20.1 Origins of Plant Life KEY CONCEPT Plant life began in the water and became adapted to land.

20.1 Origins of Plant Life Land plants evolved from green algae. Plants and green algae have many common traits. – both are photosynthetic eukaryotes – both have the same types of chlorophyll – both use starch as a storage product – both 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 –Ancestral charophyceans lived in areas of shallow water. True plants evolved through natural selection. –Those that could survive longer dry periods were favored. –First true plants probably grew at edges of water. –True plants have embryos that develop while attached to female parent.

20.1 Origins of Plant Life True plants evolved through natural selection.

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

20.1 Origins of Plant Life Stomata are tiny holes in the cuticle. stoma –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. sugars water and mineral nutrients –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

20.1 Origins of Plant Life Lignin allows plants to grow upright. –hardens cell walls of some vascular tissues –provides stiffness to stems plant cells lignin

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 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 Plants evolve with other organisms in their environment. Plants and other organisms can share a mutualistic relationship. –a mutualism is an interaction in which two species benefit –plant roots and certain fungi and bacteria –flowering plants and their animal pollinators

20.1 Origins of Plant Life Plants have adaptations that prevent animals from eating them. –defensive chemicals –spines and thorns

20.1 Origins of Plant Life KEY CONCEPT Plants can be classified into nine phyla.

20.1 Origins of Plant Life Mosses and their relatives are seedless nonvascular plants. Nonvascular plants grow close to the ground to absorb water and nutrients. Seedless plants rely on free- standing 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 Origins of Plant Life Mosses belong to phylum Bryophyta. –most common seedless nonvascular plants –sphagnum moss commonly used by humans as “peat”

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 Plant Life Ferns and their relatives belong to phylum Pterophyta. frond fiddlehead –whisk ferns and horsetails are close relatives of ferns –ferns have large leaves called fronds

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 Cycads are gymnosperms in phylum Cycadophyta. –look like palm trees with large cones –grow in tropical areas

20.1 Origins of Plant Life Ginkgos are gymnosperms in phylum Ginkgophyta. –only one species alive today, Ginkgo biloba –grown in gardens and used in urban landscaping

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 KEY CONCEPT The largest phylum in the plant kingdom is the flowering plants.

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. – 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 based on seed type. 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 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. –Herbaceous plants do not produce wood. 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. There are three types of plant life spans. –Annuals mature from seed, flower, and die in one year. Foxglove

20.1 Origins of Plant Life –Annuals mature from seed, flower, and die in one year. There are three types of plant life spans. –Perennials live more than two years. Big bluestem – Biennials take two years to compete life cycle.

20.1 Origins of Plant Life KEY CONCEPT Humans rely on plants in many ways.

20.1 Origins of Plant Life Agriculture provides stable food supplies for people in permanent settlements. Botany is the study of plants. Ethnobotany explores how people in different cultures use plants.

20.1 Origins of Plant Life People started planting for harvest about 10,000 years ago. Teosinte –wild species “tamed” through artificial selection –farming requires people to stay in one place –farming helped more socially complex centers develop

20.1 Origins of Plant Life Plant products are important economic resources. Plant products have been traded for thousands of years. –spices commonly used as currency in Middle Ages –spurred seafaring expeditions in 1400s and 1500s

20.1 Origins of Plant Life Plant products contribute to economy on a global scale today. –grains, coffee, sugar, cotton, forest products –billions of dollars of plant products traded each year

20.1 Origins of Plant Life Plant compounds are essential to modern medicine. Pharmacology is the study of drugs and their effects on the body. Many drugs are derived from plants. –Salicin from willow trees is used in aspirin. –Alkaloids are potent plant chemicals that contain nitrogen. –Alkaloids such as taxol have anti-cancer properties.

20.1 Origins of Plant Life Some medical research focuses on properties of plant compounds. –studies plants used medicinally in traditional cultures –develop synthetic drugs based on plant compounds