Sitat:
At night they do. During the day, they give off oxygen.

All normal plants, in the process of photosynthesis, take up carbon dioxide by day and release oxygen. This switches over in the dark, and they then produce carbon dioxide through respiration in the same way as animals. While they are growing, they take up more carbon dioxide overall than they give out, which gets turned into plant tissues (especially cellulose and, in the case of trees, lignin).