fertilization

fertilization and implantation

The sperm and egg dont look anything like a human baby ( Figure 1.1). After they come together, they will develop into a human being. How does a single cell become a complex organism made up of billions of cells? Keep reading to find out. Sexual reproduction happens when a sperm and an egg cell combine together. This is called fertilization. Sperm are released into the vagina during sexual intercourse. They swim through the uterus and enter a fallopian tube. This is where fertilization normally takes place. A sperm that is about to enter an egg is pictured below ( Figure 1.1). If the sperm breaks through the eggs membrane, it will immediately cause changes in the egg that keep other sperm out. This ensures that only a single sperm can penetrate an egg. It will also cause the egg to go through meiosis. Recall that meiosis, cell division that creates the egg, begins long before an egg is released from an ovary. In fact, it begins prior to birth. The sperm and egg each have only half the number of chromosomes as other cells in the body. These cells are haploid, with a single set of chromosomes. This is because when they combine together, they form a cell with the full number of chromosomes. The cell they form is called a zygote. The zygote is diploid, with two sets of chromosomes, one from each parent. A human zygote has two sets of 23 chromosomes, for a total of 46 chromosomes (23 pairs). The zygote slowly travels down the fallopian tube to the uterus. As it travels, it divides by mitosis many times. It forms a hollow ball of cells. After the ball of cells reaches the uterus, it fixes itself to the side of the uterus. This is called implantation. It usually happens about a week after fertilization. Now the implanted ball of cells is ready to continue its development into a baby boy or girl.

textbook_image

instructional diagrams

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questions

fertilization usually occurs in the uterus.

a. true

-->  b. false

implantation usually occurs in the uterus.

-->  a. true

b. false

how do eggs develop?

a) through mitosis

-->  b) through meiosis

c) through fertilization

d) through implantation

if a zygote had 50 chromosomes, how many chromosomes would be in an egg or sperm?

-->  a) 25

b) 50

c) 100

d) it cannot be determined

what does the egg provide to the zygote?

a) 23 chromosomes

b) cytoplasm

c) organelles

-->  d) all of the above

how long after fertilization does implantation occur?

a) about 1 day

-->  b) about 1 week

c) about 1 month

d) about 40 weeks

what does a sperm cell contribute to the zygote?

a) organelles

b) cytoplasm

-->  c) one set of chromosomes

d) all of the above

diagram questions

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