unit 4 overview

The human life cycle starts when the male produces sperm and the females produce eggs. The sperm exits the penis and the female transports eggs to the tubes in the uterus. The uterus allows the female to fertilize the eggs that develop into a baby. In order for all of this to happen the ovaries and the testes must produce sex hormones. Every cell has 46 chromosomes. The sperm is very small compared to the egg. Without meiosis cells would no longer be able to function.
The male reproductive system starts with the penis which is the organ used for sexual intercourse. The testes produce sperm and also sex hormones. The scrotum is where the testes are located. The epididymides are ducts where the sperm mature and is where some is also stored. The vas deferens conduct and also store the sperm. The seminal vesicles contribute nutrients and fluid to the semen. The prostate gland also contributes fluid to the semen. The urethra conducts the sperm. The bulb urethral glands contribute mucus containing fluid to the semen. An orgasm in males is when semen is ejaculated from the penis. Testosterone is the main sex hormone in males. It is essential for normal development and functioning of the organs. It also is responsible for better muscular development in males.
The female reproductive system consists of the following. The vagina which receives the penis during sexual intercourse, serves as the birth canal, and is where menstrual flow exits the body. The ovaries produce eggs and sex hormones. The oviducts conduct the eggs and lead to the uterus. It is also where fertilization takes place. The uterus is where the fetus develops. The cervix contains the opening to the uterus. The orgasm culminates in uterine and oviduct contractions. The follicle balloons out of the ovary and bursts, then releases an egg that enters the oviduct.
The female hormone goes through a monthly cycle. The ovaries contain follicles and each one contains an immature egg. Females are born with two million follicles but are reduced by puberty. The hypothalamus has control over the ovaries sexual function. During the first half of the cycle FSH is released and promotes the development of follicles. The second half LH is released and promotes the development of corpus luteum and secretes progesterone. When the person is not pregnant corpus luteum regresses. Estrogen is responsible for the sex characteristics such as body hair and fat distribution. Menopause occurs when the ovarian cycle stops.
When the sperm fertilizes an egg, the egg becomes a zygote. An embryo becomes implanted in the lining for several days. The placenta sustains the developing embryo. The placenta also produces HCG. Progesterone maintains the uterine lining where the embryo is located. When a person uses birth control pills it makes the body think that is pregnant. Birth control pills also thicken the cervical mucus which prevents sperm from entering the uterus. Birth control pills can cause a person to skip menstruation. Menstruation should not be skipped regularly.
There are many different types of birth control. Birth control pills, intrauterine device or IUD which is a small piece of molded plastic inserted into the uterus. A diaphragm which is a soft latex cup that lodges behind the pubic bone and fits over the cervix. A female condom is a large polyurethane tube with a flexible ring that fits onto the cervix. Then there are the male condoms. Contraceptive implants utilize synthetic progesterone. Then there are contraceptive injections and vaccines. Or for the extreme measures there is a vasectomy which is the cutting and sealing of the vas deferens on each side so that the sperm cannot reach the seminal fluid. And there is tubal ligation which is the cutting and sealing of the oviducts.
Infertility is when a person is unable to get pregnant after one year of unprotected intercourse. In males it could be due to low sperm count or abnormal sperm. In females weight can be a big factor in infertility. Infertility can be fixed by medication or fertility drugs. People can also use assisted reproductive technologies which is fertilization in the lab. There is artificial insemination, in vitro fertilization, gamete intrafallopian transfer. Or the couple could use a surrogate mother or intracytoplasmic sperm injections.
Sexually transmitted diseases or STD’s are very common they can be viral or bacterial. The viral infections include HIV or AIDS, genital warts, genital herpes, or hepatitis. The bacterial infections include Chlamydia, gonorrhea, and syphilis.
Fertilization is the union of a sperm and an egg to form a zygote. The zygote is the first cell of the individual. First the sperm swims toward the egg, then only one sperm enters the egg, when the sperm touches the egg it starts depolarization.
There are four steps involved with embryonic development. The first is cleavage which is cell division that occurs and each cell receives a full complement of chromosomes and genes. Next is the growth stage which is when the cell divides and increases in size of the daughter cells. This is also known as embryonic development. Next is morphogenesis which is the shaping of the embryo. The last stage is differentiation which is when a cell takes on specific structure and starts to function. The first system to develop is the nervous system.
Extraembryonic membranes are outside the embryo and they have four functions:
chorion which is the fetal half of the placenta, provides the fetus with nourishment and oxygen.
allantois is where urine produced by the kidneys starts to accumulate.
the yolk sac is the first embryonic membrane to appear and is also the first site of blood cell formation.
the amnion contains fluid to cushion and protect the embryo. This area enlarges with the fetus.
There are 280 days in a normal gestation period, but only about 5% of people arrive around their due date. Pre-embryonic developments occurs only in the first week. During this time the morula which is a compact ball of embryonic cells becomes a blastocyst. There is an inner cell mass and the layers of the cell walls become chorion. The second week is called embryonic development and this lasts until the second month. The embryo begins to implant itself. The chorion begins to secrete human chorionic gonadotropin or HCG. The inner cell mass becomes and embryonic disk this process is called gastrulation. The brain and the spinal cord start to develop in the third week. The heart also starts to develop in the third week. During the fourth and fifth weeks the umbilical cord is fully formed. The sixth through the eighth weeks the fetus starts to make changes that like more human like. The organ systems are also established during this time. During the third month the gender can be distinguished and fingernails appear. The fourth month the skeleton is visible and hair appears. The fifth month a protective coating is called the vernix caseosa is deposited. During this time the heartbeat can also be heard. The sixth month the body is covered with fine hair and the skin is wrinkled and reddish color. The seventh month the testes descend into the scrotum and the eyes open. The eighth month the hair disappears and fat is depositied. And the ninth month the baby is ready for birh.
Major changes happen to the mothers body as well. Weight gain happens and the uterus enlarges. Stretch marks also appear on the body. Many people experience Braxton hicks contractions which is false labor. The first thing that has to happen is the bloody show/mucus plug. The first stage of labor is when the contractions cause the cervical canal to disappear and ends when the cervix is fully dialated. During the next stage the contractions are 1-2 minutes apart and last about 1 minute each. This is when person feels the need to push as the babies head descends into the vagina. This is also when an episoiotomy is common. The baby is delivered and lastly the placenta is delivered.
Development continues throughout infancy, childhood, adolescence, and adulthood. Aging encompasses these changes. Aging is genetic and it happens to the whole body. The skin becomes thinner and less elastic. The heart shrinks and the blood supply to the kidneys is reduced. People also start to lose their teeth. People also start to lose skeletal muscle, bone density starts to decline, the metabolism decreases which cause weight gain.
All living things are made of cells and every cell comes from a preexisting cell. Small organic molecules were produced by reactions between the earth’s atmospheric gases. This is where the macromolecules evolved and interacted. Only a macromolecule RNA was needed for the first cell. Amino acids join to form polypeptides when exposed to dry heat. The protocell which is a heterotrophic fermenter lived on organic molecules in the ocean. Chemical evolution could have produced the protocell. The protocell did become a true cell once it had genes composed of DNA and could reproduce.
Biological evolution explains both the unity and the diversity of life. Common ancestors explains the unity of living things. These things adapted to the environmental changes that has occurred. There are four types of evidence. Fossil evidence supports evolution. A fossil record gives us the history of life in general and allows people to trace each fossil to a particular group. Biogeographical evidence is the distribution of organisms on Earth. It is explained by assuming organisms evolved in one locale. Anatomical evidence is when common anatomies and the development of a group of organisms is explainable by the descent from a common ancestor. Biochemical evidence is when all organisms have similar biochemical molecules. Darwin discovered a lot of the evidence for common descent. He also developed a mechanism for adaptation called natural selection. There are three observations: organisms have variations, organisms struggle to exist, and organisms differ in fitness. In the end organisms become more adapted with each generation.
Humans can be traced through their ancestry. Humans are primates and primates evolutionary tree shows that human share a common ancestor with African apes. The first homind or human lived about 6-7 mya.
There are two hypotheses for human evolution. The first is the multiregional continuity which says that humans evolved separately in Europe, Africa, and in Asia. The second is out-of-Africa hypothesis says that H sapiens evolved in Africa but then migrated to Asia and Europe. Neandertals were living in Europe and Asia before modern humans, but they did not look like modern humans. They did have the same culture.
Ecology is the study of interactions of organisms with each other and with the physical environment. Organisms interact with the physical and chemical environment, the result is called an ecosystem. Terrestrial ecosystems are the forests, the grasslands, and the deserts. Aquatic ecosystems are salt water or fresh water. In every community the population has a residence or habitat and a role in that community or a niche. Autotrophs produce organic nutrients for themselves and for others. Heterotrophs are consumers and they consume the organic nutrients. Then there are decomposers who feed on detritus which release the inorganic substances back into the ecosystem. An ecosystem is determined by the energy flow and the chemical cycling. Energy flows through the populations of an ecosystem and chemicals cycle inside the ecosystems.
A food web is interconnection paths of energy flow. A food web shows how various organisms are connected through their eating relationships. Grazing food webs start with some sort of vegetation that are then eaten by a herbivore who is eventually eaten by a carnivore. A dentrital food web start with detritus food for decomposers and for detritivores. The two food webs can be joined together when an above ground carnivore eats something from the dentrital food web. A trophic level is all organisms that feed on a particular link in one of the food chains.
Chemicals circulate through the ecosystems by biogeochemical cycles. These are pathways that involve biotic and geological components. Biogeochemical cycles can be gaseous or sedimentary. It has reservoirs that are available to living things, but are limited. The reservoir of the water cycle is freshwater that evaporates from the ocean. Water that falls from the sky and enters the ground which then surfaces water and evaporates again. Eventually all the water returns to the ocean.
The reservoirs of carbon cycle are organic matter, limestone, and the ocean. The exchange pool for this is the atmosphere. Photosynthesis removes carbon dioxide from the atmosphere. Respiration and combustion add carbon dioxide to the atmosphere. The reservoir of the nitrogen cycle is the atmosphere. Nitrogen gas must be converted to a form usable by plants. Nitrogen-fixing bacteria convert nitrogen gas to ammonium in a form that plants can use. Nitrifying bacteria convert ammonium to nitrate. Denitrifying bacteria are then converted back into nitrogen gas.
The reservoir of the phosphorus cycle is the ocean sediments. Phosphate that is in the ocean sediments becomes available when sedimentary rocks are exposed to weathering. Weathering slowly makes phosphate available to the biotic community.
Populations have a biotic potential to increase in size. Biotic potential is held in check by environmental resistance. Population size levels off at a certain capacity. There are five resources that are fully used by humans land, water, food, energy, and minerals. These resources are either renewable or nonrenewable. Renewable resources are replenished but are still limited in quantity. Nonrenewable resources are not able to be replenished and are also limited in quantity. Land resources are used by humans for farming, mining, and a place to live. Humans contribute to the pollution, erosion, and loss of biodiversity. Water is used the most by industry and agriculture. Water supplies are increased by damming the rivers. If industries used water conservation methods it could cut the water consumption in half. Food comes from crops, animals, and fishing. Modern farming increases food supply, but it harms the land, causes pollution, and uses fossil fuels. Genetically engineered plants increase food supply and reduce the need for chemicals. Raising livestock contributes to the water pollution and also uses up the fossil fuels. Fossil fuels are nonrenewable sources. Renewable resources are hydropower, geothermal, wind, and solar power. Minerals are a nonrenewable resource that we can mine. This include sand, gravel, phosphate, and metals. Mining cause erosion to the land, this can take up to ten years to recover. Some metals are very bad for our health. We are destroying the ozone shield with hazardous waste. There are billions of tons of waste that has been dumped on the land and in the water that is aiding in the ozone destruction.
Biodiversity is the variety of life on Earth. Five things can cause losing biodiversity and aslo exctinction. They are losing a habitat or place to live, introduction of a new species, pollution, disease, and overexploitation of the plants and animals. Biodiversity can be a good thing. We make medicines from the plants, we grow crops and raise livestock, and we consume the products. There are also some indirect benefits of biodiversity the ability of our water to purify itself even with waste put in it, how the climate regulates it self by plants taking up the carbon dioxide, and that we are able to enjoy our environment.
We as a society should work towards only using renewable resources. There are many things that we can reuse. For example we can reuse waste by recycling our garbage, we can also reuse the heat materials. Some other things we can use that does not harm our society are solar power and wind power.