ch29

Chapter 29

PLANT DIVERSITY I: HOW PLANTS COLONIZED LAND

There are about 290,000 of land plants on Earth.

LAND PLANTS EVOLVED FROM GREEN ALGAE Charophycean ance!or  Charophyceans are the green algae most closely related to land plants. Land plants probably are probably derived from a group of green algae called charophy!e. charophy!e . Land plants share with the charophyceans the following traits !. Roe!!e ce""#"oe$yn!he%&%n' co(p"e)e  land plants and charophyceans posses a rosette"shape array of proteins that synthesi#e cellulose microfibrils in their cell wall. $ther cellulose wall"containing algae %e. g. brown algae, dinoflagellates&, have linear arrays of cellulose"producing proteins. This suggests a common ancestor between the charophytes and land plants. This rosette synthesi#ing system evolved independently of the cellulose ma'ing system of other green algae. 2. Pero)%o(e en&y(e en&y(e  the charophyceans and land plants have en&y(e %n !he%r pero)%o(e that pero)%o(e  that minimi#e the loss of carbohydrate due to photorespiration. $ther alga groups do not have these en#ymes in their pero(isomes. ). S!r#c!#re o* !he *"a'e""a!e per( per( details of the sperm of charophyceans resemble those of land plants that have flagellated sperms. *. Ce"" p"a!e *or(a!%on +#r%n' cy!o,%ne%  cell division features a comple( networ' of microtubules and +olgi vesicles, the phra'(op"a!, phra'(op"a! , again as found in all land plants. . DNA an+ RNA e-#ence support e-#ence  support their close relation to the charophytes, especially Chara and Coleochaete.

TERRESTRIAL ADAPTATION OF LAND PLANTS ADAPTATIONS ENA.LING THE MOVE TO LAND  - layer of poropo""en%n protects poropo""en%n  protects charophytes from desiccation sporopollenin is found in the spore wall of land plants. /anger of desiccation reuired new adaptations transport tissue, cuticle, etc.

1upport against gravity. lants are eu'aryotic, multicellular, mostly autotrophic organisms, with haploid"diploid life cycles, which retain embryo within female se( organ on parent plant the cell wall contains cellulose. 1cientists are studying the ultrastructure of cells, analy#ing macromolecules and comparing morphology with life cycles. There are several proposals to rearrange the boundaries of the 'ingdom lantae • • •

$nly the Embryophytes the present and traditional system. E(pand it to include the charophyceans 3ingdom 1treptophyta. E(pand it further to include all the green algae, Chlorophyta 3ingdom 4iridiplantae.

DERIVED TRAITS OF PLANTS The following characteristics are common to all four groups of land plants but are absent in the charophyceans. !. Ap%ca" (er%!e( (er%!e(  cluster of embryonic cells found at the tip of shoots and roots. 2. A"!erna!%on o* 'enera!%on 'enera!%on a characteristic life cycle.  -lternation  -lternation of generation generation does does not occur occur in the charophyceans. charophyceans. This This suggests suggests that alternation of generation arose independently in land plants. - life cycle characteri#ed by a multicellular hap"o%+ 'a(e!ophy!e !a'e followed !a'e  followed by a multicellular multicellular +%p"o%+ porophy!e !a'e. !a'e. M#"!%ce""#"ar/ +epen+en! e(0ryo: The e(0ryo:  The &y'o!e is &y'o!e  is retained surrounded by tissues of the gametophyte. The parental tissue provides the embryo with nutrients. P"acen!a" !ran*er ce"" present ce"" present in the embryo and sometimes in the gametophyte as well, enhance the transfer of nutrients. ). Spore pro+#ce+ %n poran'%a poran'%a  haploid reproductive cells that become a multicellular haploid gametophyte by mitosis. The multicellular sporangium contains sporocytes, the cells that undergo meiosis to form spores. Sporopo""en%n , the most durable organic material 'nown, ma'es the walls of the spores. *. M#"!%ce""#"ar 'a(e!an'%a 'a(e!an'%a  the gametes of land plants are produced in multicellular organs called gametangia. -lgae produce their gametes in unicellular gametangia, inside a single cell. A+ap!a!%on *or 1a!er !ranpor! an+ coner2a!%on3 43 5a(y c#!%c"e to c#!%c"e to protect against desiccation.

53 S!o(a!a %sing. !o(a& !o(a& for gas e(change and control of transpiration. 63 Transport system or 2ac#"ar !%#e

Secon+ary (e!a0o"%c co(po#n+ Land plants ma'e many metabolic compounds that are produced by side branches off the primary metabolic pathways that ma'e lipids, carbohydrates, proteins and other compounds common to all organisms. Cell wall contains "%'n%n, "%'n%n, a polymer, to strengthen and support upright structures. $ther secondary compounds are al'aloids, tannins, and phenolics %flavonoids&. These compounds functions as a protection against herbivores, absorb harmful 64 radiation, and are involved in the symbiotic relationship with soil microbes.

ORIGIN OF LAND PLANTS  -bout *7 *7 million years years ago, in the mid"$rdovician mid"$rdovician,, plants were were widespread widespread all over over the world world as shown by the many spores found in sediments of this period. 8n a relatively short time of about 0 million years, plant diversified abundantly and coloni#ed many land areas. There are four main groups of land plants • • • •

ryophytes, including mosses. teridophytes, including ferns and seedless vascular plants. +ymnosperms, including conifers.  -ngiosperms  -ngiosperms including including flowering flowering plants.

Land plants are distinguished from algae by the production of multicellular embryos that remain attached to the mother plant, which protects and nourishes the embryos. ryophytes are distinguished from the other three groups of land plants by the lac' of a vascular  tissue made of special cells called (ylem and phloem. 1ome bryophytes have water and nutrient transport system made of a different 'ind of cells. •

The 2ac#"ar y!e( transports y!e(  transports water and nutrients.

teridophytes do not produce seeds. +ymnosperms and angiosperms produce seeds.  - seed consists consists of a plant embryo embryo with a food food storing storing tissue and and a surrounding surrounding coat for protection.

• •

The first vascular plants to produce seeds evolved about ):0 million years ago. Their seeds were not enclosed in any speciali#ed chamber.

 -ngiosperms  -ngiosperms produce produce flowers and and conifers conifers produce ;cones;, a speciali#ed speciali#ed reproductive reproductive structure. • •

 -ngiosperms  -ngiosperms produce produce their seeds seeds in speciali#ed speciali#ed chambers chambers called called ovaries. ovaries. +ymnosperms do not produce seed in ovaries.

The word 'ra+e is 'ra+e is used to designate a collection of organisms that shate a common level of biologial organi#ation or adaptation.

.RYOPHYTES  -bout !7,000 !7,000 species species worldwide worldwide divided divided into three three /ivisions /ivisions or phyla phyla .ryophy!a, .ryophy!a , the mosses Hepa!ophy!a, Hepa!ophy!a , the liverworts and An!hocerophy!a , the hornworts. Their life cycle is similar but the three groups may not be closely related. The bryophytes may form a polyphyletic group. ryophyta ryophyt a refers to the phylum of mosses only bryophyt e refer e refer to the three phyla mentioned above.

Charac!er%!%c o* !he 0ryophy!e 0ryophy!e  !. 1mall plants plants found in moist environments, environments, lac' lac' woody tissue tissue and usually form form mats spread spread over the ground. 2. +ametophyte +ametophyte generation generation is is dominant dominant sporophyte sporophyte is is parasitic on the gametophyte. gametophyte. ). ryophytes ryophytes have cuticle, cuticle, stomata stomata and multicellular multicellular gametangia gametangia that allow them to survive survive on land. *. ryophytes ryophytes need water to reproduce and most most species species lac' vascular vascular tissue tissue %(ylem %(ylem and phloem&. . 5ater transport is mostly through through capillary capillary action, action, diffusion diffusion and cytoplasmic cytoplasmic streaming. streaming. They They lac' true roots, stems and leaves.

The gametophyte of mosses is a one"cell"thic' filament 'nown as the protonema that eventually produces buds having meristematic tissue. These meristems produce an upright structure called the 'a(e!ophore. 'a(e!ophore . These gametophytes are one to a few cells thic' and obtain nutrients and water by direct absorption from the environment.

rom there comes the name fossil fuels. /uring the Carboniferous Europe and @orth -merica were closer to the euator and covered with e(tensive swamps. -s plants died, their body did not completely decay in the stagnant water and great depths of organic material accumulated forming peat. These layers of peat were later covered by sediments that pressed the peat. ressure and heat converted the peat into coal, petroleum and gas.