Chapter 23
The overall category of plants are 1) eukaryotic 2) multicellular 3)organisms capable of photosynthesis 4)built with cellulose 5) and have alternation of generations. Plants most likely first emerged during the Paleozoic era as an offshoot of green algae Green algae and plants both are the only organisms to contain chlorophyll a and b They also are highly similar based on RNA sequence analysis Unlike algae, plants have a protected embryo
All plants have a unique life cycle called the alternation of generations In the AofG life cycle, two multicellular individuals alternate and produce each other. The two individuals are 1) the sporophyte, which represents the diploid generation 2) the gametophyte, which represents the haploid generation
The sporophyte (2n) generation gets its name because of the spores it produces through meiosis Spores are haploid reproductive cells, but they don t need to fuse with another haploid cell to reproduce Instead, they go through mitosis and produce gametophytes The gametophyte (n) generation is named because of the gametes it produces Two gametes (egg and sperm) form a diploid zygote. The zygote undergoes a mitotic division to produce a sporophyte
Phyte means Growth of Gametophyte (n) Spore (n) Gamete (n) Sporophyte (2n) Zygote (2n)
In any given plant, only one of the two generations is dominant, or conspicuous In bryophytes, the gametophyte is dominant In seedless vascular plants, gymnoperms, & angiosperms, the sporophyte is dominant Flowering plants are so heavily dependent on sporophytes, the gametophyte is microscopic
Plant evolution can be marked by the four major events which broke them into their current 4 phyla The first event, which separated plant cells from algal cells, was formation of a protected embryo The embryo is held within the body of a female plant or female part of a plant Seed, petal, cones, etc The embryo is nourished and protected from the environment until it is capable of growth and development on its own The first plant phyla are nonvascular plants, also called Bryophytes (mosses, liverworts, hornworts)
Nonvascular plants have a leafy appearance, but they are not leaves because they don t transport any material. Nonvascular plants have difficulty with transporting water and nutrients, and therefore are highly reduced in size Gametophytes contain two reproductive structures Antheridia for producing sperm Archegonia for producing eggs A liquid film is produced (or the plant relies on water from the environment) for sperm to reach eggs
Hornworts have sporophytes that look like small green broom handles Broom handles carry on photosynthesis, but gain their nourishment from a filmy gametophyte at the base (I ll provide details about each class of organisms today, but you should be paying more attention to phyla characteristics)
Liverworts are characterized by flattened thallus (body) or a leafy appearance The lower surface contains hairlike extensions called rhizoids Rhizoids are root-like structures that dig into the soil The thallus also contains gemma cups Gemma cups are groups of cells that contain eggs, which detach in wind or rain and form a new plant
Mosses are found in nearly every ecosystem from the arctic to antarctic In ideal environments, they form large mats that cover the ground, rocks, or other plants Some only grow in rare, specific environments, such as copper moss or glowing cave moss Many plants are given the name moss even though they are not Irish moss, spanish moss, club moss
Peat moss is the most commercial form of moss Peat is one of the best plants in terms of it s ability to hold water. Peat can also be used as a fuel source
The next major event occurred 430 mya, and was the appearance of the first Seedless Vascular Plants Vascular tissue is specialized tissue for transporting nutrients and water throughout the plant Plants still have not formed seeds Xylem: conducts water and dissolved minerals upward from the roots Xylem are surrounded by a strong, waterproof compound called lignin Phloem: conducts sucrose and organic material throughout the plant
Club mosses are common in moist woodlands of the temperate zone They are characterized by a horizontal stem called a rhizome, which has multiple smaller aerial stems Club moss leaves also contain microphylls. A microphyll is only a single strand of vascular tissue Most club mosses are epiphytes, meaning they live on trees but are not parasites.
Ferns are the only members of the horsetail class that still exist today. Ferns have rhizomes like club mosses, but their branches form a whorl that looks like a horse s tail The plants are so rough and strong, Native Americans used them as scouring pads Fern leaves (called fronds) are large and conspicuous Ferns are also the only seedless vascular plant to have megaphylls (multiple strands of vascular tissue).
Ferns are harvested by florists and flower companies for bouquets and home and garden decorations. Tropical tree ferns are harvested because their wood is highly resistent to decay and termite infestation Ferns also have some medicinal value, such as astringents to stop bleeding and expectorants
The gymnosperms appeared relatively quickly next, about 400 mya. Gymnosperms are characterized by the presence of a seed. Seeds are a combination of an embryo, nutrients for the embryo, and a protective coat Seeds are highly resistive to drought, heat (to a point), rough terrain, and predators Even if they pass through a digestive system, they re still just as functional
Sylene Stenophylla
Seed plants are heterosporous, meaning they have two kinds of gametophytes Male gametophytes: drought-resistant pollen grains, carried by wind or animal pollinator to female gametophytes Unlike earlier plant phyla, no external water is needed for fertilization Female gametophytes: ovules which collect sperm and eventually form a seed Will be enclosed by a cone (or fruit in later generations) until ready for release
Conifers are plants that bear cones Conifers can grow to enormous heights (more than 300 ft) and live for incredible periods of time General Sherman (Sequoia): 2,500 years old Old Tjikko (Spruce): roots are 9,550 years old Conifers have thin leaves called needles that are covered in drought-resistant cuticle
Cycads grow naturally in the tropics, but are often used for landscaping as well Cycad trunks are unbranched, no matter their height
The only surviving member of ginkgoes are the Ginkgo biloba, or the maidenhair tree Ginkgoes are highly resistant to pollution and are often found in cities and parks Female fruits often give off a pretty ugly odor, so most of the trees seen in public are male Gnetophytes are the final phyla of gymnosperms. The 70 species are all extremely unique They are the closest relatives of angiosperms
The final major evolution of plants are the angiosperms Angiosperms emerged 200 mya and are characterized by the presence of flower structures. Flowers are reproductive structures that attract pollinators such as insects or birds, or use wind to pollinate Angiosperms were also the first to develop fruits for reproduction They contain 240,000 species, six times more than any other groups of plants Angiosperms live in all ecosystems (except arctic) and range from microscopic to 100 m in length
Flowering plants have two classes Monocots have one cotyledon in their seeds Eudicots have two cotyledons in their seeds Cotyledons are the seed leaves that nourish the developing embryos until they emerge from the ground and can begin their own photosynthesis
Angiosperms need creative ways of dispersing their seeds, which has resulted in many different flower types Wind-pollinated flowers Plain, unshowy Insect and bird-pollinated flowers Colorful and bright petals Night-blooming White and highly aromatic Fruit dispersal Flavorful; eaten by animals and deposited as waste
NIGHT
INSECT
HUMMINGBIRD
ANIMAL
WIND