D 3.1 Reproduction PDF

## D3.1 Reproduction ### SL: * Differences between sexual and asexual reproduction - Reproduction: when living organisms generate more members of their own species - 2 types: - Sexual - Asexual (Study Table 1, Page 666) - Sexual reproduction: involves 2 parents (male and female) and it br...

## D3.1 Reproduction ### SL: * Differences between sexual and asexual reproduction - Reproduction: when living organisms generate more members of their own species - 2 types: - Sexual - Asexual (Study Table 1, Page 666) - Sexual reproduction: involves 2 parents (male and female) and it brings about change (variation) - Gametes: created during meiosis - are sex cells with a haploid number of chromosomes (n) - During sexual reproduction: Male and female gametes fuse together during fertilization forming new combinations of chromosomes that makes up a new individual called zygote (fertilized egg) with a restored full number of chromosomes (2n). - Male gamete - Animal: Sperm - Plant: Pollen grain - Female gamete - Animal: egg - Plant: egg/ova * Animals and plants are anisogamous (Study Table 2, Page 667) with different male and female gametes ### Anatomy of Human Reproductive Systems * Anatomy of human male reproductive system: - Study figure 6, page 668 - Study Table 3, page 668 * Anatomy of human female reproductive system: - Study figure 7, page 669 - Study Table 4, page 669 ### Menstrual Cycle * Menstrual cycle: Study figure 8, page 670 - In most women, from puberty until menopause - Ages 11-15 (average) - Ages 45-55 (average) - Controlled by many hormones: - FSH - Oestradiol - LH - Progesterone - Follicular phase: - Follicles develop in ovary - An egg is stimulated to grow - An egg breaks open, releasing egg into the oviduct - Luteal Phase: - Wall of the follicle that released the egg is called corpus luteum. - Uterine wall becomes thicker (blood capillaries) - Endometrium (lining of the uterus) thickens. - Ovulation occurs at day 14. * During luteal phase: Endometrium thickens and is more richly supplied with blood. - Preparation in case of implantation of an embryo. - No embryo: - Thick walls start to break down towards the end of luteal phase resulting in blood shedding (menstruation) - Also called "period" (4-7 days) - Day 1 of menstrual cycle - Embryo: - Pregnancy - Endometrium wall stay thick during pregnancy - No menstruation for 9 months. ### Positive and Negative Feedback * Positive and negative feedback: - FSH & LH both produced by pituitary gland - Ovarian Steroid Hormones are produced by the wall of follicle and corpus luteum - FSH: - Follicle stimulating hormone - Stimulates development of follicles - Stimulates secretion of Oestrogen - Positive feedback - Oestradiol: - Reaches high levels - Inhibits secretion of FSH - Negative feedback - LH: - Stimulates secretion - Sharp peak middle of cycle (or end of follicular phase) - Allowing follicle to burst open releasing egg - Stimulates corpus luteum to secrete Oestrogen and Progesterone (positive feedback) - Progesterone: - at the start of luteal phase - Stimulates thickening of uterine wall and inhibits FSH and LH secretion by pituitary gland - Negative feedback ### Fertilization in Humans * Fertilization in humans: - Fertilization is the fusion of a male gamete (sperm) with a female gamete (egg) to form a zygote (fertilized egg). - Sperm plasma membrane receptors detect chemicals released from egg. - First sperm that reaches Zona pellucida and penetrates it will bind to the plasma membrane of the egg and fuse with it. The sperm nucleus then enters the egg cell. - Sperms start to push their way to the egg by digesting follicle cells surrounding the egg. - The moment sperm nucleus enters the egg cell (fertilization happens) the glycoprotein layer around the egg hardens to prevent entry of more sperm. - Retaining diploid number of Chromosomes with two sets of Chromosomes (2n) - After the first mitosis of the zygote, the nuclei of the sperm and egg join together by breaking down nuclear membranes of the sperm and egg releasing 23 chromosomes from each nucleus. - 23 Chis from mother (egg) - 23 Chis from father (sperm) - Study figure 11, page 673 - Fuse together results in 46 chromosomes (zygote) ### IVF: In Vitro Fertilization * IVF: in vitro fertilization: - Naturally fertilization takes place in vivo (inside female's body), but it can also happen outside the body (in controlled laboratory conditions) to overcome fertility problems. - Stages of IVF: - Injecting the female for 2 weeks with a drug to stop the pituitary gland secreting FSH and thus stopping oestradiol and progesterone from being secreted (suspending the female's menstrual cycle) - Injecting the female for 7 to 12 days with FSH to stimulate the follicles to develop (aim is to generate higher FSH concentration than during normal cycle) - Injecting the female with hCG hormone (human chorionic gonadotropin) - This hormone is normally secreted by the embryo when it’s 1 week old as a signal that it’s alive. - Egg collection is done 35 hours after hCG injection. Minor surgical procedure to draw the eggs out of the follicles. - Each egg is mixed with 50,000 to 100,000 sperms in a dish and incubated at 37°C until the next day. - If fertilization is successful one or more embryos are placed in the uterus when they are 48 hours old. - If the embryos implant in The wall of the uterus and continue to grow Pregnancy starts - See figure 12 page 673 - ATL: evaluating ethical positions (read) page 674 ### Sexual Reproduction in Flowering Plants * Sexual reproduction in flowering plants: - During meiosis, gametes are formed inside flowers - Male: Pollen grains - Female: Egg/ova - Male and female gametes fuse during fertilization to produce an embryo inside the seed which is then dispersed from the female part - Male parts of a flower: Stamen - Female parts of a flower: Carpel - Stamen: made up of anther supported by a stalk called filament. ­­­­­ - Carpel: made up of stigma, style and ovary where the ovary contains one or more ovules - Study figure 13, page 675 - Anther has diploid cells that divide by meiosis to produce 4 haploid cells each of which develop into a pollen grain - Nucleus divides by mitosis producing 3 haploid nuclei - 2 of which are male gametes - One cell in the centre of the ovule grows then divides by meiosis to produce 4 haploid nuclei - One of these divide 3 times by mitosis to produce 8 haploid nuclei - One is the female gamete (egg) - The others assist in fertilization and embryo development - For successful sexual reproduction in flowering plants: - Pollination - Fertilization - Embryo development - Pollination: is the transfer of pollens from the anther to the stigma either by wind or by animals - Fertilization: takes place inside the ovule in the ovary where each pollen grain on the stigma will start forming a pollen tube that grows down the style carrying the male gamete inside it. - When the pollen tube reaches the ovule the male gametes are released into the female gamete and fertilization occurs. - Embryo development: As the zygote forms, it develops into an embryo - Embryo shoot - Embryo root - Embryo leaves (cotyledons) - Most flowers are hermaphrodites meaning they have both male and female parts, while some flowers have either male or female parts rather than both. (male and female flowers may be on the same plant or on separate plants). - Pollination: - Insect pollinated flowers - Pollinators: Bees, wasps, beetles, butterflies, moths - Common features - Large flowers, brightly coloured petals and scented. - Large and spiky pollens to stick to insects. - Large and sticky stigma to collect pollens from visiting insects - Nectary glands that secrete (Nectar: sugar) are positioned deep inside the flower so insects can only reach them by brushing the anthers and stigma - Activity: Drawing Flower Structure - Page 677 - Study from book. - Pollination - Self pollination - Cross pollination - Cross-pollination: transfer of pollens from an anther of a flower to a stigma of a flower on another plant. - Cross-pollination promotes genetic variation and therefore evolution. - Cross-pollination also promotes "hybrid vigour" where crosses between genetically unrelated plants tend to be healthy and grow strongly. - Hermaphrodite plants tend to result in self-pollination: transfer of pollen from an anther to a stigma on the same plant - (in breeding: closely related individuals reproduce). - Study figure 7, page 678 - Plant strategies to prevent self-pollination - Self-incompatibility' when a pollen grain/pollen tube fail to germinate / doesn't reach ovary of the same flower to prevent inbreeding. - (rejection of non-self proteins/cells) - Self-incompatibility alleles found in the same plant will result in unsuccessful pollination with each other. - Study figure 21, page 679 - Seed dispersal: when seeds travel long distances from the parent plant - Advantages: (reduces competition between parent and offspring) and helps to spread the species - Types of seed dispersal: - Dry and explosive - Feathery/winged to catch the wind - Fleshy and attractive for animals to eat - Covered in hooks that catch onto the coats of animals. - Study table 8, page 682 ## HL: - Puberty is controlled by gonadotropin-releasing hormone and steroid sex hormones. - Study figure 27, Page 682 - GnRH starts to be secreted in a foetus at 10 weeks after fertilization and continues throughout pregnancy and after childbirth and stops when the baby is 4 to 6 months old. - GnRH secretion resumes when time of puberty arrives. - GnRH is released from the hypothalamus. - GnRH stimulates secretion of FSH and LH by pituitary gland. - FSH: Lower frequency pulse - LH: Higher frequency pulse - Both are considered gonadotropins because they cause change in gonads (testes, ovaries). ## Male and Female Hormones - Males: - FSH: Stimulates testis growth - LH: Stimulates testosterone secretion by Leydig cells - Both stimulate sperm production - Testosterone: Causes secondary sexual characteristics during puberty: - Enlargement of Penis - Growth of pubic hair - Deepening of the voice - Females: - FSH: Stimulates development of follicles in the ovary - Wall of follicle secretes oestradiol - LH: Stimulates the development of the follicle wall to the corpus luteum after ovulation - Oestradiol: Causes secondary sexual characteristics during puberty - Enlargement of uterus - Development of breasts - Growth of pubic/underarm hair - Progesterone: Stimulates developmental changes in breast (mammary glands) to prepare for milk production ### Spermatogenesis & Oogenesis in Humans - Spermatogenesis and oogenesis in humans: - Gametogenesis: production of gametes - Male gamete: spermatozoa/sperm - Female gamete: oocyte/egg - Stages of gametogenesis: - Mitosis - Cell growth - 2 divisions of meiosis - Differentiation - Spermatogenesis (study figure 29, page 684): - Starts in the testes - Seminiferous tubules (contain gaps) filled with Leydig cells (produce testosterone) - Germinal epithelium (2n) - Mitosis - Spermatogonium (2n) (growth) - Primary spermatocytes (2n) - Meiosis 1 - Secondary spermatocytes (n) - Meiosis 2 - Spermatids (n) - Attach to sertoli cells (differentiation into spermatozoa) - Oogenesis: (study figure 31, page 685) - Oogenesis happens in the ovaries. - First stages are completed before birth - Mitosis - Germinal epithelium - Grow when foetus is 4/5 months old - Only one follicle becomes mature containing an egg. - Month 7: First division of meiosis - Primary follicle - After puberty: - At the start of each menstrual cycle, a small batch of primary follicles is stimulated to develop by FSH. - 400,000 primary follicles when the female is born. - Differences between spermatogenesis and oogenesis: - Study table 9, page 685 ### Fertilization - Fertilization - Only one sperm will fuse with one egg (polyspermy is prevented/fusion of more than one sperm with an egg) - Processes that prevent polyspermy - Acrosome reaction: - Sperm binds to specific glycoproteins in the zona pellucida and trigger the release of the acrosome content. - Enzymes from the acrosome start to digest zona pellucida (weakening it) causing the sperm to be able to reach plasma membrane of the egg. - Cortical reaction: - Cortical granules are vesicles containing enzymes located near the plasma membrane of the egg. When the nucleus of the sperm enters the egg cell, cortical granules are activated and the contents will be released by exocytosis causing the toughening of the zona pellucida making it very difficult for any more sperms to penetrate it. ### Implantation - Implantation: - Zygote (after fertilization) - Rapid cell division without cell growth - Blastocyst (containing 250 cells/200 µm in diameter) - 7 days: migration to uterus from oviduct - Blastocyst upon reaching the uterus 7 days after fertilization, will need an external supply of food, it attaches itself to the endometrium (uterus lining) in a process called implantation. - Finger like projections form from the outer cell layer and grow into the endometrium. - At 8 weeks pregnancy the embryo is now called a foetus. ### Pregnancy Test - Pregnancy test: - Study figure 35, page 688 - hCG: Human chorionic gonadotropin hormone - Produced by the embryo’s trophoblast cells (blastocyst). - hCG hormone stimulates the corpus luteum to secrete Progesterone to help support pregnancy and prevent degeneration of the uterus lining. - 8-12 weeks of pregnancy, Placenta forms and starts secreting Progesterone in response to hCG ### Role of Placenta - Role of placenta: Study figure 36, page 689, figure 37, page 690 - Placenta is made from foetal tissues along with membranes to form amniotic sac. - Contains amniotic fluid (supports and protects the developing foetus) - Functional unit of placenta is a finger-like piece of foetal tissue called Placental villus. - Maternal blood flows in spaces around the villi, foetal blood circulates inside blood capillaries that are close to the surface of each villus. - Placental barrier is a selectively permeable membrane that allows some substances to pass but not others, but also separate maternal and foetal blood. - Glucose, amino acids, oxygen pass from maternal to foetal blood, while Carbon dioxide, urea, and other wastes pass from foetal to maternal blood. ### Hormonal Control During Pregnancy and Child Birth - Hormonal control during pregnancy and child birth - 8-9 weeks of pregnancy: Placenta starts to secrete oestradiol and progesterone in large quantities to support pregnancy. - Corpus luteum is no longer needed (risk of miscarriage if the switchover fails). - At the end of pregnancy, placenta stops secreting progesterone as a result Oxytocin starts to be secreted by pituitary gland. - Oxytocin stimulates contractions of the muscles of myometrium, as the oxytocin production increases, the contractions become more frequent and more vigorous. (Positive feedback) - Relaxation of the cervical muscles causes the dilation – while uterine walls contract causing amniotic sac to burst releasing the amniotic fluid. - Contractions in uterine walls (for hours) finally push the baby out through the cervix and Vagina. - Study figure 38, page 691 ### Hormone Replacement Therapy (HRT) - Hormone replacement therapy (HRT): - HRT is a treatment used to relieve menopausal symptoms - Hot flushes - Night sweats - Mood swings - Vaginal dryness - Reduced sex drive - HRT can help prevent weakening of the bones (osteoporosis) - HRT might increase the risk of CHD