Download AP Biology Animal Form and Function

AP BIOLOGY ANIMAL
FORM AND FUNCTION
Reproductive System
Reproductive System—Production of
Eggs and Sperm
Characteristics that distinguish the sexes:
 Primary sex characteristics—structures directly
involved in reproduction (ovaries, uterus, testis)
 Secondary sex characteristics—noticeable physical
characteristics that differ between males and
females (facial hair,
deepness of voice, breasts,
and muscle distribution)
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Meiosis
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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 Each sperm cell surrounding this
egg cell is trying to enter it and
chromosome number is
leave its packet of genetic
restored
information in the form of
chromosomes containing DNA. Only
one will be successful.
Male Reproductive Organs
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Sperm cells are
produced in the testis.
Males have two testes,
located in a sac called
the scrotum.
A portion of the testis
called the
seminiferous tubules
is where the sperm
cells are actually
made.
Spermatogenesis
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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 epididymis
Interstitial Cells in Testes
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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
system.
Epididymis
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After the sperm cells
are formed by meiosis,
they move into the
epididymis—the coiled
region extending from
the testes.
Here, the spermatids
mature into sperm
cells.
The Journey of the Sperm
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The prostate gland adds a basic
(pH >7) liquid to the mix to help
combat the acidity of the vaginal
region of the female.
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.
Female Reproductive System
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Ovary—the 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 uterus.
Fertilization

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
endometrium).
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 Travel
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As the sperm cells enter,
they must survive the
somewhat hostile
environment that the
female body presents
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 fertilization.
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 zygote.
Oogenesis
Oogenesis—the
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
puberty.
Oogenesis
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.
Oogenesis
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
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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
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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 progesterone.
Gastrulation
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The next major stage of embryonic development is
gastrulation.
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
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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 tissues
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 fly’s 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 homeobox.
 The homeobox is similar in organism to organism
and has been found to exist in
a variety of organisms: birds,
humans, fish, and frogs.
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Reproductive Hormones
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The hormones involved in human reproduction are
LH, FSH, estrogen, progesterone, and testosterone.
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 ovulation—the
release of a secondary
oocyte from the ovary)
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Effects of Birth Control Pills
Ovulation Caused by LH Surge
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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….
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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