Ch27

Chapter 27

 

SEED PLANTS

SEED

SPORE

1. Multicellular embryo

Single cell

2. Food supplied by tissue

Food only in the cell

3. Multicellular seed coat

Covering not cellular  

4. Diploid sporophyte

aploid cell

!. "roduct o# #ertili$ation

"roduct o# meiosis

%here are t&o groups o# seed producing plants' gymnosperms and gymnosperms  and angiosperms. angiosperms . •

•

"roduce seeds. (ascular tissue) xylem #or xylem #or &ater and mineral transport and phloem #or phloem #or dissolved sugars.

•

*ametophyte is very reduced and totally dependent on the sporophyte.

•

eterosporous) microspores and megaspores.

GYMNOSPERMS %here are about 72+ species #ound in all terrestrial habitats grouped into #our divisions ,phyla-. %hey have great economic importance) lumber' paper' chemicals. I. CARACTERISTICS O! GYMNOSPERMS 1. ood oody y trees trees and and shrub shrubs. s. 2. /ylem /ylem made made o# o# trac trache heids ids.. 3. Seeds Seeds are are borne borne'' e0pos e0posed' ed' in cone cones s ,megas ,megastrob trobilus ilus-. -. 4. "ollinat "ollinated ed by by &ind' &ind' seldom seldom by by insect insects. s. !. Singl Single e #ertili #ertili$at $atio ion) n) sperm sperm  egg egg

 embryo.

. Most ar are monoe"io#s) monoe"io#s ) male and #emale organs on the same individual.

II. CONIPEROPYTA or CONIPEROPYTA or coni#ers %here are about !!+ species o# coni#ers. Many coni#ers produce resin$ a resin$  a comple0 mi0ture o# organic compounds that protect the plant #rom insect and #ungal attac. •

esin is stored in resin ducts in the roots' stem' leaves and cones'

Cone bearing gymnosperms' e. g. pines' #irs' cypresses' etc. 5eaves are needles or scale6lie' rarely broad %ena&ion is %ena&ion  is parallel and open.  8 male cone is called mi"ros&ro'il#s ' and contains the mi"rosporangia that mi"rosporangia  that produce mi"rospores through mi"rospores  through meiosis that &ill develop into mi"rogame&ophy&es  ,pollen grains-. %he #emale cone is called the megas&ro'il#s' megas&ro'il#s ' &hich produce megasporangia in megasporangia  in each o# &hich a megaspore is megaspore  is produced through meiosis and &ill develop one megagame&ophy&e. megagame&ophy&e . 8n egg &ill #orm &ithin the megagame&ophy&e . "ollination is by &ind. No&e( Study the life cycle of pine and learn the terminology. Pages 572 - 574.

III. CYCADOPYTA or CYCADOPYTA or cycads 9mportant in the %riassic ,24:6213 m .y. a-' &hich is called sometimes the 8ge o# Cycads . Most species are e0tinct. %here are about 14+ living species in tropical and subtropical parts o# the &orld. Cy"a)s are Cy"a)s are palm or #ern6lie plants &ith compound leaves and simple seed cones. %he are )ioe"io#s) )ioe"io#s ) plants are either male or #emale. %hey have a very large motile sperm &ithin the pollen grain but do not need &ater #or pollen transport. "ollination is by air and in some cases by ants.

I*. GIN+GOPYTA or GIN+GOPYTA or gingoes %here is a single species o# gingo alive today. 9t is native to China &here it has been under cultivation #or centuries. 9t has been #ound in the &ild in only t&o locations. *ingoes are dioecious and have #lagellated sperms. "ollination is by air and seeds are borne e0posed rather than in cones. 9t is commonly planted in 8merican cities because it is very resistant to pollution.

*. GNETOPYTA %he gnetophytes consists o# three genera and about 7+ species.  8 group o# rare plants plants that share share some traits traits &ith angiosperm angiosperms. s. • •

;##icient &ater conducting cells in the 0ylem called vessel elements. eproductive structures resemble #lo&ers.

ANGIOSPERMS %here are about 23!'+++ species o# #lo&ering plants. %his is the dominant group in terrestrial habitats. oins the t&o polar polar nuclei nuclei #orming the the triploid ,3n,3n- nutritive tissue called called the endosperm. See figure 27-12, page 51, for details. Seeds develop #rom the ovule #ollo&ing #ertili$ation. %he ovary enlarges and #orms the #ruit. 9n some instances other tissues also enlarge and become part o# the #ruit. Fruits serve t&o purposes) protect the seed and aid in dispersal o# the seeds.

E*OLTION O! SEED PLANTS "rogymnosperms appeared about 37! million years ago in the Devonian. • • •

they reproduced by spores. had megaphylls. &oody tissue o# secondary 0ylem similar to modern gymnosperms.

%heir reproductive structures appear to be intermediate bet&een those o# spore producing plants and seed plants.  coni#ers "rogymnosperms  seed #erns  cycads and possibly gingoes Seed producing plants appeared in the Devonian' about 3+ m. y. a. ?y the end o# @urassic' 1:+ million years ago' several lines o# gymnosperms e0isted &ith #eatures that resembled those o# #lo&ering plants. Di##erent groups o# seed plants apparently appeared independently several times.  8ngiosperms  8ngiosperms probably probably arose #rom #rom ancient gymnosperms. gymnosperms. %hey must have been dicots' dicots' &hich &hich then gave rise to monocots. %he oldest #ossil record o# angiosperms is pollen #rom the Cretaceous' about 13+ m. y. a. %he oldest #lo&er #ossil is 12+ m.y.a. ?y late Cretaceous angiosperms had began to replace gymnosperms as the dominant group o# land plants. Many angiosperm species apparently arose #rom changes in chromosome number.

COMPARISON COMPARISON O! GYMNOSPERMS AND ANGIOSPERMS . *AM=