The structures that allow gaseous reactants and products of photosynthesis to move in and out of a plant are stomata.

Here's a breakdown:

* Stomata are small pores on the surface of leaves and stems.

* They are surrounded by specialized cells called guard cells that regulate their opening and closing.

* Carbon dioxide (CO2), a reactant in photosynthesis, enters the plant through the stomata.

* Oxygen (O2), a product of photosynthesis, exits the plant through the stomata.

* Water vapor (H2O) also escapes through the stomata in a process called transpiration.

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