2.4 Sexual Reproduction in Mammals Flashcards
give a feature of follicle cells on the ovum
secrete chemicals that activate release of enzymes from sperm
give one feature of the nucleus in an ovum
contains haploid set of chromosomes
give one feature of lipid droplets in an ovum
source of energy for growth and division
give one feature of the zone pellucida in an ovum
hardens once the sperm nucleus has entered the ovum to prevent polyspermy
give one feature of the lysosomes in an ovum
release chemicals that cause the zona pellucida to harden
give features of the acrosome in a sperm cell
contains hydrolytic enzymes
swells and bursts in contact with follicle cells and zona pellucida
enzymes in acrosome digest follicle cells and zone pellucida to allow membranes of sperm and ovum to fuse
give features of the midpiece in a sperm cell
contains lots of mitochondria that carry out aerobic respiration, generating ATP for movement
give features of the axoneme in a sperm cell
made from proteins and microtubules, which use ATP to propel the sperm forward
give a feature of cytoplasm in a sperm cell
there is very little cytoplasm so cells are small and can be released in large numbers
it also assists motility
give a feature of cytoplasm in an ovum cell
it is very large so egg can divide immediately
give 6 key features of sperm cells
- smaller than ovum and is motile
- long tail for movement
- little/no food reserves, energy comes from nutrients in seminal fluid
- head contains acrosome to hydrolyse zona pellucida
- sperm is produced in large quantities and production is continuous
- male produce over 100 million sperm per ejaculation but only one penetrates the ovum
give six features of the ovum
- bigger than sperm and incapable of independent movement
- wafted by oviducts by cilia and muscular contraction
- cytoplasm contains protein and lipid reserves
- head surrounded by zona pellucida that harden when one sperm penetrates
- only one ovum is produced
- 2 ovaries in female body so one side of the ovary will ovulate at alternative cycles
describe fully the process of fertilisation
- when sperm approaches egg, it is in seminal fluid which provides medium for sperm to swim and contains hormones, prostaglandins, which stimulate contraction of uterus and oviducts to assist sperm movement
- ACROSOMAL REACTION- membrane of acrosome and sperm fuse to release hydrolytic enzymes onto zona pellucida
- proteins on sperm head bind to receptors of ovum
- membranes of sperm and egg fuse together
- CORTICAL REACTION- cortical granules move towards ovum and release contents onto zona pellucida, which then hardens to prevent polyspermy
- FERTILISATION- haploid sperm nucleus and haploid ovum nucleus fuse to form a diploid zygote nucleus
describe the process of spermatogenesis and where it takes place
it takes place in seminiferous tubules in testes
- diploid primordial germ cell divides several times by mitosis to form diploid spermatogonia
- after several mitotic divisions, a primary spermatocyte is formed
- first meiotic division of spermatocyte results in two haploid secondary spermatocytes
- second meiotic division results in 4 haploid spermatids
- spermatids differentiate in tubules to form spermatozoa (sperm)
describe the process of oogenesis and where it takes place
occurs in ovary
- diploid primordial germ cell in ovary divides several times by mitosis to form diploid oogonia
- only one of the oogonia continues to develop- this is the primary oocyte
- `first meiotic division results in 2 haploid cells of unequal size - the large one is a secondary oocyte whereas the small one is a polar body
- the second meiotic division consists of secondary oocyte dividing to form haploid ovum and polar body
- polar body divides to form more polar bodies which degenerate and die as ovum develops
