In an open circulatory system, the cells are in direct contact with the cells in the organism. An example of this is the jellyfish. In a closed circulatory system, cells are not in direct contact with the environment.Take our own bodies for example. When we inhale oxygen fills our lungs and diffuses into our blood. When we exhale, we release waste, or carbon dioxide and other gases.
An embryo sac is said to form when the haploid megaspore nucleus divides. It possesses two haploid nuclei and six haploid cells which do not have cell walls.
