public void step() {
    	for(int x = 0; x < xSize; x++) {
			for(int y = 0; y < ySize; y++) {
				grid[x][y].grow();
				// YOU WILL NEED TO IMPLEMENT GROW() YOURSELF.
			}
		}

    	Collections.shuffle(agents);

    	for(int a = agents.size()-1; a >= 0; a--) {
			Agent agent = agents.elementAt(a);
			agent.act();
			// YOU WILL NEED TO COMPLETE ACT() YOURSELF.
	    }
    }