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Chapter 19
Plant Diversity
19.1 Land plants evolved from green algae
Origins of Plants from AlgaeCharophytes
Modern charophytes found in shallow fresh water around edges of ponds and lakes
Adaptations to land ~475 m-y-a
plant: a multicellular autotroph in which the embryo develops within the female parent
Challenges of Life on Land
Obtaining resources
Staying upright
Maintaining moisture
Reproducing
Obtaining resources
Algae - resources from water only
Plants - resources from soil and airRoots and shoots
vascular tissue: system of tube-shaped cells that branches throughout the plant
Soil= water and minerals
Air = sunlight as energy, use CO2
Staying Upright
Algae stay upright by buoyancy
Plants need support lignin: a chemical
that hardens the
plants’ cell walls
Maintaining Moisture
Need to maintain water level within cuticle: waxy coating of leaves and other parts to retain water
Cacti, apples
stomata: pores in leaf’s surface that allows gas exchange
Regulated by guard cells
Reproducing on Land
Water provides means of dispersal and prevents gametes from drying outPlants produce gametes in a “jacket” of protective cells
Prevents dehydrationMost are carried in pollen grains
Eggs are fertilized and develops into an embryo in the female parent; dispersed as seeds in protective coats
Plant Diversity Origin of plants from charophytes; aquatic algal ancestorsBryophytes: mosses and relatives
No seeds or lignin
Pteridophytes: fernsLigin-hardened vascular tissue, no seeds
Gymnosperms: conifersSeeds without protective coat
Angiosperms: flowering plantsSeeds in protective organs, ovaries
Alternation of generationsAlternation between haploid and diploid forms
gametophyte: haploid generation that produces gametes sporophyte: diploid generation that produces spores
Spores - develop into new organism on its ownSome have tough coats to survive in harsh environments
Gamete - needs to fuse with another to form a zygote
Not adapted to harsh conditions
19.2 Bryophytes
Includes mosses and relatives
Described as nonvascular plants because they lack the lignin-hardened vascular tissue
Some do have tubular cells
Male and female gametes produced separate locations
Sperm fertilizes the egg and the zygote forms a stalk-like structure that produces spores
Mosses
Many gametophyte plants in a tight pack
Sporophytes are stalks
SpongyAbsorb water
Hornworts
Hornlike sporophytes
Liverworts
19.3 Pteridophytes
Ferns
Lignin-hardened tissuesVascular tissue for water and sugar transport
Dominated Carboniferous period
Organic compounds formed fossil fuelsHeat and pressure
Reproduction
Sporophyte is dominant generation
Creates gametophytes
Gametophytes have sperm and eggs
Ferns
Most diverse and widespread
12,000 species
Large leaves
Shady forests
Some in deserts
Club “Mosses”
Looks like a little pine tree
Common on forest floors
Carboniferous ~40m
Horsetails
Marshy sandy areas
Carboniferous ~15m
Outer layer is silicaUsed as scouring pad
19.4 Gymnosperms
Bear seeds that are not enclosed in an ovary
AdaptationsSmaller gametophyte
Pollen
Seeds
Succeeded when temperatures dropped; ferns began to disappear
Smaller Gametophytes
Sporophyte is more highly developed
Pine tree is the sporophyte
Gametophytes live in cones
Pollen
Small male gametophytes that develop into sperm
Carried from male to female cones by wind
Evolved to travel without water
Seed
Consists of a plant embryo packaged along with a food supply within a protective coat
Reproduction
Cone contains spore sacs
Spores develop into pollen grains (male)
Ovules (female) hold and help gametophyte grow
Pollen blown by wind to female coneSperm mature and fertilize eggs
Develops into embryo; new plant
Pine Cone GrowthMale Cone
Female Cones
Ginkgos & Gnetophytes
Ginkgo biloba: only species of ginkgophytes
Fleshy seeds that look like fruit
Tolerates air pollution
GnetophytesMormon Tea; desert shrub
Cycads & Conifers
Conifers (Coniferophyta)
Most are evergreens
Spruce, pine, fir, juniper, cedar
Cycads
(Cycadophyta)Large, palm-like leaves
(not actual palms)
Form a cone
19.5 Angiosperms19.5 Angiosperms
Flowering plantsFlowering plantsGametophytes develop with the flowers of Gametophytes develop with the flowers of the sporophytethe sporophyte
Flower: specialized plant shoot for Flower: specialized plant shoot for reproductionreproduction
Attract insects and animals to transfer Attract insects and animals to transfer pollenpollen
Reproductive Structures
Male = stamens anther - pollen grains
Female = carpelsOvary at base
Embryo sacs develop within ovules
Stigma receives sperm
Reproduction
Pollen lands on sticky stigma Tube grows from each pollen grain down toward an ovuleTwo sperm cells are released One sperm fertilizes an egg cell
Produces zygote --> embryo
Second sperm fuses with nuclei which develops into the endospermOvule develops into a seedOvary wall thickens and forms a fruit
Monocots & Dicots
MonocotsParallel leaf veins
Petals in multiples of 3
Lilies, orchids, palms, grasses
DicotsBranched leaf veins
Petals in multiples of 4 or 5
Poppies, roses, sunflowers, oaks
Amborella & Water Lilies
Amborella“living fossil”Only surviving species of oldest branchOnly found in New Caledonia
Water LilliesEvolved before monocots and dicots
Star Anise & Others
Evolved before monocots and dicots
Fruit is called Chinese Star
Human Dependence
Crops; corn, wheat, rice, and other grainsFruits of grass speciesFeed for cows and chickens
Harvested for furniture, medicines, perfumes, decorations, and clothing fiber (cotton)Only 280,000 known plant species5000 species investigated for potential medicine sourcesHumans may be destroying plants that we could use for medicine
Cotton
Cotton-top Tamarin