23. Entry of carbon dioxide In daylight, photosynthesis occurs Carbon dioxide rapidly used up Carbon dioxide concentration in leaf becomes lower than atmospheric air Diffusion gradient exists Carbon dioxide diffuses from the external environment through the stomata into the air spaces in the leaf Film of water on surface of mesophyll cells so that carbon dioxide can dissolve; dissolved carbon dioxide diffuses into the cells
24.
25. How do we distinguish between the xylem and phloem?