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Chapter 19 Notes

by: Min-Young Kim

Chapter 19 Notes BIOL 3040

Marketplace > Clemson University > Biology > BIOL 3040 > Chapter 19 Notes
Min-Young Kim
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These notes cover the chapter in the book about angiosperms.
Biology of Plants
Christina Wells
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This 5 page Class Notes was uploaded by Min-Young Kim on Wednesday February 10, 2016. The Class Notes belongs to BIOL 3040 at Clemson University taught by Christina Wells in Spring 2016. Since its upload, it has received 28 views. For similar materials see Biology of Plants in Biology at Clemson University.


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Date Created: 02/10/16
Chapter  19  Notes:  Angiosperms     -­‐ Angiosperms  make  up  monophyletic  phylum  Anthophyta  –  largest  phylum  of   photosynthetic  organisms   o Monocotyledonae  (monocots)  ~90,000  species   o Eudicotyledonae  (eudicots)  ~200,000  species   o Almost  all  angiosperms  are  free-­‐living,  but  a  few  parasitic  and  myco-­‐ heterotrophic  forms  exist  (mistletoe,  Rafflesia)   -­‐ Parasitic  plants  form  specialized  absorptive  organs  called  haustoria  that   penetrate  tissues  of  hosts   -­‐ Myco-­‐heterotrophic  plants:  lack  chlorophyll  and  are  non-­‐photosynthetic,   have  obligate  relationships  with  mycorrhizal  fungi  that  are  also  associated   with  angiosperm   -­‐ Flower  is  a  determinate  shoot  that  bears  sporophylls  (sporangium-­‐bearing   leaves).     o Definitive  structure  =  carpel  –  contains  ovules  which  develop  into   seeds  after  fertilization.  Carpel  develops  into  fruit  wall   o Flowers  may  be  clustered  into  aggregations  called  inflorescences   o Stalk  of  inflorescence  or  solitary  flower  known  as  peduncle   o Stalk  of  individual  flower  in  inflorescence  is  pedicel   o Receptacle  –  part  of  flower  stalk  to  which  flower  parts  are  attached   o Sepals  and  petals  attached  to  receptacle  below  stamens  and  carpels   § Sepals  form  calyx,  petals  form  corolla   § Calyx  and  corolla  form  perianth   § Stamens  (microsporophylls)  collectively  called  androecium   § Stamen  consists  of  slender  stalk  (filament)  and  two-­‐lobed   anther  containing  four  microsporangia,  or  pollen  sacs,  in  two   pairs.     § Carpels  (ovule  bearing  parts)  collectively  known  as   gynoecium  (megasporophylls  enclosing  one  or  more  ovules)   § One  or  more  carpels,  may  be  separate  or  fused,  called  pistil   o Four  whorls  from  outside:     § Sepals  (calyx)   § Petals  (corolla)   § Stamens  (androecium)   § Carpels  (gynoecium)   o Individual  carpels  or  fused  carpels  differentiated  into  three  parts:   lower  part  (ovary)  which  encloses  ovules,  middle  part  (style)  which   pollen  tubes  grow,  upper  part  (stigma)  which  receives  pollen.   o Common  ovary  of  fused  carpels  generally  partitioned  into  two  or   more  locules  –  chambers  of  ovary  that  contain  ovules   o Portion  of  ovary  where  ovules  originate  and  remain  attached  until   maturity  =  placenta.  Placentation  (arrangement)  varies  among   groups.     § Parietal  –  ovules  borne  on  ovary  wall  or  on  extensions  of  it   § Axile  –  ovules  borne  on  central  column  of  tissue  in  partitioned   ovary   § Free  central  –  ovules  borne  on  central  column  of  tissue  not   connected  by  partitions  with  ovary  wall   § Basal  –  single  ovule  at  base   § Apical  –  single  ovule  at  apex   o Perfect  –  flowers  with  both  stamens  and  carpels  (bisexual)   o Imperfect  –  either  stamens  or  carpels  missing  (unisexual)   § Either  staminate  or  carpellate   o Monoecious  –  staminate  and  carpellate  flowers  occur  on  same  plant   o Dioecious  –  staminate  and  carpellate  flowers  occur  on  separate   plants   o Complete  flowers  –  all  four  floral  whorls   o Incomplete  flowers  –  lack  any  whorl   o Connotation  –  floral  parts  united  with  other  members  of  same  whorl   o Adnation  –  floral  parts  united  with  members  of  other  whorls   (stamens  with  corolla)   o Superior  –  if  whorls  attached  to  receptacle  below  the  ovary   o Inferior  –  whorls  attached  near  the  top  of  the  ovary   o Hypogynous  –  perianth  and  stamens  situated  on  receptacle  beneath   ovary  and  free  from  it  and  from  calyx   o Epigynous  –  perianth  and  stamens  arise  from  top  of  ovary   o Perigynous  –  stamens  and  petals  adnate  to  calyx,  form  short  tube   arising  from  base  of  ovary   o Radially  symmetrical  –  different  whorls  made  of  up  of  members  of   similar  shape  that  radiate  from  center  of  flower  and  equidistant  from   each  other   § Regular   o Bilaterally  symmetrical  –  one  or  more  members  of  at  least  one   whorl  are  different  from  other  members  of  same  whorl   § Irregular   -­‐ Angiosperm  gametophytes  much  reduced.     o Mature  microgametophyte  consists  of  only  three  cells   o Mature  megagametophyte  (embryo  sac)  retained  for  entire  existence   within  tissues  of  sporophyte,  or  specifically  ovule  (typically  seven   cells).     o Both  antheridia  and  archegonia  lacking;  pollination  indirect   § Pollen  deposited  on  stigma,  pollen  tube  grows  through  or  on   surface  of  tissues  of  carpel  to  convey  two  nonmotile  sperm  to   female  gametophyte;  fertilization,  ovule  develops  into  seed,   which  is  enclosed  in  ovary;  ovary  develops  into  a  fruit   o Microsporogenesis:  formation  of  microspores  within   microsporangia,  or  pollen  sacs,  of  anther   o Microgametogenesis:  later  development  of  microgametophyte  to   three  celled  stage   § Anther  is  uniform  mass  of  cells  until  it  differentiates  into  four   columns  of  sporogenous  cells  within  anther.  Each  column   surrounded  by  sterile  cells,  develop  into  wall  of  pollen  sac.   Outermost  layers  trigger  anther,  whereas  innermost  layer  of   pollen  sac  wall  forms  nutritive  tapetum  (forms  lipid-­‐rich  coat   to  surface  layer  of  pollen  grain).     § Sporogenous  cells  become  microsporocytes  (pollen  mother   cells)  that  divide  mitotically.  Each  diploid  microsporocyte  gives   rise  to  tetrad  of  haploid  microspores.     § Microsporogenesis  completed  with  formation  of  single-­‐celled   microspores  (pollen  grains)   § During  meiosis,  nuclear  division  followed  by  cell  wall   formation,  four  microspore  protoplasts  walled  off  after  second   meiotic  division;  major  features  of  pollen  grains  established   § Pollen  grains  develop  resistant  outer  wall,  exine  and  inner   wall,  intine.     • Exine  interrupted  by  pores  (preferable  for  pollen  tube   initiation)   • Exine  composed  of  resistant  substance  sporopollenin   (synthesized  primarily  by  tapetum)   • Intine  composed  of  cellulose  and  pectin,  laid  down  by   microspore  protoplasts   • Angiosperm  pollen  coat  secreted  onto  textured  exine  by   tapetum  and  is  unique  to  all  but  few  angiosperms   • Microgametogenesis  is  uniform,  begins  when   microspore  divides  mitotically,  forming  two   symmetrical  cells.  Division  forms  large  vegetative  cell,   or  tube  cell,  and  small  generative  cell,  which  moves   interior  or  pollen  grain.     • Two  celled  pollen  grain  is  immature  microgametophyte     o 2/3  angiosperm  species,  microgametophyte   remains  in  two  celled  stage  when  pollen  grains   released   o Rest  of  species,  generative  nucleus  divides,   giving  rise  to  two  sperm,  resulting  in  three  celled   microgametophyte   • Pollen  grains  vary  considerably  in  size  and  shape   o Undergo  mitosis  before  dispersal  (contrast  to   meiosis  in  seedless  plants);  have  two  or  three   nuclei  when  shed;  germinate  through  apertures   o Megasporogenesis:  involves  meiosis  and  results  in  formation  of   megaspores  within  ovule  in  nucellus   § Early  in  development  of  ovule,  single  megasporocyte  arises  in   nucellus;  diploid  megasporocyte  divides  meiotically  to  form   four  haploid  megaspores,  generally  arranged  in  linear  tetrad;   in  most  seed  plants,  three  of  four  megaspores  disintegrate.   o Megagametogenesis:  development  of  megaspore  into  the  embryo  sac   § One  nucleus  from  each  group  migrates  into  center  of  eight-­‐ nucleate  cell  and  become  polar  nuclei.  Remaining  three  eggs   at  micropylar  end  organized  into  egg  apparatus  (egg  cell  and   two  synergids).  Three  nuclei  at  chalazal  end  form  antipodals.   Central  cell  contains  two  polar  nuclei.  Eight-­‐nucleate,  seven   celled  structure  is  mature  megagametophyte,  or  embryo  sac   o Funiculus:  complex  structure  in  ovule  bearing  a  nucellus  enclosed  by   one  or  two  integuments     o Micropyle:  small  opening  at  one  end  of  the  ovule   o Functional  megaspore  enlarges,  nucleus  of  megaspore  divides   mitotically  three  times.  Eight  nuclei  arranged  in  two  groups  of  four,   one  at  micropylar  end  and  other  at  chalazal  end.     -­‐ Most  ancient  angiosperm  lineages  do  not  have  Polygonum-­‐type  embryo  sacs   -­‐ Dehiscence  of  anther  (opening  of  pollen  sacs):  pollen  grains  transferred  to   stigmas  (pollination).     o Once  in  contact  with  stigma,  pollen  grains  take  up  water  from  cells  of   stigma  surface.  Pollen  grain  germinates,  forms  pollen  tube  generative   cell  divides  within  pollen  tube,  forming  two  sperm.  This  is  mature   gametophyte.     -­‐ Wet  stigmas:  consist  of  glandular  tissue  that  secretes  proteins,  amino  acids,   and  lipids.     -­‐ Dry  stigmas:  hydrated  layer  consisting  of  proteins,  carbohydrates,  and  small   amount  of  lipid   -­‐ Pollen  tubes  grow  downward  between  cells  of  stigma  and  enter  style;  grow   between  transmitting  tissue     -­‐ Many  monocots  and  certain  eudicots  have  open  stigmas  (lined  by  glandular   epidermis  on  which  pollen  tube  grows)   -­‐ Pollen  tube  enters  ovary,  reaches  ovule,  grows  out  of  transmitting  tissue,   follows  funiculus,  enters  micropyle,  conveying  male  germ  unit  (two  sperm   cells  and  vegetative  nucleus)  in  process   -­‐ Pollen  tubes  of  angiosperms  have  considerably  longer  distances  to  grow   from  site  of  reception  to  that  of  fertilization  –  evolution  favored  greater   growth  rates  in  angiosperms   o Plastic  and  rapidly  extending  tip  and  reinforced  lateral  wall  composed   of  callose   o Many  pollen  tubes  also  deposit  callose  plugs  that  seal  off  older   portions  of  tube  from  apical  portion   -­‐ Guidance  of  pollen  tube  through  style  governed  by  cells  of  transmitting  tissue   -­‐ When  pollen  tube  reaches  embryo  sac,  enters  one  of  synergids  near  filiform   apparatus  and  discharges  contents  into  degenerated  synergid.   -­‐ Actin  form  sperm  cells  and  extend  to  egg  cell  and  central  cell   -­‐ Double  fertilization:  union  of  one  sperm  cell  with  egg  and  other  sperm  cell   with  polar  nuclei   o Primary  endosperm  nucleus  divides,  forming  endosperm   o Zygote  develops  into  embryo   o Integuments  develop  into  seed  coat   o Ovary  wall  and  related  structures  develop  into  fruit   -­‐ Triple  fusion:  most  common  type  of  embryo  sac  formation  where  one  of   sperm  nuclei  fuses  with  two  polar  nuclei  and  results  in  triploid  primary   endosperm  nucleus   -­‐ Embryogeny  in  angiosperms  resembles  that  of  seedless  vascular  plants:  first   nuclear  division  of  zygote  accompanied  by  cell  wall  formation   -­‐ In  seeds  of  some  groups  of  angiosperms,  nucellus  proliferates  into  food-­‐ storage  tissue  known  as  perisperm   -­‐ Angiosperm  seeds  differ  from  gymnosperms  in  origin  of  stored  food  –  by   endosperm  (rather  than  female  gametophyte)   -­‐ Ovule  develops  into  seed,  and  ovary  develops  into  fruit.  Ovary  wall,  pericarp,   thickens  and  becomes  differentiated  into  different  layers.      


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