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Unit 7 Plants Ch. 22 Plant Diversity What is a Plant? Plants are multicellular eukaryotes that have cell walls made of cellulose They develop from multicellular embryos & carry out photosynthesis using the green pigments chlorophyll a & b What Plants Need to Survive The lives of plants center on the need for light, water & minerals, gas exchange, & the transport of water & nutrients throughout the plant body What Plants Need to Survive Plants use the energy from the sun to carry out photosynthesis All cells require a constant supply of water, so plants must obtain & deliver water to their cells Plants require oxygen for cellular respiration, & carbon dioxide for photosynthesis Early Plants For most of Earth’s history, plants did not exist The first plants evolved from an organism similar to the multicellular green algae living today Early Plants The oldest known fossils of plants are almost 450 million years old, Cooksonia, a moss plant Overview of the Plant Kingdom The plant kingdom is divided into 4 groups based on 3 features: water-conducting tissue, seeds, & flowers Overview of the Plant Kingdom There are 235,000 flowering plant species, almost 90% of all living species of plants Bryophytes Bryophytes - includes:mosses, liverworts, & hornworts, nonvascular plants Bryophytes have life cycles that depend on water for reproduction Lacking vascular tissue, they can draw up water by osmosis only a few centimeters above ground Groups of Bryophytes Mosses are the most common, & grow in areas of water: swamps & bogs, etc. They lack vascular tissue, which means they do not have true roots Rhizoids - long, thin cells that anchor them in the ground & absorb water & minerals from surrounding soil Groups of Bryophytes Liverworts are odd little plants that look like flat leaves attached to the ground, some species resemble the shape of a liver Groups of Bryophytes Hornworts are generally found in soil that is damp nearly year-round Human Use of Mosses In certain environments, dead sphagnum moss forms thick deposits of peat Peat can be cut from the ground & burned as fuel, or used in gardening because it can improve the soil’s ability to retain water Seedless Vascular Plants Vascular tissue - specialized to conduct water & nutrients throughout the plant Evolution of Vascular Tissue: A Transport System Tracheids - thick cells that resist pressure, key cells in xylem Xylem - transport system that carries water from roots to every part of a plant Phloem - transports solutions of nutrients & carbs produced by photosynthesis Evolution of Vascular Tissue: A Transport System Both forms of vascular tissue (xylem & phloem) can move fluids through the plant body, even against the force of gravity Lignin - makes cell walls rigid, enables vascular plants to grow upright & reach great heights Ferns & Their Relatives Seedless vascular plants that include: club mosses, horsetails, & ferns Ferns have true roots, leaves, & stems Roots - underground organs that absorb water & minerals Leaves - photosynthetic organs that have 1 or more bundles of vascular tissue Ferns & Their Relatives Veins - vascular tissue (xylem & phloem) gathered together Stems - supporting structures that connect roots & leaves, carrying water & nutrients between them Club Mosses Small plants that live in moist woodlands The most common club mosses look like miniature pine trees, called “ground pines” Horsetails Named because its stems look similar to horses’ tails During Colonial times, horsetails were commonly used to scour pots & pans Ferns Ferns have true vascular tissues, strong roots, creeping underground stems (rhizomes), & large leaves (fronds) Seed Plants Seed plants are divided into 2 groups: gymnosperms & angiosperms Gymnosperms - have their seeds directly on the surfaces of cones Angiosperms - (flowering plants) - have their seeds within a layer of tissue that protects the seed Reproduction Free From Water Adaptations that allow seed plants to reproduce without water include flowers or cones, the transfer of sperm by pollination, & the protection of embryos in seeds Reproduction Free From Water Cones - the seed-bearing structures of gymnosperms Flowers - the seed-bearing structure of angiosperms Reproduction Free From Water Pollen grain - plant sperm Pollination - the transfer of pollen from male reproductive structure to female reproductive structure Reproduction Free From Water Seed - an embryo of a plant that is encased in a protective covering & surrounded by a food supply Embryo - an organism in its early stage of development Reproduction Free From Water Seed coat - surrounds & protects the embryo & keeps the contents of the seed from drying out Gymnosperms - Cone Bearers Gymnosperms include: gnetophytes, cycads, ginkgoes, & conifers Gnetophytes only have 2 huge leathery leaves, which grow continuously & spread across the ground Gymnosperms - Cone Bearers Cycads are palm-like plants that reproduce with large cones, typically found in tropical places Gymnosperms - Cone Bearers Ginkgo may be one of the oldest seed plant species alive today Often planted around temples in China Today, they are planted in urban areas where their toughness & resistance to air pollution make them popular shade trees Gymnosperms - Cone Bearers Some conifers like the bristlecone pine tree can live for more than 400 years Others like the giant redwoods, can grow to more than 100m in height Gymnosperms - Cone Bearers Today, conifers thrive in a wide variety of habitats in several biomes Most conifers are “evergreens” - they keep their leaves throughout the year Angiosperms - Flowering Plants Angiosperms develop unique reproductive organs known as flowers Flowers contain ovaries, which surround & protect the seeds Fruit - a wall of tissue surrounding the seed Diversity of Angiosperms Monocots & dicots are the 2 classes of angiosperms They are named for the # of seed leaves, or cotyledons, in the plant embryo Monocots - 1 seed leaf Dicots - 2 seed leaves Cotyledon - the first leaf or first pair of leaves produced by the embryo of a seed plant Characteristics of Monocots & Dicots Diversity of Angiosperms There are 3 categories of plant life spans: annual, biennial, & perennial Annuals - flowering plants that complete a life cycle within one growing season Diversity of Angiosperms Biennials - angiosperms that complete their life cycle in 2 years Perennials - flowering plants that live for more than 2 years