43.E: Animal Reproduction and Development (Exercises)
43.1: Reproduction Methods
During sexual reproduction the genetic material of two individuals is combined to produce genetically diverse offspring that differ from their parents. The genetic diversity of sexually produced offspring is thought to give species a better chance of surviving in an unpredictable or changing environment. Species that reproduce sexually must maintain two different types of individuals, males and females, which can limit the ability to colonize new habitats as both sexes must be present.
Review Questions
Which form of reproduction is thought to be best in a stable environment?
- asexual
- sexual
- budding
- parthenogenesis
- Answer
-
A
Which form of reproduction can result from damage to the original animal?
- asexual
- fragmentation
- budding
- parthenogenesis
- Answer
-
B
Which form of reproduction is useful to an animal with little mobility that reproduces sexually?
- fission
- budding
- parthenogenesis
- hermaphroditism
- Answer
-
D
Genetically unique individuals are produced through ________.
- sexual reproduction
- parthenogenesis
- budding
- fragmentation
- Answer
-
A
Free Response
Why is sexual reproduction useful if only half the animals can produce offspring and two separate cells must be combined to form a third?
- Answer
-
Sexual reproduction produces a new combination of genes in the offspring that may better enable them to survive changes in the environment and assist in the survival of the species.
What determines which sex will result in offspring of birds and mammals?
- Answer
-
The presence of the W chromosome in birds determines femaleness and the presence of the Y chromosome in mammals determines maleness. The absence of those chromosomes and the homogeneity of the offspring (ZZ or XX) leads to the development of the other sex.
43.2: Fertilization
Sexual reproduction starts with the combination of a sperm and an egg in a process called fertilization. This can occur either inside (internal fertilization) or outside (external fertilization) the body of the female. Humans provide an example of the former whereas seahorse reproduction is an example of the latter.
Review Questions
External fertilization occurs in which type of environment?
- aquatic
- forested
- savanna
- steppe
- Answer
-
A
Which term applies to egg development within the female with nourishment derived from a yolk?
- oviparity
- viviparity
- ovoviparity
- ovovoparity
- Answer
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C
Which term applies to egg development outside the female with nourishment derived from a yolk?
- oviparity
- viviparity
- ovoviparity
- ovovoparity
- Answer
-
A
Free Response
What are the advantages and disadvantages of external and internal forms of fertilization?
- Answer
-
External fertilization can create large numbers of offspring without requiring specialized delivery or reproductive support organs. Offspring develop and mature quickly compared to internally fertilizing species. A disadvantage is that the offspring are out in the environment and predation can account for large loss of offspring. The embryos are susceptible to changes in the environment, which further depletes their numbers. Internally fertilizing species control their environment and protect their offspring from predators but must have specialized organs to complete these tasks and usually produce fewer embryos.
Why would paired external fertilization be preferable to group spawning?
- Answer
-
Paired external fertilization allows the female to select the male for mating. It also has a greater chance of fertilization taking place, whereas spawning just puts a large number of sperm and eggs together and random interactions result in the fertilization.
43.3: Human Reproductive Anatomy and Gametogenesis
As animals became more complex, specific organs and organ systems developed to support specific functions for the organism. The reproductive structures that evolved in land animals allow males and females to mate, fertilize internally, and support the growth and development of offspring.
Review Questions
Sperm are produced in the ________.
- scrotum
- seminal vesicles
- seminiferous tubules
- prostate gland
- Answer
-
C
Most of the bulk of semen is made by the ________.
- scrotum
- seminal vesicles
- seminiferous tubules
- prostate gland
- Answer
-
C
Which of the following cells in spermatogenesis is diploid?
- primary spermatocyte
- secondary spermatocyte
- spermatid
- sperm
- Answer
-
A
Which female organ has the same embryonic origin as the penis?
- clitoris
- labia majora
- greater vestibular glands
- vagina
- Answer
-
A
Which female organ has an endometrial lining that will support a developing baby?
- labia minora
- breast
- ovaries
- uterus
- Answer
-
D
How many eggs are produced as a result of one meiotic series of cell divisions?
- one
- two
- three
- four
- Answer
-
A
Free Response
Describe the phases of the human sexual response.
- Answer
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In phase one (excitement), vasodilation leads to vasocongestion and enlargement of erectile tissues. Vaginal secretions are released to lubricate the vagina during intercourse. In phase two (plateau), stimulation continues, the outer third of the vaginal wall enlarges with blood, and breathing and heart rate increase. In phase three (orgasm), rhythmic, involuntary contractions of muscles occur. In the male, reproductive accessory glands and tubules constrict, depositing semen in the urethra; then, the urethra contracts, expelling the semen through the penis. In women, the uterus and vaginal muscles contract in waves that may last slightly less than a second each. In phase four (resolution), the processes listed in the first three phases reverse themselves and return to their normal state. Men experience a refractory period in which they cannot maintain an erection or ejaculate for a period of time ranging from minutes to hours. Women do not experience a refractory period.
Compare spermatogenesis and oogenesis as to timing of the processes and the number and type of cells finally produced.
- Answer
-
Stem cells are laid down in the male during gestation and lie dormant until adolescence. Stem cells in the female increase to one to two million and enter the first meiotic division and are arrested in prophase. At adolescence, spermatogenesis begins and continues until death, producing the maximum number of sperm with each meiotic division. Oogenesis continues again at adolescence in batches of oogonia with each menstrual cycle. These oogonia finish the first meiotic division, producing a primary oocyte with most of the cytoplasm and its contents, and a second cell called a polar body containing 23 chromosomes. The second meiotic division results in a secondary oocyte and a second oocyte. At ovulation, a mature haploid egg is released. If this egg is fertilized, it finishes the second meiotic division, including the chromosomes donated by the sperm in the finished cell. This is a diploid, fertilized egg.
43.4: Hormonal Control of Human Reproduction
The human male and female reproductive cycles are controlled by the interaction of hormones from the hypothalamus and anterior pituitary with hormones from reproductive tissues and organs. In both sexes, the hypothalamus monitors and causes the release of hormones from the pituitary gland. When the reproductive hormone is required, the hypothalamus sends a gonadotropin-releasing hormone (GnRH) to the anterior pituitary.
Review Questions
Which hormone causes Leydig cells to make testosterone?
- FSH
- LH
- inhibin
- estrogen
- Answer
-
A
Which hormone causes FSH and LH to be released?
- testosterone
- estrogen
- GnRH
- progesterone
- Answer
-
C
Which hormone signals ovulation?
- FSH
- LH
- inhibin
- estrogen
- Answer
-
B
Which hormone causes the re-growth of the endometrial lining of the uterus?
- testosterone
- estrogen
- GnRH
- progesterone
- Answer
-
D
Free Response
If male reproductive pathways are not cyclical, how are they controlled?
- Answer
-
Negative feedback in the male system is supplied through two hormones: inhibin and testosterone. Inhibin is produced by Sertoli cells when the sperm count exceeds set limits. The hormone inhibits GnRH and FSH, decreasing the activity of the Sertoli cells. Increased levels of testosterone affect the release of both GnRH and LH, decreasing the activity of the Leydig cells, resulting in decreased testosterone and sperm production.
Describe the events in the ovarian cycle leading up to ovulation.
- Answer
-
Low levels of progesterone allow the hypothalamus to send GnRH to the anterior pituitary and cause the release of FSH and LH. FSH stimulates follicles on the ovary to grow and prepare the eggs for ovulation. As the follicles increase in size, they begin to release estrogen and a low level of progesterone into the blood. The level of estrogen rises to a peak, causing a spike in the concentration of LH. This causes the most mature follicle to rupture and ovulation occurs.
43.5: Human Pregnancy and Birth
Pregnancy begins with the fertilization of an egg and continues through to the birth of the individual. The length of time of gestation varies among animals, but is very similar among the great apes: human gestation is 266 days, while chimpanzee gestation is 237 days, a gorilla’s is 257 days, and orangutan gestation is 260 days long. The fox has a 57-day gestation. Dogs and cats have similar gestations averaging 60 days.
Review Questions
Nutrient and waste requirements for the developing fetus are handled during the first few weeks by:
- the placenta
- diffusion through the endometrium
- the chorion
- the blastocyst
- Answer
-
B
Progesterone is made during the third trimester by the:
- placenta
- endometrial lining
- chorion
- corpus luteum
- Answer
-
A
Which contraceptive method is 100 percent effective at preventing pregnancy?
- condom
- oral hormonal methods
- sterilization
- abstinence
- Answer
-
D
Which type of short term contraceptive method is generally more effective than others?
- barrier
- hormonal
- natural family planning
- withdrawal
- Answer
-
B
Which hormone is primarily responsible for the contractions during labor?
- oxytocin
- estrogen
- β -HCG
- progesterone
- Answer
-
A
Major organs begin to develop during which part of human gestation?
- fertilization
- first trimester
- second trimester
- third trimester
- Answer
-
B
Free Response
Describe the major developments during each trimester of human gestation.
- Answer
-
The first trimester lays down the basic structures of the body, including the limb buds, heart, eyes, and the liver. The second trimester continues the development of all of the organs and systems established during the first trimester. The placenta takes over the production of estrogen and high levels of progesterone and handles the nutrient and waste requirements of the fetus. The third trimester exhibits the greatest growth of the fetus, culminating in labor and delivery.
Describe the stages of labor.
- Answer
-
Stage one of labor results in the thinning of the cervix and the dilation of the cervical opening. Stage two delivers the baby, and stage three delivers the placenta.
43.6: Fertilization and Early Embryonic Development
The process in which an organism develops from a single-celled zygote to a multi-cellular organism is complex and well-regulated. The early stages of embryonic development are also crucial for ensuring the fitness of the organism.
Review Questions
Which of the following is false?
- The endoderm, mesoderm, ectoderm are germ layers.
- The trophoblast is a germ layer.
- The inner cell mass is a source of embryonic stem cells.
- The blastula is often a hollow ball of cells.
- Answer
-
B
During cleavage, the mass of cells:
- increases
- decreases
- doubles with every cell division
- does not change significantly
- Answer
-
D
Free Response
What do you think would happen if multiple sperm fused with one egg?
- Answer
-
Multiple sperm can fuse with the egg, resulting in polyspermy. The resulting embryo is not genetically viable and dies within a few days.
Why do mammalian eggs have a small concentration of yolk, while bird and reptile eggs have a large concentration of yolk?
- Answer
-
Mammalian eggs do not need a lot of yolk because the developing fetus obtains nutrients from the mother. Other species, in which the fetus develops outside of the mother’s body, such as occurs with birds, require a lot of yolk in the egg to nourish the embryo during development.
43.7: Organogenesis and Vertebrate Formation
Gastrulation leads to the formation of the three germ layers that give rise, during further development, to the different organs in the animal body. This process is called organogenesis. Organogenesis is characterized by rapid and precise movements of the cells within the embryo.
Review Questions
Which of the following gives rise to the skin cells?
- ectoderm
- endoderm
- mesoderm
- none of the above
- Answer
-
A
The ribs form from the ________.
- notochord
- neural plate
- neural tube
- somites
- Answer
-
D
Free Response
Explain how the different germ layers give rise to different tissue types.
- Answer
-
Organs form from the germ layers through the process of differentiation. During differentiation, the embryonic stem cells express a specific set of genes that will determine their ultimate fate as a cell type. For example, some cells in the ectoderm will express the genes specific to skin cells. As a result, these cells will differentiate into epidermal cells. The process of differentiation is regulated by cellular signaling cascades.
Explain the role of axis formation in development.
- Answer
-
Animal bodies have lateral-medial (left-right), dorsal-ventral (back-belly), and anterior-posterior (head-feet) axes. The dorsal cells are genetically programmed to form the notochord and define the axis. There are many genes responsible for axis formation. Mutations in these genes lead to the loss of symmetry required for organism development.