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Introduction to Plants The First Plants The earliest photosynthetic organisms were plant-like protists. Even today about 70% of photosynthesis occurs in the oceans. Non-vascular Plants The earliest land plants were non-vascular plants. Non-vascular plants have no system of vessels to carry nutrients, water or waste. These mosses, liverworts, and hornworts evolved about 500 mya from green algae. Non-vascular Plant Reproduction They need a moist surface for gametes to swim together for reproduction. Non-vascular plants lack true leaves, roots or stems. All water, nutrients and waste move between cells by osmosis and diffusion. Their growth is limited. Plant Adaptations to Land The major adaptations to life on land included: 1. Protection from drying out – leaves and stems. 2. A system of vessels to transport water, nutrients and wastes – the roots, stems and leaves. 3. A system to hold the plant up and capture energy from light – the stem and leaves. Vascular Plants - Ferns As plants adapted to land they evolved more complex structures. Ferns were the first vascular plants. Ferns have vascular tissue or vessels that transport materials between different parts of the plant. Ferns have true roots to anchor them and absorb water and minerals. Fern leaves are photosynthetic and absorb gases from the atmosphere. Plants with Seeds Next plants evolved to have seeds, an evolutionary adaptation to improve reproductive success. Seeds allow a plant to reproduce sexually without needing water for the gametes to swim to each other. Gymnosperms Gymnosperms are plants that produce “naked seeds”. Gymnosperms include all the conifers or pine trees that produce cones. Angiosperms The most recent evolutionary adaptation for plants was to produce flowers, again to improve reproductive success. Angiosperms are flowering plants. The seeds of angiosperms are protected in the body of a fruit, which develops from the ovary . Links http://www.teachersdomain.org/asset/oer0 8_vid_flowers/ http://www.teachersdomain.org/asset/tdc02 _img_insideseed/ http://www.teachersdomain.org/asset/lsps0 7_int_seedplant/