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

 

 

Course-external links are in brackets

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Vocabulary words are found below

 

 

(1) Chapter title: Plant Diversity I: The Colonization of Land

(a)                    [the colonization of land, "colonization of land" plants (Google Search)] [index]

 

WHAT IS A PLANT?

 

(2) Plants

(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]

(e)                    Chara, etc.:

(f)                      [images of plants (1), images of plants (2) (Biology 122Southwest Missouri State University)] [index]

 

PLANT ADAPTATIONS TO LAND LIFE

 

(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)

 

Challenges during Algae-to-Plant Transition:

Algae:

  • Minerals from water
  • Water from water
  • Sunlight received within water
  • Weight supported by water
  • Sperm swim through water
  • Spores swim through water

Plants:

  • Minerals from soil
  • Water from soil (susceptibility to desiccation)
  • Sunlight received above soil (products require transport within plant)
  • Weight not supported by air (requires internal supporting structure)
  • Less water for sperm to swim through
  • Less water for spores to swim through

 

(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]

(4) Waxy cuticle

(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

(f)                     

(g)                    [waxy cuticle (Google Search)] [index]

(5) Stomata (singular, stoma)

(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

(d)                   

(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]

(7) Vascular tissue

(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]

(8) Woody tissue (lignin) (secondary growth)

(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

(e)                    Lignin: (no need to know)

(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]

 

BASIC VARIETIES OF PLANTS

 

(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]

 

NONVASCULAR PLANTS

 

(10) Bryophytes

(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]

 

COMPLEXITIES OF PLANT REPRODUCTION (MOSTLY IGNORING SEEDS)

 

(12) Plant reproduction

(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]

(13) Gametophyte

(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]

(14) Sporophyte

(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]

(15) Spore

(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]

(16) Sporangium

(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]

(17) Gametangium

(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]

(18) Archegonium

(a)                    Archegonia are gametangia that produce eggs

(b)                    [archegonium (Google Search)] [archegonia (Google Search)] [index]

(19) Antheridium

(a)                    Antheridia are gametangia that produce sperm

(b)                    [antheridium (Google Search)] [antheridia (Google Search)] [index]

 

THE BASIC PLANT LIFE CYCLE

 

(20) Life cycle of a moss

(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]

 

SEEDLESS, NONVASCULAR PLANTS

 

(21) Pteridophytes

(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

(d)                    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]

(23) Homosporous

(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

(d)                   

(e)                    See unnamed figures found in the second column of p. 591

(f)                      [homosporous (Google Search)] [index]

(24) Heterosporous

(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.”]

(d)                   

(e)                    See unnamed figures found in the second column of p. 591

 

 

Sporangia

Spores

Gametophyte

Gametangia

Gametes

Megasporangia

Megaspores

Megagametophyte (female)

Archegonia

Egg

Microsporangia

Microspores

Microgametophyte (male)

Antheridia

Sperm

 

(f)                      [heterosporous (Google Search)] [index]

(25) Megaspore

(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]

(26) Microspore

(a)                    In the heterosporous (especially seed-bearing) plants the microspore gives rise to the sperm-producing male gametophyte (pollen)

(b)                    [microspore (Google Search)] [index]

(27) Life cycle of a fern

(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]

 

VOCABULARY

 

(28) Vocabulary [index]

(a)                    Antheridium

(b)                    Archegonium

(c)                    Bryophytes

(d)                    Division Anthophyta

(e)                    Division Bryophyta

(f)                      Division Coniferophyta

(g)                    Division Pterophyta

(h)                    Fern (not indexed)

(i)                      Flowers

(j)                      Flowers in more detail

(k)                    Fruit

(l)                      Fruits in more detail

(m)                  Gametangium

(n)                    Gametophyte

(o)                    Heterosporous

(p)                    Homosporous

(q)                    Life cycle of a fern

(r)                     Life cycle of a moss

(s)                     Lignin

(t)                      Megaspore

(u)                    Microspore

(v)                    Moss (not indexed)

(w)                  Plant divisions

(x)                    Plant reproduction

(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