Key Features • Multicellular • Photosynthetic • Alternation of generations- All plants have a haploid-diploid life cycle in which haploid gametophytes alternate with diploid sporophytes
Haploid/Diploid • Haploid- a cell with 1 set of chromosomes. Often designated as “n” • Diploid- a cell with 2 sets of chromosomes. Often designated as “2n”
Mitosis/Meiosis • Mitosis- Cell division that produces 2 daughter cells that are identical to each other and to their parent cell. Occurs in both haploid and diploid cells • Meiosis- Cell division of a diploid cell that produces four haploid daughter cells, or gametes
Gametophyte/Sporophyte • “phyte” means plant • Anytime you have “gamete” as part of a word it refers to something that is haploid. • Gametophyte is a plant that is haploid. • Sporophyte is a plant that is diploid.
Must Know Terms • Sporangium- plant organ that makes the haploid spores • Gametangium- plant organ that makes the haploid gametes • Archegonium- female gametangia (makes eggs) • Antheridium- male gametangia (makes sperm)
Must Know Terms • Homosporus- spores the resulting gametophytes identical (characteristic of non-vascular plants) • Heterosporus spores and resulting gametophytes not identical (characteristic of vascular plants • Megaspore- spore of the female gametophyte • Microspore- spore of the male gametophyte
Alternation of Generations • The diploid generation is known as the sporophyte • Certain cells of the sporophtye undergo meiosis to produce haploid spores • These spores germinate, then divide by mitosis and develop into multicellular, haploid plants called gametophytes • The gametophyte produces male and female haploid gametes by mitosis • The gametes fuse to form a diploidzygote, which will develop into a diploidsporophyte
Plant Origins • Thought that a member of Chlorophyta gave rise to land plants • Evidence that is thought to support this is 1. Green algae and plants have similar chlorophyll 2. Green algae and plants store food as starch and have cellulose in their cell walls. 3. DNA comparisons have shown that green algae are plant’s closest living relative.
Transition to Land • Plants are thought to have made the transition to land 400 mya • They were able to invade land because the evolution of their conducting tissues, cuticle, stomata, and seeds made them progressively less dependent on external water for reproduction
Transition to Land • Need to note that the fossil record does not indicate which member of the kingdom Chlorophyta evolved into plants, nor does the fossil record indicate how or in which order green algae evolved the previously mentioned structures.
Major Plant Divisions • Nonvascular • Vascular seedless • Vascular seed plants
Nonvascular • Nonvascular plants are commonly grouped together as “Bryophytes”. In actuality, there are 3 Divisions of nonvascular plants. • Hepaticophyta- the liverworts • Anthocerophyta- the hornworts • Bryophtya- the mosses
Primary Characteristics • Gametophyte is green, manufactures own food • Gametophyte large and conspicuous (compared to sporophtye) • Sporophyte smaller than and derives food from gametophyte • Sporophyte may be completely enclosed in gametophytic tissue • Lack vascular tissue
Primary Characteristics • May or may not have distinct leaves and stems • No anatomical differentiation between roots and shoots • Possess colorless, non-absorptive, anchoring rhizoids • The do not have lignin. Size is therefore limited. • All are homosporous
Ecology • Common in temperate and tropical moist habitats • Most abundant plants in Arctic and Antarctic, rare in deserts • Require free water for growth and reproduction • Sensitive to pollutants
Hepaticophyta • Liverworts • Some have liver-shaped gametophyte that grows flat on the ground (thallose), some are leafy • Some have moss-like growth form • Sporophytes are generally unstalked and held within the gametophyte
Anthocerophyta • Hornworts • Gametophytes resemble those of liver-shaped liverworts • Sporophytes are elongate, erect sporangia that resemble horns
Bryophyta • Mosses • Gametophytes are always leafy, tufted, or creeping • Small, simple leaves spirally arranged on stem • Sporophytes yellowish at maturity and bear capsule near the tip
Moss Life Cycle • The plant that we are most familiar with is the haploid gametophyte. • The gametophyte forms haploid gametes through mitosis • The sperm swims through a film of water (remember the need for free water) and fertilizes the egg, forming a diploid zygote which is retained in the archegonium
Moss Life Cycle • The zygote develops through mitosis into a small sporophyte that remains attached to the gametophyte • The sporophyte produces haploid spores by meiosis • The spores are released and may germinate to become a gametophyte.
Differences • Hornworts resemble thallose liverworts. Difference is determined by sporophyte
Differences • Mosses always have a stem and leaves, not all liverworts do • Liverwort leaves are all in one plane, mosses leaves are arranges radially around the stem • The capsules and seta (stalk) of mosses are green, red, or brown depending on age. Capsules of liverworts are dark brown to black and oval. Seta are transparent to clear.
Differences • Leaves of mosses may have serrations, hairs, or a midrib that goes to the tip. They do not have large indentations. Leaves of liverworts never have a midrib and often are lobed.
Vascular Plants • In the vascular plants, specialized groups of conducting cells (called vessels) impregnated with the stiffening substance lignin, serve both supportive and conducting features. • Large, dominant, nutritionally independent sporophytes • Specialized leaves, stems, roots, cuticles and stoma
Vascular Plants • Heterospory- a plant regularly forms two different kinds of spores, one of which gives rise to to egg-producing gametophytes, and the other of which gives rise to sperm-producing gametophytes • Secondary growth- primary growth is cell division at the tips of stems and roots. Secondary growth results from the division of a cylinder of cells around the periphery, increasing diameter
Conducting Systems • Sieve elements- soft walled phloem cells carry carbohydrates away from area where they were manufactured • Tracheary elements- hard walled xylem cells that transport water and minerals up from the roots
Seedless Vascular Plants • There are four living divisions • Pterophyta- ferns • Psilophyta- whisk ferns • Lycophyta- club mosses • Sphenophyta- horsetails
Pterophyta • Ferns • Nearly all are homosporous • Sporophyte generation is dominant • Spores are produced in sporangia called sori • Have specialized leaves, roots, and vascular tissue
Fern Life Cycle • Gametophytes are green and resemble liverwort gametophytes • Archegonia (eggs) form on lower surface near the apical notch (see page 671) • Antheridia (sperm) form on lower surface near the tip • Mature sperm swim to archegonia to produce the zygote (requires free water)
Fern Life Cycle • Zygote develops into the sporophyte • Is nutritionally independent, typical fern form • Possess horizontal stem called a rhizome. True roots develop off the rhizome • Photosynthetic fronds arise from the rhizome
Fern Life Cycle • Coiled bud stage of fronds is called a “fiddlehead” • Sporangia develop on fronds • Meiosis produces haploid spores • Spores are released and form gametophytes
Psilophyta • Whisk Ferns • Two living genera • Vascular structure the same throughout the plant • No true leaves • Dichotomous branching in the stems • Sporangia form on stems • Homosporous