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IB biology > topic 11.4 - sexual reproduction > Flashcards

topic 11.4 - sexual reproduction Flashcards

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1
Q

what to spermatogenesis and oogenesis both involve?

A

mitosis, cell growth, two divisions of meiosis and differentiation

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2
Q

define oogenesis

A

the production of egg cells in the ovaries

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3
Q

describe the pre-puberty stage of oogenesis

A
  1. starts in the ovaries of a female fetus
  2. germ cells in the fetal ovary divide by mitosis and the cells formed move to distribute themselves through the cortex of the ovary
  3. when the foetus is four or five months old, these cells grow and start to divide by meiosis
  4. by the seventh month, they are still in the first division of meiosis and a single layer of cells (follicle cells) has formed around them.

no further development takes place until after puberty

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4
Q

define a primary follicle

A

the cell that has started to divide by meiosis, together with the surrounding follicle cells

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5
Q

describe the post-puberty stage of oogenesis

A

no more primary follicles are produced, but at the start of each menstrual cycle a small batch are stimulated to develop by FSH. Usually only one goes on to become a mature follicle, containing a secondary oocyte.

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6
Q

difference between a mature ovarian follicle and a primary follicle

A

a mature ovarian follicle has many more follicle cells, outer and inner follicle cells and cavities, and the oocyte is more fully developed

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7
Q

define spermatogenesis

A

the production of sperm in the testes

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8
Q

describe the testes

A

composed of a mass of narrow tubes, called seminiferous tubules

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9
Q

describe the germinal epithelium

A
  • outer layer of cells of seminiferous tubules.
  • where process of sperm production begins
  • contains cells in various stages of sperm production, with the most mature stages closest to the fluid-filled centre of the ST
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10
Q

Sertoli cells

A

large nurse cells in the wall of the tubule

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11
Q

spermatozoa

A

cells that have developed tails

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12
Q

draw a diagram and describe the stages of spermatogenesis

A
  1. an outer layer called germinal epithelium cells (2n) divide endlessly by mitosis to produce more diploid cells
  2. diploid cells grow larger and are then called primary spermatocytes (2n)
  3. each primary spermatocyte carries out the first division of meiosis to produce two secondary spermatocytes (n)
  4. each secondary spermatocyte carries out the second division of meiosis to produce two spermatids (n)
  5. spermatids become associated with nurse cells (Sertoli cells) which help the spermatids to develop into spermatozoa (cell differentiation)
  6. sperm detach from Sertoli cells and are eventually carried out of the testis by the fluid in the centre of the seminiferous tubule
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13
Q

draw a diagram and describe the stages of oogenesis

A
  1. The process begins during foetal development, when a large number of cells (oogonia) are formed by mitosis before undergoing a period of growth
  2. These cells begin meiosis but are arrested in prophase I until puberty
  3. At puberty, some follicles continue to develop each month is response to FSH secretion
  4. These follicles complete the first meiotic division to form two cells of unequal size
    The cell with less cytoplasm is a polar body (which degenerates), while the larger cell forms a secondary oocyte
  5. The secondary oocyte begins the second meiotic division but is arrested in prophase II (until fertilisation)
  6. It is released from the ovary (ruptured follicle develops into corpus luteum) and, if fertilisation occurs, will complete meiosis
  7. The second meiotic division will produce an ovum and a second polar body
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14
Q

draw and annotate an egg

A
  • two centrioles
  • haploid nucleus
  • cytoplasm (or yolk) containing droplets of fat
  • cortical granules
  • layer of gel composed of glycoproteins (zona pellucida)
  • layer of follicle cells (corona radiata)
  • plasma membrane
  • first polar cell
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15
Q

draw and annotate a sperm

A
  • acrosome
  • plasma membrane
  • haploid nucleus
  • centriole
  • helical mitochondria
  • mid-piece
  • tail
  • microtubules in a 9+2 arrangement
  • protein fibres to strengthen the tail
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16
Q

differences between oogenesis and spermatogenesis:
Location
Number of gametes produced
Gametes per germ cell
Beginning of process
Timing of gamete formation
End of process
Timing of gamete release
Meiotic divisions
Germ line epithelium

A

Testis
Life long production (millions)
Four
Begins at puberty
Continuous (any time)
Fertility is life long but reduces
Any time
Uninterrupted
Involved in gamete production

Oogenesis
Ovary
Fixed amount (only - 400 mature)
One
Begins during fetal development
Once a month (menstrual cycle)
Fertility stops at menopause
Monthly cycle
Arrested
Not involved in gamete production

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17
Q

define polyspermy

A

when multiple sperm enter the egg

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18
Q

state the 3 mechanisms that occur after sex

A
  1. the acrosome reaction
  2. penetration of the egg membrane
  3. the cortical reaction
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19
Q

the acrosome reaction

A

when the sperm binds to the zona pellucid and the contents of the acrosome are related, the enzymes from it digest the zona pellucida.

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20
Q

describe the acrosome

A

a large membrane-bound sac of enzymes in the head of the sperm

21
Q

penetration of the egg membrane

A
  • acrosome reaction exposes an area of the membrane on the tip of the sperm that has proteins that can bind to the egg membrane.
  • the first sperm that gets through the zona pellucid therefore binds and the membranes of sperm and egg fuse together
  • the sperm nucleus enters the egg cell (fertilisation)
22
Q

cortical reaction

A
  • sperm causes activation of the egg
  • the cortical granules (vesicles located near the egg membrane) release their contents from the egg by exocytosis
  • cortical vesicle enzymes result in the digestion of binding proteins so that no further sperm can bind, as well as a general hardening of the zona pellucida
23
Q

fertilisation in animals can be

A

internal or external

24
Q

internal fertilisation

A
  • terrestrial animals
    + ensures gametes do not dry out and sperm and ova are placed in prolonged close proximity to each other,
    + developing embryo is protected inside female
25
Q

external fertilisation

A
  • aquatic animals
    + animals have behaviours that bring eggs into proximity with sperm
  • risks including predation and susceptibility to environmental variation such as temperature and pH fluctuations and pollution
26
Q

fertilisation -> implantation

A
  1. fertilised ovum divides by mitosis to become an embryo
  2. there is migration of cells, giving the embryo the shape of a hollow ball (blastocyst)
  3. at 7 days old, the blastocyst reaches the uterus, having been moved down the oxidant by the cilia of cells in the oviduct wall
  4. at this age the zona pellucida (surrounded + protected embryo) breaks down
  5. obtains needed supply of food by sinking into endometrium/uterus wall (implantation)
27
Q

implantation onwards

A
  1. outer layer of blastocyst develops finger-like projects allowing it to penetrate uterus lining and exchange materials with mother’s blood
  2. embryo grows and develops
  3. by 8 weeks, it has started to form bone tissue and is considered a foetus rather than embryo
28
Q

role of hCG in early pregnancy

A

early in pregnancy the embryo produces human chorionic gonadotropin, which stimulates the corpus lute in the ovary to continue to secrete progesterone and oestrogen, which stimulate the continued development of uterus wall, which supplies the embryo with everything that it needs

29
Q

two main roles of placenta

A
  • facilitate exchange of materials between mother and embryo
  • secrete estrogen and progesterone
30
Q

why is the placenta needed?

A

because the body surface area to volume ratio becomes smaller as the foetus grows larger

31
Q

describe the structure of the placenta

A
  • made of fetal tissues, in contact with maternal tissues in the uterus wall.
32
Q

amniotic sacs

A

series of membranes developed by the foetus, which contain amniotic fluid which supports and protects the developing fetus

33
Q

what is the basic functional unit of the placenta?

A

a finger-like piece of fetal tissue (placental villus)

34
Q

why do these villi increase in number during pregnancy?

A

to cope with the increasing demands of the foetus for the exchange of materials with the mother

35
Q

where does maternal blood flow in the placenta?

A

in the intervillous spaces around the villi

36
Q

where does foetal blood flow in the placenta?

A

in blood capillaries, close to the surface of each villus

37
Q

placental barrier

A

cells that separate maternal and fetal blood (selectively permeable)

38
Q

draw a diagram of placenta

A

p507

39
Q

describe exchange of materials between mother and foetus

A

mother -> foetus:
- oxygen (diffusion)
- glucose (facilitated diffusion)
- antibodies (endocytosis)
- water (osmosis)

foetus -> mother:
- urea
- carbon dioxide (diffusion)
- water (osmosis)

40
Q

role of placenta in oestrogen and progesterone production

A

by about the 9th week of pregnancy, the placenta secretes these hormones in large enough quantities to sustain the pregnancy so the corpus luteum is no longer needed

41
Q

what is birth mediated by?

A

positive feedback involving oestrogen and oxytocin

42
Q

role of progesterone in parturition

A

during pregnancy, progesterone inhibits secretion of oxytocin by the pituitary gland and contractions of myometrium (contractions of the muscular outer wall of the uterus).

at the end of pregnancy, hormones produced by the foetus signal to the placenta to stop secreting progesterone, and oxytocin is therefore secreted

43
Q

role of oxytocin in parturition

A

positive feedback system:
- oxytocin stimulates contractions of the muscle fibres in the myometrium
- these contractions are detected by stretch receptors, which signal to the pituitary gland to increase oxytocin secretion
- this makes contractions more frequent and vigorous

44
Q

what is the advantage of this positive feedback system?

A

causes a gradual increase in the myometrial contractions, allowing the baby to be born with the minimum intensity of contraction

45
Q

describe parturition

A
  1. relaxation of muscle fibres in the cervix causes it to dilate
  2. uterine contraction bursts amniotic sac and amniotic fluid passes out
  3. further uterine contractions push the baby out through the cervix and the vagina
  4. placenta and umbilical cord expelled rom body
46
Q

precocial state

A

hatched or born in an advanced state and able to feed itself and move independently almost immediately.

47
Q

mammals with a large body size are more likely to be

A

precocial - this is correlated with a long gestation period

48
Q

altricial state

A

relatively helpless, incompletely developed offspring

49
Q
A

IB biology (60 decks)

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