Deck 29: Reproduction and Development

Question 1

Looking at a variety of animals, what are the advantages to restricting reproduction to a limited time period? Why do so many animals have a sharply defined reproductive season during the year?

Answer 1

Animals reproduce either asexually or sexually.
• Sexual reproduction is the process of giving birth to new ones by the union of gametes of two parents with opposite sex. This union of gametes causes genetic variation and helps in the process of evolution.
• Asexual reproduction is the process of reproduction without the union of gametes. The new individuals are exact copies of their parents. There is no genetic variation and hence they evolve less. This is common in lower invertebrates like protozoa, sponges, jellyfish, etc. the different types of asexual reproduction are- fission, budding and fragmentation.
The advantages of restricting reproduction for a limited period of time are
• Avoid wastage of gametes
• Avoid wastage of energy of the organism to produce gametes
• Giving birth to young ones under favorable condition for their development
• Abundant food and protection is available
These above benefits have led to many animal species to have sharply defined reproductive season during the year. Some animals reproduce only once a year or some twice a year depending on the favorable conditions.

Question 2

Asexual reproduction is common in

A) the protozoa.
B) sponges.
C) jellyfish.
D) flatworms.
E) all of the above (a-d).

Answer 2

E

Question 3

In invertebrates, sexual reproduction involves the fusion of gametes from different individuals of a species. Thus, each offspring has a unique combination of genes inherited from two parents. Broadcast spawning simply involves the release of gametes into the water in which the invertebrate lives (e.g., sponges and corals).
What are the different types of hermaphroditism?

Answer 3

Hermaphroditism is a phenomenon where an organism has both male and female sex organs that are functional. They are also called as monoecious (both sexes present in one organism). These organisms have the ability for self-fertilization and also mate with the members of their own species. They act as males when they transfer the sperm to another member and also as females when they receive sperm from the same member.
There are two types of hermaphroditism. They are protogynous and protoandry. These are also called as sequential hermaphroditism. Here, one half of the life cycle has one sex and the other half of the life cycle has another sex. In protogynous animals, the animal is a female in the first half of the life cycle and then later it changes to a male. Whereas, in the protoandry or protoandrous animals, the animal is a male in the first half of the life cycle and then changes into a female in the next half of the life cycle.
This type of sequential hermaphroditism is beneficial to certain animal groups where the males are killed. In such instances, the largest female changes itself into a male and takes the lead as the dominant male.

Question 4

In most sexual species, males produce far more gametes than do females. Why does this occur when, in most cases, only one male gamete can fertilize one female gamete?

Question 5

Broadcast spawning is an example of internal fertilization.

Question 6

Most female mammals have an estrus cycle. In an estrus cycle, hormones control the fertility period in order for the young to be born when environmental conditions are most favorable. One common reproductive strategy found in reptiles, birds, and mammals is shelled, desiccation-resistant eggs.
Why do you think amphibians and many fishes have external fertilization, whereas lizards, birds, and mammals rely on internal fertilization?

Question 7

Why are the accessory glands of the male so important in reproduction?

Question 8

In protandry, an animal is a male during its early life history and a female later in the life history.

Question 9

Most fishes and amphibians release eggs and sperm into the water, where the gametes unite by chance. Very few fertilized eggs grow to maturity. Nonavian reptiles and birds have internal fertilization and their embryos develop in a fluid-filled cavity surrounded by membranes and a shell to prevent desiccation. Mammals generally do not lay eggs, but give birth to their young. They are also amniotic, but most species are viviparous. Most mammals have an estrus cycle, but primates have a menstrual cycle.
Is there an advantage to internal fertilization? If so, describe this advantage.

Question 10

Why doesn't a women menstruate while she is pregnant?

Question 11

The three basic embryonic membranes that characterize the mammalian embryo are also found in

A) fishes.
B) amphibians.
C) reptiles.
D) birds.
E) Both c and d are correct.

Question 12

Semen consists of sperm from the testes and fluid from the seminal vesicles and prostate gland. Sexual stimulation causes erection of the penis and continued stimulation leads to ejaculation of semen. The production of sperm and secretion of testosterone from the testes is controlled by FSH and LH from the anterior pituitary gland.
Would natural selection favor those males that produce more sperm over those males that produce fewer sperm? Explain your answer.
FIGURE 29.8 Hormonal Control of Reproductive Function in Adult Human Males. Negative feedback mechanisms (red dashed pathways) by which the hypothalamus controls sperm maturation and the development of male secondary sexual characteristics. (GnRH = gonadotropin-releasing hormone; LH = luteinizing hormone; FSH = follicle-stimulating hormone.)

Question 13

Which of the following structures is the site of spermatogenesis?

A) Prostate
B) Bulbourethral gland
C) Urethra
D) Seminiferous tubule
E) Both a and b

Question 14

Is the fertility of a woman affected by the length of a given menstrual cycle or whether the cycles are regular or irregular? Explain.

Question 15

At puberty, some oocytes are triggered by FSH to develop with each menstrual cycle. During the follicular phase, one follicle matures; ovulation is the release of the follicle's secondary oocyte triggered by LH. This secondary oocyte only completes its division if fertilization occurs. During the luteal phase, the development of an additional oocyte is inhibited. If fertilization does not occur, the endometrium is sloughed off as menstrual bleeding. The four phases that occur in mammals with an estrus cycle are proestrus, estrus, metestrus, and diestrus.
How are the functions of FSH and LH similar in human male and females? How do they differ?

Question 16

The cnidarian, Hydra, reproduces

A) only sexually.
B) asexually by budding.
C) by parthenogenesis.
D) by fragmentation.
E) by both b and c.

Question 17

FSH and LH are produced by the

A) ovaries.
B) testes.
C) anterior pituitary gland.
D) adrenal glands.

Question 18

Those species that reproduce asexually tend to evolve very slowly, because all offspring of any one individual are alike, providing less genetic diversity for evolutionary selection. One advantage to asexual reproduction is that a constant combination of genes matches a stable, unchanging environment in which the animal lives. One disadvantage is that genetic diversity does not occur and a single environmental event may devastate an entire species.
Does parthenogenesis occur among vertebrates? If so, give an example.

Question 19

One of the most critical stages of development occurs during the first trimester of a human pregnancy. Organogenesis begins during the fourth week. During the subsequent six months, growth and maturation occur. The placenta functions as an exchange site for nutrients and gases and is also a hormone producer.
Why is the circulation through the placenta like that of the lungs (see figure 29.17)?
FIGURE 29.17 Fetus and Placenta at Seven Weeks. The circulations of mother and fetus are in close contact at the site of the chorionic villi, but they do not actually mix. Branches of the mother's arteries in the wall of her uterus open into pools near the chorionic villi. Oxygen and nutrients from the mother's blood diffuse into the fetal capillaries of the placenta. The fetal capillaries lead into the umbilical vein, which is enclosed within the umbilical cord. From here, the fresh blood circulates through the fetus's body. Blood that the fetus has depleted of nutrients and oxygen returns to the placenta in the umbilical arteries, which branch into capillaries, from which waste products diffuse to the maternal side.