IB Biology HL - D3.1

Reproduction

sexual vs asexual repdroduction

sexual - fusion of gametes, meiosis, genetic variation

asexual - mitosis, offspring are identical (clones)

fertilization

fusion of gametes

stages of fertilization

1. egg cell release chemoattractant that cause sperm cells to swim to

2. sperm cell penetrates through zona pellucida by releasing enzymes in acrosome. first sperm to reach egg fertilizes it.

3. after sperm enters egg, zona pellucida hardens to prevent polyspermy

4. gametes fuse and undergo mitosis to create embryo

prevention of polyspermy

acrosome reaction - only strongest/fastest sperm can fertilize

cortical reaction - cortical granules release enzymes that harden the zona pellucida

gametogenesis

gamete production
spermatogenesis and oogenesis

spermatogenesis

formation of sperm cells

~75 days, begins after puberty, 4 sperm cells per parent cell, occurs in seminiferous tubules

oogenesis

formation of ovum/ova cells

~14 days, begins before birth and pauses until puberty, 1 ovum per parent cell, occurs in follicles in ovary

spermatogenesis mechanism

germinal epithelial cells → primary spermatocytes → secondary spermatocytes → spermatids (nursed by sertoli cells) → spermatozoa (sperm cells)

oogenesis mechanism

puberty

sequence of developmental changes from childhood to sexual maturity

sexual hormones

FSH, LH, estrogen, testosterone, GnRH

GnRH

Gonadotropin-releasing hormone

initiates puberty, produced in hypothalamus

stimulates secretion of FSH and LH

FSH

follicle stimulating hormone, secreted by pituitary gland

men: initiates testosterone secretion (testes growth), sperm production

women: development and maturing of follicles, prepares ovaries for ovulation

LH

luteinizing hormone, secreted by pituitary gland

male: testosterone secretion by Leydig cells

female: stimulates progesterone and estrogen production, triggers ovulation

progesterone

thickens endometrial lining to prepare for egg implantation

menstrual cycle

two sub cycles: ovarian and uterine

provides opportunity for pregnancy

ovarian cycle

follicular phase - follicles develop until most matured bursts and releases oocyte into oviduct

luteal phase - follicle cells differentiate into corpus luteum and breaks down if no pregnancy

uterine cycle

involves changes of endometrium

shedding = period

thickening = preparation for implantation of embryo

menstrual cycle feedback loop

FSH increase = estrogen increase = FSH decrease

estrogen increase = LH increase = estrogen decrease

estrogen

thickens endometrium, prepares for ovulation

testosterone

production of testes and other male features male features, spermatogenesis

embryonic development

days 1: DNA replication, gene expression, and mitosis forms embryo

days 2-7: cell division forms blastocyst

day 7: implantation, blastocyst sheds zona pellucida and binds with endometrium cells

week 9: embryo develops into fetus, placenta beings to form

HCG

human chorionic gonadotropin

produced by blastocysts

detected by pregnancy tests

placenta (3)

made of fetal tissue

prevents mixing of maternal and offspring blood

exchanges gas and nutrients between fetus and mother

placenta structure

villi - high SA:V ratio

intervillous space - surrounds villi with maternal blood for exchange

trophoblast - makes HCG, ensures no mixing of maternal and fetal blood

differences between male and female reproduction (4)

motility, size, food reserves, numbers produced

male reproductive structure (7)

testes, epididymis, sperm duct, seminal vesicle/prostate glad, scrotum, penis, urethra

female reproductive structure (6)

vulva, vagina, cervix, uterus, oviduct, ovaries

stamen

male parts of flower

anthers and filaments

pistol/carpal

female parts of flower

ovary, style, stigma

anther

where pollen is produced

filament

stalk that holds anthers

ovary (plant)

where ovum is produced

style

stalk that holds up stigma

stigma

site of pollen bonding

pollen formation

1. diploid cell undergo meiosis to produce 4 haploid cell

2. each haploid cell undergoes mitosis twice to produce 3 haploid nuclei

3. 2 of these nuclei are inactive until fertilization, the other 1 actively expresses genes to assist fertilization

ovary (plant) formation

1. meiosis of diploid nucleus produced 4 haploid nuclei. 3 will not develop further

2. 4th haploid nucleus will divide by mitosis 3 times to make 8 haploid cells. 1 is gamete, others express genes to assist fertilization

purpose of cross pollination

promotes genetic variation, reduces the chances of homozygous alleles

mechanisms of cross pollintation

maturation of stamen and pistol occur at different times, flower adaptions to move pollen from one plant to another

self-pollination mechanism

some plants detect self-incompatibility genes which stop pollen tube from forming

reason for dispersal of seed

decrease competition for resource between parents and offspring

seed germination requirements

requires water, warmth, oxygen, synthesis of gibberellin