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