1. hydra
2. sponges
3. water fleas
4. sexually-reproducing frogs

Why is sexual reproduction useful when only half the individuals reproduce and two cells must combine to form a new cell?

1. It completes in a very short period of time.
2. It results in the rapid production of many offspring.
3. It increases genetic diversity, allowing organisms to survive in an unpredictable environment.
4. It needs less energy and leads to genetic variation in the offspring.

1. No, the sex of an individual is only determined by the presence of sex chromosomes.
2. Yes, temperature also determines the sex of an individual.
3. Yes, humidity and temperature determine the sex of an individual.
4. Yes, pH and humidity determine the sex of an individual.

What are some advantages of internal compared with external fertilization?

1. Internal fertilization leads to more genetic variations and increases the survival rates of offspring.
2. Internal fertilization increases the survival rates of offspring, and large numbers of offspring are produced.
3. Internal fertilization increases the survival rates of offspring, and the chance of fertilization with a specific partner also increases.
4. Internal fertilization increases the survival rates of offspring and decreases the chance of fertilization with a specific partner.

What are the mechanisms that protect and nurture the embryo in oviparous animals?

1. The hard, leathery exterior of bird eggs and the hard calcium covering of reptile eggs provides protection to the growing embryo. Nourishment is provided by yolk in the eggs.
2. The hard, leathery exterior of reptile eggs and the hard calcium covering of bird eggs provide protection to the growing embryo. Nourishment is provided by endosperm in the eggs.
3. The hard, leathery exterior of reptile eggs and the hard calcium covering of bird eggs provide protection to the growing embryo. Nourishment is provided by placenta in the eggs.
4. The hard, leathery exterior of reptile eggs and the hard calcium covering of bird eggs provide protection to the growing embryo. Nourishment is provided by yolk in the eggs.

1. In birds, an opening called the cloaca is used to transfer sperm, whereas in mammals, the presence of the penis and vagina allows direct delivery. Complete reproductive systems are formed in insects, with eggs maturing in the testes and sperm maturing in the ovaries.
2. In birds, an opening called the cloaca is used to transfer sperm, whereas in mammals, the presence of the penis and vagina allows direct delivery. Complete reproductive systems are formed in insects, with eggs maturing in the ovaries and sperm maturing in the testes.
3. In birds, sperm are transferred via the spermatheca, whereas in mammals, the presence of the penis and vagina allows direct delivery. Complete reproductive systems are formed in insects, with eggs maturing in the ovaries and sperm maturing in the testes.
4. In birds, an opening called the cloaca is used to transfer sperm, whereas in mammals, the presence of the penis and vagina allows direct delivery. Insects always use parthenogenesis.

1. If it fuses with a sperm, the resulting zygote enters the cervix for implantation. If it is not fertilized, it will return to the oviduct.
2. If it fuses with a sperm, the resulting zygote enters the uterus for implantation. If it is not fertilized, it will return to oviduct.
3. If it fuses with a sperm, the resulting zygote enters the uterus for implantation. If it is not fertilized, it will degrade and exit the body.
4. If it fuses with a sperm, the resulting zygote enters the cervix for implantation. If it is not fertilized, it will degrade and exit the body.

1. Both males and females show specific arousal, but the sexual response differs in intensity and duration.
2. Both males and females show specific arousal. In males, breathing rate and heart rate are increased. In females, there is a decrease in breathing rate and heart rate.
3. Vasodilation occurs in both males and females, allowing blood to engorge erectile tissue in the nipples, clitoris, labia, vagina, and penis. In males, breathing rate and heart rate are increased. In females, there is a decrease in breathing rate and heart rate.
4. Both males and females show an increase in heart rate, breathing rate, and blood pressure during phase one and phase two. However, sexual response differs in intensity and duration in males and females. Also, males show specific arousal, while females show non-specific arousal.

Compare and contrast spermatogenesis and oogenesis.

1. Both are the form of gametogenesis that takes place through mitosis. Spermatogenesis is the process of formation of four sperm in the testes in males. The process of formation of one ovum in the ovaries in females is called oogenesis.
2. Both are the form of gametogenesis that takes place through meiosis. Spermatogenesis is the process of formation of four sperm in the testes in males. The process of formation of four ova in the ovaries in females is called oogenesis.
3. Both are the form of gametogenesis that takes place through meiosis. Spermatogenesis is the process of formation of four sperm in the testes in males. The process of formation of one ovum in the ovaries in females is called oogenesis.
4. Both are the form of gametogenesis that takes place through meiosis. Spermatogenesis is the process of formation of one sperm in the testes in males, while the process of formation of one ovum in the ovaries in females is called oogenesis.

1. The hypothalamus releases FSH and LH at puberty by secreting of GnRH. FSH stimulates the Leydig cells in the testes and LH stimulates the Sertoli cells to synthesize and secrete testosterone.
2. The hypothalamus releases FSH and LH at puberty by the secretion of GHRH. FSH stimulates the Sertoli cells in the testes and LH stimulates the Leydig cells to synthesize and secrete testosterone.
3. The hypothalamus stimulates the release of FSH and LH at puberty by secreting of GnRH. FSH stimulates the Sertoli cells in the testes and LH stimulates the Leydig cells to synthesize and secrete testosterone.
4. The hypothalamus releases TSH and LH at puberty by the secretion of GnRH. TSH stimulates the Sertoli cells in the testes and LH stimulates the Leydig cells to synthesize and secrete testosterone.

1. Because a fertilized egg is not implanted into the uterus in a non-pregnant woman, the corpus luteum degenerates, and the levels of estrogen and progesterone decrease. The endometrium begins to degenerate as the progesterone level drops, initiating the next menstrual cycle.
2. Because a fertilized egg is not implanted into the uterus in a non-pregnant woman, the corpus luteum degenerates, and the levels of estrogen and progesterone increase. The endometrium begins to degenerate as the estrogen level increases, initiating the next menstrual cycle.
3. Because a fertilized egg is not implanted into the uterus in a non-pregnant woman, the corpus luteum degenerates and the levels of estrogen and progesterone increase. The endometrium begins to degenerate as the progesterone level rises, initiating the next menstrual cycle.
4. Because a fertilized egg is not implanted into the uterus in a non-pregnant woman, the corpus luteum degenerates and the levels of estrogen and progesterone decrease. The myometrium begins to degenerate as the progesterone level drops, initiating the next menstrual cycle.

The side effects of menopause can be diminished by hormone replacement therapy (HRT). However, many doctors are hesitant to recommend it. What are the possible reasons for this?

1. Its negative side effects, which include increased risk of colon cancer, osteoporosis, heart disease, macular degeneration, and possibly depression.
2. Its negative side effects, which include increased risk of stroke or heart attack, blood clots, breast cancer, ovarian cancer, endometrial cancer, gall bladder disease, and possibly depression.
3. Its negative side effects, which include increased risk of stroke or heart attack, blood clots, breast cancer, colon cancer, endometrial cancer, gall bladder disease, and possibly dementia.
4. Its negative side effects, which include increased risk of stroke or heart attack, blood clots, breast cancer, ovarian cancer, endometrial cancer, gall bladder disease and possibly dementia.

What determines whether a zygote will undergo total or partial cleavage?

1. Total cleavage takes place in eggs having a large amount of yolk, whereas partial cleavage occurs in eggs having very little or no yolk.
2. Total cleavage occurs when eggs have equal concentration of yolk at both poles, whereas partial cleavage occurs when the yolk is not equally distributed.
3. Total cleavage takes place in eggs having little or no yolk, whereas partial cleavage occurs in eggs having a large amount of yolk.
4. Total cleavage occurs when divisions of the blastomeres are separate, whereas partial cleavage occurs when blastomeres stay partially connected.

During organogenesis, the ectoderm forms the neural cells and the epidermal cells. How do the ectoderm cells determine which type of cells to form?

1. Growth factors signal some of the ectodermal cells to form epidermal cells, and the remaining cells form the neural plate.
2. The notochord cells of the mesoderm signal the ectodermal cells to form epidermal cells as well as the neural plate.
3. Growth factors signal some of the ectodermal cells to form epidermal cells, and the remaining cells form neural crest cells.
4. Proteins involved in the Wnt signaling pathway signal the ectodermal cells to form the epidermal cells and the neural plate.

What will be the outcome if the axis is not formed during the developmental stages?

1. The animal will have two notochords and may not have a dorsal-ventral or anterior-posterior side.
2. The animal will lack an anterior-posterior or dorsal-ventral side and may not have complete differentiation of cell layers.
3. The animal will lack an anterior-posterior or lateral-medial side and may not have complete differentiation of cell layers.
4. The animal will have incorrect positioning of the dorsal-ventral and lateral-medial sides and differentiation of cell layers will be incomplete.

What is the mesoderm, and what does it eventually differentiate into?

1. The mesoderm develops into various connective tissues. It is reorganized into groups of cells called somites, which develop into facial cartilage, ribs, and lungs.
2. The mesoderm develops into various connective and muscle tissues such as the ribs, lungs, segmental muscle, and the notochord, which forms the central axis of body of most animals.
3. The mesoderm develops into various connective and muscle tissues. It is reorganized into groups of cells called somites, which develop into ribs, lungs, segmental muscle, and the notochord.
4. The mesoderm develops into various connective tissues such as the facial cartilage, ribs, and lungs.

Which best describes the three stages of labor?

1. During stage one, the cervix thins. During stage two, the cervix is dilated to about 10 cm and the baby is expelled from the uterus. The last stage is the passage of the placenta after the baby has been born.
2. During stage one, the cervix thins and is dilated to about 10 cm. During stage two, the baby is expelled from the uterus. The last stage is the passage of the placenta after the baby has been born.
3. During stage one, the cervix thins. During stage two, the cervix is dilated to about 10 cm. During the last stage, the baby is expelled from the uterus, followed by the placenta.
4. During stage one, the cervix thins and may or may not be dilated. During stage two, the baby is expelled from the uterus. The last stage is the passage of the placenta after the baby has been born.

If multiple sperm were to combine with an egg in an animal, what would be the outcome?

1. A cortical reaction would occur if multiple sperm combine with an egg, resulting in a genetically inviable embryo.
2. The embryo would be genetically inviable and would die in a few days. The zygote might have multiple sets of chromosomes.
3. The zygote might have multiple sets of chromosomes, which will result in a neural tube defect in the developing fetus.
4. The zygote would be viable, but the resulting embryo would be genetically inviable.

After the blastula is formed, where do the embryonic stem cells and germ layers originate?

1. The inner cell mass has embryonic stem cells, which arrange themselves into the three germ layers.
2. The trophoblast in the blastula has embryonic stem cells, which arrange themselves into three germ layers.
3. The inner cell mass has embryonic stem cells, whereas the germ layer cells originate from the trophoblast.
4. The embryonic stem cells and germ layers originate from the blastocoel present inside the blastula.