Gas Exchange in Plants

Key Stage 3

Unlike animals plants do both respiration and photosynthesis. This means sometimes they take in more Oxygen and release more Carbon Dioxide and other times they take in more Carbon Dioxide and release more Oxygen. Overall a plant makes more Oxygen than Carbon Dioxide.


During the day time the sunlight allows the plant to photosynthesize so it takes in more Carbon Dioxide and releases more Oxygen than it needs for respiration.	During the night time where there is no light, photosynthesis cannot happen but the cells still need to respire so the plant takes in more Oxygen and releases more Carbon Dioxide.


A diagram of the cross section of a leaf.

Leaves have air gaps between the spongy mesophyll cells to allow gas exchange.

Leaves usually have more guard cells and stomata on the underside (lower epidermis) than the top side (upper epidermis). These close when the leaf gets dehydrated, stopping carbon dioxide getting into the leaf which stops them using water for photosynthesis.


The under side of a leaf showing guard cells and stomata.