All of the crops shown here (potatoes, rice, and oats) are all examples of C3 Plants. C3 plants are widely distributed and important in agriculture (i.e. rice, oats, and wheat are all big agriculture crops). A problem that farmers face when cultivating these plants, though, is that dry weather affects photosynthesis rates (and, therefore, crop yield) in a negative way.
When it’s hot and dry, C3 plants have an adaptation to reduce water loss- they close their stomata (the stomata is the opening where CO2 enters the leaf and O2 leaves [no pun intended..]). Although this prevents water loss, it also prevents loss of O2 and prevents CO2 from entering. As O2 levels rise and CO2 levels depreciate, the plant goes through photorespiration. Photorespiration modifies the Calvin Cycle by having rubisco (the first enzyme in the Calvin Cycle) add O2 to RuBP instead of CO2, as it normally does. The product of this is a two-carbon molecule. This molecule is then broken down to CO2 and H2O. This process does not yield any ATP or sugar and even drains 50% of the carbon fixed by the Calvin Cycle! It’s still a mystery as to what its purpose is exactly as it seems to have no useful product.