Chapter 30
Chapter 30
PLANT DIVERSITY II.
PLANT DIVERSITY II.
THE EVOLUTION OF SEED PLANTS
THE EVOLUTION OF SEED PLANTS
OVERVIEW OF SEED PLANT EVOLUTION OVERVIEW OF SEED PLANT EVOLUTION
The most important reproductive adaptations of seed plants are: The most important reproductive adaptations of seed plants are:
1.
1. ConContinutinued reed reductduction ion of thof the gae gametometophyphytete 2.
2. EvEvololututioion of tn of the she seeeed.d. 3.
3. EvEvoluolutiotion on of tf the he popollellen.n.
The reduced gametophyte can develop from spores retained within the sporangia of the The reduced gametophyte can develop from spores retained within the sporangia of the parental sporophyte.
parental sporophyte.
•
• Retaining the female gametophyte within the sporangium protects it from environmentalRetaining the female gametophyte within the sporangium protects it from environmental
stresses. stresses.
•
• The gametophyte otains food from the sporophyte.The gametophyte otains food from the sporophyte.
!ll seed p
!ll seed plants halants have two difve two different "iferent "inds of sponds of spores. Theres. They arey are heterosporousheterosporous.. 1.
1. Megasporangu!Megasporangu! produces produces !egaspores!egaspores# which # which produceproducess "e!a#e ga!etoph$tes"e!a#e ga!etoph$tes.. 2.
2. M%rosporangu!M%rosporangu! produces produces !%rospores!%rospores# which # which producesproduces !a#e ga!etoph$tes!a#e ga!etoph$tes.. $n seed plants# the megaspores and the female gametophyte are retained on the parent $n seed plants# the megaspores and the female gametophyte are retained on the parent sporophyte.
sporophyte.
%ayers of sporophyte tissue envelop the megasporangium. These tissues are called %ayers of sporophyte tissue envelop the megasporangium. These tissues are called ntegu!ents
ntegu!ents..
The megasporangium# megaspore and integuments are called the
The megasporangium# megaspore and integuments are called the o&u#eo&u#e..
The female gametophyte develops inside the megaspore and produces one or more egg cells. The female gametophyte develops inside the megaspore and produces one or more egg cells.
Megasporangu!
Megasporangu! & & !egaspores '!egaspores ' "e!a#e ga!etoph$tes ' egg %e##."e!a#e ga!etoph$tes ' egg %e##. M%rosporangu!
M%rosporangu! & & !%rospores!%rospores & & !a#e ga!etoph$tes (po##en)!a#e ga!etoph$tes (po##en) & & sper!s.sper!s. 'ollen does not need a li(uid for fertili)ation.
'ollen does not need a li(uid for fertili)ation. Po##naton
Po##naton is the transfer of pollen to ovules. *ind and animals carry out pollination. is the transfer of pollen to ovules. *ind and animals carry out pollination. 'ollen grains are well protected y
'ollen grains are well protected y sporopo##ennsporopo##enn..
+poropollenin contains only caron# hydrogen and o,ygen- it is an isoprene polymer. +poropollenin contains only caron# hydrogen and o,ygen- it is an isoprene polymer.
The seed is a sporophyte emryo pac"aged along with a food supply within a protective coat. The seed is a sporophyte emryo pac"aged along with a food supply within a protective coat. +eeds can e very resistant and can e dispersed widely y animals and wind.
SEED
SEED SPORESPORE
1
1.. uullttiicceelllluullaar r eemmrryyoo ++iinngglle e cceellll 2
2.. //ooood d ssuupppplliieed d y y ttiissssuuee //ooood d oonnlly y iin n tthhe e cceellll 3
3.. uullttiicceelllluullaar r sseeeed d ccooaatt CCoovveerriinng g nnoot t cceelllluullaar r
.. iippllooiid d ssppoorroopphhyyttee aappllooiid d cceellll
.. ''rroodduucct t oof f ffeerrttiillii))aattiioonn ''rroodduucct t oof f mmeeiioossiiss
There are two groups of seed producing plants#
There are two groups of seed producing plants# g$!nosper!sg$!nosper!s and and angosper!sangosper!s..
•
• 'roduce seeds.'roduce seeds.
•
• 4ascular tissue: *$#e!4ascular tissue: *$#e! for water and mineral transport and for water and mineral transport and ph#oe!ph#oe! for dissolved for dissolved
sugars. sugars.
•
• 5ametophyte is much reduced and totally dependent on the sporophyte.5ametophyte is much reduced and totally dependent on the sporophyte.
•
• eterosporous: microspores and megaspores.eterosporous: microspores and megaspores.
+YMNOSPERMS +YMNOSPERMS
There are aout 620 species found in all terrestrial haitats grouped into four divisions 7phyla8. There are aout 620 species found in all terrestrial haitats grouped into four divisions 7phyla8. They have great economic importance: lumer# paper# and chemicals.
They have great economic importance: lumer# paper# and chemicals.
9y the late evonian period 736 million years ago8 some plants had egun to ac(uire some 9y the late evonian period 736 million years ago8 some plants had egun to ac(uire some adaptations that characteri)e seed plants.
adaptations that characteri)e seed plants.
The first fossils of seed earing plants appeared in the Caroniferous# some 3;0 million years The first fossils of seed earing plants appeared in the Caroniferous# some 3;0 million years ago.
ago.
The 'ermian was warmer and drier and the gymnosperm egan to diversify ecause they were The 'ermian was warmer and drier and the gymnosperm egan to diversify ecause they were etter adapted than %ycopods to this type of climate.
etter adapted than %ycopods to this type of climate.
5ymnosperms dominated the landscape during the eso)oic era# which egan aout 20 5ymnosperms dominated the landscape during the eso)oic era# which egan aout 20 million years ago.
million years ago.
The eso)oic ended ; million years ago and the Ceno)oic egan. ! great e,tinction too" The eso)oic ended ; million years ago and the Ceno)oic egan. ! great e,tinction too" place at the end of the eso)oic# which included the elimination of the dinosaurs.
place at the end of the eso)oic# which included the elimination of the dinosaurs. The Ceno)oic is dominated y flowering plants ut gymnosperms remain an important The Ceno)oic is dominated y flowering plants ut gymnosperms remain an important component of the flora.
,HARA,TERISTI,S OF +YMNOSPERMS ,HARA,TERISTI,S OF +YMNOSPERMS
1.
1. *o*oodody ty treerees as and nd shshrurus.s. 2.
2. +ee+eeds are ods are orne# e,rne# e,posposed# in coed# in cones 7menes 7megasgastrotroilusilus8.8. 3.
3. 'oll'ollinatinated ed y wy wind# ind# seldseldom om y iny insectsects.s. .
. +in+inglgle ferte fertiliili)at)atioion: spn: sperm < eerm < egggg emryo. emryo.
.. oosst at arree !onoe%ous!onoe%ous: male and female organs on the same individual.: male and female organs on the same individual.
There are four phyla studied in this te,too": There are four phyla studied in this te,too":
•
• 5in"gophyta# Cycadophyta# 5netophyta# Coniferophyta5in"gophyta# Cycadophyta# 5netophyta# Coniferophyta
See the Life Cycle of a pine on page 597 See the Life Cycle of a pine on page 597
AN+IOSPERMS AN+IOSPERMS
There are aout 23#000 species of flowering plants. There are aout 23#000 species of flowering plants.
This is the dominant group in terrestrial haitats. =ur survival depends on them. This is the dominant group in terrestrial haitats. =ur survival depends on them.
•
• /ood# medicine# lumer# etc./ood# medicine# lumer# etc.
There are two groups of angiosperms:
There are two groups of angiosperms: !ono%ots!ono%ots and and -%ots-%ots.. /irst appeared in the Cretaceous aout 130 million years ago. /irst appeared in the Cretaceous aout 130 million years ago. I. ,HARA,TERISTI,S
I. ,HARA,TERISTI,S 1.
1. *o*oodody or hy or hereraaceceouous.s. 2.
2. 'r'rododucuce e flflowowerers.s. 3.
3. 'o'ollillinanated ted y wy wind oind or anr animaimals.ls. .
. ououlle ferte fertiliili)a)atiotion: egn: egg < sperg < spermm emryo and emryo and 2 2 polar polar nuclei nuclei < < spermsperm endosperm. endosperm. .
. +e+eededs ens encloclosed sed in a in a frufruit.it.
II. THE FLOWER II. THE FLOWER
The flower is a reproductive shoot or ranch. The flower is a reproductive shoot or ranch.
$t has four parts arranged in whorls or circles on a stal" or peduncle. $t has four parts arranged in whorls or circles on a stal" or peduncle. The parts of the flower are the
The parts of the flower are the sepa#ssepa#s 7caly,8# 7caly,8# peta#speta#s 7corolla8# 7corolla8# sta!enssta!ens and and %arpe#s%arpe#s..
•
• +tamens consist of a filament and an anther.+tamens consist of a filament and an anther. •
• Carpels are also referred to asCarpels are also referred to as pst#spst#s. They consist of an ovary# a style and a. They consist of an ovary# a style and a
stigma. stigma.
/lowers may e orne singly or in clusters called
/lowers may e orne singly or in clusters called n"#ores%en%en"#ores%en%e.. /lower parts are considered modified leaves.
/lower parts are considered modified leaves. III. DOULE FERTILI/ATION
III. DOULE FERTILI/ATION..
$t is characteristic of flowering plants. $t is characteristic of flowering plants.
oule fertili)ation results in the formation of a
oule fertili)ation results in the formation of a -p#o- 0$gote-p#o- 0$gote and a and a trp#o- en-osper!trp#o- en-osper!.. The female
The female ga!etoph$te or e!1r$o sa%ga!etoph$te or e!1r$o sa% has an egg nucleus and two polar nuclei. has an egg nucleus and two polar nuclei. =ne sperm fertili)es the egg nucleus and forms the )ygote# 2n.
=ne sperm fertili)es the egg nucleus and forms the )ygote# 2n. !nothe
!nother sperm >oins r sperm >oins the two pthe two polar nucleolar nuclei forming thi forming the triploid 73e triploid 73n8 nutritive n8 nutritive tissue caltissue called theled the endosperm.
endosperm.
IV. FRUIT ,LASSIFI,
IV. FRUIT ,LASSIFI,ATATIONION.. !
! fruit is a mafruit is a mature ovaryture ovary.. A%%essor$ "ruts
A%%essor$ "ruts include other parts in addition to the ovaries# e.g. strawerry# apple# and pear. include other parts in addition to the ovaries# e.g. strawerry# apple# and pear. S!p#e "ruts
S!p#e "ruts develop from a single carpel or several united carpels. develop from a single carpel or several united carpels. Aggregate "ruts
Aggregate "ruts are produced from separate carpels in one gynoecium# e.g. lac"erries# are produced from separate carpels in one gynoecium# e.g. lac"erries# magnolia.
magnolia.
•
• The individual parts of the aggregate fruit are "nown as fruitlets.The individual parts of the aggregate fruit are "nown as fruitlets.
Mu#tp#e "ruts
Mu#tp#e "ruts consist of several female structures and accessory flower parts that ecome consist of several female structures and accessory flower parts that ecome fused into one fruit# e.g. pineapple# =sage orange.
fused into one fruit# e.g. pineapple# =sage orange. See the angiosperm life cycle on page 600.
See the angiosperm life cycle on page 600. V. EVOLUTION OF AN+IOSPERMS
V. EVOLUTION OF AN+IOSPERMS !ngiosp
!ngiosperms evolveerms evolved some 1d some 1 million y million years ago dears ago during the uring the early Cretaearly Cretaceous 7eceous 7eso)oic8 orso)oic8 or possily in the late ?urassic.
possily in the late ?urassic. !ngiosp
!ngiosperm egan erm egan to dominato dominate the late the landscape ndscape at the enat the end of the d of the eso)oic aeso)oic and they nd they form nowform now the dominant plant form.
There are different opinions aout the origin of the angiosperms and their flower. There are different opinions aout the origin of the angiosperms and their flower.
=@=C=T+ have floral parts in multiples of three and the seed contains one cotyledon. The =@=C=T+ have floral parts in multiples of three and the seed contains one cotyledon. The endosperm provides the food for the emryo. 4enation is usually parallel 7there are e,ceptions8. endosperm provides the food for the emryo. 4enation is usually parallel 7there are e,ceptions8. Their vascular undles are scattered throughout the ground tissue. The root system is firous. Their vascular undles are scattered throughout the ground tissue. The root system is firous. $C=T+ have floral parts in multiples of four or five# and their seeds contain two cotyledons. $C=T+ have floral parts in multiples of four or five# and their seeds contain two cotyledons. The cotyledons usually asor the food from the endosperm first# and then provide the food for The cotyledons usually asor the food from the endosperm first# and then provide the food for the emryo. 4enation is netted. The vascular undles in the stem crossAsection are arranged in the emryo. 4enation is netted. The vascular undles in the stem crossAsection are arranged in circles 7rings8. They usually have a taproot system for at leas part of their life.
circles 7rings8. They usually have a taproot system for at leas part of their life. Ths s not aThs s not a !onoph$#et% group.
!onoph$#et% group.
Current research supports the hypothesis that monocots are monophyletic and form a single Current research supports the hypothesis that monocots are monophyletic and form a single clade.
clade.
The dicots# however# appear to e a polyphyletic grouping. ost of the dicots elong to the The dicots# however# appear to e a polyphyletic grouping. ost of the dicots elong to the eu-%ots.
eu-%ots.
Three lineages of the remaining dicots form what is called the
Three lineages of the remaining dicots form what is called the 1asa# angosper!s1asa# angosper!s ecause ecause they include what are considered to e the oldest lineages.
they include what are considered to e the oldest lineages. !nothe
!nother group is car group is called thelled the !agno#-s!agno#-s..
VI. ,OEVOLUTION OF FLOWERIN+ PLANTS AND ANIMALS. VI. ,OEVOLUTION OF FLOWERIN+ PLANTS AND ANIMALS. ,oe&o#uton
,oe&o#uton is the process y which two or more species act as selective forces on one is the process y which two or more species act as selective forces on one another and each undergoes evolutionary change.
another and each undergoes evolutionary change. The earliest seedAearing plants were pollinated. The earliest seedAearing plants were pollinated.
'ollen ecame a source of food for insects and those flowers that could etter attract insects 'ollen ecame a source of food for insects and those flowers that could etter attract insects were visited more often thus increasing the chances of passing those characters to the ne,t were visited more often thus increasing the chances of passing those characters to the ne,t generation.
generation. !ny muta
!ny mutation that tion that made thomade those visits mose visits more fre(uere fre(uent offent offered a selered a selective advanctive advantage.tage.
9ise,ual flowers have the advantage that visiting insects can pic" up pollen from the anthers 9ise,ual flowers have the advantage that visiting insects can pic" up pollen from the anthers and deliver pollen from a neighoring plant at the same time.
$n the early part of the Tertiary# 0 A ;0 million years ago# speciali)ed groups of flowerAvisiting $n the early part of the Tertiary# 0 A ;0 million years ago# speciali)ed groups of flowerAvisiting insects ecame more diverse.
insects ecame more diverse. VII. Hu!an 2e#"are
VII. Hu!an 2e#"are
ost of our food comes from angiosperms. ost of our food comes from angiosperms.
+i, crops produce B0 of the calories consumed y humans: +i, crops produce B0 of the calories consumed y humans:
A *heat# rice# mai)e# potatoes# cassava and sweet potatoes. A *heat# rice# mai)e# potatoes# cassava and sweet potatoes.
=ur food crops are derived from wild ancestors that have een domesticated very much li"e we =ur food crops are derived from wild ancestors that have een domesticated very much li"e we have domesticated animals.
have domesticated animals.
A The domestic dog is derived from the wild wolf. A The domestic dog is derived from the wild wolf.
any of our medicines are derived from plants or ased on plant natural products. any of our medicines are derived from plants or ased on plant natural products. aitat destruction is the iggest threat to plant e,tinction.
