Bio chap 27
_________ is the creation of genetically unique offspring by two parents.
Sexual reproduction
What is likely to happen if the placenta of a young human embryo prematurely stopped releasing HCG? The heart might not develop. Gas exchange for the developing embryo would dramatically increase. The nervous system would not develop properly. The embryo might be aborted.
The embryo might be aborted. The drop in HCG might cause a drop in progesterone and estrogen secretion by the corpus luteum, leading to menstruation and a spontaneous abortion.
asexual reproduction
(reproduction without sex); creation of genetically identical offspring by a lone parent;
oogenesis is one part of a female mammal's reproductive cycle:
1) a recurring sequence of events that produces gametes; 2) makes them available for fertilization; 3) prepares the body for pregnancy; the reproductive cycle repeats every 28 days on average; reproductive cycle is actually two closely linked cycles: ovarian cycle and menstrual cycle
steps of fertilization
1) a sperm touches the egg's jelly coat, and its acrosome releases enzyme molecules 2) the sperm's acrosomal enzymes digest the egg's jelly coat 3) proteins on the sperm head bind to the egg receptors; 4) the plasma membranes of sperm and egg fuse 5) the sperm nucleus enters the egg cytoplasm 6) vitelline layer separates and becomes impenetrable
cleavage makes 2 important contributions to early development
1) creates a multicellular embryo (the blastula) from a single celled zygote; 2) cleavage is also an organizing process; the cytoplasm of zygote contains variety of chemicals that control gene expression during early development; during cleavage, regulatory chemicals become localized in particular groups of cells, where they later activate the genes that direct the formation of specific part of animals
labor occurs in 3 stages
1) dilation of cervix until it reaches 10 cm; longest stage of labor; 2) expulsion stage; full dilation to delivery; 20 mins - 1 hour; 3) delivery of placenta within 15 mins after the birth of baby
oogenesis vs spermatogenesis
1) only one mature egg results from each diploid cell that undergoes meiosis; the other products of oogenesis (polar bodies) degenerate; by contrast, in spermatogenesis, all four products of meiosis develop into mature gametes; 2) spermatogenesis occurs from puberty till death, while the mitotic divisions of oogenesis are completed before birth and the production of mature gametes stops at menopause; 3) oogenesis has long resting periods, whereas spermatogenesis produces mature sperm in an uninterrupted sequence
Ovulation usually occurs on or about day _____ of a 28-day ovarian cycle. 1 7 14 21 28
14
About _____ of couples who want children are unable to conceive. 15% 3-5% 25% 8-10%
15%
About _____ of couples who want children are unable to conceive. 25% 8-10% 3-5% 15%
15% This percentage may grow higher in the future as more women wait until after the age of 35 to have children.
cleavage starts about
24 hours after fertilization and continues as the embryo moves down the oviduct toward the uterus; about a week after fertilization, the embryo has reached the uterus and cleavage has produced about 100 cells; the embryo is now a hollow sphere of cells called blastocyst
Assume 2n = 12 in a hypothetical species. In gametogenesis, the number of chromosomes in a developing sperm cell would be _____ and in a first polar body would be _____. 6 ... 3 3 ... 6 3 ... 3 6 ... 6
6 ... 6
How does a zygote differ from an ovum? A zygote has more chromosomes. A zygote is smaller. A zygote divides by meiosis. A zygote consists of more than one cell.
A zygote has more chromosomes.
New techniques can help many infertile couples
About 15% of couples wanting children experience infertility, the inability to conceive; Drug therapies can help address problems of impotence (erectile dysfunction) and induce ovulation.
Which of the comparisons between oogenesis and spermatogenesis is accurate? An ovum is not produced in the absence of sperm, but sperm are produced regardless of what the ova are doing. Follicle-stimulating hormone promotes only egg, not sperm, development. Primary oocytes and primary spermatocytes follow a similar pattern of development through meiosis. Luteinizing hormone triggers ovulation in females and has no other role in reproduction.
An ovum is not produced in the absence of sperm, but sperm are produced regardless of what the ova are doing.
Which of the comparisons between oogenesis and spermatogenesis is accurate? Follicle-stimulating hormone promotes only egg, not sperm, development. Luteinizing hormone triggers ovulation in females and has no other role in reproduction. Primary oocytes and primary spermatocytes follow a similar pattern of development through meiosis. An ovum is not produced in the absence of sperm, but sperm are produced regardless of what the ova are doing.
An ovum is not produced in the absence of sperm, but sperm are produced regardless of what the ova are doing. The final meiotic division of a secondary oocyte will occur only when a sperm has connected to the oocyte's cell membrane.
______ is the creation of genetically identical offspring by a lone parent.
Asexual reproduction
Many people with XY chromosomes and androgen insensitivity syndrome (AIS), like Katie, are not diagnosed until later in life, rather than at birth. Why is that? Babies with XY chromosomes and AIS usually appear to be normal females at birth. It is not until they have a hernia, or fail to menstruate, before a doctor would investigate further. People with XY chromosomes and AIS can get pregnant, but often have a miscarriage. The frequent miscarriages cause doctors to investigate further. Babies with XY chromosomes and AIS are born with one set of external genitals, but their genitals change to appear like that of the other sex later in life. This change causes doctors to investigate further. People with XY chromosomes and AIS have ovaries that do not develop until later in life.
Babies with XY chromosomes and AIS usually appear to be normal females at birth. It is not until they have a hernia, or fail to menstruate, before a doctor would investigate further.
____________ is the splitting off of new individuals from outgrowths of existing ones.
Budding
Which of the following events is part of gastrulation? Cells are sorted into three cell layers. The blastocoel is maintained intact. Cells do not migrate. The archenteron is destroyed.
Cells are sorted into three cell layers.
Which of the following events is part of gastrulation? The archenteron is destroyed. Cells remain fixed in location and do not migrate. Cells are sorted into three cell layers. The blastocoel is maintained intact.
Cells are sorted into three cell layers. The formation of the three embryonic tissue layers is a main feature of gastrulation.
How do ovulated oocytes get into the uterus? Because ovaries are within the uterus, the ovulated egg is already within the uterus. Cilia within an oviduct create currents that sweep the egg toward the uterus. Fimbriae sweep over the oviduct. The oocyte actively swims through the oviduct, using its flagellum.
Cilia within an oviduct create currents that sweep the egg toward the uterus.
Which of the following processes, if any, occurs during cleavage? gene transcription meiosis DNA replication fertilization
DNA replication This occurs during cleavage. The embryonic cells are dividing rapidly by mitosis and cytokinesis and, therefore, must be rapidly replicating their DNA.
The anterior pituitary gland, under the control of the hypothalamus, produces _____, which stimulate _____. estrogen and progesterone ... thickening of the endometrium FSH and LH ... thickening of the endometrium FSH and LH ... egg maturation and ovulation estrogen and progesterone ... egg maturation and ovulation
FSH and LH ... egg maturation and ovulation
________ is the fusion of two haploid sex cells (sperm and egg) to form a diploid cell
Fertilization
_______________ involves the development and migration of the three tissue layers - ectoderm, mesoderm, and endoderm. Fertilization Cleavage Gastrulation Blastulation
Gastrulation
Which of the following is a difference between oogenesis and spermatogenesis? Oogenesis uses mitosis, and spermatogenesis uses meiosis. In oogenesis and spermatogenesis, the four cells that result from meiosis are each about the same size. In sexually mature adults, oogenesis occurs in monthly cycles whereas spermatogenesis occurs continuously. In oogenesis and spermatogenesis, the four cells that result from meiosis become mature gametes.
In sexually mature adults, oogenesis occurs in monthly cycles whereas spermatogenesis occurs continuously. Women typically produce one gamete, roughly every 28 days that has the potential to be fertilized. Men produce millions of sperm per day that are capable of fertilization.
Which is a true statement about luteinizing hormone in the female reproductive system? It causes mitosis of the primary oocyte. It is produced by the hypothalamus. It is responsible for mediating the production of estrogen and progesterone simultaneously. It inhibits ovulation.
It is responsible for mediating the production of estrogen and progesterone simultaneously.
What is the function of the thickened endometrium? It nourishes the early embryo during the process of implantation. It prevents unfertilized eggs from implanting in the wall of the uterus. It facilitates fertilization of the egg by nourishing sperm cells. It stimulates the follicles to mature an egg cell.
It nourishes the early embryo during the process of implantation.
A peak in _____ triggers ovulation around the _____ day of the monthly cycle. LH ... 7th FSH ... 2nd progesterone ... 14th LH ... 14th
LH ... 14th
A surge in which hormone(s) immediately precedes ovulation? FSH only progesterone only LH and FSH LH only
LH and FSH
hormonal events at ovulation and after
LH stimulates the completion of meiosis I, transforming the primary oocyte in the follicle into the secondary oocyte; it also signals enzymes to rupture the follicle (allowing ovulation to occur) and triggers the development of the corpus luteum from the rupture follicle; LH also promotes the secretion of progesterone and estrogen by corpus luteum. high level of estrogen and progesterone in blood following ovulation have a strong influence on both ovary and uterus; the combination of two hormones exerts negative feedback on the hypothalamus and pituitary, which drop FSH and LH levels;
Meiosis II
Meiosis II then forms four cells, each with the haploid number of chromosomes; a sperm cell develops by differentiation of each of these haploid cells and is gradually pushed toward the center of the seminiferous tubule; from there it passes into epididymus (where it matures) and becomes motile and is stored until ejaculation;
Which of the following statements about reproductive technology and infertility is FALSE? Abnormally shaped sperm or a low sperm count may lead to infertility. During in vitro fertilization, fertilization occurs in a laboratory culture dish. Only about 2% of couples are unable to conceive after one year of trying to get pregnant. In the ART procedure, fertilization occurs after secondary oocytes are removed from the ovaries, stimulated with hormones, fertilized, and returned.
Only about 2% of couples are unable to conceive after one year of trying to get pregnant. This is the FALSE statement. About 15% of couples are unable to conceive after one year of trying to get pregnant.
Which of the following is a function of oxytocin? Oxytocin maintains the corpus luteum during pregnancy. Oxytocin stimulates the urinary tract to make prostaglandins. Oxytocin stimulates powerful contractions of smooth muscles in the wall of the uterus. Oxytocin stops the secretion of milk.
Oxytocin stimulates powerful contractions of smooth muscles in the wall of the uterus. These contractions serve to expel the fetus from the uterus.
How are the ovulation cycle and the menstruation cycle coordinated? A single gland releases a pair of hormones that control both processes. Each cycle is independent of the other; the cycles frequently drift out of phase with each other, resulting in infertility. The processes regulate each other through a system that involves four major hormones. The anterior pituitary gland releases one of four different hormones to stimulate each phase of the overall coordinated cycle.
The processes regulate each other through a system that involves four major hormones.
Two mammals of different species mate, but the mating does not produce offspring. Which of the following could explain this occurrence? The sperm cannot penetrate the jelly coat inside of the egg's plasma membrane. The sperm of different species cannot bind to receptors on the egg cell. The sperm are not the correct size. The sperm do not possess acrosomes.
The sperm of different species cannot bind to receptors on the egg cell. Even if members of different species do happen to mate, the production of offspring can be blocked because the sperm simply cannot access the egg.
Which of the following statements about early human development is FALSE? Implantation occurs about a week after fertilization. The trophoblast cells release enzymes that promote implantation. The trophoblast stage implants in the endometrium. The trophoblast cells will form the baby.
The trophoblast cells will form the baby. Only cells of the inner cell mass form the baby.
Which of the following INCORRECTLY pairs up an extraembryonic membrane with its function? The yolk sac provides a developing human embryo with nourishment. The allantois is the site of a mammal's waste disposal. The amnion encloses an embryonic mammal or bird in a fluid-filled sac. The chorion forms part of a mammal's placenta.
The yolk sac provides a developing human embryo with nourishment. This is the INCORRECTLY matched pair. This is true of chicks, but in humans the yolk sac produces the embryo's first blood and germ cells.
Birth control pills contain synthetic estrogen and progesterone. How might these hormones prevent pregnancy? They trigger premature ovulation, before an egg is mature. They cause the corpus luteum to degenerate. They keep the pituitary from secreting FSH and LH, so ovulation does not occur. They cause the lining of the uterus to be sloughed off.
They keep the pituitary from secreting FSH and LH, so ovulation does not occur.
Birth control pills contain synthetic estrogen and progesterone. How might these hormones prevent pregnancy? They cause the corpus luteum to degenerate. They keep the pituitary from secreting FSH and LH, so ovulation does not occur. They trigger premature ovulation, before an egg is mature. They cause the lining of the uterus to be sloughed off.
They keep the pituitary from secreting FSH and LH, so ovulation does not occur. Estrogen and progesterone are maintained at high concentrations during pregnancy and provide negative feedback that suppresses the release of FSH and LH. This type of birth control pill mimics pregnancy.
primary oocyte
a diploid cell that is resting in prophase of meiosis I
The onset of menstruation is triggered by __________. a drop in the levels of FSH and LH a sudden increase in the levels of progesterone and FSH a drop in the levels of progesterone and estrogen a drop in the level of estrogen
a drop in the levels of progesterone and estrogen If implantation of an embryo does not occur within a few days, the corpus luteum stops secreting progesterone and estrogen. This leads to disintegration of the endometrium.
blastocoel
a fluid filled cavity; as cleavage continues, this forms in the center of the embryo; at the completion of the cleavage, there is a hollow ball of cells called blastula;
What do an ovum and a sperm have in common? a haploid set of chromosomes a huge mitochondrion very little cytoplasm an external food source
a haploid set of chromosomes
if an egg is surgically removed from a woman's ovary, in what stage of meiotic development will that egg be?
a mature egg within the ovary ( secondary oocyte) is arrested at metaphase II
hormones that regulate the ovarian and menstrual cycles
a releasing hormone from hypothalamus in the brain regulates secretion of the two pituitary hormones FSH and LH; changes in the blood levels of FSH AND LH, and two other hormones - estrogen and progesterone - correspond with specific events in the ovarian and menstrual cycles
cleavage
a series of rapid cell divisions that produces a multicellular ball; development begins with this; after the zygote divides for the first time, it is called an embryo; nutrients stored in the egg nourish the dividing cells; DNA replication, mitosis and cytokinesis occur rapidly but gene transcription shuts down and few new proteins are synthesized; the embryo doesn't enlarge significantly; instead as the number of cells doubles with each division, the cytoplasm of the one celled zygote is partitioned into many smaller cells, each with its own nucleus; as a result, each cell in the ball is much smaller than the original cell that formed the zygote; in human, cleavage takes around four days;
Sperm have
a streamlined shape, which moves easily through fluids; many mitochondria, which provide ATP for tail movements; a head that contains a haploid nucleus and is tipped with an acrosome containing enzymes that help it penetrate the egg.
positive feedback
a type of control in which a change triggers mechanisms that amplify that change; in the case of labor, oxytocin and prostaglandins cause uterine contractions that in turn stimulate the release of more oxytocin and prostaglandins; the result is steady increase in contraction intensity, climaxing in forceful muscle contractions that propel the baby from uterus
in nature, asexual reproduction has two advantages and one disadvantage, what are they?
advantages: animals that do not move from place to place or that are in isolation have the ability to reproduce without finding mates; 2) enables the animal to produce many offspring quickly; asexual reproduction makes a particular genotype faithfully, precisely and quickly (effective for animal that are genetically well suited to their environment) disadvantage: since asexual reproduction produces genetically uniform populations, if the environment changes all individuals may die out
At what point does the secondary oocyte complete meiosis? when the secondary oocyte implants in the endometrium of the uterus when acrosomal enzymes begin to break down the egg's jelly coat when the luteinizing hormone triggers ovulation after it is penetrated by a sperm cell
after it is penetrated by a sperm cell
Which of the following embryonic membranes forms part of the umbilical cord and contributes to the formation of the urinary bladder? fertilization envelope amnion allantois chorion
allantois
Which of the following embryonic membranes forms part of the umbilical cord and contributes to the formation of the urinary bladder? chorion amnion fertilization envelope allantois
allantois In birds and reptiles, the allantois is a sac for the disposal of uric acid.
one disadvantage of sexual reproduction
although sexual reproduction has advantages, it presents a problem for nonmobile animals and for animals that are isolated (how to find mate?); one solution is hermaphroditism;
amnion
amniotic cavity is filled with fluid, which encloses and protects the embryo; usually breaks just before childbirth and the amniotic fluid leaves the mother's body through vagina; surrounds the embryo
From a single cell, oogenesis will produce _____. four ova (eggs) four spermatozoa an ovum and three polar bodies a primary oocyte
an ovum and three polar bodies
A developing embryo depends on a cellular process that causes specific cells to commit suicide to give form to a developing animal. The process is called _____. apoptosis pattern formation induction gastrulation
apoptosis This is the term for self-destruction of cells, which is an important embryonic developmental process.
External fertilization occurs mostly in _____. animals that reproduce asexually aquatic animals land animals insects
aquatic animals
During oogenesis, polar bodies _____________. are discarded divide into secondary oocytes become part of the placenta contribute to the outer coating of an ovum
are discarded
certain drugs cause their most serious damage to an embryo very early in pregnancy, often before the mother even realizes she is pregnant. why?
because organ systems such as circulatory and nervous systems have begin to develop early in the first trimester and are susceptible to such drugs
why does testing for hCG in a woman's urine or blood work as an early test of pregnancy?
because this hormone is secreted by the chorion of embryo after implantation in the wall of placenta
follicle stimulating hormone
between puberty and menopause, about every 28 days, follicle stimulating hormone (FSH) from the pituitary stimulates one of the dormant follicles to develop; the follicle enlarges, and the primary oocyte within it completes meiosis I and begins meiosis II. meiosis then stops again at metaphase II; in female, the division of the cytoplasm in meiosis I is unequal, with a single secondary oocyte receiving almost all of it; the smaller of the two daughter cells, called the first polar body, receives almost no cytoplasm
The function of homeobox peptide is to _____. bind to specific DNA sequences to turn genes on or off promote secretion of progesterone and estrogen by the corpus luteum induce the pituitary to secrete FSH and LH allow fusion of the sperm and egg membrane
bind to specific DNA sequences to turn genes on or off
Which of the following is a similarity between spermatogenesis and oogenesis? the time during development during which each process begins equal partitioning of cytoplasm during cell division the number of sperm/ova produced by a single diploid cell both involve meiosis and the production of haploid cells
both involve meiosis and the production of haploid cells
how are oogenesis and spermatogenesis the same?
both produce haploid gametes
In an experiment, a researcher colored a bit of tissue on the outside of a frog gastrula with a fluorescent dye. The embryo developed normally. When the tadpole was placed under an ultraviolet light, the _____ glowed bright orange. pancreas heart brain muscles
brain Nervous tissue develops from the ectodermal layer of the gastrula.
In an experiment, a researcher colored a bit of tissue on the outside of a frog gastrula with a fluorescent dye. The embryo developed normally. When the tadpole was placed under an ultraviolet light, the _____ glowed bright orange. brain pancreas heart muscles
brain Nervous tissue develops from the ectodermal layer of the gastrula.
several types of asexual reproduction found among animals; they are:
budding, fission, fragmentation, regeneration;
The drug RU-486 was developed in France and is widely used in Europe as a method of birth control. Its introduction to the United States has been controversial, however. The drug is taken after sexual intercourse. It blocks implantation, and in this sense it prevents pregnancy _____. in a manner similar to tubal ligation by blocking progesterone receptors in the uterus, thus preventing progesterone from maintaining pregnancy like the familiar birth control pill used for the last 30 years like spermicidal foam
by blocking progesterone receptors in the uterus, thus preventing progesterone from maintaining pregnancy
embryonic stem cells
cells removed from human blastocyst; have great therapeutic potential to develop into and replace just about any kind of mature cells that have been lost to damage or illness; harvesting these destroys the embryo
the onset of labor is marked by dilation of the ________
cervix
After ovulation occurs, the empty follicle _____. can be recycled to produce more eggs immediately initiates menstruation quickly degenerates changes into the corpus luteum and makes hormones
changes into the corpus luteum and makes hormones
prostaglandins
chemical regulator that stimulate the uterine muscle cells to contract more
If you wanted to examine the extraembryonic membranes surrounding a mouse embryo, you would have to cut through which of the following to see all the others? yolk sac allantois chorion amnion
chorion
Cell divisions called _____ proceed so rapidly in the developing embryo that there is no growth of the cells between divisions. meiosis cleavage binary fission fragmentation
cleavage
The process that results in the formation of a multicellular embryo from the single cell of the zygote is _____. cleavage induction gastrulation ovulation
cleavage
Which of the following describes the correct sequence of stages during embryogenesis? cleavage, blastula formation, gastrulation cleavage, gastrulation, blastula formation blastula formation, gastrulation, cleavage blastula formation, cleavage, gastrulation
cleavage, blastula formation, gastrulation
the first two phases of embryonic development are _________, which forms the blastula, followed by ___________, which forms the ___________
cleavage; gastrulation; gastrula
Which of the following best reduces the chances of both conception and the spread of sexually transmitted diseases? condom birth control pill intrauterine device diaphragm
condom
Which of the following birth control methods also provides the best protection against STDs? condoms oral contraceptives tubal ligation or vasectomy withdrawal
condoms
A hermaphrodite is an animal that _____. can create zygotes of either sex fuses with one of the opposite sex contains both male and female reproductive systems in its body reproduces only asexually
contains both male and female reproductive systems in its body
zygote
contains unique combinations of genes inherited from the parents via the egg and sperm
ovarian cycle
controls the growth and release of an egg;
What is the source of the hormones that, when suddenly absent, are directly responsible for the onset of menstruation? corpus luteum hypothalamus ovarian follicle pituitary
corpus luteum
The function of the amnion is to _____. create a fluid-filled environment in which development can occur digest yolk and form a network of blood vessels to distribute nutrients to the embryo produce gamete-forming cells transport oxygen to the embryo
create a fluid-filled environment in which development can occur
sexual reproduction
creation of offspring through the process of fertilization; increases genetic variability among offspring; meiosis and random fertilization can generate enormous genetic variation; such variation is the raw material of evolution by natural selection
During cleavage, cell division is accompanied by a(n) ______________. decrease in cell size increase in cell size increase in chromosome number per cell decrease in chromosome number per cell
decrease in cell size
hormones continue to be important after baby is born:
decreasing levels of progesterone and estrogen allow the uterus to start returning to its state before pregnancy; pituitary secretes prolactin and oxytocin; these hormones promote milk production and release (lactation);
extraembryonic membranes
develop as attachments to the embryo and help support it;
oogenesis
development of a mature egg (ovum); most of the process occurs in ovary; begins prior to birth, when a diploid cell in each developing follicle begins meiosis; at birth, each follicle contains a dormant primary oocyte; a primary oocyte can be hormonally triggered to develop further;
In general, what is the ploidy (n) state of human cells? diploid early in life, becoming haploid with age haploid except for zygotes diploid except for gametes haploid early in life, becoming diploid with age
diploid except for gametes
In general, what is the ploidy (n) state of human cells? diploid early in life, becoming haploid with age haploid except for zygotes diploid except for gametes haploid early in life, becoming diploid with age
diploid except for gametes Human somatic cells are diploid, and meiosis produces haploid gametes.
Secondary spermatocytes
divide by meiosis II to produce round spermatids, and spermatids differentiate into elongate sperm
hermaphroditism
each individual has both female and male reproductive systems; each animal serves both as male and female, donating and receiving sperm; there is only one sex, so any two individuals can mate; some hermaphrodites (like tapeworms) can fertilize their own eggs;
Which of the following biologically describes a hermaphrodite? A human baby is born with XY chromosomes, but lacks a penis and has a vagina. Earthworms can fertilize each other to produce offspring. A human baby is born with XX chromosomes, but has a very large clitoris that resembles a penis. Pistachio trees have female flowers on one plant, and male flowers on another plant.
earthworms can fertilize each other to produce offspring.
The nervous system is derived from _____. both ectoderm and mesoderm ectoderm mesoderm endoderm
ectoderm
the three layers produced by gastrulation are
embryonic tissues called ectoderm, endoderm, and mesoderm; eventually, these three layers develop into all the parts of the adult animal;
What is the embryonic origin of the linings of the digestive tube and respiratory system? ectoderm endoderm mesoderm both endoderm and mesoderm
endoderm
The precise site of embryo implantation in a normal pregnancy is the _____. oviduct vagina cervix endometrium
endometrium
Which of the following is NOT found in or on the human ovary? egg cell corpus luteum follicle endometrium
endometrium The endometrium is the lining of the uterus where the zygote implants and grows to become an embryo.
The precise site of embryo implantation in a normal pregnancy is the _____. cervix oviduct endometrium vagina
endometrium This is the capillary-rich inner wall of the uterus, where implantation is accomplished for the developing human embryo.
Which part of the male reproductive tract warehouses sperm prior to their exit from the male's body? glans vas deferens epididymis seminal vesicle
epididymis
elevated levels of which hormone(s) most likely stimulate the LH/FSH surge just before ovulation? progesterone and estrogen progesterone testosterone estrogen
estrogen
If there is no fertilization, degeneration of the corpus luteum results in a drop in _____, which results in the sloughing off of the uterus's endometrium. FSH estrogen and progesterone hypothalamic secretion of releasing hormones HCG LH
estrogen and progesterone
After ovulation, high levels of _____ inhibit _____ secretion. estrogen and progesterone ... FSH and LH FSH and LH ... estrogen and progesterone HCG ... estrogen and progesterone estrogen ... FSH androgens ... FSH and LH
estrogen and progesterone ... FSH and LH
hormonal changes induces birth
estrogen reaches its highest level in mother's blood during last weeks of pregnancy; an important effect of this estrogen is to trigger the formation of oxytocin receptors on cells of uterus; cells of fetus produce oxytocin and late in pregnancy the mother's pituitary gland secretes it in increasing amounts; oxytocin stimulates the smooth muscles in the wall of the uterus, producing the series of increasingly strong, rhythmic contractions characteristic of labor. it also stimulates the placenta to make prostaglandins
Developing ovarian follicles primarily secrete _____. progesterone estrogens luteinizing hormone follicle-stimulating hormone human chorionic gonadotropin
estrogens
overview of ovarian and menstrual cycles
events in the menstrual cycle are synchronized with the ovarian cycle; the first day of a woman's period is designated day 1 of the menstrual cycle; the menstrual discharge (consisting of blood, small clusters of endometrial cells, and mucus) leaves the body through vagina; after menstruation, the endometrium regrows; it continues to thicken through the time of ovulation, reaching a maximum thickness at about 20-25 days; if an embryo has not implanted in uterine lining, menstruation begins again
egg
female gamete; much larger cell that is not self propelled
The completion of meiosis II during oogenesis occurs at ________________. implantation ovulation cleavage fertilization
fertilization
embryonic development begins with ___
fertilization (the union of sperm and egg to form a diploid zygote); fertilization combines haploid sets of chromosomes from two individuals and also activates the egg by triggering metabolic changes that start embryonic development
trimester 2
fetus continues to grow and has human features; changes are not as dramatic as the 1st trimester; fetus's eyes can open, its teeth are forming and its bones have begun to harden; placenta begins to secrete progesterone (and the corpus luteum stops secreting progesterone), which helps maintain the placenta; placenta stops secreting hCG, and the corpus luteum (no longer needed to maintain pregnancy) degenerates
Consider the below figure, which involves hormonal control of testes function. If FSH were produced in smaller quantities than that produced in normal males, _____. this would inhibit the secretion of FSH by the anterior pituitary there would be less LH produced and therefore less androgen fewer sperm would be formed the prostate gland would secrete less fluid to nourish sperm
fewer sperm would be formed
chorionic villi
finger like outgrowths on the outside of the chorion; are larger and contain mesoderm; the mesoderm cells have formed into embryonic blood vessels in the chorionic villi; placenta is fully developed; the villi are bathed in tiny pools of maternal blood; the mother's and embryo's blood is not in direct contact; instead, the chorionic villi absorb nutrients and oxygen from the mother's blood and pass these to embryo via the chorionic blood vessels; the chorionic vessels in blue carry wastes away from embryo; the wastes diffuse into mother's bloodstream and are excreted by her kidneys
The ovary undergoes several structural changes or events during the human female's menstrual cycle. Which of the following sequences is correct, beginning with the oocyte? corpus luteum development, follicle development, ovulation corpus luteum development, ovulation, follicle development follicle development, ovulation, corpus luteum development follicle development, corpus luteum development, ovulation
follicle development, ovulation, corpus luteum development
About every 28 days:
follicle stimulating hormone (FSH) from the pituitary stimulates one of the dormant follicles to develop; one primary oocyte resumes meiosis; a secondary oocyte arrested at metaphase of meiosis II is ovulated, and meiosis of the ovum is completed after fertilization
Which of the following hormones is the first to increase significantly every 28 days or so, initiating the ovarian cycle? follicle-stimulating hormone estrogen luteinizing hormone progesterone
follicle-stimulating hormone
spawning
for external fertilization, environment cues such as temperature and day length or chemical signals released by individuals cause a whole population to release gametes all at once
trimesters
for humans, pregnancy is divided into 3 trimesters, each lasting for about 3 months
Which of the following is a form of sexual reproduction? formation of a zygote fragmentation formation of a bud fission
formation of a zygote
gametogenesis
formation of gametes; significant differences in gametogensis between human males and females;
Primary spermatocytes
formed by mitosis and divide by meiosis I to produce secondary spermatocytes.
endoderm
forms an embryonic digestive tract; organs and tissues in adults: epithelial lining of the digestive tract (except mouth and rectum); epithelial lining of respiratory system; liver; pancreas; thyroid; parathyroids; thymus; lining of urethra, urinary bladder, and reproductive system
allantois
forms part of the umbilical cord; it also forms part of embryo's urinary bladder; in birds and reptiles, the allantois expands around the embryo and functions in waste disposal
ectoderm
forms the outer layer of the gastrula; organs and tissues in adults: epidermis of skin; epithelial lining of mouth and rectum; sense receptors in epidermis; cornea and lens of eye; nervous system
In spermatogenesis, each primary spermatocyte gives rise to _____ sperm. one two millions of four
four
Suppose you wanted to get started in the animal-breeding business. You could start out with only one of most of the following animals, but you would have to start with at least two _____. frogs whiptail lizards tapeworms sea anemones
frogs
fertilization
fusion of two haploid (n) sex cells (gametes) to form a diploid (2n) zygote (fertilized egg)
A ______________ is a haploid sex cell (a sperm in males and an egg in females).
gamete
The three embryonic tissue layers—ectoderm, mesoderm, and endoderm—are first seen at the _____ stage. neural fold gastrula blastula nine-cell stage
gastrula
Organs begin to form after _____. contraception ovulation reproduction gastrulation
gastrulation
Gametogenesis is to spermatogenesis and oogenesis as _____________________. sperm are to primary and secondary spermatocytes fertilization is to sperm and zygote gonads are to testes and ovaries ovaries are to testes and ova
gonads are to testes and ovaries
The amount of cytoplasm found in an egg is _____ that found in the polar bodies. greater than about the same as less than equal to
greater than
blastocyst
has a fluid filled cavity, an inner cell mass that will actually form the embryo and the outer layer cells called trophoblast; starts to implant in the uterus about a week after conception;
Which part of the human sperm carries a haploid set of chromosomes? middle piece head neck acrosome
head
yolk sac
homologous structure in birds and reptiles; produces embryo's first blood cells and first germ cells; provides nourishment to developing embryo
If there is fertilization, secretion of _____ by the early embryo maintains the corpus luteum. progesterone estrogen luteinizing hormone follicle-stimulating hormone human chorionic gonadotropin
human chorionic gonadotropin
What happens if after the sperm and egg fuse the vitelline layer doesn't harden?
if egg plasma membrane and vitelline layer are still penetrable by other sperms after fusion, egg will be fertilized by more than one sperm; the resulting zygote nucleus would contain too many chromosomes, and the zygote could not develop normally
Oogenesis in comparison to spermatogenesis is somewhat unusual in humans in that _____. the sequence from primary oocyte to ovum is interrupted by relatively short resting periods; this does not happen in spermatogenesis in oogenesis, the division of the cytoplasm is unequal during meiosis, but this is not so for spermatogenesis the first meiotic division produces an egg, but in spermatogenesis, meiosis II must be complete for a functioning sperm ova can be produced throughout the life of the individual, whereas sperm are all produced at birth
in oogenesis, the division of the cytoplasm is unequal during meiosis, but this is not so for spermatogenesis The cells receiving little cytoplasm become polar bodies and die.
fertilization occurs
in oviduct
Where are you less likely to find complete semen (in which all the components are present)? in the urethra in the epididymis in the vagina of a woman who's trying to become pregnant at the junction of the bulbourethral duct and the urethra
in the epididymis
infertility
inability to conceive
what happens when external fertilization is not synchronized?
individuals may exhibit specific courtship behaviors; for example, many fishes, amphibians and some marine invertebrates have specific rituals that trigger simultaneous gamete release in the same vicinity by the female and male
Cells relocated from the optic cup of an amphibian embryo to an abnormal position result in the development of a lens at the graft location. This is an example of _____. apoptosis developmental potential pattern formation induction
induction
From which part of a developing embryo are stem cells derived? mesoderm endoderm inner cell mass ectoderm
inner cell mass
Which reproductive method is used most frequently by mammals? external fertilization fragmentation internal fertilization regeneration
internal fertilization
PID _____. will not cause sterility and is therefore not a serious consequence of STDs is caused as the result of STDs caused by bacterial infections will cause scarring, but is not a problem causes no pain so is hard to diagnose
is caused as the result of STDs caused by bacterial infections
structure of sperm cell
its thick head contains a haploid nucleus and is tipped with a vesicle, the acrosome; the acrosome contains enzymes that help the sperm penetrate the egg; the middle section of sperm contains mitochondria; the sperm absorbs high energy nutrients (especially sugars) from semen; thus fueled, its mitochondria provide ATP for movement of the tail which is flagellum;
mesoderm
lies between ectoderm and endoderm; organs and tissues in adults: skeletal system; circulatory system; excretory system; reproductive system (except gamete forming cells); dermis of skin; lining of body cavity
acrosome
lies just inside the plasma membrane
A rapid increase in the _____ level stimulates ovulation. progesterone estrogen luteinizing hormone follicle-stimulating hormone human chorionic gonadotropin
luteinizing hormone
The hormone that initiates the development of specialized cells in the ovaries of women and triggers androgen production by the testes of men is _____. luteinizing hormone (LH) progesterone follicle-stimulating hormone (FSH) estrogen
luteinizing hormone (LH)
hCG
maintains production of estrogen and progesterone by the corpus luteum of the ovary during the first few months of pregnancy; without these hormones, menstruation would occur, and the embryo would abort at the same time; levels of hCG in maternal blood are so high that some are excreted in the urine, which is how you find out you are pregnant
sperm
male gamete; relatively small cell that moves by means of flagellum;
Compared to animals that have separate sexes, an animal that is a hermaphrodite has the advantage of _____. producing offspring with greater genetic variability mating with any other member of its species being able to reproduce during times of stability or stress using less energy to produce gametes
mating with any other member of its species
first polar body
may also undergo meiosis II, forming two cells; these and the second polar body receive virtually no cytoplasm and quickly degenerate, leaving mature egg with nearly all the cytoplasm and thus the bulk of the nutrients and organelles contained in the original diploid cell
control of the menstrual cycle
menstrual cycle is controlled by estrogen and progesterone alone; around day 5 of the cycle, the endometrium thickens in response to the rising levels of estrogen and progesterone; when the levels of these hormones drop, the endometrium begins to shed; the menstrual bleeding begins soon after
The skeleton and muscles form from the embryonic _____. haploderm endoderm mesoderm ectoderm
mesoderm
from slides- Cleavage is a rapid series of cell divisions that produces
more cells, smaller cells, and a fluid-filled cavity, the blastocoel, in an embryo called a blastula.
In vitro fertilization (IVF)
most common assisted reproductive technology. Fertilization occurs in a culture dish and incubated for several days to allow fertilized eggs to start developing; when they have developed into embryos of at least eight cells each, the embryos are carefully inserted into woman's uterus, timed to coincide with her natural ovarian cycle
During cleavage, the single large cell of the zygote is converted to a _____. three-layered embryo called a gastrula multicellular embryo with a yolk plug and an archenteron multicellular embryo consisting of a vitelline layer and a zygote multicellular embryo consisting of smaller cells
multicellular embryo consisting of smaller cells
n refers to the haploid number of chromosomes and 2n refers to diploid number; what is n in humans?
n = 23, 2n = 46;
internal fertilization
occurs when sperm are deposited in or near the female reproductive tract and gametes unite within the tract; some fish and amphibian species and nearly all terrestrial animals exhibit this, which is an adaptation that enables sperm to reach egg despite dry external environment; usually requires copulation (sexual intercourse);
Someone may have webbed toes because _____. of a failure of gestation they are displaying characteristics of humans' avian ancestry of a failure of apoptosis of a failure of pattern formation
of a failure of apoptosis
explain how IVF can involve up to 3 different people in the birth of a child.
one woman may become pregnant with an embryo created using the sperm of a man and the mature egg of a second woman
chorion
outermost extraembryonic membrane; completely surrounds the embryo and other extraembryonic membranes; becomes part of placenta; cells in chorion secrete hormone called human chorionic gonadotropin (hCG);
Meiosis to produce the female egg cell is initiated in the _____. vagina oviduct ovary uterus
ovary
On its way to fertilize a human egg, a sperm cell does not have to pass through which of the following? oviduct cervix vagina ovary
ovary
What is the usual site of the fertilization of an egg cell? uterus ovary oviduct abdominal cavity vagina
oviduct
Into which structure is a human oocyte released upon ovulation? corpus luteum oviduct, and then toward the uterus uterus ovary
oviduct, and then toward the uterus
The uterine contractions during labor are stimulated by _____. androgen and LH prolactin and releasing hormone oxytocin and prostaglandins estrogen and progesterone
oxytocin and prostaglandins
The uterine contractions during labor are stimulated by _____. prolactin and releasing hormone oxytocin and prostaglandins estrogen and progesterone androgen and LH
oxytocin and prostaglandins
All of the following structures are derived from mesoderm except the _____. dermis of skin pancreas notochord heart
pancreas
There are nearly 30 different disorders of sexual development. Who can have these disorders? people with neither XX nor XY chromosomes people with either XX or XY chromosomes only people with XY chromosomes only people with XX chromosomes
people with either XX or XY chromosomes
gestation
pregnancy; carrying of developing young within female reproductive tract; begins at fertilization and continues till birth;
the drop in FSH and LH
prevents follicles from developing and ovulation from occurring during the post ovulatory phase; also the LH drop is followed by the gradual degeneration of the corpus luteum; near the end of the post ovulatory phase, unless an embryo has implanted in the uterus, the corpus luteum stops secreting estrogen and progesterone; as blood levels of these hormones decline, the hypothalamus once again can stimulate the pituitary to secrete more FSH and LH and a new cycle begins
After a human sperm penetrates an egg, a fertilization envelope forms. This membrane _____. attracts additional sperm to the egg prevents more than one sperm from entering the egg enables the fertilized egg to implant itself in the wall of the uterus secretes important hormones
prevents more than one sperm from entering the egg
After a human sperm penetrates an egg, a fertilization envelope forms. This membrane _____. enables the fertilized egg to implant itself in the wall of the uterus prevents more than one sperm from entering the egg attracts additional sperm to the egg secretes important hormones
prevents more than one sperm from entering the egg The fertilization envelope, along with other changes to the egg's surface, prevents the entry of more than one sperm cell into the egg, thus assuring the normal complement of 46 chromosomes per zygote.
Which of the following options lists cell types in the correct order of their appearance during spermatogenesis? secondary spermatocyte, primary spermatocyte, spermatid, sperm spermatid, secondary spermatocyte, primary spermatocyte, sperm spermatid, primary spermatocyte, secondary spermatocyte, sperm primary spermatocyte, secondary spermatocyte, spermatid, sperm
primary spermatocyte, secondary spermatocyte, spermatid, sperm
Meiosis I of primary spermatocyte
produces two secondary spermatocytes, each with the haploid number of chromosomes (n = 23);
A large number of hormones function in the human menstrual cycle, but only two of them are called female sex hormones. These are _____. follicle-stimulating hormone and progesterone follicle-stimulating hormone and estrogen progesterone and estrogen follicle-stimulating hormone and luteinizing hormone
progesterone and estrogen
why are the protein receptors on the outside of the egg cell particularly important among aquatic animals that use external fertilization?
protein receptors on the vitelline layer match with species specific proteins on the sperm; this ensures that sperm of a different species will not fertilize the egg
Which of the following is a function of the placenta? utilizing fetal cells to provide immunity for the mother allowing enzymes to enter the fetus's circulation from the mother's bloodstream collecting the mother's waste providing oxygen to the fetus
providing oxygen to the fetus
Sperm have several components; the function of the acrosome is to _____. metabolize the sugars provided by the semen for energy propel the sperm as they swim through the fluid of the female reproductive tract release an enzyme that breaks down the membrane of the ovum produce base to neutralize the acidic environment of the female reproductive system
release an enzyme that breaks down the membrane of the ovum
secondary oocyte
released by the ovary during ovulation; it enters oviduct, and if a sperm cell penetrates it, the second oocyte completes meiosis II; meiosis II is also unequal, yielding a second polar body and the mature egg; the haploid nucleus of the mature egg can then fuse with the haploid nucleus of the sperm cell, producing zygote;
Assisted reproductive technologies (ART)
require eggs to be harvested from the ovaries, fertilized, and returned to a woman's body.
Which of the following is the least effective method of birth control? the pill rhythm method vasectomy IUD
rhythm method
trophoblast
secretes enzymes that enable the blastocyst to implant in the endometrium (the uterine lining); trophoblast cells form part of placenta
Developing sperm cells undergo meiosis in the _____. vas deferens seminal vesicle seminiferous tubules epididymis
seminiferous tubules
labor
series of events that expel an infant from the uterus; several hormones play key roles in this process; induction of labor involves positive feedback
A vasectomy is an effective technique for birth control in males because it _____. causes the prostate gland to enlarge and seal off the ejaculatory duct severs the capillaries to the spermatozoa, which then die severs the route used by the sperm to exit the male's body reduces the alkaline secretions in the semen, and the sperm are then destroyed in the female reproductive tract
severs the route used by the sperm to exit the male's body
reproduction: two modes
sexual and asexual
During gastrulation, a(n) _____ forms. heart nervous system eye simple digestive cavity
simple digestive cavity
after cleavage, the rate of cell division ____
slows dramatically
how does the reduction of cell size during cleavage increase oxygen supply to cell's mitochondria?
smaller cells have a greater plasma membrane surface area relative to cellular volume and this makes diffusion of oxygen from the environment to the cell's cytoplasm easier
In humans, the testes are located outside the abdominal cavity within the scrotum because _____. blood flow to the scrotum is not interrupted during erection this location allows for a shorter pathway to the urethra sperm are unable to mature properly at the higher temperatures found within the abdominal cavity the elevated pressure within the abdominal cavity would collapse the small passageways within the testes
sperm are unable to mature properly at the higher temperatures found within the abdominal cavity
seminiferous tubules
sperm develop inside the testes in coiled tubes; diploid cells are located near the outer wall of the tubules; these cells multiply continuously by mitosis, and each day about 3 million of them differentiate into primary spermatocytes;
In males, FSH _____. is directly responsible for facial hair growth beginning at puberty stimulates the production of sperm cells in the testes is produced by the hypothalamus is not produced; it is a female hormone
stimulates the production of sperm cells in the testes
Which of the following correctly traces the path of sperm from their site of production to their exit from a man's body? testis, epididymis, vas deferens, ejaculatory duct, urethra epididymis, ejaculatory duct, urethra, testis, vas deferens ejaculatory duct, epididymis, testis, vas deferens, urethra testis, ejaculatory duct, vas deferens, epididymis, urethra
testis, epididymis, vas deferens, ejaculatory duct, urethra Sperm are produced in the testis, mature in the epididymis, and during ejaculation pass through the vas deferens to the ejaculatory duct and into the urethra.
Hypothetically speaking, if a diploid sperm fertilized a diploid ovum, the zygote would be ____________. tetraploid triploid diploid haploid
tetraploid
germ cells
the cells that will give rise to gamete forming cells in gonads
Asexual reproduction involves _____. integration of genetic information from two individuals a haploid phase of reproduction the creation of genetically identical offspring by a lone parent the union of two gametes
the creation of genetically identical offspring by a lone parent
reproduction
the creation of new individuals from existing ones
If a woman wants to become pregnant, what is the optimal day on which to have sexual intercourse? the day before menstruation is due to begin one week before ovulation three days before ovulation the day of ovulation
the day of ovulation
which hormonal change triggers the onset of menstruation?
the drop in the levels of estrogen and progesterone; these changes are caused by negative feedback of these hormones on the hypothalamus and pituitary after ovulation
the embryo develops from the 3 inner cell layers
the ectoderm layer will form the outer part of the embryo's skin and its nervous system; the ectoderm layer is continuous with amnion; the embryo's digestive tract will develop from the endoderm layer which is continuous with the yolk sac; the bulk of most other organs will develop from mesoderm
to reach the egg nucleus, the sperm nucleus must pass through three barriers; what are they?
the egg's jelly coat, a middle region of glycoproteins called vitelline layer, and the egg cell's plasma membrane
Pregnancy tests detect a hormone in a woman's urine that is present only when an embryo is developing in her uterus. This hormone is secreted by _____. the ovary the embryo the pituitary a follicle
the embryo
Menstruation results in the discharge of _____. the endometrium the corpus luteum of the uterus blood from the outer surface of the uterus the follicle
the endometrium
During the first trimester, _____. the fetus's eyes are open the mother may feel movements, and fetal activity may be visible through the abdominal wall an ultrasound can be performed to determine the gender of the fetus the fetus is most vulnerable to exposure to drugs and radiation
the fetus is most vulnerable to exposure to drugs and radiation
During the first trimester, _____. the mother may feel movements, and fetal activity may be visible through the abdominal wall an ultrasound can be performed to determine the gender of the fetus the fetus is most vulnerable to exposure to drugs and radiation the fetus's eyes are open
the fetus is most vulnerable to exposure to drugs and radiation During the first trimester, organogenesis is taking place. During this time, exposure to certain drugs, radiation, or disease organisms can cause profound effects.
spermatogenesis
the formation and development of sperm cells; takes about 10 weeks; because pre- sperm cells continuously replenish themselves, there is a never ending supply of spermatocytes
One difference between the blastula and gastrula stages of development is that _____. the blastula consists of more cell layers there are many more cells in a blastula blastula cells are more differentiated than gastrula cells the gastrula consists of three tissue layers
the gastrula consists of three tissue layers
umbilical cord
the lifeline between embryo and placenta
in terms of genetic makeup, what is the most important difference between the outcome of sexual reproduction and that of asexual reproduction?
the offspring of sexual reproduction are genetically diverse, whereas the offspring of asexual reproduction are genetically identical
placenta
the organ that provides nourishment, immune protection, and oxygen to the embryo and helps dispose of its metabolic wastes; consists of both embryonic and maternal tissues; in here, the yolk sac cells, amnion cells, and trophoblast cells will give rise to four structures called extraembryonic membranes; cannot always protect the embryo from substances circulating in mother's blood, like HIV, measles, alcohol, drugs
budding
the outgrowth and eventual splitting off of a new individual from a parent; many invertebrates (hydra) reproduce asexually by doing this;
fertilization during the cycles
the ovarian and menstrual cycles are put on hold if fertilization and pregnancy occur; early in pregnancy, the developing embryo (implanted in endometirum) releases a hormone called human chorionic gonadotropic (hCG). this hormone maintains the corpus luteum which continues to secrete progesterone and estrogen, keeping the endometirum intact
external fertilization
the parents discharge their gametes into water, where fertilization occurs, often without the male and female even making physical contact; timing is important because both eggs and sperms must be available for fertilization at the same time; exhibited by many aquatic invertebrates and most fishes and amphibians;
Pregnancy tests detect a hormone in a woman's urine that is present only when an embryo is developing in her uterus. This hormone is secreted by __________. the pituitary the ovary the placenta a follicle
the placenta The chorion, a portion of the placenta, produces human chorionic gonadotropin (HCG), which maintains the corpus luteum and its production of progesterone and estrogen.
regeneration
the regrowth of lost body parts
hormonal events before ovulation
the releasing hormone from hypothalamus stimulates the anterior pituitary to increase its output of FSH and LH; FSH stimulates the growth of an ovarian follicle, starting the ovarian cycle; in turn, the follicle secretes estrogen; early in the pre-ovulatory phase, the follicle is small and secretes relatively little estrogen; as the follicle grows, it secretes more and more estrogen and the rising (but still relatively low level of estrogen) exerts negative feedback on the pituitary; this keeps the blood levels of FSH and LH low for most of the pre-ovulatory phase; as the time of ovulation approaches, hormone levels change drastically, with estrogen reaching a critical peak just before ovulation; the high level of estrogen exerts positive feedback on the hypothalamus which then makes the pituitary secrete surges of FSH and LH; peaks in FSH and LH occur just after the estrogen peak
at random, a cell in early embryo may separate and reset as if it were the original zygote; the result is :
the result is the development of identical twins;
ovulation
the rupture of the follicle and expulsion of the secondary oocyte; the rupture of the follicle develops into a corpus luteum (yellow body); unless fertilization occurs, the corpus luteum degenerates before another follicle starts to develop
The gamete of a female has _____ the gamete of the male. the same number of chromosomes as fewer chromosomes than twice as many chromosomes as more chromosomes than
the same number of chromosomes as
Which of the trimesters primarily involve(s) an increase in size and general refinement of the human features? the third trimester the second and third trimesters the second trimester the first trimester
the second and third trimesters The first trimester is a time of radical change. The second and third trimesters primarily involve an increase in size and general refinement of the human features.
gastrulation
the second major phase of embryonic development; group of cells undergo this; during gastrulation, cells take up new locations that will allow later formation of all the organs and tissues; as gastrulation proceeds, the embryo is organized into 3 layer stage called gastrula; gastrulation completes when cell migration has resulted in 3 layered embryo;
fission
the separation of parent into two or more offspring of about equal size;
What is shed from the body in menstruation? excess immature egg cells the thickened endometrium; its removal allows for implantation of a fertilized egg unsuccessful zygotes or early embryos the thickened endometrium when fertilization has not occurred
the thickened endometrium when fertilization has not occurred
menstrual cycle
the uterus is prepared for possible implantation of an embryo;
Right after the fusion of sperm and egg plasma membranes, _____. the vitelline layer hardens and separates from the plasma membrane the sperm and egg nuclei fuse cleavage begins there is a change in the egg membrane that prevents the entry of other sperm
there is a change in the egg membrane that prevents the entry of other sperm
how are sperm and egg cells developed?
they are haploid cells that develop by meiosis from diploid cells in gonads
The ovaries release increasing levels of estrogen and progesterone immediately after ovulation. This results in _____. menstruation and increased FSH and LH production thickening of the endometrium and reduced production of FSH and LH, which feeds back to prevent further ovulation maturation of additional egg cells formation of a zygote
thickening of the endometrium and reduced production of FSH and LH, which feeds back to prevent further ovulation
trimester 3
time of rapid growth as the fetus gains the strength to survive in world; babies born prematurely (as early as 24 weeks) may survive but they will require special medical care after birth; as the fetus grows and the uterus expands around it, the mother's abdominal organs become squeezed, causing frequent urination, digestive troubles, and backaches
trimester 1
time of the most radical change for both mother and embryo; embryo is particularly likely to damage by radiation, drugs, or alcohol, all of which can lead to birth defects or miscarriage
nonidentical twins
two separate eggs fuse with two separate sperm to produce two genetically unique zygotes that develop in the uterus at the same time;
fragmentation
two step process; the breaking of parent body into several pieces, followed by regeneration
what kind of environments would likely be advantageous to asexually reproducing organisms? why?
unchanging environments favor asexual reproduction because well adapted genotypes are made in the genetically identical offspring
What structure is part of both the excretory and reproductive systems in males? urethra ureter seminal vesicle vas deferens
urethra
a typical ovary has thousands of dormant follicles, each containing a primary oocyte;
usually only one follicle has a dividing oocyte at any one time; meiosis I occurs as the follicle matures; about the time the secondary oocyte forms, the pituitary hormone LH triggers ovulation,
menstruation
uterine bleeding caused by the breakdown of the endometrium; usually lasts for 3-5 days; this corresponds to the beginning of the pre-ovulatory phase of the ovarian cycle;
A fertilized egg usually implants itself and develops in the _____. uterus ovary oviduct abdominal cavity none of these
uterus
gastrulation begins
when a small groove, called blastopore, appears on one side of the blastula; cells of the outer layer roll inward at the blastopore with the future endoderm surrounding a simple digestive cavity; the cells that will form ectoderm spread downward over more of the surface of the embryo, and the cells that will form mesoderm begin to spread into a thin layer inside the embryo, forming a middle layer between the other two
The allantois is an extraembryonic membrane that develops from the _____. yolk sac trophoblast cells amnion chorion
yolk sac
A __________ is a fertilized egg (the diploid cell created by the fusion of sperm and egg).
zygote
Which of the following options lists the sequence of stages in embryonic development in the correct order? zygote, gastrula, blastocyst zygote, blastocyst, gastrula gastrula, blastocyst, zygote blastocyst, zygote, gastrula
zygote, blastocyst, gastrula
