fertilisation Flashcards
gameotogenesis
gametes that make sexual reproduction possible formed in this process
special cells of ova
primordial germ cells in gonads
role of mitosis in gameotogenesis
provides precursor cells
spermatogenesis
formation of spermatoza
precursor cells of sperm
primoridal germ cell
1 stage of spermatogenesis
-diploid primordial germ cell divides by mitosis to form diploid spermatogonia
second stage of spermatogenesis
spermatogenia grows without further division until big enough to be called primary spermatocytes
third stage of spermatogenesis
spermatocytes undergo meiosis
first meiotic division results in two haploid cells called secondary spermatocytes
fourth stage of spermatogenesis
second meiotic division results in four haploid cells called spermatids
fifth stage of spermatogenesis
spermatids differentiate in tubule of testes to form spermatozoa
active gametes capable of fertilising an ovum
oogenesis
formation of ova
difference of roles of germ cell of ova and sperm
germ cell in testes forms lots of sperm
germ cell in ovaries forms only one egg per cell
first step of oogenesis
diploid germ cell divides by mitosis to make diploid oogenia
most oogenia dont develop further
degenerate
second step of oogenesis
only one diploid oogenia grows lots of material go into making egg
this cell known as primary oocyte
third stage of oogenesis
primary oocyte undergoes meiosis
results in 2 cells
larger cell secondary oocyte
smaller sticks to oocyte called first polar body
fourth stage of oogenesis
oocyte dont further divide until after ovulation
ova in ovaries secondary oocyte
fifth stage of oogenesis
second meiotic division after fertilisation occurs
-secondary oocyte divides to form haploid ovum
another polar body formed
first polar body divides to make 2 more
degenerate and die as ovum develops
function of polar bodies in ova
recieve chromosomes in meiotic division
tasks of sperm
-remain in suspension in semen to transport in female duct
-penetrate protective ova barrier
deliver male haploid genome safely
millions made in mans lifetime because their trash
acrosome of sperm
membrane bound storage site for enzymes that digest layers surrounding ovum and allow sperms head to go through
nucleus of sperm
has highly condensed halpoid chromosomes
condensed state of genetic material reduced amount of energy needed to transport it
mitochondria in sperm
tightly packed in middle section provide atp for lashing of tail
microtubules
produce whip like movements of tail that keep mature sperm in suspension and help swim towards ovym
tail of sperm
flagellum that propels sperm by movement in liquid enviorment
zona pelludica of ova
clear jelly like layer
features of ova
-zona pelludica
haploid polar body
-cell surface membrane of oocyte
-cytoplasm with food reserves
sporophyte generation
first phase of plant is diploid and produces spores by meiosis
gametoohyte generation
second stage of plant is haploid and gives rise to gametes in plants by meiosis
sporophyte
main body of plant and is diploid
what happens to haploid gametophytes
reduced to parts of anther and ovary
-produced by meiosis from spore mother cells
where does meiosis occur in flowering plants
anthers resulting in lots of pollen grains that carry male gametes
what does each anther have
four pollen sacs where pollen grains develop
are diploid
whats in each pollen sac
large number of microspores which are gametophyte generation
features of gametes
have 2 haploid nuclei
names of two haploid nuclei in gametes
tube nucleus and generative nucleus
function of tube nucleus
produces pollen tube that penetrates through stigma style and ovary into ovule
function of generative nucleus
then fuses with nucleus of ovule to form new individual
function of tube nucleus
-produced by tube nucleus
-penetrates through stigma and ovary into ovule
-generative nucleus then fuses with nucleus of ovule to form new individual
formation of egg cells in plants
-meiosis results in number of ova in ovules inside ovary
-ovula attached to wall of ovary by pad of placenta
-nucellus forms
-diploid megaspore- four haploid megaspores by meiosis
-3 die and one grows
-megaspore has 3 miotic divisions
-results in embryo sac that has egg cell
two polar nuclei
synergids
antipodal cells
nucellus
complexe structure of coverings that form around tissue of placenta
pollination
transfer of pollen from anther to stigma often from one flower to another
how pollen is transfered
insects
mammals
bird
wind
external fertilisation
female and male gametes released outside parental bodies and meet and fuse in outside enviorment
internal fertilisation
of female gamete by male gamete which takes place in body of mother
disadvantages of internal fertilisation
not sure if gametes will meet
good for complex and simple water animals
dis and ad of internal fertilisation
gametes in body makes sure ova and sperm in moist enviorment maximises chance of fertilisation
-might not fertilise
how sperm move to ova
as sperm move through tract acrosome matures so releases enzymes and penetrates ovum
features of ovum in tract
not fully completed meiosis
-secondary oocyte with polar body
zona pelludica
-ovum released surrounded by protective jelly like layer and some folicles of hair
what happens when head of sperm touches ovum
-acrosome reaction triggered
-enzymes digest follicle hairs and zona pelludica
-one not enough so lots of sperm in ejaculation provide enough enzymes to break down barrier
what happens when one sperm manages to touch barrier of ovum
oocyte completes second meiotic devision
-haploid egg nucleus fuse with haploid male nucleus
why is it important not loads of sperm touch egg
-egg fertilised by to many sperm (polyspermy) and would produce nucleus with to many sets of chromosomes
how are lots of sperm prevented form coming to egg
-ion channels in cell membrane of ovum open and close inside of cell
-becomes positive instead of negative outside
-
fertilisation membrane
tough layer that forms around fertilised ovum to prevent entry of other sperm
what happens when head of sperm enters ova but not tail
-it absorbs and swells
-releases chromosomes
-to fuse with those of ovum and form diploid zygote
-conception has occurred
what happens when pollen land on surface of stigma during pollination
-molecules interact
-if recognise each other, pollen grain germinates
-
where does pollen tube begin to grow
-out from tube cell of pollen grain through stigma into style
tip of pollen down tube
-uses hydrolytic enzymes to digest throuugh tube
-digested tissues acts as nutrients source and pollen tube grows
double fertilisation
in plants where male nucleus fuses with nuclei of two polar nuclei to form endosperm nucleus and other fuses with egg cell to form diploid zygote
totipotent
-zygote totipotent
-potential to form all types of cells for new person
first stage of developing embryo
cleavage
-special mitosis which cell divide without normal interphase
-happens as embryo travels down oviduct
result small identical ball of cells
blastocyst
small ball of unspecialised cells as a result of cleavage process
embryonic stem cells
tiny cells of early human embryo
role of outer layer cells in blastocyst
form placenta and inner cells already lost some ability to specialise
pluripotent
can all types of cells for future but not tissue like placenta
pluripotent embryonic stem cells
cells that can change into any cell but not tissue like placenta
cell determination
cells already predestined and determined to become one type of tissue
-even if surgically removed and paced on other part of body will still produce what predertimined to
