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Biology - Reproduction

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    Study Guide Biology – Reproduction 1. Human Reproduction Reproduction is a vital process because it allows a species to continue from one generation to the next. In humans, reproduction depends on the proper working of the male and female reproductive systems. Each system has specific roles, but they work together toward the same goal — creating new life. 1.1 The Role of the Reproductive Systems The main job of the reproductive systems is to produce gametes , which are reproductive cells. • In males, the gametes are sperm . • In females, the gametes are eggs . These cells are specially designed for reproduction and contain half the usual number of chromosomes. Before fertilization can happen, the reproductive systems also prepare these gametes so they are ready to function properly. 1.2 The Male Reproductive System The male reproductive system produces sperm and delivers them into the female reproductive tract. This delivery is essential because fertilization can only occur when a sperm meets an egg. The system is built to protect, nourish, and transport sperm efficiently. 1.3 The Female Reproductive System The female reproductive organs have several important roles. They receive the sperm and allow fertilization to occur. After fertilization, they provide nourishment and a safe environment for the fertilized egg. This environment supports the developing embr yo as it grows into a fetus and eventually into a baby.

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    Study Guide 1.4 Fertilization and Development Human reproduction happens through the coordination of both reproductive systems. When a sperm and an egg come together, they fuse to form a zygote . This single cell begins dividing and developing, eventually forming an embryo and then a growing fetus. 1.5 Hormonal Control A network of hormones controls the reproductive systems in both males and females. These hormones regulate the production of gametes and help guide the growth and development of the fetus. They also play a key role in preparing the body for childbirth. 2. Female Reproductive System The female reproductive system is designed to produce egg cells, allow fertilization, and support the growth of a baby. It includes several organs that work together in a carefully timed cycle. 2.1 Main Reproductive Organs The ovaries are two small, oval - shaped organs located in the pelvic cavity. Their main job is to produce egg cells and female hormones. Next to the ovaries are the fallopian tubes , also called oviducts . When an egg is released from an ovary, it enters a fallopian tube. These tubes act as passageways that carry the egg toward the uterus. The fallopian tubes lead to the uterus , or womb. The uterus is a strong, muscular organ in the pelvic cavity. Its inner lining is called the endometrium . Each month, this lining thickens with extra blood and tissue to prepare for a possible pregnancy. If no fertilized egg arrives, the endometrium breaks down and is shed from the body during menstruation . 2.2 Cervix and Vagina At the lower end of the uterus is a narrow opening called the cervix . This opening connects the uterus to the vagina , a muscular tube that leads to the outside of the body.

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    Study Guide During sexual arousal, the vagina receives the penis and semen. The sperm in the semen travel through the vagina, pass the cervix, move through the uterus, and enter the fallopian tubes. Fertilization usually occurs in the fallopian tubes . 2.3 Egg Cell Production In human females, egg cell production begins before birth . At that time, about 2 million immature cells , called oogonia , are present in the ovaries. These cells are formed during the early stages of meiosis , the process that produces reproductive cells. After puberty, egg development continues at a rate of about one egg per month . The oogonia develop into primary oocytes and eventually into mature egg cells. This entire process also occurs through meiosis. 2.4 Follicle Development and Hormones Each egg cell develops inside the ovary within a group of supporting cells called a Graafian follicle . This follicle releases estrogen , a hormone that helps regulate the development of secondary female characteristics. Egg development inside the follicle takes about 14 days . This process is controlled by two hormones: • Follicle - stimulating hormone (FSH) • Luteinizing hormone (LH) Both hormones are released by the anterior lobe of the pituitary gland . 2.5 Ovulation and the Corpus Luteum While the egg is developing, the endometrium in the uterus becomes thicker and richer in blood supply, preparing for a fertilized egg. Around day 14 , the egg is released from the follicle in a process called ovulation . The egg is then swept into the fallopian tube and begins moving toward the uterus. After ovulation, the empty follicle changes into a structure called the corpus luteum . This change is triggered by LH. The corpus luteum produces progesterone , a hormone that works with estrogen to:

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    Study Guide • Maintain the thickened endometrium • Prevent contractions of the uterus These actions help prepare the uterus for possible pregnancy. 2.6 What Happens If Fertilization Does Not Occur The egg cell can survive in the fallopian tube for 24 to 72 hours . If it is not fertilized, it continues moving toward the uterus and eventually breaks down. At the same time, the corpus luteum begins to degenerate , causing progesterone and estrogen levels to drop. Within about two weeks , hormone levels become too low to maintain the endometrium or prevent uterine contractions. As a result, the uterus contracts and the endometrium is shed during menstruation . After this, a new cycle begins, usually with egg development starting in the opposite ovary . 3. Quiz Female Reproductive System 1. Question The opening at the lower end of the uterus is called the: Answer Choices • cervix • fallopian tube • vagina Correct Answer cervix Why This Is Correct The cervix is the narrow, lower portion of the uterus that opens into the vagina. It acts as a passageway between the uterus and the vagina and plays an important role during menstruation and childbirth.

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    Study Guide For example: During labor, the cervix dilates (opens) to allow the baby to pass from the uterus into the vagina. 4. Fertilization and Development Human development begins when fertilization occurs and continues through a series of well - organized stages. Each step builds on the previous one, turning a single cell into a developing human embryo. 4.1 Fertilization: The Beginning of Life For fertilization to happen, sperm cells must be released into the vagina while the egg cell is still alive . After entering the vagina, sperm travel through the cervix and uterus and into the fallopian tube . This is where fertilization usually takes place. When one sperm cell successfully enters the egg cell, fertilization occurs. At this moment: • The sperm contributes 23 chromosomes • The egg contributes 23 chromosomes

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    Study Guide Together, they form a single cell with 46 chromosomes . This fertilized egg cell is called a zygote . The zygote contains all the genetic information needed to develop into a new individual. 4.2 Early Cell Division About 36 hours after fertilization , the zygote begins dividing by mitosis . First, it splits into two identical cells that remain attached. These cells continue dividing rapidly. As division continues, the cells form a solid ball known as a morula . This stage is reached about six days after fertilization . During this time, the developing structure is still moving through the fallopian tube toward the uterus. 4.3 Formation of the Blastocyst Within the next two days , the morula changes into a blastocyst , which is a hollow ball of cells. The blastocyst then enters the uterus. Inside the blastocyst, a cluster of cells called the inner cell mass forms at one end. These cells are important because they will continue developing into the embryo. 4.4 Implantation and Support Structures Around eight days after fertilization , the blastocyst attaches itself to the uterine lining, or endometrium . This process is called implantation . During implantation: • The outer layer of cells, called the trophoblast , grows into the endometrium. • The trophoblast forms projections that develop into blood vessels. • These vessels connect with the mother’s blood supply, forming the placenta . The trophoblast also develops into three protective membranes: • Amnion • Chorion • Yolk sac membrane These membranes help protect and nourish the developing embryo.

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    Study Guide 4.5 Formation of Germ Layers The inner cell mass undergoes major changes and forms three basic layers called germ layers : • Ectoderm – develops into the skin and nervous system • Mesoderm – forms muscles and many internal organs • Endoderm – becomes the gastrointestinal (digestive) tract Each layer has a specific role and gives rise to different parts of the body. 4.6 Development of the Embryo By about the fourth week , the basic structure of all major organs has formed. At this stage, the developing organism is called an embryo . From this point on, growth continues as the organs mature and become more complex. 5. Quiz Fertilization and Development 1. Question Where does fertilization take place? Answer Choices • fallopian tubes • uterus • vagina Correct Answer fallopian tubes Why This Is Correct

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