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29 Cards in this Set
- Front
- Back
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Sexual reproduction |
Sexual reproduction is the creation of offspring through the process offertilization, the fusion of 2 gametes (2 haploid sexcells - an egg and a sperm), to produce an offspring (a diploidzygote/fertilized egg) which is geneticallynot identical to the parents. |
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Meiosis in S.R. |
- A cell divides to produce daughter cells with haploid (n) number ofchromosomes - During fertilization, the combination of two gametes restores thediploid (2n) number of chromosomes - For human, the haploid number (n) is 23, and the diploid number (2n) is46. |
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Advantage for SR |
Meiosis and random fertilization can generate enormous genetic variation. Such variation isthe raw material for natural selection.The variability produced by the reshuffling of genes in sexual reproduction mayprovide greater ability to adapt to changing environment. → Highersurvival rate |
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Disadvantages SR |
- Time-consuming, exhausting and dangerous. o Requires greater energy expenditure in producing sperm/egg and inmating. - Favourable combinations of genes are at risk of being broken up/reshuffledduring meiosis - Must pair up/ find a mate to create each offspring makes them reproduceslower. (Less efficient → right age, place and competition) |
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Testes |
produce sperms and testosterone |
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Scrotum |
Protect and support the testes |
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Problem of the inability for testes to descend in thescrotum |
- Testes are exposed to the bodytemperature/remaining within the body - The temperature is higher thanoptimum temperature for spermproduction hence reducing theindividual’s fertility. |
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Epididymis |
Acts as a reservoir for storage and maturation ofsperms until ejaculation |
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Vasdeferens |
Transport the sperms fromthe site of production to the urethra |
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Seminal vesicle |
Produce a seminal fluid tonourish, activate, protect and suspend the sperms in a watery medium |
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Prostategland |
Produces a thin fluid thatfurther nourishes the sperm |
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Penis |
A male copulatory organ for the ejaculation of semen into vagina offemale; it also conveys urine to exterior via urethra |
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Urethra |
The duct by which urine isconveyed out of the body from the bladder, and which in male vertebrates alsoconveys semen |
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Ovaries |
Produce eggs,progesterone and oestrogen |
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Oviducts/fallopian tubes |
Bring the egg cells from ovaries to uterus by peristaltic movement of the walls, sites for fertilization of egg cells. |
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Uterus |
Site for the development of embryo/foetus |
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Cervix |
The entrance for the sperms passing from the vagina into uterus and fallopian tubes, produces mucus to lubricate vagina for intercourse. |
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Vagina |
The female copulatory organ which receives sperms from the male during intercourse, a birth canal through which the baby is born |
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Functions of amniotic fluid |
- Protection from mechanical injury by cushioning sudden blows ormovements - Allowing for freedom for foetal movement - Maintaining a relatively constant temperature for the environmentsurrounding the foetus, thus protecting the foetus from heat loss. - Permitting proper lung development of the fetus |
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Placenta |
Placenta is a vital organ with both embryonic and maternal parts thatmediates exchanges of nutrients, gases and the products of excretion betweenthe embryo and the mother. |
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Placenta function 1/3 |
Allows exchange of substances · Oxygen and dissolved nutrients such as glucose and amino acids diffuse acrossthe villi membranes of the placenta into the fetal blood through umbilical vein · Waste substances such as urea and carbon dioxide diffuse out of thefoetus’ blood into the mother’s blood through the umbilical artery. |
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Placenta function 2/3 |
Produces progesterone · To maintain the thickness of uterine lining so that embryo is firmlyattached to the uterine wall in the uterus |
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Placenta function 3/3 |
Transport antibodies · To protect foetus from diseases |
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Umbilical cord |
§ The embryo is attached to the placenta by the umbilical cord § The umbilical cord contains 2 umbilical arteriesand 1 umbilical vein. § Umbilical arteries carry deoxygenated blood andembryonic wastes from the foetus to the placenta. § Umbilical vein transports blood and foodsubstances form the placenta to foetus. |
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Features of umbilical cord |
§ Chorionic villi closely associated with the blood vessels of themother’s endometrium. § Large surface area of the chorionic villi. § Thin villi membrane of the placenta |
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Q1. How umbilical cord involved in nutrition and gaseous exchange of thefoetus with the maternal blood. |
The arteries will carry the wastesand carbon dioxide form the foetusto the chronic villi from which theycan diffuse in to mother’s bloodstream. The vein takes nutrition and oxygen from the villi after exchange and send back tothe foetus. |
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Q2. How vasectomy will affect a man’s fertility? |
Vasectony prevents the transportof sperms stored in epididymis to the urethra. Hence he man’s semen willcontain only the fluid without sperms, rendering infertile. |
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Q3. Will vasectomy affect male characteristics? |
No. Testerone produced in the testes is transported in the blood stream to various targetorgans, giving a rise to a man’s secondary sexual characteristics. |
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Q4. Will menstruation still occur in a young lady who has received tuballigation? |
Yes.As the ovaries are not affected, ovulation will still occur and oestrogen andprogesterone is produced by corpusluteum after ovulation. Oestrogen and progesterone is transported to theuterus thorough blood, causing theuterine to become thicker. As eggcould not come out from the oviduct, there will be no implantation of embryo,therefore corpus luteum degenerates following by a drop in oestrogen and progesterone level and blood shedding. |
