Photosynthesis requires a few main components. Mainly, Sunlight, Water and Carbon dioxide.
For this reaction, the reactants are 1) Water 2) Carbon dioxide
For water, it enters the cell by Osmosis. Water enters a cell through a partially permeable cell surface membrane.
When water enters a space through a partially permeable membrane from a high water potential to a low water potential, the process is called osmosis.
For carbon dioxide, it enters the cell through diffusion.
Diffusion involves particles moving from a region of higer concentration to a region of lower concentation. Therefore, the answer is Diffusion.
Extra knowledge: Carbon dioxide dissolves into the thin film of moisture on the surface of the spongy mesophyll layer for easy transportation to the cells involved in photosynthesis.
Stem cells are differentiated into different types of cells by a process called signaling, which leads to changes in gene activity, causing the cell to differentiate.