D3.1 Reproduction (year 6) Flashcards
Diff btwn sexual and asexual repro
Sexual
- 2 parents required
- offspring genetically unqiue compared to both parents
- provides new gene combinations and thus promotes genetic variation
- allows adaptations for changing environment
Asexual:
- 1 parent required
- offspring genetically identical to parent
- provides no new gene combniations, relatively little genetic variation
- promotes little change in adaptation but may be benefical in an exsisting non-changing environment
Role of meiosis and fusion of gametes in the sexual life cycle
Meiosis breaks up parental combinations of alleles:
- reduction division as the no. of chromosomes in each gamete is reduced to 1/2 of the original number.
- so each homologous pair has maternal and paternal chromosomes.
Fusion of gamates produces new combinations. (fertilisation)
- purpose of fertilisation is to restore the diploid no. of chromosomes to homologous pairs.
How is gamete genetic variation achieved
- crossing over leading to recombination of alleles during metaphase I
- random oreintation and division of chromosomes during metaphase I (independent assortment)
- random fertilisation
Diff btwn male/female gamates
Male:
- travels to the female gamete, motile
- smaller to increase swimming efficiency, with less food reserves than the egg
- males produce millions of sperm each day, an ejaculation contains millions of sperm cells
Female:
- not motile
- large (x1000+) times bigger, contains all nutrients needed for early embryonic growth. (egg provides the initial source of nutrition for the developing embryo)
- females release only one egg during the menstrual cycle (although 2 or more are possible)
Practice drawing and labeling male and female repro systems
Pearson page 712
Name the structures + functions for female repro system
Ovaries: female gonads (primary sex organs). Produce and secrete oestradiol. Produce and release eggs (in the form of secondary oocytes). The area where ovulation occurs grows into the CORPUS LUTEUM, which temporarily produces progesterone.
Fallopian tubes (oviducts): ducts that carry the egg/early embryo to the uterus
Uterus: Muscular structure where the early embryo implants and develops if a pregnancy occurs
Endometrium: highly vascular lining of the uterus
Cervix: lower portion of uterus, has opening to the vagina that allows sperm to enter for fertilization and provide pathway for childbirth
Vagina: muscular tube that leads from the external genitals to the cervix. Semen is ejaculated during sexual intercourse
Name the structures + functions for male repro
Testes: male gonads. Sperm produced in small tubes called SEMINIFEROUS TUBULES
Epididymis: area where sperm are received, become mature and capable of swimming motion via flagella
Scrotum: Sac that holds the testes outisde the body cavity so that sperm production and maturation can occur at a temperature cooler than body temp
Vas deferens: muscular tube that carries mature sperm from the epididyis to the urethra during ejaculation
Seminal vesicles: small glands that produce and add seminal fluid to semen
Prostate gland: gland produces much of the semen, including carbohydrates for the sperm
Penis: becomes erect as a result of blood engorgement to facilitate ejaculation
Urethra: aft all glands have added fluids to semen, semen leave penis via urethra
Describe the hormonal regulation during the menstrual cycle
Menstrual cycle lasts on avg 28 days.
- time the release of an egg (ovulation) for possible fertilization and alter implantations into the endometrium. Can be divided into 2 cycles
PnS = prodcution and secretion
Ovarian cycle:
- controls PnS of eggs and cyclic release of oestradiol and progesterone
- Hypothalamus produces Gonadotropin-releasing hormone (GnRH). GnRH targets the pituitary gland to PnS follicle-stimulating hormone (FSH) and luteinizing hormone (LH). These 2 hormones target the ovaries.
- FSH and LH increase the PnS of oestradiol by ovaries.
- Oestradiol enters the bloodstream, targeting the endometrium to increase density of blood vessels to become highly vascular.
- +ve feedback loop = oestradiol stimulates the pituitary gland to PnS more FSH and LH.
- increase in FSH and LH also results in production of GRAAFIAN FOLLICLES. FSH and LH stimulate oocytes (possible future eggs) to be surrounded by follicle cells which take on a particular cellular arrangement to form a Graafian follicle
- the spike in FSH and LH leads to ovulation. The oocytes with the Graafian follicle’s inner ring of follicile cells enters the Fallopian tube after ovulation.
Uterine cycle
- controls preparation and maintenance of the endometrium to receive a fertilized egg
- During ovulation, the outer ring of Graafian follicle remains within the ovary, dividing and fill the “wound” area left by ovulation, forming a CORPUS LUTEUM.
- the corpus luteum produces progesterone, and is only active 10-12 days after ovulation if fertilization does not occur.
- progesterone maintians the thickened, higly vascular endometrium. As long as progesterone is maintained, endometrium does not break down and embryo can implant.
- the high levels of oestradiol and progesterone at the same time provide -ve feedback signal to hypothalamus and prevent production of GnRH.
- as hypothalamus does not produce GnRH, FSH and LH remain at low levels = another Graafian follicle not produced
- if there is no fertilization, corpus luteum breaks down after 10-12 days = decline in progesterone and oestradiol levels = endometrium not maintained.
- the endometrium ruptures and menstruation begins.
- drop in progesterone and oestrdiol also signals the hypothalamus to begin PnS GnRH, beginning the menstrual cycle again.
Describe the process of fertilisation
- sperm ejaculated into vagina
- motile sperm absorb sugar in semen as fuel
- sperm find they way through the cervix to the uterus
- swim up the endometrial lining, enter Fallopian tubes.
- sperm penetrate the follicle cell layer and a coating called the ZONA PELLUCIDA by releasing hydrolytic enzymes contained in their acrosomes to help penetrate.
- vesicles are released from the egg to destroy the sperm flagellum and mitochondria such that only the sperm nucleus enters the egg
- paternal and maternal sets of chromosomes remain separate for a time, DNA undergoes replication in preparation for mitosis. This is called a pronucleus.
- dissolution of nuclear membranes of sperm and egg nuclei, the pronuclei join tgt.
- All condensed chromosomes participate in a joint mitosis to produce 2 diploid nuclei.
Describe the use of hormones in IVF treatment
In Vitro Fertilization (IVF) treatment:
- female undergoes hormone therapy, treated with a drug that suspends the hormones associated with her natural menstrual cycle
- Takes hormone injections that include FSH, ensuring that she produces many Graafian follicles in each ovary = many potential eggs for harvesting. (SUPEROVULATION)
- eggs harvested surgically when time is right.
- male ejaculates into container to obtain sperm cells, mixed with harvested eggs in culture dishes.
- healthy embryos are later introduced into the females uterus for implantation
Describe the where gametes of flowering plants are located
- gametes of flowering plants are produced within ovules (f) and pollen grains (m)
- reduction division is not required to produce haploid gametes as reproductive structures are already haploid
Describe self pollination
Hermaphroditic plants:
- flowers have both male and female structures (e.g. orchids, sunflowers)
- gametes are produced by meiosis and there is a fusion of gamete nuclei to form an embryo = a form of SEXUAL REPRO
- disadvantage: loss of genetic variation as chromosomes from same individual
Describe cross-pollination
- pollen develops on anthers. Anthers (m) are positioned in a flower so that pollinators can come into contact with them.
- pollen is transferred to the stigma (f) which is held upright and is sticky
- pollen that adheres to a stigma grows into a pollen tube (equivalent to sperm), rather than swimming, pollen grains grow tubes that penetrate other parts of the flower to take the male reproductive nuclei to the ovule where female nuclei await fertilization.
- 1 pollen tube carries 2 male nuclei which can each cause a fertilization = double fertilization process.
- within the ovule there are 3 haploid nuclei. 1 pollen nuclei fertilizes 1 ovule nuclei to create a zygote. The other polen nuclei fertilizes the other 2 ovule nuclei to create an ENDOSPERM.
- endosperm is TRIPLOID, 3n. Growth of endosperm produces nutritive endosperm to nourish the embryo
Draw + label diagram of an insect-pollinated flower
pearson pg 719
Describe the structures + functions of insect-pollinated flowers
Sepal - protecting the developing flower while it is inside the bud
Petal - colourful to attract pollinators
Anther - part of stamen (male portion of flower) that produces pollen
Pollen - contain male nuclei used for ferilization
filament - stalk of stamen to hold up anther
Stigma - sticky top of a carpel (female portion of a flower) on which pollen lands
Style - part of carpel which supports the stigma
Ovary - base of carpel, containing 1 or more ovules
Ovule - chamber within ovary where female nuclei develop
Describe methods of cross pollination in plants
In some species,
- different maturation times for the pollen and ovules of the same flower to ensure that self-pollination cannot occur
- pollen and stigma use chemical self-incompatibility mechanisms. If self pollination occurs, the pollen tube does not grow bc chemical incompatibility
-flowering species produce flowers w only male/female parts
- entire plant is either male/female and can only produces flowers of their own sex
- pollen is transferred by wind, taking pollen away from the parent plant
Adv of cross pollination
benefit from genetic variation.
Disadv of self pollination in plants
leads to inbreeding, decreasing genetic diversity and vigour
Describe how self-incompatibility mechanisms work.
If self pollination occurs, protein interactions occur that reduce/stop growth of the pollen tube
for some species,
- pollen grain on stigma fails to germinate into pollen tube
- pollen grain germinates but does not enter through the stigma into the style
- pollen tube enters the ovule but nuclei degenerate before fertilization can occur
- fetilization occurs but plant embryo degenerates during early growth.
Describe speed dispersal in plants
- once a successful double fertilization has occured, seeds develop
- 1 ovule = 1 seed
- the ovary ripens and becomes a fruit
- Chemical energy inested into production of fruits to attract more animals as a means of dispersing seeds away from the parent plant
- seeds are protecting from ingestion and digestion by a seed coat, depositied in animal faeces away from parent plant
- other seeds have structures for different dispersal, e.g. coconut to float on water, pods that dry out and explode when seeds are ripe
Describe the process of seed germination in plants
- Dormancy
- when seeds are formed within ovary, they begin dormancy
- seed loses most of its water content, displaying a low metabolism with no growth or development.
- domancy time period is variable
- is an adaptation to overcome harsh but temporary environmental conditions. - Germination
- water, oxygen, appropriate temp is needed
- food reserves are called endosperm tissue, and are transferred to plant embryo by cotyledons.
- seeds begin germination by absorbing water (IMBIBITION), activating the biochemistry of the seed.
- rate of cell respiration and protein synthesis greatly increases
- embryonic plant prepares to emerge from seed coat, where the radicle emerges first, growing down into the soil
- the hypocotyl is the first structure to appear above ground. Leaves develop and photosynthesis begins as endosperm tissue is depleted.
- root structures develop, forming secondary roots and root hairs.
- all plant growth from this point on occurs at MERISTEM TISSUES, located at the tips of shoots and roots
Descrbe developmental changes in m/f during puberty
Hypothalamus increases production of gonadotropin-releasing hormone (GnRH), targeting the pituitary gland which secretes Follicle-stimmulating hormone (FSH) and luteinizing hormone (LH). FSH and LH are gonadotropins because they target gonads (ovaries in f and testes in males), stimulating steroid production by gonads, e.g. testosterone, oestradiol, progesterone.
Females and males
- increase in height and body mass
- growth of underarm and pubic hair
- acne begins
Females:
- development of breasts
- menstrual cycle begins
- bone structure of hips widens to prepare for possible childbirth
Males:
- growth of pubic, facial, chest hair
- voice depends
- enlargement of testes, penis
- erections begin
Describe spermatogenesis
The male process of meiosis, to produce spermatozoa.
- testes located outside the human body to provide cooler temperature (lower than internal body temp) necessary for production of spermatozoa.
- Spermatogenesis occurs within SEMINIFEROUS TUBULES.
- Near the outer wall of seminferous tubules lie SPERMATOGONIA.
- Each spermatogonium can undergo mitosis to replenish their numbers/meiosis to produce spermatozoa at any time.
- meiosis is reduction division as it reduces original diploid no. of chromsomes to haploid no. in gametes.
- mitosis produce 2 1/2 sized cells capable of growing again for later cell division
- meiosis produces 4 spermatozoa.
- Spermatozoa have flagellum for motility and acrosome to contain enzymes.
- developing spermatozoa get nutrients from cells in seminiferous tubules called SERTOLI CELLS
- there is lumen/cavity in centre of each seminiferous tubule. Once spermatozoa complete differentiate, they detach from Sertoli cell, move through lumen to the spididymis (storage area in testis)
Briefly describe steps of meiosis using human spermatogonia
- Human spermatogonia are diploid and contain 23 homologous pairs of chromosomes.
- In preparation for meiosis, DNA replication occurs, each of the 46 chromosomes now exsist as a pair of chromatids.
- Meiosis I: 2 cells produced with haploid no. of chromosomes (23) because the homologous pairs are separated. Each chromosomes still exsists as a pair of chromatids.
- Meiosis II: chromatids are separated, there is another cell division. 4 haploid cells, each containing 23 chromosomes, are created from the parent cell that originally contained 23 homologous pairs.
- Each cell must differentiate into fully functioning, motile spermatozoon.
Describe the process of oogenesis
The female process of meiosis.
- oogenesis also produces 4 cells as “end products” of meiosis (like spermatogenesis)
- unlike spermatogenesis, 3 of 4 cells are not used as gametes as they are too small to produce a viable zygote if fertilized.
- 3 cells are called POLAR BODIES, being a cellular “container” for divided chromosomes during meiosis I/II.
- the 4th cell is OVUM and is very large.
- within ovaries of female foetus, OOGONIA undergo mitosis many times to build no. of oogonia in ovaries.
- oogonia grow into primary oocytes. both are diploid.
- primary oocytes begin early stages of meiosis but are arrested during prophase I
- (in ovaries) FOLLICLE CELLS undergo mitosis repeatedly
- a single layer of follicle cells surround each primary oocyte to form a PRIMARY FOLLICLE.
- during each menstrual cycle, a few primary follicles finish meiosis I.
- the 2 haploid cells arising from a primary follicle (from meiosis I) are not equal in size.
- the small cell is the 1st POLAR BODY, acting as a reservoir for half of the chromosomes, later degenerates.
- the large cell is the SECONDARY OOCYTE
- single ring of follicle cells divide and form a fluid. 2 rings of follicle cels formed, with a fluid-filled cavity separating them. This forms a GRAAFIAN FOLLICLE.
- the increase in fluid btwn the 2 follicle cell layers creates a bulge on the surface of ovary, leading to ovulation.
secondary oocyte with innter ring of follicle cells = ovum.
- meiosis II is not completed until fertilization.
Diff/similarity btwn spermatogenesis and oogenesis
Spermatogenesis:
- produces millions of cells daily
- 4 gametes produced from each cell
- gamete cells produced are smallest in the body
- gamete cells contain minimal cytoplasm and organelles
- gamete cells are motile
Oogenesis:
- thousand of cells produced total
- 1 gamate produced from each cell + 2 polar bodies
- gamete cells produced are largest in body
- gamete cells contain huge quantities of cytoplasm, organelles, nutrients
- gamete cells are not motile
Describe mechanisms to prevent polyspermy
polyspermy - more than 1 spermatozoon fertilize the ovum. Results in the ovum not developing
- the 1st spermatozoon uses enzymes in acrosome to penetrate the plasma membrane of the ovum.
- this initiates a series of events called the CORTICAL REACTION.
- within the cytoplasm of the ovum are many small vesicles called CORTICAL GRANULES.
- the initial fertilization causes cortical granules to fuse with the ovums internal plasma membrane and release enzymes to the outside.
- these enzmes result in a chemical change in the glycoprotein layer surrounding the ovum called the ZONA PELLUCIDA. This makes the ovum impermeable to any more spermatozoa.
Describe the process of embryo development
Fertilization stimualte the embryo to begin mitosis.
Early embrbyo continues to move within Fallopian tubes towards cavity of uterus as it divides.
Upon reaching the uterine cavity, it is a hollow ball of cells called BLASTOCYST.
The blastocyst enters inner cavity of uterus, in direct contact with the endometrium.
Endometrium is highly vascular. Embryo sinks into the endometrial tissue (IMPLANTATION).
The ovum is so large becuase it contains the nutreints needed for early embryonic development
characteristics of blastocyst
blastocyst has:
- surrounding layer of cells called tropoblast which form the foetal portion of the placenta, embryonic membranes and umbilical cord.
- group of cells in interior called INNER CELL MASS, located towards 1 end of the blastocyst, becoming the body of the embryo
- fluid-filled cavity
How does pregnancy testing work
the trophoblast layer of embryonic cells and later the embryonic placenta cells produce human chorionic gonadrotopin (hCG).
hCG enters the bloodstream of the mother and allows continuation of CORPUS LUTEUM within moms ovaries. This allows the continued PnS of progesterone to maintain the vascular tissue of the endometrium.
hCG is hence a reliable indicator of pregnancy. Researches develop B-lymphocytes that produce only 1 antibody that recognises hCG as an antigen. These antibodies are called MONOCLONAL ANTIBODIES.
Upon detection, the antibodies chemically bond to an enzyme that changes colour.
Basically the anti-hCG antibodies bind to the hCG and colour change occurs.
Role of placenta in foetal development in uterus
Placenta forms from the trophoblast later of the blastocyst and from tissue from mom.
Side of placenta located further in uterine wall made of connective tissue and blood vessels formed by mom body.
Side closer to embryo formed by embryo and also contains connective tissue and blood vessels.
Foetal side of placenta there is umbilical cord, a protective sheath covering 3 foetal blood vessels.
When fully formed, 2 foetal blood vessels carry foetal blood to placenta, carrying CO2, urea, waste products, water, hormones.
The foetal blood vessel exchanges materials with the maternal bloodstream, and the 3rd foetal blood vessel returns oxygen, water, hormones, nutrients and alcohol/drugs used by mother during pregnancy to the foetus.
NO BLOOD IS EXCHANGED. The foetal blood vessels from umbilical cord divide into PLACENTAL VILLI to increase SA:V for molecular exchange.
which hormone is key in pregnancy/childbirth
PROGESTERONE.
- intiially secreted from the corpus luteum then from placenta.
- maintain the vascular tissue of the placenta.
- when foetus reaches full term (ready to be born), less progesterone is secreted by placenta, siganlling that birthing is about to begin
Changes in childbirth are triggered by a decrese in progesterone levels, allowing increases in oxytocin secretion due to +ve feedback.
What is parturition
Parturition is the process of giving birth.
- not part of normal mammalian homeostasis.
- characterized by uterine contractions
- as birth continues, uterine contractions become more and more intense and frequent (+ve feedback)
- oxytocin is involved (produced by hypothalamus, secreted by pituitary gland). Decrease progesterone stimulate gland to release oxytocin. Oxytocin receptors in uterine respond with contractions. Contractions stimulate the release of more oxytocin.
describe HRT and its risks
menopause is the period of a females life when her menstrual cycle first becomes less predictable, than stops altogether.
- this is caused as ovaries stop producing oestradiol and progesterone
- in order to alleviate symptoms (trouble sleeping, hot flushes, loss of musculature) females use HRT in the form of oestradiol.
Risks: could have relation to coronary heart disease.
- some researches believe there is no connection btwn HRT and heart disease
