Fertilization

Question 1

A prenatal human is considered an____ for the first 8 weeks.

Answer 1

embryo

Question 2

The embryo in the first week is considered to be in a “______” stage because it has not yet settled into the uterine lining. Some biologists do not consider a prenatal human an embryo until it begins to develop tissue layers, at about 2 weeks.

Answer 2

preimplantation

Question 3

Prenatal development after the eighth week is the_____ period, when structures grow and specialize.

Answer 3

fetal

Question 4

From the start of the ninth week until birth, the prenatal human organism is a_____.

Answer 4

fetus

Question 5

A sperm cell can survive in the woman’s body for up to____ days, but the oocyte can only be fertilized in the ______hours after ovulation.

Answer 5

3 days

12 to 24 hrs

Question 6

A process in the female called____ chemically activates sperm, and the oocyte secretes a chemical that attracts sperm.

Answer 6

capacitation

Question 7

Sperm are also assisted by contractions of the female’s muscles and by their moving tails. Still, only____ or so sperm come near the oocyte.

Answer 7

200

Question 8

A sperm first contacts a covering of follicle cells, called the______ that guards a secondary oocyte.

The sperm’s____ then bursts, releasing enzymes that bore through a protective layer of glycoprotein (the_____) beneath the corona radiata.

Answer 8

corona radiata

acrosome

zona pellucida

Question 9

_______, begins when the outer membranes of the sperm and secondary oocyte meet

Answer 9

Fertilization, or conception

Question 10

Within 12 hours of the sperm’s penetration, the ovum’s nuclear membrane disappears, and the two sets of chromosomes, called______, approach one another.

Answer 10

pronuclei

Question 11

Fertilization completes when the two genetic packages meet and merge, forming the genetic instructions for a new individual. The fertilized ovum is called a_____.

Answer 11

zygote

Question 12

About a day after fertilization, the zygote divides by mitosis, beginning a period of frequent cell division called______

The resulting early cells-are called______.

Answer 12

cleavage

blastomeres

Question 13

When the blastomeres form a solid ball of sixteen or more cells, the embryo is called a_____

Answer 13

morula

Question 14

The ball of cells hollows out, and its center fills with fluid, creating a_____—the “cyst” refers to the fluid-filled center.

Some of the cells form a clump on the inside lining called the_______

Answer 14

blastocyst

inner cell mass

Question 15

Formation of the_____ is the first event that distinguishes cells from each other in terms of their relative positions, other than the inside and outside of the morula

Answer 15

inner cell mass

Question 16

A week after conception, the blastocyst begins to nestle into the woman’s uterine lining (endometrium).

This event, called______, takes about a week

Answer 16

implantation

Question 17

As implantation starts, the outermost cells of the blastocyst, called the_____, secrete the “pregnancy hormone” _________which prevents menstruation. _____ detected in a woman’s urine or blood is one sign of pregnancy.

Answer 17

trophoblast

human chorionic gonadotropin (hCG)

Question 18

Key Concepts

1. Following sexual intercourse, sperm are_____ and drawn to the secondary oocyte.

2.____ enzymes assist the sperm’s penetration of the oocyte. Chemical and electrical changes in the oocyte’s surface block additional sperm.

3. The two sets of chromosomes meet, forming a_____.
4. Cleavage cell divisions form a____ and then a_____.
5. The outer layer of cells invades and implants in the_____
6. The______ develops into the embryo.
7. Certain blastocyst cells secrete____.

Answer 18

1. capacitated
2. Acrosomal
3. zygote
4. morula/ blastocyst
5. uterine lining
6. inner cell mass
7. hCG

Question 19

During the second week of prenatal development, a space called the_____ forms between the inner cell mass and the outer cells anchored to the uterine lining.

Answer 19

amniotic cavity

Question 20

The layer nearest the amniotic cavity is the

Answer 20

ectoderm

Question 21

the inner layer, closer to the blastocyst cavity, is the

Answer 21

endoderm

Question 22

Shortly after, a third layer, the______, forms in the middle.

Answer 22

mesoderm

Question 23

The three-layered structure is called the primordial embryo, or the

Answer 23

gastrula

Question 24

Cells in the____ become skin, nervous tissue, or parts of certain glands.

Answer 24

ectoderm

Question 25

cells form parts of the liver and pancreas and the linings of many organs

Answer 25

Endoderm

Question 26

the____, forms many structures, including muscle, connective tissues, the reproductive organs, and the kidneys.

Answer 26

mesoderm

Question 27

Genes called____ control how the embryo develops parts in the right places

Answer 27

homeotics

Question 28

As an embryo develops, structures form that support and protect it. These include

Answer 28

chorionic villi
placenta
yolk sac
allantois
umbilical cord
amniotic sac

Question 29

By the third week after conception, finger-like outgrowths called ____extend from the area of the embryonic disc close to the uterine wall, and these project into pools of the woman’s blood.

Answer 29

chorionic villi

Question 30

By 10 weeks, the____ is fully formed.

Answer 30

placenta

Question 31

The_______ is an organ that links woman and fetus for the rest of the pregnancy.

The ______ secretes hormones that maintain pregnancy and alter the woman’s metabolism to send nutrients to the fetus.

Answer 31

placenta

Question 32

The________ manufactures blood cells, as does the______, a membrane surrounding the embryo that gives rise to the umbilical blood vessels.

The umbilical cord forms around these vessels and attaches to the center of the placenta.

Answer 32

yolk sac

allantois

Question 33

Toward the end of the embryonic period, the yolk sac____, and the amniotic sac_____ with fluid that cushions the embryo and maintains a constant temperature and pressure.

The_______ contains fetal urine and cells.

Answer 33

shrinks

swells

amniotic fluid

Question 34

Key Concepts

1.________ form in the second week. Cells in a specific ____ later become parts of particular organ systems as a result of differential gene expression.

2. During week 3, ______extend toward the maternal circulation, and the_____ begins to form.
3. Nutrients and oxygen enter the embryo, and wastes pass from the embryo into the maternal circulation.
4. The ____&_____manufacture blood cells, the umbilical cord forms, and the amniotic sac expands with fluid.

Answer 34

1. Primary germ layers
2. chorionic villi ; placenta
3. yolk sac and allantois