Development of an offspring from an unfertilized egg, as seen in aphids and water fleas, is called parthenogenesis.
Missing Word
parthenogenesis
Parthenogenesis is a form of asexual reproduction in which an egg develops without being fertilized by a sperm. It occurs in many invertebrates and in some fish, amphibians and reptiles.
Category: Asexual Reproduction
Question 2
Human pregnancy is divided into three periods of roughly equal length called trimesters.
Missing Word
trimesters
A trimester is one third of a pregnancy, about three months. Major organs begin forming in the first trimester, the mother usually first feels fetal movement in the second, and the third is the period of fastest growth.
Category: Pregnancy and Birth
Question 3
The release of eggs and sperm by females and males into the water at the same place and time is called spawning.
Missing Word
spawning
Spawning is the coordinated release of gametes that makes external fertilization work. Cues such as water temperature or day length often trigger it.
Category: Fertilization and Development Modes
Question 4
The single diploid cell formed when the egg and sperm nuclei fuse is called a zygote.
Missing Word
zygote
A zygote is the first cell of a new organism, carrying one haploid set of chromosomes from each parent. It goes on to divide by cleavage.
Category: Embryonic Development
Question 5
The fluid-filled cavity at the center of a blastula is called the blastocoel.
Missing Word
blastocoel
The blastocoel is the hollow space surrounded by the layer of cells that makes up the blastula. Its presence is what makes the blastula a hollow ball of cells.
Category: Embryonic Development
Question 6
Both spermatogenesis and oogenesis rely on meiosis to produce haploid cells.
Missing Word
meiosis
Meiosis is the two-step cell division that halves the chromosome number, so gametes are haploid and fertilization restores the diploid number.
Category: Gametogenesis
Question 7
Diploid stem cells in the seminiferous tubules that divide by mitosis to begin sperm production are called spermatogonia.
Missing Word
spermatogonia
Spermatogonia are the stem cells of sperm production. Some of their mitotic daughters become primary spermatocytes, which then undergo meiosis.
Category: Gametogenesis
Question 8
Sertoli cells secrete the hormone inhibin, which reduces FSH release when sperm counts are high.
Missing Word
inhibin
Inhibin is a hormone that provides negative feedback on FSH release. When sperm counts drop too low, inhibin release falls and FSH can again stimulate sperm production.
Category: Gametogenesis
Question 9
Fingerlike projections called fimbriae at the open end of the oviduct sweep the released egg into the tube.
Missing Word
fimbriae
Fimbriae surround the funnel-shaped opening of each oviduct and guide the egg into it after ovulation. Cilia and smooth muscle then move the egg toward the uterus.
Category: Female Cycles and Hormones
Question 10
The release of an egg from a ruptured follicle, which happens around day 14 of a typical 28-day cycle, is called ovulation.
Missing Word
ovulation
Ovulation divides the ovarian cycle into the follicular phase before it and the luteal phase after it. The ruptured follicle left behind becomes the corpus luteum.
Category: Female Cycles and Hormones
Question 11
The inner lining of the uterus, which thickens each cycle and is where an embryo implants, is the endometrium.
Missing Word
endometrium
The endometrium is the uterine lining that rebuilds under the influence of estrogen and progesterone. If no embryo implants, its functional layer is shed.
Category: Female Cycles and Hormones
Question 12
Shedding of the functional layer of the uterine lining at the start of a new cycle is called menstruation.
Missing Word
menstruation
Menstruation occurs when estrogen and progesterone fall after the corpus luteum degenerates, so the lining can no longer be maintained and is discharged.
Category: Female Cycles and Hormones
Question 13
The placenta is the organ that exchanges nutrients, gases and wastes between mother and developing baby and also secretes hormones.
Missing Word
placenta
The placenta forms during the first trimester from embryonic and maternal tissue. It takes over nutrition, waste removal and hormone production, and passes maternal antibodies to the baby.
Category: Pregnancy and Birth
Question 14
After about 8 weeks of development, the growing human embryo is referred to as a fetus.
Missing Word
fetus
Fetus is the name for the developing human from about the eighth week until birth, by which time the major organs have begun to form.
Category: Pregnancy and Birth
Question 15
During the first stage of labor, the cervix thins and dilates to about 10 centimeters.
Missing Word
cervix
The cervix is the narrow lower end of the uterus that opens into the vagina. It must open fully before the baby can be pushed out in the second stage of labor.
Category: Pregnancy and Birth