Wednesday, April 15, 2009


Chapter 46

Mechanisms of Sexual Reproduction

Mechanisms of Sexual Reproduction

Fertilization is the union of sperm and egg

External fertilization occurs when eggs are shed by the female and fertilized by the male outside the female's body

Internal fertilization occurs when sperm are deposited in the female reproductive tract and fertilization occurs within the tract

Gonads are the organs that produce gametes in most animals

Mammalian Reproduction

The Male:

The male's external reproductive organs are the scrotum and penis, and the internal organs are gonads (which produce gametes and hormones), accessory glands (which secrete necessary fluids), and ducts (which carry sperm and glandular secretions).

The testes are made up of many highly coiled tubules surrounded by connective tissue. The tubules are seminiferous tubules, the sites of sperm production. In between the tubules are Leydig cells, which produce testosterone and other androgens.

The testes are held in the scrotum (equivalent to the female labia majora), which is located outside the lower abdominal pelvic cavity

The sperm from the seminiferous tubules into the epididymis (where it is stored). During ejaculation, the sperm is propelled through the vas deferens, which ultimately meets up w/a duct from the seminal vesicle and forms an ejaculatory duct, which opens into the urethra (which serves as an excretory and reproductive duct)

The seminal vesicles, the prostate gland, and the bulbourethral gland all contribute secretions to create semen. These secretions which are usually alkaline supply necessary nutrients and a medium for the sperm cells

The penis is composed of three masses of spongy tissue derived from modified veins and capillaries

The Female:

The female gonads are the two ovaries. Each ovary contains many microscopic follicles. The ovaries secrete estrogen and progesterone

Follicles consist of one egg surrounded by one or more layers of follicle cells, which help to develop, nourish, and protect the egg cell. All of the follicles a woman has are formed before her birth. One follicle matures and releases its egg cell during each menstrual cycle

The follicle cells also produce estrogens, the female hormones

The egg cell is released from the follicle during ovulation. The remaining follicle tissue heals and grows in the ovary to form a body called a corpus luteum. This secretes estrogens and progesterone. Progesterone helps to maintain the uterine wall during pregnancy. If the egg cell isn't fertilized, the corpus luteum disintegrates

Multiple Choice Questions:

1. Why is sexual reproduction important?
A) It can result in numerous offspring in a short amount of time.
B) The resulting diverse phenotypes may enhance survival of a population in a changing environment.
C) It allows animals to conserve resources and reproduce only during optimal conditions.
D) It enables isolated animals to colonize a habitat rapidly.
E) Both A and D are important.

2. Which of the following is not required for internal fertilization?
A) internal development of the embryo
B) copulatory organ
C) sperm receptacle
D) behavioral interaction
E) All of the above are necessary for internal fertilization.

3. Why is internal fertilization considered more advantageous than external fertilization?
A) Usually fewer offspring are produced, so ample food supply is available.
B) The increased survival rate results in rapid population increases.
C) The smaller number of offspring often receive a greater amount of parental protection.
D) Usually a smaller number of genes are present, which promotes genetic stability.
E) The time and energy devoted to reproduction is decreased.

4. Internal and external fertilization both
A) produce a zygote.
B) occur in vertebrates.
C) occur in eutherian animals.
D) A and B only are correct.
E) A and C only are correct.

5. Which reproductive method is the most prevalent in mammals?

A) fragmentation

B) budding

C) regeneration

D) external fertilization

E) internal fertilization

6. The _______is (are) the site of testosterone production in the testis

A) seminiferous tubules

B) epididymis

C) Leydig cells

D) seminal vesicle

E) prostate gland

7. Which structure is part of the excretory and reproductive systems in males?

A) Ureter

B) Urethra

C) Seminal vesicle

D) Urinary bladder

E) Vas deferens


1. B 2. A 3. C 4.D 5.E 6. C 7.B

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