sexual reprodution Flashcards
what is sexual reprodution
The process involving the fusion of the nuclei of two gametes to form a zygote (fertilised egg cell) and the production of offspring that are genetically different from each other
gametes
gamete is a sex cell
- contain half the number of chromosomes found in other body cells - a haploid nucleus
- contain one copy of each chromosomes - 23 chromosomes
zygotes
- fertilised egg cell
- 46 chromosomes
- diploid nucleus
fertilisation
- fertilisation - haploid male and a haploid female gamete fuse
to produce a diploid zygote - The diploid zygote undergoes cell mitosis to develop into
an embryo - sperm nucleus (23 chromosomes) enters egg cells and fuses with it
(23 chromosomes)
process of fertilization
- sperm cells move along the sperm duct
- The sperm cells then follow a chemical trail and travel through the plug of mucus in the cervix to reach the uterus (the womb)
- The sperm cells then travel into the oviducts
- If a sperm cell meets an egg cell in the oviduct, fertilisation can occur
adaptations of sperm + egg
sperm :
- flagellum (tail) - to swim to egg
- enzymes in head region - (digest through jelly coat and cell membrane of an egg cell
- mitochondria - power sperm - give energy for respire for flagellum can move
- locomoation
egg :
- cytoplasm contacting store of energy - for mitosis
- jelly like coating from impermeable barriers after fertilisation so no other sperm can enter egg
adaptations of sperm + egg
sperm :
- flagellum (tail) - to swim to egg
- enzymes in head region - (digest through jelly coat and cell membrane of an egg cell
- mitochondria - power sperm - give energy for respire for flagellum can move
- locomotion
egg :
- cytoplasm contacting store of energy - for mitosis
- jelly like coating from impermeable barriers after fertilisation so no other sperm can enter egg
understand the roles of oestrogen
Oestrogen – repairs the uterus lining and inhibits FSH (follicle
stimulating hormone) production and stimulates LH (luteinising
hormone) production
- Oestrogen levels rise from day 1 to peak just before day 14
this causes the uterine wall to start thickening and the egg to mature
The peak in oestrogen occurs just before the egg is released - produced in ovary
- targets Uterus wall and Pituitary gland
understand the roles of LH in the menstrual cycle
LH: causes the egg to be released (ovulation)
- ## produced in Pituitary gland
understand the roles of FSH
Stimulates a follicle (immature egg) to mature within the ovary
(before it can be released)
o Stimulates the oestrogen production by the ovaries
- produced in Pituitary gland
- targets ovary
understand the roles of progesterone in the menstrual
cycle
Progesterone – maintains the uterus lining and also inhibits FSH
production
- If pregnancy occurs - progesterone levels remain high for nine
months, maintaining the lining and inhibiting FSH, so preventing
a new follicle maturing
- If pregnancy does not occur: progesterone levels drop towards
the end of the 28 day cycle and so the uterus lining breaks
down (menstruation) and FSH production is no longer inhibited,
so allowing a new follicle to mature
Progesterone stays low from day 1 – 14 and starts to rise once ovulation has occurred
The increasing levels cause the uterine lining to thicken further; a fall in progesterone levels causes the uterine lining to break down (menstruation / ‘period’)
- produced - ovary
- targets - Uterus wall and Pituitary gland
mitosis
single parent cell divides once to from two new identical diploid daughter cells
meiosis
a single parent cell divides twice to produce four non-identical haploid sex cells
understand how the developing embryo is protected by amniotic fluid
The embryo is surrounded by amniotic fluid, which is produced by the
amniotic sac
This fluid cushions the developing embryo, protecting it from impacts and
also provides a sterile environment, to ensure there is no infection
placenta role
The placenta connects the developing embryo to the mother’s uterus wall,via the umbilical cord
The placenta has adaptations for exchange of substances between the
mother and the developing embryo:
o Highly folded to increase surface area to speed up diffusion
o Very rich blood supply to maintain steep concentration gradient
o Thin walls, leading to a short diffusion pathway
Substances moving from the foetus to the mother include metabolic
wastes such as carbon dioxide and urea and substances moving from the
mother to the foetus would include oxygen, glucose and amino acids
