Mastering Biology Chapter 47
Ovulation usually occurs on or about day _____ of a 28-day ovarian cycle.
14
During fertilization in sea urchins, Steinhardt and his colleagues observed that the sperm-induced rise in cytoplasmic Ca2+concentration correlates with the formation of the fertilization envelope, which blocks fusion of other sperm with the egg. Look at the image below to review the terms. Note that the vitelline layer is sometimes called the vitelline envelope. An increase in the concentration of Ca2+ in the egg's cytoplasm triggers what is called the cortical reaction. In this activity, you will place the events of the cortical reaction in the correct sequence. Drag the labels to the appropriate targets to indicate the sequence of events occurring between fusion of the sperm and egg and formation of the fertilization envelope.
2.)Cortical granules fuse with egg plasma membrane. 3.)Sperm-binding receptors on egg plasma membrane are degrated. 4.)Vitelline layer is released from egg plasma membrane. 5.)Perivitelline space expands due to osmotic water movement.
Sex hormones, including androgens, estrogens, and progesterone, are produced by the gonads in males and females and control the development of primary sex characteristics—the structures directly involved in reproduction. The sex hormones also trigger the development of secondary sex characteristics—the physical and behavioral characteristics that appear during puberty that are not directly related to reproduction. Because the principal sex hormones differ in males and females, different secondary sex characteristics develop. Sort the following secondary sex characteristics and hormones based on whether they are related to androgens, estrogens and progesterone, or neither. Drag each phrase to the appropriate bin.
Androgens: testosterone deepening of voice development offacial hair increasedaggressiveness increased muscle mass Estrogens and progesterones: estrogens and progesterone fat depositionin hips changes in calciummetabolism breast development estradiol increased waterretention Neither: none
Which of the following statements about oogenesis in humans is true?
Beginning at puberty, a primary oocyte completes its first meiotic division to form a secondary oocyte and a polar body approximately every month.
Based on what they knew about the fertilization envelope (a protective layer that forms around the egg when a sperm fuses with it), Steinhardt, Shatten, and their colleagues hypothesized that changes in the distribution of Ca2+ ions in sea urchin eggs are involved in the formation of the fertilization envelope. In sea urchin eggs (as in most eukaryotic cells) the concentration of Ca2+ ions is much higher in the endoplasmic reticulum (ER) than in the cytoplasm. To see how cytoplasmic Ca2+ concentration changes in the egg during fertilization, the researchers injected a Ca2+-specific fluorescent dye into the cytoplasm of unfertilized eggs. After adding sperm to the eggs, they observed the eggs with a fluorescence microscope. The following images show the changes in fluorescence that occurred after a single sperm entered the egg. The fluorescence of the dye increased with increasing cytoplasmic Ca2+ concentration. The green color indicates the region of the cell with the highest fluorescence at that point in time. Sort the labeled regions of the fertilized egg above based on the status of the ER Ca2+ channels and Ca2+ pumps in that region.
Ca2+ channels closed, Ca2+ pumps operating slowly a c f Ca2+ channels open b h e Ca2+ channels closed, Ca2+ pumps operating rapidly g d
How does spermatogenesis differ from oogenesis?
Diploid cells give rise to four functional gametes in spermatogenesis.
Which pituitary secretion stimulates sperm production?
FSH
True or false: The corpus luteum is retained upon implantation due to the presence of the hormone Luteinizing hormone (LH) .
False
True or false? The production of sperm begins at puberty when spermatogonia undergo meiosis I to form primary spermatocytes, which then undergo meiosis II to form secondary spermatocytes. These secondary spermatocytes go on to form spermatids, which mature into sperm cells.
False
What products are formed when a diploid cell undergoes meiosis?
Four haploid cells.
Many frogs and mice are similar in size, yet a frog egg is vastly larger than a mouse egg. Propose a plausible explanation for this difference in the egg size. Match the words in the left column to the appropriate blanks in the sentences on the right.
Frogs are oviparous, and the egg must contain everything the embryo needs to develop. Mice are viviparous, and the embryo obtains almost everything it needs from the mother. Therefore, there is no need for large eggs provisioned with everything required for development.
Hormones control the two closely linked reproductive cycles in human females—the uterine (or menstrual) cycle and the ovarian cycle. During one uterine cycle, which is approximately 28 days long, the lining of the uterus undergoes hormonally-regulated changes, if no pregnancy has occurred. At the same time, the hormones also cause a series of changes to take place in an ovary, known as the ovarian cycle. The flowchart below describes the events of the ovarian cycle. Drag the names of the hormones to their appropriate locations on the flowchart, starting with the release of a hormone from the hypothalamus. Labels may be used once, more than once, or not at all. (Note: GnRH = gonadotropin-releasing hormone; LH = luteinizing hormone; FSH = follicle-stimulating hormone.)
GnRH, LH and FSH, estradiol, LH and FSH, estradiol and progesterone, LH and FSH, estradiol and progesterone
How can a cell respond to more than one hormone? See Section 47.1 (Page) .
It has different receptors for each hormone.
Which pituitary secretion stimulates the testes to secrete androgens?
LH
The role of Ca2+ ions in the formation of the fertilization envelope and blocking polyspermy can be further studied using Ca2+ channel blockers. As their name suggests, Ca2+ channel blockers block the movement of Ca2+ ions through channels. In the case of gated Ca2+ channels, the channel blockers prevent the channels from opening even if the signal to open is present. Suppose that you conduct an experiment in which you test whether the fertilization envelope forms and polyspermy occurs under the following conditions:Control group: An unfertilized sea urchin egg is left untreated (no Ca2+ channel blockers added). Then sperm are added.Experimental group: Ca2+ channel blockers are added to an unfertilized sea urchin egg. Then sperm are added. Drag the labels (yes or no) to predict whether or not the following events can occur under control conditions and experimental conditions.
No channel blocker:yes, yes, yes, no Channel blocker: yes, no, no, yes
Which diploid cells are produced by an embryonic germ cell?
Spermatogonia.
How does the birth control pill prevent pregnancy? In the 1960s, the U.S. Food and Drug Administration approved a contraceptive that allowed women to plan desired pregnancies and prevent unwanted pregnancies. Oral hormonal contraception ("the pill") uses synthetic hormones similar in structure to progesterone and/or estradiol. What is the pill's mechanism of action? Part A Part complete Scientists confirmed the pill's mechanism of action by measuring plasma hormone levels in women before and after they went on the pill (∗ means P<0.05, ∗∗ means P<0.01, and ∗∗∗ means P<0.001). Do the data shown here support the hypothesis that the pill affects hormonal signaling?
The data from the study do support the hypothesis that the pill interferes with normal hormonal signaling because the women showed statistically significant declines in all four groups of major reproductive hormones after they started using the pill.
Why does external fertilization typically occur much more often in aquatic animals than in terrestrial animals?
The gametes must be kept wet to avoid desiccation
As shown in the diagram below, the ovarian cycle is regulated by hormones secreted by the hypothalamus (top panel) and the anterior pituitary (panel 2), as well as by the maturing follicle and corpus luteum in the ovary (panels 3 and 4). At the same time, the hormones also cause the endometrium (the lining of the uterus) to thicken and then shed (bottom panel). Some methods of contraception, such as birth control pills and patches, use synthetic hormones to manipulate the ovarian cycle in females.Some hormone-based contraceptives contain a combination of a synthetic estradiol and a synthetic progestin (progesterone-like hormone).Other hormone-based contraceptives contain progestin only. Which statements correctly explain how the hormone-based contraceptives affect the female reproductive cycle? Select all that apply.
The low doses of progestin and estradiol in the combination pill have a negative feedback effect on the hypothalamus, blocking ovulation. The low dose of estradiol in the combination pill prevents the surge in LH production. The progestin in the progestin-only pill causes changes in the endometrium that prevent implantation.
What role do germ cells play in gametogenesis?
They produce cells that divide by mitosis and then undergo meiosis to form gametes.
Why is progesterone production in the corpus luteum important in the first trimester of pregnancy? See Section 47.6 (Page) .
To maintain the uterine lining
True or false? Humans form gametes by a process called gametogenesis.
True
Which hormone(s) is(are) directly responsible for triggering the development of the secondary sex characteristics of males, such as beard growth?
androgens
Sperm become capable of movement while in the _____.
epididymis
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.
estrogen and progesterone
After ovulation, high levels of _____ inhibit _____ secretion.
estrogen and progesterone ... FSH and LH
Developing ovarian follicles primarily secrete _____.
estrogens
Fertilization of a human egg takes place in the ________.
fallopian tube
If there is fertilization, secretion of _____ by the early embryo maintains the corpus luteum.
human chorionic gonadotropin
A rapid increase in the _____ level stimulates ovulation.
luteinizing hormone
The secretion of androgens is regulated by a _____ feedback mechanism involving the _____ and _____.
negative ... hypothalamus ... pituitary gland
An oocyte released from a human ovary enters the ________.
oviduct
What is the usual site of the fertilization of an egg cell?
oviduct
For water fleas of the genus Daphnia, switching from a pattern of asexual reproduction to sexual reproduction coincides with _____.
periods of temperature or food stresses on adults
Sperm develop in the _____.
seminiferous tubules
In humans, the follicular cells that remain behind in the ovary following ovulation become ________.
the corpus luteum, which secretes the steroid hormones progesterone and estradiol.
In vertebrate animals, spermatogenesis and oogenesis differ in that ________.
the division of cytoplasm is unequal in oogenesis, whereas it is equal in spermatogenesis
A fertilized egg usually implants itself and develops in the _____.
uterus
Among human males, the passage within the penis through which sperm moves is the ________.
vas deferens
Sperm exit a male's body via the _____.
vas defrens