BIOL120 Lecture Notes - Lecture 4: Phloem, Vascular Cambium, Archegonium
Document Summary
Naked seeds that are exposed on modified leaves rather than being enclosed within fruits. Strobili (cones: recognizable pollen cones, may have fleshy ovulate cones that make them look like fruits. 760 species of gymnosperms, about 250,000 species of angiosperms. Seeds are exposed and not completely enclosed within a fruit. Seeds result from a single fertilization of sperm and egg. Angiosperms: double fertilization with two nuclei of megagametophyte. Seeds evolved relatively late; allows success on land. Sexual biologic link (transfer of genes to next genera. Seed: embryonic plant combined with food supply and protective seed coat. Seed advantages: dormant seed allows survival of cold or drought; seed coat is a barrier; attract seed- eating animals; seeds include food for developing embryo. Adaptations for land: hollow pollen tube from microgametophyte delivers sperm to egg so fertilization in most sp. is possible without water; gametophytes are reduced in size and are nourished within the sporophyhte.