seed & embryo development Flashcards
describe alternation of generations in angiosperms
-sporophytes are larger and live longer than gametophytes
-3 derived traits = flowers, double fert, production of fruits
describe gametophyte development
-most reduced gametophytes are in angiosperms
-dependent on sporophyte for nutrients (enclosed in sporophyte tissues)
what are the first 3 steps in female gametophyte formation?
1) carpel develops
2) 1 or more ovules form in ovary
3) embryo sac develops in ovule
what happens to the megasporocyte in the production of female gametophytes?
megasporocyte enlarges and undergoes meiosis
what happens to the one megaspore that survives?
it undergoes mitosis 3 times w/o cytokinesis to give rise to one cell with 8 haploid nuclei
what happens to the cell with 8 haploid nuclei?
the cell divides and forms the embryo sac (synergids help guide pollen to sac)
how are microsporangia produced?
stamens grow and each anther produces 4 microsporangia
what do the sporangia contain?
microsporocytes that undergo meiosis to form haploid microspores
what do the microspores undergo?
mitosis to produce pollen grain with 1 generative cell and 1 tube cell
what makes up the pollen grain?
tube/generative cells + sporopollin protective wall
how does pollination occur in angiosperms?
microsporangia release pollen which sticks to the stigma of another flower. pollen grain absorbs water and germinates to release tube nucleus that divides into two sperm cells
why is double fertilization beneficial?
ensures the endosperm develops only in ovules where the egg has been fertilized
how does the seed carry out development?
stockpiles proteins, oils, and starch allowing embryo to develop into a new sporophyte
how does the endosperm develops?
triploid nucleus divides to form a supercell and cytokinesis forms membranes to produce cell walls & endosperm becomes solid
how does the embryo develop?
1) mitosis splits egg -> basal cell
2) basal cell divides -> suspensors
3) terminal cells give rise to embryo
4) several divisions lead to pre embryo and cotyledons
what are suspensors?
thread of cells that transfer nutrients to the embryo
what are cotyledons?
part of the seed embryo which may become the 1st leaf
what is inhibition?
delay of germination until conditions are ideal for growth
what is the first organ to emerge in the seed?
radicule which develops into the primary root
what is synchrony in flowering plants?
when multiple plants flower at the same time encouraging outbreeding (sexual reproduction)
what is a developmental switch?
switch in shoot apical meristems from leaves/stems (vegetative structures) to flowers (reproductive structures)
how is the transition into a floral meristem triggered?
external cues and internal signals
what is a simple fruit?
fruit that develops from a single carpel
what is an aggregate fruit?
fruit that develops from multiple carpels from one flower
