Important words and concepts from Chapter 29,
Campbell & Reece, 2002 (3/25/2005):
by Stephen T. Abedon (abedon.1@osu.edu)
for Biology 113 at the Ohio State University
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Course-external links are
in brackets Click [index] to access site index Click here to access
text’s website Vocabulary
words
are found below |
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(1) Chapter title: Plant Diversity I: The
Colonization of Land
(a)
[the colonization of land,
"colonization of
land" plants (Google Search)]
[index]
(a)
Plants evolved in terrestrial environments from a green algae ancestor which itself was presumably adapted to
very shallow waters, ones prone to drying
(b)
Plants resemble their ancestral algae in
terms of shared
(i)
Chloroplast types
(ii)
Cell-wall material (cellulose)
(iii)
Energy storage molecule (starch)
(iv)
Etc. (the etc. is actually rather important in this case since it
includes more meaningful shared derived characters than the above listed, but
nevertheless we’re not going to concern ourselves with these additional resemblances
here)
(c)
Plants
(i)
Are eukaryotic
(ii)
Are multicellular
(iii)
Display an alternation of generations
(alternating haploid and diploid generations)
(iv)
Are heteromorphic (morphologically differing
haploid and diploid generations)
(v)
Are autotrophic (they are the most important
terrestrial primary producers)
(vi)
Display various adaptations to terrestrial
life that differentiate them from their green algae ancestors
(vii)
Develop their embryos protected and nourished by maternal tissue (the
are “embryophytes”)
(d)
[“…single-celled algae, living in the cracks of rocks and in soil along
streams at least 450 million years ago, evolved into mosses that gradually
crept out of the water and became the first land plants.. Mesostigma, a scaly,
unicellular alga, [potentially lies] at the base of this freshwater algal line…
Others suggest that the Eve of the green plants that first took root on land
must resemble either Chara or Coleochaete algae, which still thrive in lakes
and streams today.” Kathryn S. Brown, 1999, Deep Green rewrites
evolutionary history of plants. Science 285:990-991]
(f)
[images of plants (1),
images of plants (2)
(Biology 122 –
(3) Plant
terrestrial adaptations
(a)
"Living on land poses very different problems from living in the
water. As plants have adapted to the terrestrial environment, complex
bodies with extensive specialization of cells for different functions have
evolved."
(b)
These innovations include
(i)
Waxy cuticles
(ii)
Stomata
(iii)
Development of the sporophyte as the dominant generation
(iv)
Vascular
tissue
(xylem and phloem, which are lignin-lined conduits of water and minerals up and
nutrients down stems, respectively)
(v)
Woody tissue (lignin)
(vi)
Pollen (considered next chapter)
(vii)
Seeds (considered next chapter)
(viii)
Flowers (considered next chapter)
(ix)
Fruit (considered next chapter)
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Challenges during Algae-to-Plant Transition: |
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Algae: |
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Plants: |
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(c)
Imagine the first "plant" as an algae with most of its
thallus "rooted" in the water but with a portion lifted slightly
above the water, or extending slightly past the shoreline, in a effort to
better compete against its fellow algae found only at and below the water line
(i)
Such an alga might not initially require a waxy cuticle (since
water would always be available from the portion of the organism found below
the water line and, especially, given humid environments), but might have given
those individuals who first displayed such a cuticle above the water line less
of a requirement for water movement within the algae from beneath the water to
beyond the water, therefore allowing slightly greater height and extension out
over the shore
(ii)
Once a waxy cuticle was in place, diffusion of gasses could limit
overall plant height (or spreading beyond the water), thereby selecting for
small holes (stomata) in the waxy cuticle
(iii)
In an effort to better control moisture retention, it would be
beneficial for the organism to selectively open and close the holes
(iv)
Such a algae could be essentially preadapted at this point to existing
in the presence of less water, e.g., periodic desiccation due to fluctuating
water levels
(v)
At this point the algae would be preadapted to survival in an
environment containing only periodic water (as opposed to periodic lack of
water)
(vi)
At some point during the above sequence we essentially have seen the
transition from status as a green alga to that of a moss
(d)
["adaptation to land"
plants (Google Search)]
[plants and their structure
(lots of great images) (Online Biology Book)]
[index]
(a)
The transition from a watery environment to a terrestrial one most
obviously involves an exposure to air
(b)
Air is drying (unless relative humidity is 100%)
(c)
Any organism periodically exposed to air must develop a means of
delaying desiccation
(d)
In plants a key innovation was the development of a waxy (essentially
waterproof) cuticle covering the plant body
(e)
This cuticle keeps water inside the plant, thus allowing prolonged
exposure to air
(g)
[waxy cuticle (Google Search)]
[index]
(a)
The trouble with a waxy cuticle is that along with waterproofing comes
air-proofing
(b)
That is, a waxy cuticle prevents the diffusion of O2 and CO2
into and out of the plant, interfering with carbon fixing as well as cellular respiration
(c)
The innovation that solved this dilemma were small, opening and closing
holes, called stomata, through which gasses can diffuse into and out of the
plant
(e)
[stomata (Google Search)]
[index]
(6) Sporophyte as
dominant generation
(a)
Like many algae, plants undergo an alternation of generations
(b)
In the ancestral algae as well as the morphologically more primitive
plants, the haploid generation is the more conspicuous (dominant) generation
(as we shall see in discussing plant life cycles,
below)
(i)
(indeed, the ancestral algae probably did not even display alternation
of generations, with the zygote the sole diploid stage)
(c)
In more morphologically complex plants (particularly, the vascular
plants) the sporophyte generation dominates
(d)
The big plants you see around you are all sporophytes (i.e., not gametophytes)
(e)
["dominant generation"
sporophyte (Google Search)] ["conspicuous
generation" sporophyte (Google Search)]
[index]
(a)
To a photoautotroph, lack of access to sunlight
can serve as a limit on growth and reproduction
(b)
In a world of very short plants, a plant which can grow taller may
be able to sequester increased access to sunlight, as well as decrease the
access of neighboring (and competing) short plants to sunlight
(c)
The trouble with growing tall, however, is that plants are also tied to
the soil for their access to water and other nutrients: roots need the energy
that comes from sunlight and leaves need water and other nutrients that come
from soil
(d)
One key innovation that allowed the development of height among plants
is vascularization, essentially cells (both dead and living) that transport
substances between the roots and the leaves
(e)
The alternative is simply diffusion across normal plant cells, a
process which is only so efficient or capable of supporting only so much
increase in plant height
(f)
["vascular tissue"
plant (Google Search)]
[xylem, phloem (Online Biology Book)]
[index]
(a)
Ultimately height is also limited by the ability of a plant to support
its own weight (in addition to the need for vascular tissue)
(b)
Lignin serves to rigidly bind together cellulose (together these form
wood), thus providing strong structural support to plants
(c)
Also important is the evolution of secondary growth, the ability of
stems to grow wide as well as long (the latter called primary growth)
(d)
Thus, woody plants could grow tall, shading out shorter plants
(f)
Cellulose (making up cell wall in all plants):
(g)
["woody tissue" plant
(Google Search)]
[plant secondary growth
(Google Search)]
[secondary growth (Online Biology Book)]
[index]
(h)
[lignin (Google Search)]
[image: structure of lignin
(Ray Fort)] [lignin holds keys to plants’
past, future (Warnell School of Forest Resources)] [aspen engineered to produce
less lignin (Environmental News Network)] [research on the effect of
lignin on paper permanence (Council on Library and
Information Resources)] [index]
(9) Plant divisions (called “phyla” by your
text and we will employ both descriptors interchangeably)
(a)
For plants, the term division has historically been employed in
the stead of the term phylum
(b)
Thus, plant taxonomic categories, going from largest to smallest, read:
domain, kingdom, division, class,
order, family, genus, species ("Do Keep D___ Clean Or Forget Getting
S___")
(c)
There are 12 (or, more recently, 10) recognized divisions (phyla) of
extant plants (these 10 are listed in Table 29.1)
(d)
Here we will only consider four of these (though we'll get a look at
some of the rest during lab)
(i)
Division Bryophyta, the mosses (an
example of a bryophyte)
(ii)
Division Pterophyta, the ferns (an example of a pteridophyte)
(iii)
Division Coniferophyta, the conifers (next chapter)
(iv)
Division Anthophyta, the angiosperms (next chapter)
(e)
See Figure 29.1, Some highlights of plant evolution
(f)
[“In crafting a phylogenic tree, Deep Green scientists confirmed that
classic categories like monocot (one seed leaf) and dicot (two seed leaves) often fail to group plants
accurately; that fungi are more closely related to animals than plants; and that some green algae are more like land plants than algae. Moreover… brown, red, and green [algae] each arose independently from a
common single-celled ancestor and thus deserve their own kingdoms. Overall [perhaps]
at least half the Linnaean classifications are wrong. ¶ [Various researchers]
would prefer to name plants according to clade, or genetically related group—a system called the
PhyloCode. For example, the herb Prunella vulgaris and hundreds of other
plants might simply go by the name vulgaris, with a tag in some master
directory that scientists could refer to for phylogenetic data… ‘A plant’s rank
is arbitrary, and naming it by clade is a far more relevant, practical way to
go. ¶ Not everyone agrees. ‘The new phylogenetic information is absolutely
wonderful, but renaming all these plants is going too far… A red oak is not a
white oak, and without rank, we lose the ability to make that distinction
easily.’ … Not too long from now… botanists will have to cope with two
systems—one Linnaean, the other cladistic.” Kathryn S. Brown, 1999, Deep Green rewrites evolutionary history of plants. Science
285:990-991]
(g)
[(Google Search)]
[kingdom Plantae
(many links) (Wendy’s Conservation Homepage)]
[Green Plant Phylogeny Research
Coordination Group (investigation of the evolutionary relationships
of plants)] [index]
(a)
The bryophytes are all non-vascular plants and
include three divisions (phyla), the most common of which is division (phylum) Bryophyta, the mosses (the other two are
division/phylum Hepatophyta, the liverworts; division/phylum Anthocerophyta,
the Hornworts)
(b)
When I speak of very primitive plants, it is the bryophytes of which I
am speaking, at least in terms of the most primitive, still-living plants
(c)
The bryophytes all lack vascularization or,
at least, vascularization that is as fully developed as that seen in vascular
plants
(d)
Consequent to their lack of efficient movement of nutrients between
soil and leaves, non-vascular plants are short
(e)
Other features of the bryophytes include
(i)
An inconspicuous sporophyte generation
(ii)
Reliance on motile sperm
(iii)
Reliance on haploid spores for
dispersal
(iv)
A lack of specialized roots
(f)
“Most photosynthesis occurs in the upper part of the plant, which has
many small stemlike and leaflike appendages. The “stems,” “leaves,” and “roots”
(rhizoids) of a moss, however, are not homologous to these structures in
vascular plants.” p. 553, Campbell et al.,
1999
(g)
Basically, the bryophytes are limited in where they live by the
availability of significant water as well as a requirement for protection from
desiccating sunlight, e.g., they live on forest floors
(h)
[Bryophte, Hepatophyta, Anthocerophyta (Google Search)]
[index]
(11) Division Bryophyta (moss)
(a)
Division/phylum Bryophyta are the bryophytes commonly called mosses.
(b)
[Bryophyta, division Bryophyta,
phylum Bryophyta, moss (Google Search)] [index]
(a)
Recall that plants exhibit an alternation of generations
(b)
To understand plants it is necessary to understand this alternation of
generations
(c)
To better understand alternation of generations as they occur in real
plants it is important to learn a number of terms that are applicable to plant
reproductive structures
(d)
The following terms are discussed by your text in conjunction with moss reproduction:
(i)
Gametophyte - multicelled haploid plant
(ii)
Sporophyte - multicelled diploid plant
(iii)
Sporangium - plant organ that makes the haploid spores
(iv)
Gametangium - plant organ
that makes the haploid gametes
(v)
Archegoneum
- female gametangia (makes eggs)
(vi)
Antherideum
- male gametangia (makes sperm)
(e)
The following terms are discussed by your text in conjunction with fern reproduction:
(i)
Homosporous - spores and resulting gametophytes
identical
(ii)
Heterosporous - spores and resulting gametophytes not
identical
(iii)
Megaspore - spore of the female gametophyte (makes
egg)
(iv)
Microspore - spore of the male gametophyte (makes
sperm)
(f)
We will also consider the life cycles of
(i)
A moss
(ii)
A fern
(iii)
A pine (next chapter)
(iv)
An angiosperm (next
chapter)
(g)
Remember to keep in mind the following as you walk through these life
cycles and various terms:
(i)
Any product of meiosis is haploid
(ii)
Any spore is haploid (at least as far as the plants
are concerned)
(iii)
Any mitotic product of a spore (i.e., gametophyte)
is haploid
(iv)
All gametes are haploid
(v)
Any product of fertilization is diploid
(vi)
Any zygote is diploid
(vii)
Any mitotic product of a zygote (i.e., sporophyte) is diploid
(h)
[plant reproduction
(Google Search)]
[seedless "plant
reproduction" (Google Search)] [index]
(a)
The gametophyte is the haploid plant
generation
(b)
Gametophytes mitotically produce haploid gametes
(c)
See Figure 29.6, Alternation of generations: a generalized scheme
(d)
[gametophyte (Google Search)]
[index]
(a)
The sporophyte is the diploid plant
generation
(b)
Sporophytes meiotically produce haploid spores
(c)
See Figure 29.6, Alternation of generations: a generalized scheme
(d)
See Figure 29.17, Sporophyte of Marchantia,
a liverwort
(e)
[sporophyte (Google Search)]
[index]
(a)
Spores are haploid cells
(b)
Spores are the first cell of gametophyte
generations
(c)
In seedless plants the spore is the means of plant dissemination
(d)
“A spore is a reproductive cell that can develop into a new organism
without fusing with another cell (in contrast to gametes, which cannot develop
into a multicellular organism; they must first fuse to form zygotes).” (p. 580,
Campbell & Reece, 2002)
(e)
See Figure 29.7, A fern
spore
(f)
[plant spore (Google Search)]
[index]
(a)
The sporangia are reproductive structures of the sporophyte
generation of plants (as well as fungi) in which haploid spores form via meiotic division
(b)
That is, the cells that make up the sporangium are diploid and members of the sporophyte generation
(c)
See Figure 29.8, Sporangium
of a hornwort (a bryophyte) sporophyte
(d)
See Figure 29.18, A moss
sporangium
(e)
See Figure 29.24, Fern
sporophyll, a leaf specialized for spore production
(f)
[sporangium (Google Search)]
[sporangia (Google Search)]
[index]
(a)
The gametangia are the reproductive structures of the gametophyte
generation of plants, in which haploid gametes form via mitotic division
(b)
That is, the cells that make up gametangia are haploid and are members of the gametophyte generation
(c)
The gametes produced within the gametangia are, of course, also haploid
(d)
See Figure 29.9, Gametangia
(e)
[gametangium (Google Search)]
[gametangia (Google Search)]
[index]
(a)
Archegonia are gametangia that produce eggs
(b)
[archegonium (Google Search)]
[archegonia (Google Search)]
[index]
(a)
Antheridia are gametangia that produce sperm
(b)
[antheridium (Google Search)]
[antheridia (Google Search)]
[index]
(a)
See Figure 29.16, The life
cycle of Polytrichum, a moss
(b)
Note particularly
(i)
The gametophyte generation is dominant
(ii)
The sporophyte generation is shorter lived and nutritionally
dependent on the gametophyte generation (the sporophytes are the things that
look like lamp posts in the figure)
(iii)
Sperm and egg are produced by separate (different) plants
(iv)
The sperm is released from the male plant and must travel though water
to the female plant
(v)
The egg, zygote, and embryo are all retained within the female
gametophyte
(vi)
The sporophyte grows up from within the female gametophyte
(vii)
The sporophyte produces and releases spores that grow
into gametophytes
(c)
[life cycle of moss
(Google Search)]
[index]
(a)
These are the vascular, non-seed bearing plants, the most common of
which are the members of division/phylum Pterophyta called ferns
(b)
(the others are members of division/phylum Lycophyta, which include the
club mosses)
(c)
See Figure 29.21, Examples
of pteridophytes (seedless vascular plants)
(d)
[Pteridophyte(s), Lycophyta (Google Search)]
[index]
(22) Division Pterophyta (fern)
(a)
Division Pterophyta, the ferns, are one of four divisions of seedless, vascular
plants
(b)
The ferns are able to capitalize on their ability to efficiently
transport nutrients back and forth between roots and leaves, thus achieving
height, and the advantages associated with greater height (outcompeting shorter
plants for access to light, for example)
(c)
Historically this allowed the ferns (and other seedless, vascular
plants) to achieve the status of the first trees, and the remains of these
first trees today exist as and within deposits of coal
(e)
However, the ferns and other seedless, vascular plants are still tied
to water for their reproduction, using motile sperm to achieve fertilization
(f)
Additionally, these plants employ haploid spores to achieve
dissemination, just as do the bryophytes
(g)
Besides possessing vascularization, the seedless, vascular
plants additionally differ from the bryophytes in terms of the fern (etc.) sporophyte
generation being dominant to the gametophyte generation
(h)
(based on molecular and additional evidence, recent additions to clade
Pterophyta are the horsetails and whisk ferns)
(i)
[division Pterophyta,
ferns, horsetails, whisk ferns (Google Search)]
[index]
(a)
Plants that produce spores of only a single morphology are considered
homosporous
(b)
Homosporous plants develop into bisexual gametophytes (bisexual meaning that individual plants display
both archegonia and antheridia)
(c)
Ferns (most, at least) are examples of homosporous plants
(e)
See unnamed figures found in the second column of p. 591
(f)
[homosporous (Google Search)]
[index]
(a)
Plants that produce spores of more than one morphology are considered
heterosporous
(b)
An example of heterosporous plants are the seed-bearing plants
(which do not produce bisexual gametophytes)
(c)
[“Among the ferns, those that returned to aquatic habitats during their
evolution—the water ferns—are the only heterosporous species. However, we will
see in Chapter 30 that the heterosporous condition was very important
in the evolution of seeds.”]
(e)
See unnamed figures found in the second column of p. 591
|
Gametes |
||||
|
Megasporangia |
Megagametophyte (female) |
Egg |
||
|
Microsporangia |
Microgametophyte (male) |
Sperm |
(f)
[heterosporous (Google Search)]
[index]
(a)
In the heterosporous (especially seed-bearing)
plants the megaspore gives rise to the egg-producing female gametophyte (which remains associated with the parental sporophyte)
(b)
[megaspore (Google Search)]
[index]
(a)
In the heterosporous (especially seed-bearing)
plants the microspore gives rise to the sperm-producing male gametophyte (pollen)
(b)
[microspore (Google Search)]
[index]
(a)
See Figure 29.23, The life
cycle of a fern
(b)
Note particularly
(i)
The sporophyte generation is the conspicuous generation
(ii)
The sporophyte does, nevertheless, still grow out of the gametophyte with all previous steps also very much resembling those of a moss including moss steps iv through vi
(iii)
The gametophytes tend to express both genders
on the same plant (i.e., individual plants produce both sperm and eggs)
(iv)
Just as with the moss, the sporophyte produces
and releases spores that grow into gametophytes
(c)
[life cycle of fern
(Google Search)]
[index]
(28)
Vocabulary [index]
(a)
Antheridium
(b)
Archegonium
(c)
Bryophytes
(h)
Fern
(k)
Fruit
(m)
Gametangium
(n)
Gametophyte
(o)
Heterosporous
(p)
Homosporous
(s)
Lignin
(t)
Megaspore
(v)
Moss
(w)
Plant divisions
(y)
Plant terrestrial adaptations
(z)
Plants
(aa)
Pteridophytes
(bb)
Sporangium
(cc)
Spore
(dd)
Sporophyte
(ee)
Sporophyte
as dominant generation
(ff)
Stoma
(gg)
Stomata
(hh)
Vascular
tissue
(ii)
Waxy cuticle
(jj)
Woody tissue