue). I want to try this having read about the differences between synchronous cellular automata (conways game of life, in which every cell is updated at once) vs asynchronous cellular automata (of which there aren't as many examples).

I am however quite new to Unity and scripting in general so I'm not sure how to achieve this. Can anyone point me in the right direction?

Thanks very much for any help in advance.