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20.1 Origins of Plant Life Chapter 20 : Plant Diversity 20.1 Origins of Plant Life KEY CONCEPT Plant life began in the water and became adapted to land. Land plants evolved from green algae. • Plants and green algae have many common traits: –photosynthetic eukaryotes –have the same types of chlorophyll –use starch as a storage product –have cell walls with cellulose 20.1 Origins of Plant Life • Genetic analysis points to the common ancestor of all plants. – extinct green algae species in class Charophyceae – modern charophyceans common in lakes and ponds 20.1 Origins of Plant Life • Important plant characteristics likely originated in charophyceans. – multicellular body allowing for specialization of cells and tissues – cell division that allows for chemical communication between cells – reproduction involving sperm swimming to egg 20.1 Origins of Plant Life 20.1 Origins of Plant Life Plants have adaptations that allow them to live on land. • Challenges of living on land have selected for certain plant adaptations. • A cuticle allows plants to retain moisture. – waxy, waterproof layer – holds moisture in • Stomata are tiny holes in the cuticle. – can open and close – allow air to move in and out 20.1 Origins of Plant Life • A vascular system allows resources to move to different parts of the plant. – collection of specialized tissues – brings water and mineral nutrients up from roots – disperses sugars from the leaves – allows plants to grow higher off the ground water and mineral nutrients sugars 20.1 Origins of Plant Life • A seed is a storage device for a plant embryo. – seed coats protect embryos from drying wind and sunlight – embryo develops when environment is favorable 20.1 Origins of Plant Life • Pollen grains allow for reproduction without free-standing water. – pollen grains contain a cell that divides to form sperm – pollen can be carried by wind or animals to female structures 20.1 Origins of Plant Life • Plants have adaptations that prevent animals from eating them. – spines and thorns – defensive chemicals 20.1 Origins of Plant Life KEY CONCEPT Plants can be classified into nine phyla. Mosses and their relatives are seedless nonvascular plants. • Nonvascular plants grow close to the ground to absorb water and nutrients. • Seedless plants rely on freestanding water for reproduction. • Liverworts belong to phylum Hepatophyta. – often grow on wet rocks or in greenhouses – can be thallose or leafy 20.1 Origins of Plant Life • Hornworts belong to phylum Anthocerophyta. – found in tropical forests and along streams – flat, lobed body with little green “horns” 20.1• Mosses Originsbelong of Plant Life Bryophyta. to phylum – most common seedless nonvascular plants – sphagnum moss commonly used by humans as “peat” 20.1 Origins of Plant Life 20.1 Origins of Plant Life Club mosses and ferns are seedless vascular plants. • A vascular system allows club mosses and ferns to grow higher off the ground. • Both need free-standing water for reproduction. • Club mosses belong to phylum Lycophyta. – not true mosses – oldest living group of vascular plants 20.1 Origins of relatives Plant Life • Ferns and their belong to phylum Pterophyta. – whisk ferns and horsetails are close relatives of ferns – ferns have large leaves called fronds frond fiddlehead 20.1 Origins of Plant Life Seed plants include cone-bearing plants and flowering plants. • Seed plants have several advantages over their seedless ancestors. – can reproduce without free-standing water, via pollination – pollination occurs when pollen meets female plant parts – seeds nourish and protect plant embryo – seeds allow plants to disperse to new places 20.1 Origins of Plant Life • Gymnosperms do not have seeds enclosed in fruit. – most gymnosperms are cone-bearing and evergreen. – the cone is reproductive structure of most gymnosperms. – pollen is produced in male cones. – eggs are produced in female cones. – seeds develop on scales of female cones. 20.1 Origins of Plant Life • Conifers are gymnosperms in Phylum Coniferophyta. – most common gymnosperms alive today – includes pines, spruce, cedar, fir, and juniper 20.1 Origins of Plant Life • Angiosperms have seeds enclosed in some type of fruit. – A flower is the reproductive structure of angiosperms. – A fruit is a mature ovary of a flower. • Angiosperms, or flowering plants, belong in Phylum Anthophyta. 20.1 Origins of Plant Life Flowering plants have unique adaptations that allow them to dominate in today’s world. • Flowers allow for efficient pollination. – animals feed on pollen or nectar – pollen is spread from plant to plant in process 20.1 Origins of Plant Life • Fruit allows for efficient seed dispersal. – a fruit is flower’s ripened ovary – Surrounds and protects seed(s) – Many forms, each function in seed dispersal 20.1 Origins of Plant Life Botanists classify flowering plants into two groups monocots and dicots • A cotyledon is an embryonic “seed leaf.” • Monocots have a single seed leaf. – leaf veins usually parallel – flower parts usually in multiples of 3 – bundles of vascular tissue scattered in stem 20.1 Origins of Plant Life • Dicots have two seed leaves. – leaf veins usually netlike – flower parts usually in multiples of 4 or 5 – bundles of vascular tissue in rings in stem 20.1 Origins of Plant Life Flowering plants are also categorized by stem type and lifespan. • Stem type can be woody or herbaceous. – Wood is a fibrous material made up of dead cells. – Wood has high concentrations of lignin and cellulose. – Woody stems are stiff. Oak 20.1 Origins of Plant Life – Herbaceous plants have no woody growth - only green stems and leaves Iris 20.1 Origins of Plant Life • There are three types of plant life spans. – Annuals mature from seed, flower, and die in one year. Wheat 20.1 Origins of Plant Life – Biennials take two years to compete life cycle. Foxglove 20.1 Origins of Plant Life – Perennials live more than two years. Big bluestem