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AP Biology Animal Form and Function


AP BIOLOGY ANIMAL FORM AND FUNCTION Reproductive System – PowerPoint PPT presentation

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Title: AP Biology Animal Form and Function

AP Biology Animal Form and Function
  • Reproductive System

Reproductive SystemProduction of Eggs and Sperm
  • Characteristics that distinguish the sexes
  • Primary sex characteristicsstructures directly
    involved in reproduction (ovaries, uterus,
  • Secondary sex characteristicsnoticeable physical
    characteristics that differ between males and
    females (facial hair,
  • deepness of voice, breasts,
  • and muscle distribution)

  • In order for the newly formed organism to have
    the same number of chromosomes as its parents,
    the chromosome number must be halved when the egg
    and sperm are made.
  • This is accomplished by a process called meiosis.
    Then, when one sperm successfully fertilizes the
    egg, the diploid chromosome number is restored

Each sperm cell surrounding this egg cell is
trying to enter it and leave its packet of
genetic information in the form of chromosomes
containing DNA. Only one will be successful.
Male Reproductive Organs
  • Sperm cells are produced in the testis. Males
    have two testes, located in a sac called the
  • A portion of the testis called the seminiferous
    tubules is where the sperm cells are actually

  • Sperm cells begin as diploid body cells located
    in the testes called Primary Spermatocytes.
  • After dividing in Meiosis I, they are now haploid
    cells called Secondary Spermatocytes
  • After dividing again in Meiosis II, they are
    called spermatids.
  • They then mature into sperm cells in the

Interstitial Cells in Testes
  • Most of the cells in the testes are destined to
    become sperm cells by meiosis.
  • In between these cells are other cells, called
    Interstitial Cells.
  • These are the structures that produce the
    hormones involved in the male reproductive

  • After the sperm cells are formed by meiosis, they
    move into the epididymisthe coiled region
    extending from the testes.
  • Here, the spermatids mature into sperm cells.

The Journey of the Sperm
  • From the epididymis, the sperm moves through the
    vas deferens to the urethra
  • The urethra is the tube that releases both sperm
    and urine (not at the same time!)

The seminal vesicles dump fluids into the vas
deferens as the sperm cells pass through. This
fluid adds fructose for energy, prostaglandins
(which stimulate uterine contractions) and mucus,
which helps the sperm swim more efficiently.
  • The prostate gland adds a basic
  • (pH gt7) liquid to the mix to help combat the
    acidity of the vaginal region of the female.

Female Reproductive System
  • Ovarythe site of egg production
  • The egg leaves the ovary before it is fully
    mature and enters a structure called the oviduct
    (aka Fallopian Tube)
  • The oviduct carries the egg from the ovary to the

  • When fertilized by a sperm cell in the oviduct
    (fallopian tube), after several days travelling
    in the tube, the egg will usually attach itself
    to the inner wall of the uterus (called the

The uterus connects to the vaginal opening via a
narrowed portion called the cervix. The narrow
opening through which the sperm travels up to the
Fallopian tube is the vagina.
The Environment Through Which the Sperm Must
  • As the sperm cells enter, they must survive the
    somewhat hostile environment that the female body
  • Its task is to find its way to the fallopian
    tube, where it must meet the egg and penetrate
    its outer surface to achieve successful

The sperm works its way through the vaginal
region, up through the cervix, through the
uterus, and into the fallopian tube. If the
timing is right, an egg is in the tube and the
sperm can fertilize the egg to produce a diploid
Oogenesisthe development of the egg, begins
while the female is still an unborn embryo. Some
of the fetal cells in the ovary of the embryo
begin meiosis and stop at Prophase I. These are
called Primary Oocytes and they stop further
meiosis and development until the female enters
After puberty begins, each month, one of the
Primary Ooctyes completes meiosis I. This
produces a polar body and one Secondary Oocyte, a
haploid cell. As the menstrual cycle continues,
ovulation frees the Secondary Oocyte to travel
into the Fallopian Tube.
The Secondary Oocyte travels down the Fallopian
Tube and, if a sperm cell is present, may be
fertilized. If a successful fertilization occurs,
the secondary oocyte enters Meiosis II, again
producing a Polar Body, as well as an egg which
combines with the sperm to form an embryo.
Embryonic Development
  • Embryonic development begins as soon as the egg
    is fertilized to produce a diploid zygote.
  • This zygote then divides by mitosis many times
    without increasing the size of the embryo.
  • During these cleavage divisions, cytoplasm is
    distributed unevenly to the daughter cells, but
    genetic information is distributed equally.
  • Different cells will play different roles in the
    body of the future embryo.

Embryonic Development
By Day 4 after fertilization, the embryo is a
ball of cells called a morula. As it undergoes
the next round of divisions, fluid will fill the
middle and it will form a hollow ball of cells
called a blastula. The blastula has two parts
the inner cell mass which becomes the embryo and
a trophoblast, which becomes the placenta.
The Trophoblast
  • The trophoblast aids in attaching the embryo to
    the endometrium (the inner wall of the uterus).
  • It also produces human chorionic gonadotropin
    (HCG), which maintains the endometrium by
    ensuring the continued production of

  • The next major stage of embryonic development is
  • During gastrulation, cells separate into three
    primary layers called germ layers, which
    eventually give rise to the different tissues of
    an adult.

Endoderm, Mesoderm, Ectoderm
  • The three germ layers of the embryo are the
    endoderm, mesoderm and ectoderm.
  • Endoderm inner germ layer gives rise to the
    inner lining of the gut and the digestive system,
    liver, thyroid, lungs, and bladder
  • Mesoderm intermediate germ layer gives rise to
    muscle, the circulatory system, reproductive
    system, excretory organs, bones, and connective
  • Ectoderm outer germ layer gives rise to the
    nervous system and skin, hair and nails.

How Do Cells Know What to Do?
  • Induction the influence of one group of cells on
    the development of another through physical
    contact or chemical signaling.
  • Hans Spemann, a German embryologist showed, for
    example, that the cells of the notocord influence
    the development of the neural plate (which
  • eventually becomes the nervous system).
  • When the notocord was transplanted into
  • a different part of an embryo, the neural
  • plate grew in the new location.

Homeotic Genes
  • Homeotic genes regulate or direct the body plan
    of organisms.
  • For example, a flys homeotic genes help
    determine how its segments will develop and which
    appendages should grow from each segment.
  • Scientists interfering with the development of
    these animals have shown
  • that mutations in these
  • genes can lead to growth
  • of organs where they
  • should not be.

Homeotic Genes
  • These genes regulate the body plan of animals.
  • The DNA sequence of a homeotic gene that tells
    the cell where to put things is called the
  • The homeobox is similar in organism to organism
    and has been found to exist in
  • a variety of organisms birds,
  • humans, fish, and frogs.

Reproductive Hormones
  • The hormones involved in human reproduction are
    LH, FSH, estrogen, progesterone, and
  • Estrogen and progesterone continually circulate
    in the female bloodstream. The hypothalamus
    monitors these levels to determine when to
    release certain hormones.
  • When estrogen and progesterone are low, the
    hypothalamus secretes GnRH (gonadotropin-releasing
    hormone), which travels to the pituitary gland
    to induce the release of FSH and LH.

FSH and LH
  • FSH Follicle-stimulating hormone (induces the
    development of the follicle that surrounds the
    primary oocyte during its development) it also
    causes the follicle to release estrogen
  • LH luteinizing hormone
  • (initiates ovulationthe
  • release of a secondary
  • oocyte from the ovary)

Effects of Birth Control Pills
Ovulation Caused by LH Surge
  • The LH surge causes further release of estrogen
    and progesterone from the follicle (which has now
    become a structure called the corpus luteum).

The corpus luteum induces the thickening of the
endometrium, the site of future egg
attachment. At this point, the levels of estrogen
and progesterone elevate enough so that the
hypothalamus cuts off prodution of GnRH so that
the LH and FSH levels drop back down.
If Fertilization Occurs.
  • If fertilization has occurred in the fallopian
    tube, and if the embryo attaches successfully to
    the uterine wall, HCG will be secreted, which
    works to keep the corpus luteum alive.
  • As a result, estrogen and progesterone will
    remain high and will keep the endometrium intact.

Left Implanted Embryo at 6 days Right
Implanted Embryo at 6 weeks
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