[Solved] Explain the physiological basis of why a pill containing estrogen and progesterone can prevent pregnancy. Angiosperms: A large group of flowering plants whose seeds are enclosed within a fruit, comprising a vast majority of plant species. Gymnosperms: A group of seed-producing plants that includes conifers, cycads, Ginkgo, and gnetophytes, characterized by having naked seeds not enclosed in an ovary. Naked Seeds: Seeds not enclosed in an ovary or fruit, typical of gymnosperms like pine trees. Conifers: A group of cone-bearing seed plants with vascular tissue, mostly evergreens, that includes pines, spruces, and firs.