unit 21 diversity of plants
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19.4 Origins of Plant Life
Unit 21
Plants
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
• 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
• 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 have adaptations that prevent animals from eating them.
– defensive chemicals
– spines and thorns
20.1 Origins of Plant Life
• What category of plants evolved directly from ferns?
• A. Flowering plants • B. Mosses • C. Charophyceans • D. Cone-bearing plants
20.2 Classification of Plants
KEY CONCEPT Plants can be classified into nine phyla.
20.2 Classification of Plants
• Mosses belong to phylum Bryophyta.
– most common seedless nonvascular plants– sphagnum moss commonly used by humans as “peat”
20.2 Classification of Plants
• 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
20.2 Classification of Plants
• Cycads are gymnosperms in phylum Cycadophyta.– look like palm trees with large cones– grow in tropical areas
20.2 Classification of Plants
• Ginkgos are gymnosperms in phylum Ginkgophyta.– only one species alive today, Ginkgo biloba– grown in gardens and used in urban landscaping
20.2 Classification of Plants
• Conifers are gymnosperms in phylum Coniferophyta.– most common
gymnosperms alive today
– includes pines, spruce, cedar, fir, and juniper
20.2 Classification of Plants
• 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.
20.2 Classification of Plants
• Which plants do not depend on free-standing water to carry sperm to eggs?
• A. Mosses • B. Ferns • C. Club mosses• D. Seed plants
20.2 Classification of Plants
• D. Seed plants
20.3 Diversity of Flowering Plants
KEY CONCEPT The largest phylum in the plant kingdom is the flowering plants.
20.3 Diversity of Flowering Plants
• Fruit allows for efficient seed dispersal. – Fruit is flower’s ripened ovary– Surrounds and protects seed(s) – Many forms, each function in seed dispersal
20.3 Diversity of Flowering Plants
• There are three types of plant life spans. – Annuals mature from seed,
flower, and die in one year.
Wheat
20.3 Diversity of Flowering Plants
– 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
20.3 Diversity of Flowering Plants
– 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.
20.3 Diversity of Flowering Plants
KEY CONCEPT Humans rely on plants in many ways.
20.3 Diversity of Flowering Plants
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.
20.3 Diversity of Flowering Plants
• 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
20.3 Diversity of Flowering Plants
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
20.3 Diversity of Flowering Plants
• 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
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