In photosynthesis co2+h2o gives carbohydrates and oxygen, while co2+h2o=h2co3
In photosynthesis, CO2 + H2O gives carbohydrates and oxygen in the presence of various other factors such as chlorophyll, sunlight etc and it occurs specifically in the chloroplasts of the plants. While reaction of carbon dioxide with water to form carbonic acid (H2CO3) is a general chemical reaction and does not require such specific factors as photosynthesis requires. This reaction occurs in the blood.