Plants A Freshmen Overview Ya dig.
What are plants? • Plants are • Multicellular: made of more than 1 cell • Photosynthetic: make food and energy from sun • Eukaryotes: cells have membrane bound organelles • Their cells are surrounded by a cell wall made of cellulose. • Most reproduce sexually (pollen), but some can reproduce asexually (spores).
Evolution:Where do today’s plants come from? • Ancestors of today’s plants date back 450 million years ago. • Plants evolved from living in an underwater environment to living on dry land. They still required lots of water to survive so retaining water was very important. • Plants also adapted to have a stronger structure so that they could hold themselves up in order to take in the most amount of sunlight possible to start photosynthesis.
Bryophytes & Tracheophytes • Two groups emerged based on their structures, bryophytes and tracheophytes. • Bryophytes (mosses): Have NO vascular tissue. Must live in very wet areas and need a lot of water to survive . They stop growing during dry spells.
Bryophytes & Tracheophytes cont. • Tracheophytes: the first true land plants and have vascular tissues that transport water and nutrients to help the plants be more able to live in different places. • ferns • Gymnosperms: plants with cones: conifers, evergreens • Angiosperms: flowering plants
Gymnosperms and Angiosperms • Gymnosperms (evergreens, conifers) introduced the world to seeds, cone-shaped structures that hung on the outside of the plant. • Angiosperms (flowering plants) mature more quickly than gymnosperms by the use of flowers and seeds as reproduction tissues.
Adaptations for land • Roots: They anchor the plant into the ground and absorb nutrients and water from the soil. • Leaves: Broad and flat leaves allow more surface area to take in sunlight for photosynthesis and little openings in the leaf called stomata for gas exchange and preventing water loss • Vascular Tissue: Xylem and phloem carry nutrients and products of photosynthesis through the plant to where they need to go.
Adaptations for land cont. • Stems: Hold up leaves to capture as much light as possible. • Gametes and spores: Zygotes that a fertilized through a sperm grows into a sporophyte, creates spores through meiosis. The spores disperse and create gametophyte plants that can either produce sperm or be fertilized by them. • Pollen and Seeds: Pollination through pollen grains that produce sperm is carried by insects or the wind. Fertilization occurs when the female flower come in contact with the pollen grain