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