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chapter 9 Flowers and reproduction (Fruit Types and seed dispersal (the…
chapter 9 Flowers and reproduction
Asexual Reproduction
Fragmentation
a large spreading or vining plant grows to several meters in length and individual parts become self sufficient by establishing adventitious roots
if middle portions of the plant dies, the ends become separated and act as individuals
in willows and many thistles adventurous shoot buds form on roots and then grow into plants
adventitious buds may grow out even while the parent plant is still alive
The plant life cycle
diploid adults have sex organs that produce haploid sex cells called gametes
eggs
megagametes
sperm
microgametes
sperm and egg recalled a zygote
meiosis in plants results in haploid gametes
syngamy or fertilization
gametes fussing with other gametes
sporophyte phase
herbs, trees, shrubs
sporophyte generation
always diploid
plant spores undergo mitosis and form a gametophyte
alteration of generations
a life cycle with two generations
flower structure
stalk is a pedicel
flowers attach receptacle
complete flowers have all four appendages
incomplete flowers do not have all four appendages
Sepals
lowermost and outermost of floral appendages
Petals are above the sepals and on receptacle and make up a the corolla
sepals and petal together constitute the flowers perianth
stamen
above petals are stamens
known collectively as the androecium
stamens have two parts aka the filament
androecium
microspores are initially called pollen
[Carpels]
constitute the gynoecium
three main parts
stigma
style
ovary
inside ovary are placentae
singer for placentae is ovules
ovules have a small central mass of parenchyma called a nucellus
Gametophytes
microgametophyte
vegetative cells and small lens-shaped generative cell divides and forms two sperm cells
after a pollen grain lands on a stigma it germinates by producing a pollen tube
penetrates into the loose open tissues of the stigma
pollen tube absorbs nutrients from the stigma and grows downward through the style
pollen grains are filled with a giant vacuole
megagametophyte
multinucleate megametophyte
called an embryo sac
the seven cells are one large central cell with two polar nuclei three small antipodal cells and an egg apparatus consisting of two synergids and an egg
Fertilization
syngamy of sperm and egg involves both plasmogamy, fusion of the protoplastof the gametes and karyogamy
in angiosperms only the second sperm nucleus released from the pollen tube migrates from the singed into the central cell
it undergoes karyogamy with with both polar nuclei establishing a large endosperm nucleus that is triploid containing three set of genes
Embryo and seed development
has a suspensor which pushes the embryo deep into the endosperm
two primordial cells that grow into two cotyledons
Later in the torpedo stage the embryo is an elongate cylinder: a short axis is established consisting of radicle, epicotyl, hypocotyl
once mature the embryo becomes quiescent and partially dehydrates and the funiculus may break leaving a small scar, the hilum
a mature seed in which endosperm is rather abundant is an albuminous seed
if endosperm is sparse or absent at maturity the seed is exalbuminous
the integuments that surround the nucellus expand and mature into the seed coat also the testa
Fruit development
ovule develops into a seed the ovary mature into a fruit
often three layers become distinct during growth
exocarp is the outer
mesocarp is the middle
endocarp may be tough like the stones or pit of a cherry
entire fruit wall is the pericarp
Cross-pollination
pollination of a carpel by pollen from a different individual
self-pollination is pollination of a carpal by pollen from the same flower or another flower on the same plant
no possibility exists of bringing in new alleles that might provide more fitness than those inherited from the parent
Stigma and pollen incompatibility
compatibility barriers
chemical reactions between pollen and carpels that prevent pollen growth
in one compatibility system as a pollen tube grows the stigma and style test proteins on the tubes surface
Monocious and Dioecious Species
the latter two organs are essential organs because they produce the critical important spores if either organ is absent sexual reproduction dramatically affected
Flowers that either lack or both essential organs are not only incomplete but are also imperfect flowers
if a flower has both it is a perfect flower
a species may have individuals that produce only staminate flowers and others that produce only carpellate flowers
dioecy and the species is called dioecious
Monoecy is condition of having staminate flowers located on the same plant as carpellate flowers
monoecious species include cattails and corn
Inflorescence and pollination
many flowers grouped together is called an inflorescence
inflorescence give a collective visual signal to pollinators
small flower may be overlooked but not 100 close together is the idea here
when grouped into inflorescences two basic arrangements occur
determinate inflorescences
limited potential growth bc the inflorescence apex is converted into a flower
indeterminate inflorescence
the lowest or outermost flowers open first and even while these flowers are open new flowers are being initiated at the apex
Fruit Types and seed dispersal
the red flesh of a strawberry is the receptacle not the carpel tissue therefor an accessory fruit
pineapples develop from the coalescence of all the many true fruits of one inflorescence so they are a multiple fruit
true fruit
accessory fruit
true fruit is used to refer to the fruits containing one ovarian tissue
accessory fruits used if any non ovarian tissue is present
aggregate fruit would be raspberries
multiple fruit would be figs
Classification of fruit types
dry or fleshy
dry
not typically eaten by the natural seed-distribution animals
fleshy fruit fruits are eaten during the natural seed distribution process
fruit opening
Dehiscent fruits break open and release their seeds
indehiscent fruits do not break open
these are usually fleshy fruits
animals chew or digests the fruits, opening it if uneaten the fruit rots and liberates the seeds
simplest fruits are the ones of grasses
all corn and wheats
