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Chapter 9: Diversity of Plant Life (Alternation of Generations…
Chapter 9: Diversity of Plant Life
The Three-Domain System
had to create more kingdoms when many things did not fit into either plant or animal kingdom
current classification of living organisms into three domains
domain is a taxonomic category above the rank of kingdom
Eukarya
includes all the eukaryotic kingdom
includes the kingdoms Plantae, Fungi, Animalia, and varied group of organisms often called the kingdom Protista
Protista includes unicellular and simple multicellular organisms
other three can be distinguished by modes of nutrition
members of Plantae are autotrophic
autotroph
:
self-feeder; an organism that can synthesize organic compounds from single inorganic ones
can make own food through photosynthesis
Fungi and Animalia cannot make own food and rely on external sources for nutrition
heterotroph
:
other feeder; organism that is incapable of synthesizing its own food and must obtain its nutrition from other organisms
animals are ingestive heterotrophs, engulf food and digest it internally
fungi secrete into surroundings enzymes that break down food, which is then absorbed
absorptive heterotrophs
:
organisms, such as fungi, whose mode of nutrition is to secrete digestive enzymes into a substrate and then absorb the products of digestion
includes many algae and fungi that were once considered plants
Archaea
a prokaryotic domain
include methane producers as well as organisms that live in hot springs and environments with high salt content
Bacteria
a prokaryotic domain
contains majority of prokaryotic organisms
Survey of Plant Kingdom
large groupings of similar organisms are called divisions or phyla
this kingdom includes 12 divisions with living representatives, including two divisions of green algae
other 10 often called land plants; all similar in retention of embryo (multicellular embryo develops while still enclosed in female gametangium)
embryophyte
:
a land plant in which the zygote develops into a multicellular embryo while still enclosed in the female gametangium
although some algae found on land, none retain embryos
land plants first evolved 420 million years ago from freshwater green algae along a common evolutionary path
plants in divisions Hepatophyta, Bryophyta, and Anthocerophyta lack vascular tissue, other seven divisions contain both xylem and phloem
all land plants produce spores and gametes at different stages of life cycles, but five divisions also produce seeds
members of one division of seed plants (Magnoliophyta) produce flowers
Division - Common Name - Vascular Tissue - Reproduction
Hepatophyta - liverworts - absent - no seeds
Bryophyta - mosses - absent - no seeds
Anthocerophyta - hornworts - absent - no seeds
Lycophyta - lycophytes - present - no seeds
Pterophyta - ferns, whisk ferns, horsetails - present - no seeds
Cycadophyta - cycads - present - naked seeds
Ginkgophyta - ginkgo - present - naked seeds
Coniferophyta - conifers - present - naked seeds
Gnetophyta - gnetophytes - present - naked seeds
Magnoliophyta - flowering plants - present - seeds in fruit
Alternation of Generations
antheridium
:
(pl: antheridia) male gametangium in which the male gametes, sperm, are produced
archegonium
:
(pl: archegonia) female gametangium in which the female gamete or egg is produced and housed
sporangium
:
(pl: sporangia) a structure in which spores are produced
sorus
:
(pl: sori) a cluster of sporangia found on a fern leaf
characteristic of land plants is life cycle with alternation of gametophyte and sporophyte generations
each cell in sporophyte generation has two sets of chromosomes, while cells in gametophyte generation have only one
links between two generations are fertilization and meiosis
haploid gametes fuse to form a diploid zygote, which develops into an embryo and then the mature sporophyte
in time, diploid sporophyte undergoes meiosis to produce haploid spores, which begin gametophyte generation
in mosses, the division of the gametophyte is conspicuous (gametophyte is the dominant form)
at certain times during the year, moss undergoes sexual reproduction, resulting in a sporophyte that is attached to and dependent on the gametophyte
gametophytes of mosses are usually either male or female
male gametophyte develops structures known as antheridia, where the sperm form
female gametophyte produces flask-shaped archegonia, each which contains a single egg cell
sperm will leave antheridium and swim to the archegonium of a female gametophyte, fertilize the egg, and form a zygote, which establishes the diploid sporophyte
sporophyte consists of a stalk and a capsule (sporangium)
stalk is embedded in the fame gametophyte and receives both water and nutrients from it
within sporangium, meiosis occurs, forming haploid spores
if spores land on suitable environment, will germinate into a threadlike structured called a protonate, from which the mature moss gametophyte develops
similar life cycles for liverworts and hornworts
vascular plants in Lycophyta and Pterophyta all share similar life cycle, with a dominant sporophyte and a small but free-living gametophyte
unlike mosses, it is the sporophyte stage of terms that is the dominant form
in sporophyte, sporangia generally form on the underside of the leafy frond, often clustered into sori
meiosis occurs in these sporangia, producing haploid spores
spores give rise to small, flat, often heart-shaped gametophytes that bear both archegonia and antheridia
sperm from the antheridia swim to the archegonia, fertilizing the eggs, but only one sporophyte will emerge from each gametophyte
although initially attached to the gametophyte, the sporophyte soon grows and becomes independent, while the gametophyte dies
gymnosperms have an extremely reduced, dependent gametophyte generation, with sporophyte generation being the dominant and familiar form
characteristic pollen and seed (or ovule) cones of the pine are the reproductive structures
pollen cone consist of sporophylls, which are modified leaves that bear microsporangia; two occur in each sporophyll
microspores are produced following meiosis in these microsporangia, which develops into the pollen grain that constitutes the male gametophyte generation
at the time the pollen grain is released from the cone, it consists of four cells (two body cells, one generative cell, and one tube cell)
pollen grains are carried to the seed cone, where they are trapped by sticky fluid
pollen grain germinates with the tube cell, producing a pollen tube that will eventually carry non flagellated sperm to the egg
seed cone larger and more complex structurally than pollen one
usually two ovules on each cone scale
ovules develop on upper surfaces of cone scales, which are arranged around a central axis
ovule is megasporangium surrounded by integuments, with opening (micropyle) facing the central axis
meiosis produces four megaspores within each ovule, but three dissolve
surviving megaspore develops into female gametophyte, which usually contains two archegonia, each with single egg, at maturity
while female gametophyte is developing, pollen tube is slowly growing through the surrounding tissue, while the generative cell within the pulled the divides to form two sperm
one sperm fertilizes the egg, giving rise to the new sporophyte generation
one embryo produced in ovule, with female gametophyte as its nutrient Aussie
as fertilized ovule develops into seed, integuments develop into seed coat
when seeds are mature, seed coat opens and sheds the seeds, which are wind dispersed
Liverworts, Mosses, and Hornworts
traditionally put together, but put into three different divisions (Hepatophyta or Marchantiophyta - liverworts; Bryophyta - mosses; Anthocerophyta - hornworts)
bryophyte can refer to any of these three
small plants generally restricted to moist environments, but many can withstand extended dry periods
estimated about 25,000 species of bryophytes
bryophytes are among first organisms to colonize barren areas and help retain soil and minerals in these areas
mosses have small appendages, similar to leaves
liverworts are either leafy or flat and ribbonlike
hornworts have flattened and somewhat lobed appearance
presence of stomata in sporophyte distinguishes mosses and hornworts from liverworts
in hornworts, find meristem near the base of the sporophyte that permits continued growth of the sporophyte under favorable conditions
peat moss (Sphagnum) grows in acid water, making water even more acidic
commonly used as potting/bedding material for gardeners since has great water-holding capacity
also has antiseptic properties, used medicinally until WWI
Lycophytes and Ferns
remaining divisions in plant kingdom are all vascular plants containing vascular tissue that conduct water and food through plant body
vascular plant
:
a general name for any plant that has xylem and phloem
vascular tissue
:
tissue that is specialized for the long-distance transport of water or photosynthetic products; xylem and phloem
division Lycophyta consists of club mosses, spike mosses, and quillworts; include prostrate forms found on forest floor and epiphytes
epiphyte
:
plant that grows on top of another plant for support and position
resemble mosses because stems covered with small, overlapping, scalelike leaves but have conducting tissue in roots, stems, and leaves
leaves of club mosses are very simple, single unbranched vascular bundle
in many species of Lycopodium (member of division Lycophyta), sporangia are arranged in compact cluster at end of erect or hanging stems; often have club-like appearance
division Pterophyta (aka Monilophyta) consists of horsetails, whisk ferns, and ferns
horsetails are small group of widely distributed plants in genus Equisetum that have ribbed, jointed, photosynthetic stems with whorls of tiny leaves that soon become brown and nonphotosynthetic
sporangia are grouped into bonelike structures at tops of some stems
interesting feature is presence of silica in cell walls, which makes stems abrasive
whisk farms are small group of primitive-looking vascular plants with only two genera- Psilotum and Tmesipteris
Psilotum consists of green, branching stems with tiny, scalelike appendages and globose yellow sporangia
ferns are largest group of nonseed vascular plants
about 12,000 species now
ferns that we are most familiar with have large divided leaves called fronds that arise from horizontal underground stem (rhizome), which also gives rise to roots
rhizome
:
a horizontal, underground stem
sporangia of some ferns borne on underside of fronds; distribution of sporangia helps in identification
young fern leaves first appear as tightly coiled fiddleheads, which gradually unroll as they grow
Gymnosperms
remaining five divisions in plant kingdom are all seed plants, the dominant vegetation in the world
seed plant
:
common term for gymnosperms and angiosperms
seeds found in either cones or fruits
in cones, seeds exposed at maturity and said to be ‘naked’ (gymnosperms)
gymnosperm
:
plants that bear naked or exposed seeds
angiosperm
:
a flowering plant whose seeds are contained within fruits
four divisions of gymnosperms - Coniferophyta, Cycadophyta, Ginkgophyta, and Gnetophyta
conifers are most familiar, include pines, spruces, yews, firs, cedars, redwoods, and larches
cone bearers, typically producing both pollen and seed cones
pollen cones are usually small and inconspicuous and produce pollen, while seed cones (aka ovulate cones), which produce seeds, are larger and often take several years to mature
pollen and seed cones may be on same or different trees
wind-pollinated
cycads are small group of short shrubs to moderate-sized, long-lived trees native to tropical and subtropical regions
leaves are large and palm like
most cycads bear cones
cycads are dioecious, with seed cones and pollen cones on separate individuals
pollinated by weevils and beetles
only about 250 species of cycads in 11 genera found today
rich in starch, which is found in roots, stems, and seeds, and have long history as food source and medicinal plants
contain toxic compounds which must be removed by processing starch before flour is used
concentration of BMAA highest in cycad reproductive structures, but also present in other parts of plant
present in modified roots called coralloid roots (short, wide, lateral roots that grow at soil surface and form a symbiotic relationship with cyanobacteria present within small vanities of root
symbiosis
:
a relationship in which two organisms live in intimate association with each other
the ginkgo biloba (maidenhair tree) is the only living species of the Ginkgophyta
today, popular in cities because of toleration for air pollution
moderate-sized tree with unique fan-shaped leaves that may or may bot be notched in the middle
seeds partially surrounded by fleshy coat that smells like rancid butter when seed is mature
dioecious, with separate male and female trees
Gnetophyta is very small group of gymnosperms with unusual morphological and anatomical features
three genera- Ephedra, Gnetum, and Welwitschia
Ephedra (commonly called Mormon tea) is economically important members
desert shrub that produces the alkaloids ephedrine and pseudoephedrine
leaves of tropical Gnetum are used as a vegetable in parts of central/west Africa
Welwitschia mirabilis possibly most unusual member of Gnetophyta
only species in the genus; produces a very long taproot and a short, barrel-shaped stem with two leathery traplike leaves that continue to grow throughout the life of the plant
may live for 1,000-2,000 years, and leaves split into strips as they age
Angiosperms
angiosperms (aka Magnoliophyta) are flowering plants
most widespread vegetation in world today
over 350,000 species; possibly as many as 1 million undescribed species in tropical forests
Amber: a Glimpse into the Past
many economically useful products derived from conifers
if conditions are right and resin is buried before it can oxidize, it fossilizes
amber is fossilized tree resin
amber mostly produced by conifers, but also a few angiosperms
resins from different tree species have slightly different chemical signatures
more than 200 species of angiosperms have been found fossilized in amber
amber especially good at preserving ancient DNA because the resin contains compounds that dry and fix living tissue and inhibit bacterial decomposition