Chapter 19 Plant Diversity

19.1 Land plants evolved from green algae Origins of Plants from Algae Charophytes 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 air Roots 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 out Plants produce gametes in a “jacket” of protective cells Prevents dehydration Most 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 ancestors Bryophytes: mosses and relatives No seeds or lignin Pteridophytes: ferns Ligin-hardened vascular tissue, no seeds Gymnosperms: conifers Seeds without protective coat Angiosperms: flowering plants Seeds in protective organs, ovaries

Alternation of generations Alternation between haploid and diploid forms gametophyte: haploid generation that produces gametes sporophyte: diploid generation that produces spores Spores - develop into new organism on its own Some 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 Spongy Absorb water

Hornworts Hornlike sporophytes

Liverworts

19.3 Pteridophytes Ferns Lignin-hardened tissues Vascular tissue for water and sugar transport Dominated Carboniferous period Organic compounds formed fossil fuels Heat and pressure

Reproduction Sporophyte is dominant generation Creates gametophytes Gametophytes have sperm and eggs

Ferns Most diverse and widespread Large leaves Shady forests 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 silica Used as scouring pad

19.4 Gymnosperms Bear seeds that are not enclosed in an ovary Adaptations Smaller 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 cone Sperm mature and fertilize eggs Develops into embryo; new plant

Pine Cone Growth Male Cone Female Cones

Ginkgos & Gnetophytes Ginkgo biloba: only species of ginkgophytes Fleshy seeds that look like fruit Tolerates air pollution Gnetophytes Mormon Tea; desert shrub

Cycads & Conifers Conifers (Coniferophyta) Cycads (Cycadophyta) Most are evergreens Spruce, pine, fir, juniper, cedar Cycads (Cycadophyta) Large, palm-like leaves (not actual palms) Form a cone

19.5 Angiosperms Flowering plants Gametophytes develop with the flowers of the sporophyte Flower: specialized plant shoot for reproduction Attract insects and animals to transfer pollen

Reproductive Structures Male = stamens anther - pollen grains Female = carpels Ovary 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 ovule Two sperm cells are released One sperm fertilizes an egg cell Produces zygote --> embryo Second sperm fuses with nuclei which develops into the endosperm Ovule develops into a seed Ovary wall thickens and forms a fruit

Monocots & Dicots Monocots Dicots Parallel leaf veins Petals in multiples of 3 Lilies, orchids, palms, grasses Dicots Branched leaf veins Petals in multiples of 4 or 5 Poppies, roses, sunflowers, oaks

Amborella & Water Lilies “living fossil” Only surviving species of oldest branch Only found in New Caledonia Water Lillies Evolved 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 grains Fruits of grass species Feed for cows and chickens Harvested for furniture, medicines, perfumes, decorations, and clothing fiber (cotton) Only 280,000 known plant species 5000 species investigated for potential medicine sources Humans may be destroying plants that we could use for medicine

Cotton Cotton-top Tamarin