Reproduction Flashcards
Sperm acrosome
Membrane bound storage for enzyme that digest the layers of the ovum and allow the sperm head to penetrate
Sperm mitochondria
Mitochondria is tightly packed into the middle section of the perm provide the ATP for the lashing of the tail
Sperm nucleus
Contail highly dense haploid chromosome
Sperm microtubles
Produce whip-like movement of the tail that keep the mature sperm in suspension and help it swim towards the ovum
Sperm flagellum
Helps propel the sperm by its movement in a liquid environment
Ovum cell surface membrane
Upon fertilisation with a sperm, ion channels in the membrane opne and close so that the inside of the cell becomes electrically postive
This blocks the entry of the further sperm
Ovum Zona pellucida
Layer of protective jelly around the unfertilised ovum
These will combine with cortical granule upon fertilisaton to form a tough membrane to prevent other sperm from entering the ovum
Protective layer of jelly
—> forms an impermeable barrier after fertilisation to prevent otther sperm nuclei to enter the zona pellucida
Ovum Cytoplasm
Cytoplasm contains nutrient for growth of the developing embryo
—> provides energy for divding zygote after fertilisation
Ovum Nucleus
The haploid chromosome contains genetic material for fertilisation
Ovum polar body
A small haploid cell formed at the end of the second division of meiosis. This allows for the ovum go be haploid. The polar body will not be fertilised
Fertilisation in human process
1) when sperm are close to the ovum they use their flagella to swim through the follicle cells. A few huhdred sperm reach the ovum from the million that are released. The acrosome of the sperm mature along the way so that they are ready to release enzyme
2) when sperm reach the zona pellucida (jelly coat) the acrosome reaction is triggered. The enzyme stored in the head of the sperm are released and start to digest the zona pellucida
3) the membrane of the first sperm to reach the memrbanr of the ovum cell fuses with the ovum (oocytes) cell membrane and the nucleus of the sperm cell enters the cytoplasm of the ovum
Once the ovum has been fertilised a reaction called the cortical reaction occurs which causes cortical granule to harden the zona pellucida forming a tough fertilisation membrane, repelling and preventing any more sperm from entering
The sperm nucleus entering the ovum triggers meiosis 2 to occur in the egg cell. This result in three polar bodies (which are degraded) and the ha0loid ovum.
The chromosome of the male and female nuceli replicate then the cell which is now diploid and known as a zygote, start to undergo mitosis
State two difference between sporophyte and gametophete generation
Sporophyte generation
—> the diploid generation in plants that produces spores by meiosis
Gametophyte
—> the haploid generation in plants that gives rise to the gametes by mitosis
Describe a microgamete
A male gamete produced in plants , the pollen grains
Describe the difference between a generative nucleus and tube nucleus
Generative nucleus
—> the male nucleus that will fuse with female nucleus
Tube nucleus
—> a male nucleus that will control the production of the pollen tube in fertilisation
Define double fertilisation
A process that occurs in plants in which one male nucleus fuses with two polar nuclei to form the triploid endosperm nucleus and other fuses with the egg vell to form the diploid zygote
Define external fertilisation
the process of fertilisation in which the female and male gamete are released outside of the parental bodies to meet and fuse in the environment
Define internal fertilisation
The fertilisation of the female gamete by the male gamete whcih takes places inside the body of the female
Define megagamete
The female gamete, the egg cell, in plant
External fertilisation
- aquatic species
- female and male gamete discharged directly into the environemnt where they meet & fuse
DISADVANTAGES
-Wasteful
EX jellyfish
-release male & female gamete into the sea
—> a matter whether it will fertilise
Internal fertilisation
-transfer of the male gamete directly to the female
EX insect
-whereby male gamete are released directly into the body of the female during mating
-this makes it keep moist environment
—> placed as close as possible
Plant fertilisation
A pollen grains lands on the stigma and germinates
A pollen tube grows from the pollen grain down the style
Hydrolytic enzyme digest the style producing the tube and the digested tissue provides the nutrients for the growth of the pollen tube
The generative nucleus divide by mitosis as it travels down the style
Upon reaching the ovule one of the generative nuclei fuses with the two polar nuclei to form endosperm which is triploid and provide food for germination of the seed
The other male generative nucleus fuses with the egg cell to form a zygote which is diploid
Define polyspermy
The fertilisation of an egg by more than one sperm
Why it cant be polyspermy
the entry of more than two spermatozoa into the egg cytoplasm, referred to as polyspermy, causes aberrant effects on meiosis completion or embryo development and hence embryonic death, due mainly to excess male centrosomes delivered into the egg.