Grade 9 Science Unit #3: Reproduction Topic #3 Reproduction

Transcription

1 Grade 9 Science Unit #3: Reproduction Topic #3 Reproduction Lesson Topic What you will learn: 1 Asexual Reproduction - Asexual reproduction involves only one parent - Plants can reproduce asexually by binary fission, spore production, vegetative reproduction, fragmentation, or grafting. Animals can reproduce asexually by budding or parthenogenesis - Asexual reproduction can produce lots of identical individuals very quickly but produces entire populations of individuals that may not survive if the environmental conditions are not optimal - Asexual reproduction is a fundamental part of the agriculture 2 Sexual Reproduction 3 The Male Reproductive System 4 The Female Reproductive System 5 Human Development and forestry sectors in Saskatchewan - Sexual reproduction in animals is achieved by the union of male and female gametes - Gametes are produced through the process of meiosis - Sexual reproduction produces individuals with many variations of characteristics, so they are very rarely identical; this form of reproduction may require a large amount of energy to produce only a small number of offspring - The main function of the male reproductive system is to produce sperm for reproduction - Testosterone is an important hormone in the functioning of the male reproductive system - Each structure in the male reproductive system has an important function - The production of sperm is a continuous process - The main functions of the female reproductive system are to produce eggs for reproduction and to provide a safe place for fertilization and offspring development - Each structure in the female reproductive system has an important function - The release of eggs occurs in a cycle - The development of an individual human being begins when an egg cell is fertilized by a sperm cell - Females show physical signs of pregnancy once an egg has been fertilized

2 6 Contraceptive and Reproductive Technology - A human baby requires approximately nine months of forty weeks in the mother s uterus in order to develop fully - There are many methods of contraception that prevent pregnancy from occurring - Infertility can sometimes be treated using science and technological advances - In various different ways, society affects how science and technology proceed - Scientific and technological advances can be controversial because of the different social and cultural believes that exist in society

3 1. Asexual Reproduction Asexual reproduction is a method of reproduction where a single parent reproduces its offspring. There is no genetic recombination; therefore the DNA of the offspring is identical to that of its parent. Offspring that are identical copies of each other are called clones. In some cases, asexual reproduction can produce lots of identical individuals very quickly. Over a 12-hour period, a single bacterium can divide to produce 10 million copies of itself. This is a great advantage in environments that do not change very much. Ex. Bacteria that live in the gut of an animal will always have a warm, moist environment to live in while the animal is alive. Producing many copies of a bacterial cell that is suited to that environment is a safer bet for survival than producing a smaller number of bacteria with many variations that may never be needed. The main disadvantage of asexual reproduction is that all the offspring are identical to the parent. Any factor that negatively affects the parent, such as disease or drug, will also affect all the offspring. Also, if the environmental conditions become unfavorable, the entire population may be wiped out. Budding Grafting Definition/Process Diagram Examples of plants The parent produces a small bud, or a miniaturized clone. In some parents, the buds eventually detach and become separate individuals. In other animals, the offspring remain attached to the parent, forming a large structure composed of many identical individuals. One plant is joined with another plant, called the parent tree or the root stock. The two plants heal together and grow as a single plant, but the two plants maintain their own characteristics. Can be used to strengthen the stem of a plant to ensure that it grows and develops a strong, healthy stem. Hydra Yeast Coral This is commonly used by gardeners to produce flowers with certain colours or trees that grow different types of apples on different branches. Binary Fission Occurs when single-celled organisms divide into two identical daughter cells to produce two new individuals that are identical to each other and are clones of the parent cell. Bacteria Amoeba algae

4 Spore Production Spores are haploid cells that can develop into new organisms. Spores are similar to seeds because they contain and protect the DNA of the organism against unfavourable conditions. Spores remain alive, but they do not grow until environmental conditions are suitable for growth. Fungi Green algae Mould Non-flowering plants Fragmentation New individuals are formed from a piece of the existing parent organism. Some animals can grow two identical individuals after being cut into two pieces. Worms Starfish Many plants Vegetative Reproduction Parthenogenesis Method 1 take a cutting from a coleus plant and place it in water, the cutting will grow roots and eventually develop into a whole new plant. Method 2 Plant produce modified stems that run horizontally over the ground (runners) or under the ground (rhizomes) and produce new plants along their length. An unfertilized haploid egg matures into new organisms. In some species unfertilized eggs become male drones and fertilized eggs become female workers and queens. Coleus plants Strawberries Spider plants Potatos Onions Tulips Ants Bees Snakes Lizards

5 Plant Tissue Cultures Plant cells are placed in a petri dish or a bottle containing nutrients and other chemicals and grown into a new individual. Once the cells develop into seedlings, they can be transplanted into soil and grown like a normal plant. Often happens with plants that have desirable features such as disease resistance or good fruit production. Or to conserve endangered plant species. Potatoes are an excellent example of how different methods of asexual reproduction are used in agriculture in Saskatchewan. A parent plant with desirable features is selected, cuttings are taken and either planted and grown or used to create plant tissue cultures. The clones are grown and produce seed potatoes. Seed potatoes are potatoes that are grown for replanting, not eating. The plants grown from seed potatoes produce potatoes sold for eating. Assignment: Page 23 # 1 6, 8, 11, Sexual Reproduction Sexual reproduction is a method of reproduction that typically involves two parents, a male and female such as with humans and other animals, but can occur with species that we wouldn t consider male and female, such as in plants and coral. Sexual reproduction is the combination of two gametes, male and female sex cells, to produce an offspring. Gametes in females are called eggs or ova, whereas sex cells from a male are called sperm. These cells are produced through meiosis. The union of the sperm cell with the egg cell occurs during mating and is called fertilization. DNA recombines to create offspring with a combination of characteristics from both parents. So offspring are not clones of their parents. Variation helps a species survive by giving it the ability to survive changes in its environment. Although, a major disadvantage or sexual reproduction is that the gametes need to meet. Flowering plants must have wind or attract insects to move pollen to the stigma. Also, the embryo must be protected and nurtured during development. In mammals, the

6 embryo grows within the body of the female parent. Because this takes a large amount of time and energy needed for this development, only a limited number of offspring can be produced. Flowering Plant Structures

7 Pollination is the transfer of pollen grains to the stigma. Pollen transferred to the stigma of the same flower is called self-pollination. If pollen grains are transferred to the stigma of another flower, it is called cross-pollination. Cross-pollination can be caused by various sources, such as: wind, water, bees, birds, bats or other animals (including humans). Fertilization is the process that occurs after pollination. If the pollen grain has landed on a compatible stigma, a pollen tube grows to transport the pollen to the egg. Once the pollen reaches the egg, the two gametes fuse and create a zygote. The zygote then forms into a seed. Germination is the process a plant undergoes as the seed grows into a new plant. Once the seed absorbs water, it begins to expand and open as the new plant grows within it. Sexual Reproduction in Animals In animals, sexual reproduction uses eggs (female gamete) and sperm (male gamete) as the reproductive cells. After the two gametes fuse, a zygote is formed. Fertilization can occur within and exterior to the animal body depending on the specific animals form of reproduction. Once the zygote has undergone cellular division, it forms an embryo, which is a multi cellular structure. The embryo will begin to form small organs and appendages. Once the organs begin to function, it is called a fetus this occurs at approximately the nine week mark in humans. The fetus is final structure an organism will take before birth. Hermaphrodites can produce both male and female gametes. Worms and slugs are examples of hermaphrodites. Although hermaphrodites usually mate with other individuals of their species, in time of environmental stress, members of some species can fertilize themselves. Sequential hermaphrodites are species that are born as one sex, but then become the opposite sex. One example is the clownfish. Clownfish travel in packs that consist of a large reproductive female, a smaller reproductive male as well as numerous smaller nonreproductive males. If the female dies or leaves, the large reproductive male becomes a female and the largest of the non-reproductive males becomes the new reproductive male. Organisms that Reproduce Both Sexually and Asexually Some species have the ability to reproduce both sexually and asexually. Most plants that produce seeds by sexual reproduction can also reproduce asexually, either from cuttings or by producing structures such as bulbs or runners. Some plants can use their seeds to reproduce both asexually and sexually. In the asexual method, embryos develop in the seeds without the contribution of sperm cells. These offspring are genetically identical to their parent.

8 Some animal species can also reproduce both ways. Aphids are small insects that feed on the sap of certain plants. Throughout the growing season, females produce live female young through asexually. Over the summer, several generations are produced. In the fall, when days shorten and the temperature drops, the females produce a generation that includes both males and females. These males and females reproduce sexually and lay eggs that will hatch in the spring to produce new colonies. Sponges can also produce sexually and asexually. Assignment: Page 34 #3, 4, 6 9, 11, 12

9 3. Male Reproductive System Structure/ Function The organs of the male reproductive system are specialized for the following functions: To produce, maintain and transport sperm (the male reproductive cells) and protective fluid (semen) To discharge sperm within the female reproductive tract To produce and secrete male sex hormones Most of the male reproductive system is located outside of the man s body. The external structures of the male reproductive system are the penis, the scrotum and the testicles. Penis The penis is the male organ for sexual intercourse. It has three parts: the root, which attaches to the wall of the abdomen; the body, or shaft; and the glans, which is the cone-shaped end of the penis. The glans, which also is called the head of the penis, is covered with a loose layer of skin called foreskin. (This skin is sometimes removed in a procedure called circumcision.). The opening of the urethra, the tube that transports semen and urine, is at the tip of the glans. Semen, which contains sperm, is expelled (ejaculated) through the end of the penis when the man reaches sexual climax (orgasm). When the penis is erect, the flow of urine is blocked from the urethra, allowing only semen to be ejaculated at orgasm. Scrotum The scrotum is the loose pouch-like sac of skin that hangs behind the penis. It contains the testicles (also called testes). The scrotum has a protective function and acts as a climate control system for the testes. For normal sperm development, the testes must be at a temperature slightly cooler than the body temperature. Special muscles in the wall of the scrotum allow it to contract and relax, moving the testicles closer to the body for warmth and protection or farther away from the body to cool the temperature. Testicles (testes) The testes are oval organs about the size of large olives that lie in the scrotum, secured at either end by a structure called the spermatic cord. Most men have two testes. The testes are responsible for making testosterone, the primary male sex hormone, and for generating sperm. Within the testes are coiled masses of tubes called seminiferous tubules. These tubules are responsible for producing the sperm cells through a process called spermatogenesis.

10 Epididymis The epididymis is a long, coiled tube that rests on the backside of each testicle. It functions in the transport and storage of the sperm cells that are produced in the testes. It also is the job of the epididymis to bring the sperm to maturity, since the sperm that emerge from the testes are immature and incapable of fertilization. During sexual arousal, contractions force the sperm into the vas deferens. The internal organs of the male reproductive system, also called accessory organs, include the following: Vas deferens The vas deferens is a long, muscular tube that travels from the epididymis into the pelvic cavity, to just behind the bladder. The vas deferens transports mature sperm to the urethra in preparation for ejaculation. Ejaculatory ducts These are formed by the fusion of the vas deferens and the seminal vesicles. The ejaculatory ducts empty into the urethra. Urethra The urethra is the tube that carries urine from the bladder to outside of the body. In males, it has the additional function of expelling (ejaculating) semen when the man reaches orgasm. When the penis is erect during sex, the flow of urine is blocked from the urethra, allowing only semen to be ejaculated at orgasm. Seminal vesicles The seminal vesicles are sac-like pouches that attach to the vas deferens near the base of the bladder. The seminal vesicles produce a sugar-rich fluid (fructose) that provides sperm with a source of energy and helps with the sperms motility (ability to move). The fluid of the seminal vesicles makes up most of the volume of a man s ejaculatory fluid, or ejaculate. Prostate gland The prostate gland is a walnut-sized structure that is located below the urinary bladder in front of the rectum. The prostate gland contributes additional fluid to the ejaculate. Prostate fluids also help to nourish the sperm. The urethra, which carries the ejaculate to be expelled during orgasm, runs through the center of the prostate gland. Cowper s glands The Cowper s glands are pea-sized structures located on the sides of the urethra just below the prostate gland. These glands produce a clear, slippery fluid that empties directly into the urethra. This fluid serves to lubricate the urethra and to neutralize any acidity that may be present due to residual drops of urine in the urethra. Hormones The entire male reproductive system is dependent on hormones, which are chemicals that stimulate or regulate the activity of cells or organs. The primary hormones involved in the functioning of the male reproductive system are follicle-stimulating hormone (FSH), luteinizing hormone (LH) and testosterone. FSH and LH are produced by the pituitary gland located at the base of the brain. FSH is necessary for sperm production (spermatogenesis), and LH stimulates the production of testosterone, which is necessary to continue the process of spermatogenesis. Testosterone also is important in the development of male characteristics, including muscle mass and strength, fat distribution, bone mass and sex drive. Does a man go through menopause? Menopause is a term used to describe the end of a woman's normal menstrual function. Female menopause is characterized by changes in hormone production. The testes, unlike the ovaries, do not lose the ability to make hormones. If a man is healthy, he may be able to make sperm well into his 80s or longer.

11 On the other hand, subtle changes in the function of the testes may occur as early as 45 to 50 years of age, and more dramatically after the age of 70. For many men, hormone production may remain normal into old age, while others may have declining hormone production earlier on, sometimes as a result of an illness, such as diabetes. Whether waning testicular function contributes to such symptoms as fatigue, weakness, depression or impotence often remains uncertain. Can "male menopause" be treated? If testosterone levels are low, hormone replacement therapy may help relieve symptoms, such as the loss of interest in sex, depression and fatigue. However, replacing male hormones can worsen prostate cancer and, perhaps, atherosclerosis (hardening of the arteries). A man should receive a complete physical examination and laboratory tests should be performed starting hormone replacement therapy. How many middle-aged men will benefit from such therapy remains an open question. Assignment: Page 84 #1-5, 8 4. Female Reproductive System Structure/ Function The female reproductive system is designed to carry out several functions. It produces the female egg cells necessary for reproduction. The system is designed to transport the egg to the site of fertilization. Conception, the fertilization of an egg by a sperm, normally occurs in the fallopian tubes. After conception, the uterus offers a safe and favourable environment for a baby to develop before it is time for it to make its way into the outside world. If fertilization does not take place, the system is designed to menstruate (the monthly shedding of the uterine lining). In addition, the female reproductive system produces female sex hormones that maintain the reproductive cycle.

12 What parts make-up the female anatomy? The female reproductive anatomy includes internal and external structures. The function of the external female reproductive structures (the genital) is twofold: To enable sperm to enter the body and to protect the internal genital organs from infectious organisms. The main external structures of the female reproductive system include: Labia majora: The labia majora enclose and protect the other external reproductive organs. Literally translated as "large lips," the labia majora are relatively large and fleshy, and are comparable to the scrotum in males. The labia majora contain sweat and oil-secreting glands. After puberty, the labia majora are covered with hair. Labia minora: Literally translated as "small lips," the labia minora can be very small or up to 2 inches wide. They lie just inside the labia majora, and surround the openings to the vagina (the canal that joins the lower part of the uterus to the outside of the body) and urethra (the tube that carries urine from the bladder to the outside of the body). Clitoris: The two labia minora meet at the clitoris, a small, sensitive protrusion that is comparable to the penis in males. The clitoris is covered by a fold of skin, which is similar to the foreskin at the end of the penis. The internal reproductive organs include: Vagina: The vagina is a canal that joins the cervix (the lower part of uterus) to the outside of the body. It also is known as the birth canal. Uterus (womb): The uterus is a hollow, pear-shaped organ that is the home to a developing fetus. The uterus is divided into two parts: the cervix, which is the lower part that opens into the vagina, and the main body of the uterus, called the corpus. The corpus can easily expand to hold a developing baby. A channel through the cervix allows sperm to enter and menstrual blood to exit. Ovaries: The ovaries are small, oval-shaped glands that are located on either side of the uterus. The ovaries produce eggs and hormones. Fallopian tubes: These are narrow tubes that are attached to the upper part of the uterus and serve as tunnels for the ova (egg cells) to travel from the ovaries to the uterus. Conception, the fertilization of an egg by a sperm, normally occurs in the fallopian tubes. The fertilized egg then moves to the uterus, where it implants to the uterine wall. Endometrium The endometrium functions as a lining for the uterus. During the menstrual cycle or estrous cycle, the endometrium grows to a thick blood vessel-rich, glandular tissue layer. This layer also acts as a bed for the embryo during pregnancy. Cervix The cervix is the lower, narrow portion of the uterus where it joins with the top end of the vagina. What happens during the menstrual cycle? Females of reproductive age (anywhere from years) experience cycles of hormonal activity that repeat at about one-month intervals. (Menstru means "monthly"; hence the term menstrual cycle.) With every cycle, a woman s body prepares for a potential pregnancy, whether or not that is the woman s intention. The term menstruation refers to the periodic shedding of the uterine lining. The average menstrual cycle takes about 28 days and occurs in phases: the follicular phase, the ovulatory phase (ovulation), and the luteal phase.

13 There are four major hormones (chemicals that stimulate or regulate the activity of cells or organs) involved in the menstrual cycle: follicle-stimulating hormone (FSH), luteinizing hormone (LH), estrogen, and progesterone. The following steps occur in the menstrual cycle: - The brain releases FSH into the blood stream - FSH reaches the ovary and signals it to begin developing the follicles. Many follicles begin growing, although only one will mature while the other disintegrate - The developing follicles produce estrogen and release it into the bloodstream - Estrogen reaches the uterus and the brain. The endometrium begins to thicken. The brain produces and releases LH into the bloodstream - LH reaches the ovary and causes the mature follicle to release and egg (ovulation) - Once the egg is released, LH signals the empty follicle to develope into the corpus luteum - The corpus luteum produces progesterone and some estrogen and releases it into the blood stream. The corpus luteum continues to produce progesterone and estrogen for about two weeks until it disintegrates - Progesterone reaches the uterus and the brain. The uterus continues to thicken the endometrium even more. The brain stops producing FSH and LH to prevent another egg from being released until the progesterone levels decrease again. - Once the copus luteum begins to disintegrate, the progesterone level int he body decreases. This signals the tick endometrium to break down and be shed from the body, along with the dead, unfertilized egg in a process called menstruation. This usually lasts four to seven days. - After menstruation, the progesterone level in the body reaches a certain low level, which tells the brain to being releasing FSH again. How many eggs does a woman have? During fetal life, there are about 6 million to 7 million eggs. From this time, no new eggs are produced. The vast majority of the eggs within the ovaries steadily die, until they are depleted at menopause. At birth, there are approximately 1 million eggs; and by the time of puberty, only about 300,000 remain. Of these, 300 to 400 will be ovulated during a woman's reproductive lifetime. The eggs continue to degenerate during pregnancy, with the use of birth control pills, and in the presence or absence of regular menstrual cycles. Assignment: Page 90 #1-3, 8, 12

14 5. Human Development Signs of Pregnancy Although pregnancy symptoms differ from woman to woman and pregnancy to pregnancy, the most significant symptom is a delayed or missed menstrual cycle. The growing embryo will also begin producing hcg, a hormone, which is detected by most pregnancy tests. The following are some other common symptoms of pregnancy. Implantation bleeding occurs about 6-12 days after conception, the embryo implants itself into the uterine wall causing minor bleeding. Delay/Difference in Menstruation menstruation may not immediately stop once conception occurs. Some women bleed during the beginning of their pregnancy, but it will be shorter or lighter than their normal menstrual cycle. Swollen/Tender Breasts may begin as early as 1-2 weeks, commonly caused by a hormone imbalance. Tiredness may begin as early as the first week after conception. Nausea/Morning Sickness often begins between 2-8 weeks after conception. X and Y Chromosomes Females only have copies of the X chromosome; therefore the male sex gamete contains the genes that will determine the sex of the offspring. If the male gives its offspring the X chromosome, the offspring will be female. If the male gives its offspring the Y chromosome, the offspring will be male. From Fertilization to Birth Once the sperm fertilizes the egg a zygote is formed. Approximately 24 to 30 hours after fertilization, the zygote completes its first cell division. Through the process of mitosis, one cell spits into two, two into four, and so on. Once the embryo reaches the uterus, it attaches itself into the endometrium that lines the uterus in a process called implantation. Once implantation has taken place, hormonal changes prevent the corpus luteum from breaking down in the ovary. Because the corpus luteum does not break down until approximately 16 weeks of pregnancy, progesterone continues to be produced and the endometrium is not shed. The vastly altered entometrium remains in the uterus, providing nutrients to the developing embryo and helping to form the placenta. At weeks, the placenta begins to take over the role of maintaining the pregnancy. Once the fetus has developed for nine months, it is ready to leave the support and safety of the mother s uterus and enter the outside world. It is not known precisely what begins the process of birth.. The release of a hormone called oxytocin makes the uterus contract rhythmically. These contractions may cause the amiotic sac to burst before contractions begine. The amniotic fluid is released from the body. This is commonly known as the water breaking.

15 Assignment: Page 99 # Contraceptive and Reproductive Technologies Reproductive Technology In vitro fertilization - In vitro fertilization (IVF) is the joining of a woman s egg and a man s sperm in a laboratory dish. In vitro means outside the body. Fertilization means the sperm has attached to and entered the egg. In order to do this, a large number of eggs are required in order to increase fertilization odds. These are the five basic steps to In vitro fertilization: Artificial Insemination 1. Stimulation (super ovulation) fertility drugs cause the woman s body to release more than one egg. 2. Egg retrieval a minor surgery is done to remove the eggs from the woman s body. 3. Insemination the man s sperm is placed together with the best quality eggs and stored in a controlled environment 4. Embryo culture Within about 5 days, a normal embryo has sever4al cells that are actively dividing. Couples with a high risk of transferring a genetic (hereditary) disorder to a child may consider pre-implantation genetic diagnosis (PGD). Scientists remove a single cell from each embryo and screen the material for genetic disorders. Parents can then decide which embryo to implant. This process is very controversial and not offered at all centers. 5. Embryo Transfer Embryos are placed in the woman s womb 3-5 days after egg retrieval and fertilization. If an embryo implants into the lining of the womb and grows, pregnancy results. More than one embryo may be placed into the womb at the same time, which can lead to twins, triplets, or more.

16 Artificial insemination is the process of placing sperm in the reproductive tract of a female, for the purpose of impregnating the female. Fertilization occurs within the females body. Contraceptive Technologies The following are various methods of contraception. No method of contraception is 100% preventative of a pregnancy. Contraception technologies are not protective against sexually transmitted infections. Condoms o a rubber sheath placed over an erect penis o prevents semen from entering the vagina. o ~85% effective when used properly Oral Contraceptive Pill o Composed of synthetic hormones that stop the ovary from releasing an egg (Prevents ovulation), menstrual cycle still occurs o ~99% effective o Side effects include: nausea, breast tenderness, weight gain o Dangerous to use if over 35 and a smoker o Do not use someone else s pills, these must be obtained by a physician Diaphragm o Large rubber cap which covers the cervix. o Must be used with spermicide o ~85% effective o Can be inserted 2 hours before intercourse, but must be left in place for 6 hours afterwards Intra-Uterine Devices o IUD o Interferes with the sperm s ability to reach the egg or with a fertilized egg s ability to implant o ~97% effective o Must be inserted into the uterus by a gynaecologist o May prevent pregnancy for several years o Can cause increased bleeding and cramps. o Not recommended for women who have not had families o May cause pelvic inflammatory disease Emergency Contraception o Taken within 72 hours after sexual intercourse o Disrupts ovulation or fertilization to prevent pregnancy o Contains higher doses of the same hormones found in Oral contraceptive pills o Effectiveness varies depending on when the pill is taken

17 o o May cause nausea or vomiting, less commonly abdominal pain, fatigue, headache, dizziness, and breast tenderness Should not be used as a regular method to birth control Permanent Methods of contraception Sterilization o o Tubal Ligation (Female) the fallopian tubes are cut and tied or clamped. The egg cannot be fertilized by the sperm. >99% effective Usually requires general anesthesia and a brief hospital stay Will cause initial discomfort Ovulation and menstruation still occur Vasectomy (Male) The vas deferens is cut and tied No sperm is in the semen Operation usually takes minutes Will cause initial discomfort at the site of the surgery Assignment: Page 107 #2-6