Cell Division and Reproduction PDF

Biology L1 UNIT 3 Cell Division Asexual reproduction is the formation of new individuals from the cell(s) of single parent. The offspring will be exact genetic copies of the parent. It is very common in plants....

Biology L1 UNIT 3 Cell Division Asexual reproduction is the formation of new individuals from the cell(s) of single parent. The offspring will be exact genetic copies of the parent. It is very common in plants. Asexual reproduction is of various types and vegetative propagation is one of its type. Types of asexual reproduction 1- Simple binary fission in bacteria: The DNA in bacterial cell is duplicated, then a septum occurs in the cell dividing it into two. 2- Parthenogenesis in plants (asexual seed formation): Is the development of eggs into plants without fertilization. Meiosis does not occur to form a gamete. The egg is diploid and divides by mitosis and develop into a plant. The offspring are genetically identical to their female parent. 3- Vegetative propagation in plants: Many plants can undergo asexual reproduction to produce genetically identical offspring (clones) of themselves, which then develop into independent plants. This process is called vegetative propagation or (cloning), or vegetative reproduction. One way in which vegetative propagation occurs is through: 1- fragmentation, a process in which a plant part (cuttings), can grow into a whole new plant. The part is dipped in nutrient solution and allowed to grow. Cuttings of stems can be dipped in rooting powder and implanted into wet soil, roots develop. 2- other modes of vegetative propagation include the production of specialized structures such as tubers and strawberry plant. advantages to this kind of asexual reproduction, which can occur either naturally or artificially, is that it is: 1- more rapid than seed propagation. 2- it produces genetically identical offspring so can allow a genetically superior plant to produce unlimited copies. 3- Produce big number of offspring. 4- Spore formation in fungi. 5- Budding in yeasts. Page 30 Dr. Elham Samy  Biology L1 Cell cycle The cell cycle is the regular sequence of events occurring from one cell division to another. It has 3 phases: 1- interphase 2- nuclear division 3- cell division Cell division Mitosis - When a parent cell divides by mitosis, it produces 2 genetically identical daughter cells. - To divide into two equal cells, the chromosomes copy themselves before the start of mitosis. - Stages of mitosis are seen in the figure. - Cancer cells divide by mitosis. The cells formed are the exact copies of the parent cell. - Cancer results from mutation in the genes that regulate the rate of cell division. - Cancer results from uncontrolled cell division, increasing the rate of division. Page 31 Dr. Elham Samy  Biology L1 Main stages of mitosis Importance of Mitosis 1- Growth of the organism 2- Tissue repair 3- Asexual reproduction Growth is an increase in dry mass by the increase in cell number or size or both. Development is an increase in complexity of cells to be specialized in certain function. - Shortly after a zygot is formed, it begins to divide by mitosis several times to produce a ball of genetically identical cells. - Each group of cells start to differentiate to take on different roles. As being muscle tissue blood cells, liver cells …..etc All cells carry the same genes, but in each type only particular set of genes is switched on. So differentiation involves switching on of particular genes. Page 32 Dr. Elham Samy  Biology L1 Stages of Meiosis (Reduction division) Page 33 Dr. Elham Samy  Biology L1 Importance of meiosis: - Meiosis is a reduction division in which the chromosome number is halved from diploid to haploid to produce gametes. - It occurs in sexual organs only. - When fertilization occurs, both gametes fuse to produce diploid zygot again. - Gametes are variable due to: 1- Crossing over of homologous chromosomes. 1- Linkage 2- Independent assortment of homologous chromosomes into daughter cells (gametes). Stem cells Stem cells are undifferentiated (unspecialized cells), that divide by mitosis to produce many daughter cells that become differentiated into different cells. 1- Embryonic Stem cells: the cells in the early embryo before they differentiate are called Toti potent Stem Cells. These cells are able to produce every kind of specialized cells. But once differentiated they can not change their role. A muscle cell for example can not change to liver cell or skin cell. 2- Adult stem cells: as we grow up to adults few cells are able to divide into different types of cells. For example a bone marrow cell can differentiate into red blood cells, white blood cells and platelets. Many researches are carried now to use stem cells to cure some diseases. For example the use of stem cells to regenerate insulin producing cells (B cells) in the pancreas. This may cure young people with diabetes 1. Scientific and ethical arguments for and against the use of stem cells in medicine: 1- Some people support SC researches with the hope of treating serious diseases, 2- Others oppose SC researches since it is a potential human being. One of the issues involved in this type of research is whether or not, the embryos used were developed specifically for stem cell research or sometimes fertility clinics produce extra fertilized eggs, also called embryos, that are not implanted in a woman’s womb. These extra embryos are usually discarded. Page 34 Dr. Elham Samy  Biology L1 3- There is another kind of research using stem cells that come just from adults and do not come from embryos at all. The research results in no injury to the person from whom the stem cells are taken. 4- Now There are a few questions about a different topic—a process called cloning. Medical researchers are on the verge of discovering a way to create new embryos, called clones, from a fertile egg. The original embryo and its clones can grow into babies that are identical copies of each other. A cloned embryo can be frozen and put into a mother’s womb for development at any time. Do you approve or disapprove to make it possible for societies to clone and reproduce large numbers of individuals with genetically desirable traits? Lab 1: “Observing Mitosis in Plant and Animal Cells” In order to examine cells in the tip of an onion root, a thin slice of the root is placed onto a microscope slide and stained so the chromosomes will be visible. Lab Procedure 1.Clean both the slide and the objective before beginning the lab 2.Place the prepared slide on the microscope stage. 3.Scan the slide under low power first and locate the apical meristem, directly behind the protective root cap. 4. Switch to high power and center your slide in the apical meristem region, so that you have a field of view that has a wide selection of cells in various stages of mitosis (including interphase). Be sure to adjust your light for optimum view. 5. Identify one cell that clearly represents each phase. Carefully sketch the cell. Draw only what you can see but include everything that is visible. Be sure to label everything you include in your drawing. Page 35 Dr. Elham Samy  Biology L1 Page 36 Dr. Elham Samy  Biology L1 LabTwo: Determining the Rate of Mitosis in Plant and Animal Cells. 1. Focus the microscope on the 4X setting with the onion root tip in view, making sure the diaphragm again was at its widest setting. 2. locate the meristem root tissue of the onion root tip and changed to the 40X high power lens, so the cells of the onion root were visible. 3. Using the first onion root’s meristem root tissue, I found a large collection of cells in many stages of mitosis. 4. I counted the number of cells in each stage and recorded the values in my data table. 5. I repeated steps 3 and 4 twice, each time using a different onion root tip to locate the cell clusters. 6. I totaled the number of cells in each stage in the three microscope views, and determined the percentage of the total number of cells in each stage. 7. multiply the percent of the total number of each cell in a phase by 1440, the number of minutes in a day, which is the time an onion cell takes to undergo mitosis. Results Interphase prophase metaphase anaphase Telophase Total No. of 20 10 3 2 1 36 cells % cells 55.6 27.8 8.3 5.6 2.8 100 To calculate time taken by each stage of mitosis, multiply the % of cells x the total minutes / day (1440 min). Page 37 Dr. Elham Samy  Biology L1 to UNIT 4 Plant Reproduction Differences between sexual and asexual reproduction Asexual reproduction Sexual reproduction Parents One parent Two parents Sex organ -No organ -Specialized sex organ -No gametes -Gametes (sex cells) Division Mitosis Meiosis Zygote No zygote formation Fertilization and zygote formation Offspring Genetically identical to Variable parent Characters Rapid, simple and Slow, complex and producing a large number producing few of identical offspring offspring Occurrence Very common in plants In flowering plants and and simple animals. most animals Advantage -Rapid, simple -Variation favors -Produces large number survival and evolution. -Maintains good strain -No overcrowding or competition Disadvantages -overcrowding and -slow, complex competition -produces a few -no varieties, so species number of offspring. are liable to extinction by disease Page 38 Dr. Elham Samy  Biology L1 Sexual reproduction in “Flowering plants” The flower: - Is the reproductive organ of a plant. - It is either bisexual (hermaphrodite) male and female organs. Or unisexual  has male or female organs only Structure of a typical flower of a dicotyledonous plant (Lupin): Structure Function Sepals 5 small, green leaves -Protect the flower in the bud Petals -5 large, bright -Attracts insects for colored, scented pollination by coloured leaves scent. -have guide line on -Protects male and female their surfaces. organs Stamens 10,each is formed of: -male organs producing -Anther: has 4 pollen pollen grains (male sacs containing gametes) pollen grains -filament Carpel One, made of : -female organs producing -ovary :has 10 ovules female egg cells (female -style gametes) -stigma(has sticky surface) N.B. the ovary may have one ovule or many ovules. Other -Expanded flower -In some flowers after structures stalk to which all fertilization it becomes not structures are fleshy and edible present in attached e.g. apple (Lupin) Page 39 Dr. Elham Samy  Biology L1 Receptacle Nectary -glands present at the -produce sugary solution glands base of the ovary which attracts insects for pollination Functions of the flower: 1. Production of male and female gametes (sex cell) 2. The stigma receives pollen grains on its sticky surface in pollination 3. Fertilization and production of the fruit and seeds in the ovary 4. Protection of seeds inside the fruit Page 40 Dr. Elham Samy  Biology L1 Page 41 Dr. Elham Samy  Biology L1 Pollination It’s the transfer of pollen grains from an anther to a stigma Type of pollination Self-pollination Cross pollination Transfer of pollen grains from Transfer of pollen grains from an an anther to a stigma of : anther of a flower to a stigma in  The same flower another flower on another plant of Or the same species  Another flower of the e.g. Cherry and peas same plant e.g. Cereal crops and grasses - Bisexual flower - Unisexual or bisexual (sex) - Filaments and anthers are - Shorter (stamen is shorter than longer than stigma and style carpel - Gametes mature at the same - Different times, stamens usually time mature first - Pollination may occur before - Stigma secretes chemicals opening of the flower which kill the pollens of the same flower -increase the variation of the fruit so biologically desired Advantages and disadvantages of self and cross pollination Self-pollination Cross pollination Increases homozygosity (TT or RR) Decreases homozygosity, increases heterozygosity(Tt, Rr) Less variation More variation Harmful recessive characters may be Harmful recessive characters are expressed less likely to be expressed Easy if there is no plants near by. Page 42 Dr. Elham Samy  Biology L1 Methods or agent of pollination 1. Insects pollinated flowers: e.g. Wall flower and Lupin flower. - Insects are attracted to the flower by their bright color and scent. - They follow the guide lines to the nectar glands. - When they dip their heads into the flower, the hairy bodies of the insect get covered with pollens. 2. Wind pollinated flowers: e.g. grass flower. - The anthers hang outside the flower, they are shaken by slight wind and thus pollen grains are scattered. - The feathery stigma of another flower projecting out trap some pollen grains. Adaptation of the flower for pollination Wind pollination Insect pollination Flower - Small inconspicuous - Large, conspicuous - Green petals - Bright colored petals - No scent, or nectar - Scented and has nectar Stamen - Stamen, hangs out of the flower to expose the pollen to the wind (long filament) - Anther, large loosely attached to the filament. - Pollen grains: - Filament, long.  Spiky or sticky to - Pollen grains: stick to the body of  Smooth (not sticking the insects. together to be easily  Small in number carried by the wind). because not much  Large in number (some are lost. are lost). Carpel - Stigma, is a feathery - Stigma, is flat or projecting out of the flower lobed, sticky and to increase the surface inside the flower to area and to be exposed to receive pollen grains the wind. and stick them. Season Flower appears in the cold Hot weather weather Page 43 Dr. Elham Samy  Biology L1 Development of pollen grains and male gametes - Pollen grains are formed inside the anther in a structure called pollen sacs. - Inside the pollen sacs are many pollen mother cells which are diploid. - Each mother cell divides many times to give rise to mature pollen grain. The mature pollen grain has:  outer thick wall (exine) made of an extremely resistant chemical which enables pollen grains to survive for a long time.  Inner wall (intine).  2 nuclei: 1- generative nucleus (n) that later divides to give 2 male gametes (sperms). 2- pollen tube nucleus (n). When the pollen mature, the anther dries and split open releasing the pollens. Page 44 Dr. Elham Samy  Biology L1 Development of ovules and female gametes The embryo sac nucleus divides many times to produce 8 haploid nuclei, 2 of them migrate to the center and later fuse together, they will fuse with male gamete to form the triploid nucleus of endosperm. One haploid nucleus acts as the female gamete (egg cell), fuses with the other male gamete during fertilization to form the diploid zygot which will develop into the embryo. The double integuements (wall) of the ovule will form the seed coat, testa. Double fertilization ensures that endosperm develops only in ovules where the egg has been fertilized, so preventing waste of nutrients on infertile ovules. Near the time of double fertilization, all other nuclei degenerate. Double fertilization is described by Navashine and Guignard. Fertilization in plants - Pollination: is complete when pollens from an anther have landed on a stigma. - Fertilization: is the union of the pollen grain (male) and female gamete (egg cell) in the ovule. Steps of fertilization: - The pollen grain lands on the stigma. The stigma secretes a sticky fluid, which nourishes the pollen grains allowing them to germinate. - Each pollen grain bursts and develops a long hollow, tube called pollen tube. - The pollen tube pushes its way between the cells of the style from it absorbs more nourishment. Page 45 Dr. Elham Samy  Biology L1 - The tube grows towards the ovule, and then a male gametes descend along the tube and enters the ovule through a tiny hole called the micropyle to reach the female gamete. - One male sperm fuses with female gametes to form the zygote (fertilization).the other sperm will fuse with the two polar nuclei to form the endospem. Formation of fruit and seeds (fate of the flower): - After the fertilization, the stamen, petals shrivel up and drop off. - The fertilized eggs form the zygotes, which will develop into embryo of the seed. - The ovule will form the seed. - The wall of the ovule will form the testa of the seed. - The micropyle remains. - The whole ovary will form the fruit. (Wall of the ovary will be the wall of the fruit). - Sometimes the flesh of the fruit is derived from the enlarged receptacle. e.g. apple. N.B. -The biological definition of the fruit is a fertilized ovary. -The fruit has 2 scars, one was attached to the plant and one was attached to the style. -The seed has one scar, was attached to the ovule. Page 46 Dr. Elham Samy  Biology L1 Dispersal of fruit & seeds The carriage of fruits & seeds a long distance from parent plant, Advantages: 1- Avoid competition for space, water and light. 2- Avoid crowding which increases chance of disease. 3- Colonization of new areas where the plant can grow. 1-Wind dispersal Types: Seeds and fruits are adapted to increase the surface area by various ways to delay their fall on the ground. They are usually light to be carried by slightest air current. Examples: 1- Pepperpot effect e.g Poppy The flower stalk is usually long, the ovary becomes dry hollow capsule with one or more openings. The wind shakes the stalk & seeds are scattered in all directions through the holes. 2- Parachute fruits & seeds e.g Dandelion Feathery hairs projects of the fruit & seed --> they float over a long distance by slight air current 3- Winged fruits e.g Sycamore Page 47 Dr. Elham Samy  Biology L1 The wings help the fruit to spin as it falls down so it takes time to fall to the ground, so a chance to be taken by air currents. 2- Animal dispersal Carried by animal fur : The fruit is hooked e.g Burdok and clover fruit. Eaten by the animal or birds --> fruits are juicy, soft, bright to attract the animal --> seeds are not digested & comes out with the animal excreta e.g the Blackberry 3- Self dispersal (explosive fruits) The fruit is a pod --> dries in the sun --> fibers in its wall shrinks --> tension --> fruit splits & seeds are dispersed out e.g Lupin & peas. 4-Water dispersal The fruits of coconut palms are dispersed by water. They can float many hundreds of miles before reaching the beach where they germinate. Page 48 Dr. Elham Samy  Biology L1 The structure of non-endospermic seeds (Broad bean) The seed consists of: 1. Testa: arises from the double wall around the ovule. It is hard coat, which protects the seed from fungi, bacteria and insects. 2. Hilum: it is a scar left by the stalk, which attaches the ovule to the ovary wall. 3. Micropyle: it is the opening in the integuments through which the pollen tube enters to fertilize the egg cell. 4. Radicle: is the embryonic root that grows and develops into the shoot system plant. 5. Plumule: is the leafy part of the embryonic shoot and develops into the shoot system of the plant. 6. Cotyledons: are the modified leaves and contain the food reserves which are used in the early stages of germination. Page 49 Dr. Elham Samy  Biology L1 Seed germination - Seeds develop from fertilized ovules. - Seeds formed inside the fruit dries out and become dormant as without water, no metabolic reactions take place inside the cell. This is very useful to the seed to survive hard condition as cold or draught. When seed germinates: - It first takes up water through the micropyle or thin testa. - The cotyledons swell and the testa burst. - Water activates enzymes in the seed. - Catabolic enzymes act on starch and proteins in the cotyledons. Amylase Starch maltose + glucose Protease Proteins amino acids - The small molecules of glucose and amino acids are absorbed by the embryo and it uses them for growth. anabolic enzymes Glucose cellulose cell wall and energy. anabolic enzymes Amino acids proteins forming cytoplasm, nucleus and every structure in the cell. - The radicle forms root. - The plumule form the shoot. - The testa falls and the cotyledons are raised above the ground, they form the green leaves, start photosynthesis and form food for the plant. -Plumule grows into the shoot. Conditions for germination: 1. Water activates the enzymes. 2. O2 for aerobic respiration to supply energy for growth. 3. warmth for optimum temperature for ezymes. Light is not a condition for seed germination. Page 50 Dr. Elham Samy  Biology L1 Practical work 1- To find the conditions necessary for the germination of mustard seeds: 1. Set up five tubes as shown in Fig. 2. Put tubes A, D and E in a warm place in the laboratory, in the light. 3. Put tube B in a refrigerator. 4. Put tube C in a warm, dark cupboard. 5. Fill in each the results table to show what conditions the seeds in each tube have. 6. Leave all the tubes for several days, then examine them to see if the seeds have germinated or not. Tube A B C D E Water Warmth Oxygen Light Did seed germinate? Page 51 Dr. Elham Samy  Biology L1 2- Experiment to show pollen tube growth: The purpose of this activity is:  to examine pollen from a range of sources under the microscope  to observe pollen tubes growing as pollen grains germinate Procedure SAFETY: There are no hazards associated with this practical. Investigation a Place a filter paper in each of four Petri dishes, moisten the paper with water and replace the lids. These will form chambers in which your slides of germinating pollen can be kept humid. b Take 5 cm3 of pollen culture solution which contains 20% sucrose to stimulate germination. c Take four absolutely clean microscope slides and place a drop of medium in the center of each slide. Label the slides with the names of the flowers you are investigating. d Use a low power of the microscope to help to select two or three flowers of each type that are mature and shedding pollen. e Place a microscope slide under the field of view of the microscope and gently rub the point of a mounted needle over the anthers so that pollen falls onto the medium. f Note the time of adding pollen to the medium and place the slides in the Petri dishes. Handle the slides with great care so that the drops of pollen medium remain in the center of the slides. g Use a microscope, with x100 magnification and an eyepiece graticule, to observe the slides after the next 15 minutes for signs of pollen germination. h Once the pollen tubes have started to grow, measure the length of four or five tube and calculate the average. i Work out the average rate of growth for each type of pollen, in each medium using eyepiece units. Page 52 Dr. Elham Samy  Biology L1 Preparing solutions: 1- Pollen culture solution: it is a mix of mineral salts with certain concentration: ca nitrate, boric acid (prevents osmotic bursting), potassium nitrate, magnesium sulphate, ammonium hydroxide with certain concentration. 2- Sugar solution 10% sucrose solution. Page 53 Dr. Elham Samy  Biology L1 UNIT 5 Reproduction in Humans Structure and function of the male reproductive system: 1. Testes: - Primary sex glands – 2 in number - Consists of 1000 seminiferous tubules for sperm production Functions: -Sperm production. -Secretion of testosterone. 2. Epididymis: - Coiled tubules (about 6 meters) transfer sperms to sperm duct (Vas deferens). Function: -Temporary storage of sperms until their maturation or until ejaculation. 3. Vas deferens: (Sperm duct) - 2 tubes, extend from the epididymis, and open in the urethra. Function: -Conduct sperms to the urethra by peristalsis. 4. Urethra: - About 20 cm in length, S shaped and divided into 3 parts. Function: -Conveys both sperms and urine. 5. Prostate and seminal vesicles: - Prostatic secretion forms the main bulk of semen. - Seminal fluid from 2 seminal vesicles. Function: -Lubrication of sperms. -nutritive medium for sperms. 6. External genitalia: a) Penis: - is the organ of copulation - Contains erectile tissue Function: -Copulation and passage of semen the cervix. -Micturition Page 54 Dr. Elham Samy  Biology L1 b) Scrotum: Function: - keeps the testes at temperature about 2°C below body temperature for sperm production. Structure and function of female reproductive system: 1. Ovaries: - 2 oval shaped structures 3 cm long (sex glands), located in the lower part of the abdomen. - Functions: -Release of ova at the time of ovulation. -Secretion of female sex hormones. 2. Oviduct (fallopian canal): - 2 in number, long narrow tubes. - Have funneled shaped end to receive the released ova. - Function: -Conduction of the ova to the uterus. -They are the site of fertilization. 3. Uterus: - Thick muscular, hollow organ. - Function: -Is the site of implantation of the embryo. -Is the site of development of the embryo. 4. Cervix: - A ring of muscle at the base of the uterus and is continuous below with the vagina. - Function: -Allows passage of the sperms during copulation. -Allows passage of the baby or any uterine secretion down. 5. Vagina: - A tube of 10 cm long opens at the vulva. - Function: -Is the site of insertion of penis during copulation. -Allows the passage of the baby or menstrual blood out. Page 55 Dr. Elham Samy  Biology L1 Puberty Is the age of sexual maturity. It is from 12-14 in females and about 14-16 in males. 1. Release of ova in females – formation and secretion of sperms in males. 2. Secondary sexual characteristics appear due to the release of sex hormones (Oesterogen in females and testosterone in males). 2ry sexual characters in 2ry sexual characters in female male Hair - Growth of hair in pubic - Growth of hair in pubic region, arm pit. region, arm pit, chest and later on the face. Voice - High pitched voice - Deeper and lower pitched - Signs of - Menstruation - Erection of penis puberty - Increase size of uterus &ejaculation &vagina - Enlargement of penis & testes Breast - Increase in size. Growth - Increase in growth - Rapid increase in the rate of growth Emotional - Sudden changes in emotion - Same changes. changes - Embarrassment at physical change. - Attraction to opposite sex Page 56 Dr. Elham Samy  Biology L1 Gametes P.O.C Female gamete (ovum) Male gamete (sperm) Size Large – 0.1mm in diameter Smaller 0.05 mm in length Number Less in number formed before Numerous, made birth -after puberty one matures continually from puberty and is released every month. onwards. Structure Has a jelly coat protecting it & Has a flagellum (tail), contains energy store in the enzymes in the acrosome, cytoplasm. and mitochondria to move. Human egg cell Human sperm Page 57 Dr. Elham Samy  Biology L1 Female sexual cycles The female has 2 cycles occurring every month, each one takes 4 weeks. Ovarian cycle and menstrual cycle. 1- Ovarian cycle: occurring in the ovary. 2- Menstrual cycle: occurring in the uterus. Ovarian cycle The pituitary gland starts to secrete FSH and LH into the blood starting from puberty. - FSH stimulate only one follicle to develop each month. - As the follicle grows, it secrets oestrogen into the blood. - The mature follicle (Graafian follicle), ruptures under the effect of L.H, and the Ovum is released from the Ovary (ovulation). - The wall of the follicle forms the Corpus, it continues to secrete progesterone for two weeks, then disappear. If pregnancy occurs, corpus lives for 3 months to keep secreting progesterone. - Usually, one egg is released into the oviduct every month in an adult woman. - If the egg cell is not fertilized, it is dead by the time it reaches the uterus, it doesn’t sink into the spongy wall, but continues onwards, down through the vagina. Page 58 Dr. Elham Samy  Biology L1 The menstrual cycle - Changes in the lining of the uterus during 28 days. - Menstruation is the shedding of the lining of the uterus (endometrium) accompanied by bleeding. It occurs in approximately monthly cycles throughout a woman's reproductive life, except during pregnancy. Menstruation starts during puberty and stops permanently at menopause. - The menstrual cycle begins with the first day of bleeding, which is counted as day 1. The cycle ends just before the next menstrual period. Menstrual cycles normally range from about 25 to 36 days. Only 10 to 15% of women have cycles that are exactly 28 days. - Menstrual bleeding lasts 3 to 7 days, averaging 5 days. - The menstrual cycle is regulated by hormones. The menstrual cycle has three phases: 1- menstruation 2-follicular phase. 3- lutesl phase. Hormonal Control of the cycles: - FSH  stimulate development of one follicle each month. - Oestrogen  causes growth of the spongy layer of the uterus. helps release of LH for ovulation. - LH  stimulates ovulation. - Progesterone  it maintains uterine lining. Page 59 Dr. Elham Samy  Biology L1 Changes During the Menstrual Cycle Page 60 Dr. Elham Samy  Biology L1 Fertilization and Implantation How do sperms reach the egg? - At the end of copulation (mating) ejaculation (release) of semen in the top of the vagina near the cervix. - The sperms begin to swim upwards by their tail movements  to the uterus to the oviduct. 1. Fertilization: Definition: is the fusion of male gamete with the female gamete to form a zygote. Site: Outer part of oviduct (1/3) Time:14-15 days of menstruation (time of ovulation). Mechanism: - Only one sperm of the many in the female vagina is required to fertilize an ovum. - The sperm secretes an enzyme from head to dissolve the surrounding of the ovum. - Only the head of the sperm enters and the tail is left out. - Fusion occurs between the sperm nucleus and the ovum nucleus (containing chromosomes). - Fertilization membrane forms as soon as one the sperm enters preventing entering of the other sperms. Sequences of fertilization: Restoration of diploid number of chromosomes. Sperm + ovum  zygote (23 Chromosomes) + (23 Chromosomes)  46 Chromosomes Beginning of the cell division by mitosis. Page 61 Dr. Elham Samy  Biology L1 2. Implantation: Definition: it is the process of sinking of the developing embryo into the lining epithelium (endometrium) of the uterus. Site: upper part of the posterior wall Mechanism: after the fertilization, a series of cell divisions occur and the embryo travels the fallopian tube (oviduct), helped by the cilia and peristalsis until it reaches the site of implantation. Stages leading to implantation The work of Prevost and Demos The first evidence suggesting the importance of sperm in reproduction came from a series of experiments performed by Lazzaro Spallanzani in the late 1700s. Spallanzani demonstrated that filtered toad semen devoid of sperm would not fertilize eggs. He concluded, however, that the viscous fluid retained by the filter paper, and not the sperm, was the agent of fertilization. He, like many others, felt that the spermatic “animals” were parasites. The combination of better microscopic lenses and the cell theory led to a new appreciation of spermatic function. They were not parasites, but rather the 1824, J. L. Prevost and J. B. Dumas claimed that sperm are the active agents of fertilization. They noted the universal existence of sperm in sexually mature males and their absence in immature and aged individuals. These observations, coupled with the known absence of spermatozoa in the sterile mule, convinced them that “there exists an intimate relation between their presence in the organs and the fecundating capacity of the animal.” They proposed that the sperm entered the egg and contributed materially to the next generation. Page 62 Dr. Elham Samy  Biology L1 Embryonic membranes 1- The chorion: is the membrane that contains the chorionic villi and surrounds the developing embryo, it contributes to the development of the placenta. 2- The amnion: is another membrane that develops around the embryo about week two and is filled with amniotic fluid. 3- Amniotic Fluid: fluid filling the amniotic sac. Functions: 1- Protection of the baby against external trauma. 2- Facilitates movement of the embryo. 3- Plays an important role in early stages of delivery by opening the cervix and lubrication of birth. Care of the mother during pregnancy (antenatal care) 1. Balanced diet (proteins, vitamins, iron, Ca and folic acid) 2. No smoking or alcohol  low birth weight baby 3. No drugs except under doctor’s supervision. 4. Avoid catching infections (German measles causes deformities) 5. Girls are advised to have antirubella vaccine (against German measles) at 12 years old to be immune during pregnancy. of uterus. Page 63 Dr. Elham Samy  Biology L1 Feeding of a baby The advantage of breast-feeding over bottle-feeding Breast Milk Bottle Milk ( formula milk) Good adjusted (contains all food High in protein hard to digest, high in substances the body needs in right salts, less vitamins, less sugar. amount). It is deficient in iron. The body uses its store of iron in the first week. Easily digested, no constipation or colic. May cause constipation or colic. Good psychology for baby and mother. No. Good immunity for the baby because it No antibodies. contains mother’s antibodies. Suitable temperature. Has to be heated. Sterilized. Not sterilized, may contain bacteria. Available all the time free. Not available all the time to be bought. Disadvantages of breast milk: 1- The mother may not produce enough milk. 2-Cann’t know the amount of milk taken by the baby. 3- Risk of transfer of drugs or infections. 4- No other individual can help in feeding. Infertility Inability to have an offspring. Causes in males: -No or few sperms produced. -Low motility of sperms. -High percentage of abnormal forms. -Block in the sperm ducts. Causes in females: - No ova are released. - Block in the oviduct. Treatment: 1- Fertility drugs. 2- Surgery to treat blocked oviducts or blocked sperm duct. 3- In vitro fertilization. Page 64 Dr. Elham Samy  Biology L1 Fertility drugs: Are drugs given to the female to stimulate the release of ova. (e.g. FSH hormone). Social aspects: 1- May make the family stronger by having a child. 2- May cause multiple pregnancies (twins)  social and economic problems. 3- It is accepted if husband sperms are used for wife, donors are unaccepted. In vitro fertilization: IVF - Sperms and Ova are collected by the doctor - The husband sperms are used to fertilize the wife’s ova in a laboratory. - If a fertilized ovum becomes an embryo, then it is placed into the wife’s uterus, so pregnancy can continue as normal. Page 65 Dr. Elham Samy