Seeds Flashcards
what is seed
structure containing an embryonic plant, nutritive substance and a protective outer coating
what is an embryo
an immature plant
what is a seed coat
a tough coating protecting the interior of the seed from external environmental conditions
what is the seed coat composed of
sclerenchyma cells
what is an endosperm
the nutritive substance in the seed that provides energy that germinating seed needs before it can photosynthesize
traits of angiosperm endosperm
- contains stored energy in form of starches, oils and some proteins
- produced by the comnining of sperm and the central cell of the ovule
- often a triploid
traits of gymnosperm endosperm
- composed of the remains of the female gametophyte
what is the most common seed type
standard dicot seed with cotyledons
what is fertilization
the uniting of male and female gametes to produce a diploid zygote
what are the components of fertilization
male
female
what is a pollen grain
the male gametophyte in all seed plants
how many pollen grains are produces from 1 microspore
4
role of generative cell
produces 2 sperm cells
role of pollen tube nucleus
facilitates growing of the pollen tube
what is steps of pollen grain germination
- growth of pollen tube from pollen cell delivers sperm directly in egg
- pollen tube nucleus synthesizes materials to allow pollen tube growth
- generative cell produces sperm one pollen tube reaches micropyle
traits of pollen germination in gymnosperms
- naked seed
- pollen tube doesnt need to grow large to deliver sperm to egg
- pollen grains are often winged
what is an egg cell
cell which will become the zygote once united with a sperm cell
where is egg cell found
in archegonia
what is the role of female gametophyte in gymnosperms
- produces archegonia
- becomes nutritive tissues in gymnosperms
role of integument
single layer in gymnosperms
protective coat for the ovule
becomes seed coat
what is micropyle in ovule gymnosperms
opening to the ovule
steps of fertilization in gymnosperms
- 4 megaspored produced through meiosis (one lives)
- pollination occurs (before egg cell formation)
- surviving female megaspore divides through mitosis and produces multicellular archegonia
- archegonia goes through mitosis and produces many egg cells
- some species all eggs cells survive others not
- fertilization by uniting sperm and egg
what is the difference in pollen in angiosperms from gymnosperms
pollen tube must grow down a longer structure
pollen grains in angiosperms are often spherical
what is a synergid in angiosperm ovules
2 per ovule
help guide fertilization
role of antipodals in angiosperm ovules
contribute to endosperm development and growth
how is the integument in angiosperm ovules
two layers
ovule angiosperm includes
egg cell synergids polar nuclei central cell antipodals integument micropyle
ovule gymnosperm includes
egg cell
female gametophyte
integument
micropyle
steps of angiosperm fertilization
- 4 megaspores produced by meiosis (one lives)
- survivng megaspore= female gametophyte
- fem gameto undergoes mitoss x3 = 8 daughter cells= parts of the ovule
- pollination
- sperm and egg unite = fertilization
what is double fertilization
each pollen cell releases 2 sperm which fertilizes 2 different structures with the ovule
egg cell -> zygote
polar nuclei -> triploid endosperm
what happens after fertilization
seed development = zygote goes through a complex pattern of development to grow into a seed
what are the stages in seed development
embryogenesis
maturation
desiccation
what is embryogenesis
formation of the embryo from the fertilized zygote
what are the 4 stages of embryogenesis
globular heart torpedo mature (aka shapes of embryo)
what is maturation
when embryo reaches torpedo stage, seed begins to focus on storing nutritious tissues and on formation of endosperm
what is desiccation
the loss of water in the seed
what is seed dormancy
delayed germination
what are the types of dormancy
morphological
chemical
physical
what is morphological dormancy
seeds are released from the mother plant before they are fully mature
what is chemical dormancy
chemical signs in the seed prevent germination
seed waits for environmental sign that environment is favorable for germination
what is physical dormancy
seed coat is resistant to germination or water uptake
seed coat must be worn down to germinate
what are recalcitrant seeds
seeds with no dormancy mechanism
limited to plants in wt environments
if dried out, they die
what are the steps of seed germination
imbibition
respiration
growth of the embryo
what is imbibition in seed germination
seed must uptake water
cellular material absorbs water in the seed and will expand
seed coat will rupture and primary root can emerge
what is respiration in seed germination
anaerobic respiration is first since no oxygen under soil
needs to convert stored sugars into ATP
what is development of embryo axis n seed germination
shoot part of embryo begins to swell and emerge from the coat
seedling is produced
what is a seedling
a young plant sporophyte newly emerged from a seed coat
what are structures of the seedling
radicle/primary root hypocotyl epicotyl cotyledons true leaves
what is the radicle
first root to emerge from seed
what is the hypocotyl
stem section between the radicle and the cotyledons
what is the epicotyl
stem section between cotyledons and true leaves
what are true leaves
first leaves to emerge from the seedling that actually look like the typical leaves of the plant
what are cotyledons
specialized structures found in some plants
storage organs
cotyledons in monocots
one
cotyledons in dicots
two
what are 2 patterns in seed germination
hypogeous
epigeous
what is hypogeous germination
cotyledons remain underground after full germination
hypocotyl remains in the seed coat
epicotyl emerges from seed coat
what is the epigeous germination
cotyledons emerge from seed coat and are aboveground
hypocotyl emerges first from the seed
