IB Biology 2015

1. 6.6 & 11.4 Reproduction
Essential idea: Sexual reproduction involves the development and
fusion of haploid gametes.

2. Understandings
Statement Guidance
6.6 U.1 A gene on the Y chromosome causes embryonic gonads to develop as testes and
secrete testosterone.
6.6 U.2 Testosterone causes pre-natal development of male genitalia and both sperm
production and development of male secondary sexual characteristics during
puberty.
6.6 U.3 Estrogen and progesterone cause pre-natal development of female reproductive
organs and female secondary sexual characteristics during puberty
6.6 U.4 The menstrual cycle is controlled by negative and positive feedback mechanisms
involving ovarian and pituitary hormones.
11.4 U.1 Spermatogenesis and oogenesis both involve mitosis, cell growth, two divisions of
meiosis and differentiation.
11.4 U.2 Processes in spermatogenesis and oogenesis result in different numbers of
gametes with different amounts of cytoplasm.
11.4 U.3 Fertilization in animals can be internal or external Fertilization involves the acrosome
reaction, fusion of the plasma
membrane of the egg and sperm and
the cortical reaction.
11.4 U.4 Fertilization involves mechanisms that prevent polyspermy
11.4 U.5 Implantation of the blastocyst in the endometrium is essential for the
continuation of pregnancy
11.4 U.6 HCG stimulates the ovary to secrete progesterone during early pregnancy.
11.4 U.7 The placenta facilitates the exchange of materials between the mother and fetus.
11.4 U.8 Estrogen and progesterone are secreted by the placenta once it has formed.
11.4 U.9 Birth is mediated by positive feedback involving estrogen and oxytocin.

3. Applications and Skills
Statement Guidance
6.6 A.1 The use in IVF of drugs to suspend the normal secretion of hormones,
followed by the use of artificial doses of hormones to induce
superovulation and establish a pregnancy.
6.6 A.2 William Harvey’s investigation of sexual reproduction in deer
6.6 S.1 Annotate diagrams of the male and female reproductive system to show
names of structures and their functions
11.4 A.1 The average 38-week pregnancy in humans can be positioned on a
graph showing the correlation between animal size and the
development of the young at birth for other mammals.
11.4 S.1 Annotation of diagrams of seminiferous tubule and ovary to show the
stages of gametogenesis.
11.4 S.2 Annotation of diagrams of mature sperm and egg to indicate functions.

4. Male Reproductive System
6.6 S.1 Annotate diagrams of the male and female reproductive system to show names of structures and their functions

5. Male Reproductive System:Male Reproductive System:
1.1. EpididymusEpididymus::
•Large coiled tube (23 ft. long) that surrounds testes.
•Stores sperm (about 20 days).
•During ejaculation, about 400 million sperm cells are propelled
from epididymis.
6.6 S.1 Annotate diagrams of the male and female reproductive system to show names of structures and their
functions

6. 2.2. Vas Deferens:Vas Deferens:
• Long muscular ducts from scrotum to
back of bladder.
• During ejaculation, the sperm pass
from epididymis into these two ducts.
*Vasectomy: Each vas deferens is cut to
prevent sperm from entering urethra.
3.3. Ejaculatory DuctEjaculatory Duct::
• Short duct after two vas deferens
ducts unite.
4.4. UrethraUrethra::
• Deliver sperm to the exterior.
• In males, urine and sperm pass
through the urethra.
5. Scrotum
• maintains temperature (lower than body)
that sperm require for normal
development

7. Accessory Glands: Produce semen.
Functions of semen:
• Activate sperm cells
• Provide nutrients for motility
• Counteract acidity of vagina and male urethra
A. Seminal vesicles (2): Secrete fluid that nourishes sperm. Contribute about 60% of
semen volume.
B. Prostate gland: Produces a thin milky secretion.
• Largest of semen secreting glands.
• Contributes 30% of semen volume.
C. Bulbourethral glands
• Secrete a clear mucus that neutralizes acid from urine in urethra.
6.6 S.1 Annotate diagrams of the male and female reproductive system to show names of structures and their functions

8. Front View of Male Reproductive SystemFront View of Male Reproductive System

9. Semen production

10. 6.6 U.1 A gene on the Y chromosome causes embryonic gonads to develop as testes and secrete testosterone.
• Initially the development of the
embryo is the same in all embryos
and embryonic gonads could
develop into testis of ovaries.
• The developmental pathway for
the gonads depends on presence
or absence of one gene
• When SRY is present the gonads
develop into testes.
• SRY codes for a DNA binding
protein called TDF (testis
determining factor).
• TDF stimulates the expression of
other genes that cause the
development of the testis

11. Structure of the Testis
•Each testis is composed of a tubular
structure. It is from these seminiferous
tubules where sperm are produced.
•From puberty these tubules will
produce sperm cells throughout the life
of the man.
•Note the basement membrane which
surrounds each tubule. Inside the
basement membrane can be seen
various cells which are the stages of the
developing spermatozoa.
11.4 S.1 Annotation of diagrams of seminiferous tubule and ovary to
show the stages of gametogenesis

12. Micrograph of testis
•This light micrograph
shows the cross section
of seminiferous tubules,
blood vessels and also
the interstitial Leydig
cells.
•Leydig cells are
responsible for the
production of
testosterone
11.4 S.1 Annotation of diagrams of seminiferous tubule and ovary to
show the stages of gametogenesis

13. • Each testis is composed of a
tubular structure. It is from
these seminiferous tubules
that sperm are produced.
• From puberty these tubules
will produce sperm cells
throughout the life of the man.
• Note the basement membrane
which surrounds each tubule.
• Inside the basement
membrane can be seen various
cells which are the stages of
the developing spermatozoa.
• Between the seminiferous
tubules are groups of cells
called interstitial or Leydig cells
that produce the male sex
hormone, testosterone.
Please Sing a Song for Me
11.4 S.1 Annotation of diagrams of seminiferous tubule and ovary to
show the stages of gametogenesis

14. This image is of the wall of a
seminiferous tubule.
a) Basement membrane
b) Germinal epithelium (2n) which divide
by mitosis to produce
c) Spermatogonium (2n) which grow and
enlarge
d) Primary spermatocytes (2n) go through
Meioses I (n) converting into
Secondary Spermatocytes .
e) Secondary Spermatocytes go through
Meiosis II to produce spermatids (n)
*Sertoli cells nourish and allow the
spermatids to differentiate to
spermatozoa. These are released into
the lumen
11.4 S.1 Annotation of diagrams of seminiferous tubule and ovary to
show the stages of gametogenesis

15. 11.4 U.2 Processes in spermatogenesis and oogenesis result in different numbers of gametes with different amounts of cytoplasm.
Spermatogenesis
•The male sex cell is
designed to deliver
just DNA.
•The sperm cell
contains no
cytoplasm and
delivers no
organelles

16. Spermatogenesis
•It is a process by which spermatogonia are
transformed into spermatozoa. It begins at puberty.
•At birth: germ cells in the male infant present in the
sex cords of the testis are surrounded by supporting
cells (Sertoli cells).
•At this time the primordial germ cell divides to give
spermatogonia.
•Spermatogonia gives rise to primary spermatocyte.
•1ry
spermatocyte by 1st
meiotic division gives secondary
spermatocyte wg gives haploid spermatids (4 in no.).
11.4 U.1 Spermatogenesis and oogenesis both involve mitosis, cell growth, two divisions of meiosis and differentiation.

17. Spermatogenesis
•Spermatogonium are found at or
near the basement membrane.
•They have a high rate of cell
division by mitosis to produce
spermatogonia.
•Primary Spermatocytes are large
diploid cells which form from
rapidly growing spermatogonia.
•The Primary spermatocytes
separate the homologous pairs of
chromosomes in meiosis
I(reduction division) to form the
haploid Secondary
Spermatocytes.
•The spermatids are formed from
the separation of the sister
chromatids in meiosis II.
11.4 S.1 Annotation of diagrams of seminiferous tubule and ovary to
show the stages of gametogenesis

18. Spermatogenesis
(continued)
The spermatids are found
in association with the
sertoli cells which
nourish the spermatids
as they differentiate into
spermatozoa.
•The rate of spermatozoa is
high and continuous
throughout the life on
the sexually mature
male.
•The average number of
spermatozoa in
ejaculated semen is 32 x
106
ml-1

19. 11.4 S.1 Annotation of diagrams of seminiferous tubule and ovary to
show the stages of gametogenesis

20. 6.6 U.2 Testosterone causes pre-natal development of male genitalia and both sperm production and development of male secondary sexual
characteristics during puberty.
•There are two hormones secreted from
the anterior pituitary FSH and LH.
•FSH stimulates the primary
Spermatocytes which carry out
meiosis I (reduction division) to
separate homologous pairs of
chromosomes and produce haploid
secondary spermatocytes.
•LH stimulates the interstitial cells to
produce testosterone
•Testosterone stimulates the maturation
of secondary spermatocytes through
meiosis and differentiation to
spermatozoa.

21. Hormonal Control of Spermatogenesis

22. Structure of Sperm
• The acrosome vesicle contains the enzymes required to digest
its way though the ovum wall.
• Haploid nuclei (n=23) containing the paternal chromosome s
• The 'mid-section' of the sperm contains many mitochondria
which synthesis ATP to provide the energy for the movement of
the tails structure.
• Protein fibers add longitudinal rigidity and provide a mechanism
of propulsion.
11.4 S.2 Annotation of diagrams of mature sperm and egg to indicate functions

23. Structure of Sperm
11.4 S.2 Annotation of diagrams of mature sperm and egg to
indicate functions

24. 6.6 U.3 Estrogen and progesterone cause pre-natal development of female reproductive organs and female secondary sexual
characteristics during puberty
Side View of Female Reproductive System

25. Major Organs of Female Reproductive System:
1. Ovaries: Produce ova (egg) and sex hormones.
»Size and shape of large almond.
*Follicles:: A single egg with surrounding cells
that nourish and protect it. Women are born
with all of their follicles (40,000 to 400,000).

26. Major Organs of Female Reproductive System:
2. Oviducts (Fallopian Tubes): Transport the egg from the
ovary to the uterus. FertilizationFertilization occurs here.
3. Uterus
• Has thick walls of smooth muscle responsible for uterine
contractions and cramps.
• Inner mucous lining, which thickens each month in
preparation for pregnancy. If fertilization does not occur,
breaks down and is discharged during menstruation.
• If fertilization occurs, the egg implants and helps support
growth until the placenta develops.

27. 4. Cervix: Lower portion of the uterus, which projects into
the vagina.
*Pap smear: Examination of cervical tissue to detect
abnormalities. Recommended yearly.
*Cervical cancer: Most cases caused by a viral infection.
5. Vagina: Thin walled, muscular chamber.
• Receives the sperm and penis
• Acid pH kills bacteria and sperm cells
• Part of birth canal

28. Frontal View of Female Reproductive System
6.6 S.1 Annotate diagrams of the male and female reproductive system to show names of structures and their functions

29. Feedback Regulation of
Oogenesis
•feedback regulation of female
reproductive cycle is negative and
positive
•leads to female cycles
•hypothalamus and pituitary
control ovaries
•ovarian hormones control uterus
6.6 U.4 The menstrual cycle is controlled by negative and positive feedback mechanisms involving ovarian and pituitary hormones.

30. Two Parts to Female ReproductionTwo Parts to Female Reproduction
1.1. Uterine CycleUterine Cycle
• Days 1-5 – Menstruation (“no” steroids)
• Days 6-13 - Proliferative phase (Estrogen effect)
• Day 14 – Ovulation (LH effect)
• Days 15-28 - Secretory phase (Progesterone effect)
2. Ovarian Cycle2. Ovarian Cycle
•Follicular Phase - FSH promotes development of an ovarian
follicle containing an egg ready to be ovulated
secretes increasing levels of estrogen
•Luteal Phase –LH promotes ovulation and development of
corpus luteum that secretes progesterone
6.6 U.4 The menstrual cycle is controlled by negative and positive feedback mechanisms involving ovarian and pituitary hormones.

31. Ovarian Hormones Regulate
Uterine Endometrium
• Estrogen stimulates proliferation for implantation of embryo
• Progesterone stimulates secretion to nourish embryo until
implantation

32. Female Sex HormoneFemale Sex Hormone
Effect on EndometriumEffect on Endometrium
• also has effects on breast and other body tissues
• PMS: “hormone withdrawal”

33. Female Cycle

34. Female Menstrual Cycle /Uterine Cycle : Approximately
28 days.
• Menstruation: Days 1-5 of cycle.
– Walls of endometrium break down.
– Caused by falling levels of progesterone and estrogen.
– Can last 3 to 7 days.
• Pre-Ovulatory /Proliferative phase (Estrogen effect):
Starts around day 6 of cycle.
– Rising estrogen levels cause the endometrium to start
thickening.

35. • Ovulation (LH effect) : Occurs around day 14 of cycle.
– FSH stimulates growth of ovarian follicle.
– LH causes follicle to finish meiosis I (secondary oocyte) and
to be released by ovary.
– Corpus luteum: Starts to secrete estrogen and
progesterone.
• Post-ovulatory Secretory phase (Progesterone effect):
Starts around day 15.
– Endometrium continues to grow in response to rising
estrogen and progesterone.
– If no fertilization occurs, corpus luteum degenerates and
menstruation occurs.
– If fertilization occurs, embryo maintains corpus luteum.

36. Oogenesis
•Oogonium (2n) divide by mitosis to produce
many oogonia
•Each oogonia grows within the follicle of
cells. Meiosis begins but stops in at prophase
I. The oogonia are found within the primary
follicles.
•There are approx 400,000 primary follicles
present in the ovary prior to puberty.
•A Primary Follicles (prophase I) may develop
to secondary follicles (metaphase II) under
the influence of FSH.
•Note that the first polar body ( haploid set
chromosomes) does not progress beyond
metaphase II.
•The Oocyte does not progress to the end of
meiosis unless fertilization takes place.
11.4 U.1 Spermatogenesis and oogenesis both involve mitosis, cell growth, two divisions of meiosis and differentiation.

37. 11.4 U.2 Processes in spermatogenesis and oogenesis result in different numbers of gametes with different amounts of cytoplasm.

38. Ovary structure
11.4 S.1 Annotation of diagrams of seminiferous tubule and ovary to show the stages of gametogenesis

39. A) Primary follicles in the medulla region (center) each one contains an
oogonia arrested at prophase I.
b) Sequence showing the development of the primary follicle (PI) into
the secondary follicle (MII).
c) The mature secondary follicle is also known as a graffian follicle. The
size of this follicle will make the wall of the ovary bulge prior to
ovulation. Note the exclusion of the 1st
polar body that will
degenerate

40. d) Ovulation, with the rupture of the follicle wall the oocyte is released
into the oviduct.
e) The Oocyte moves into the oviduct. This oocyte is at metaphase II
and will complete meiosis only with fertilization.
f) The Corpus luteum forms from the now empty secondary follicle. This
structure is responsible for the production of higher levels of
progesterone.

41. Mammalian Oocyte
• During follicle development unequal division of the cell during
meiosis produces the 1st polar body that can be seen outside the
plasma membrane. This will not develop be continues to be part of
the follicle.
• Zona pellucida surrounds the structure and is composed of
glycoproteins.
• Cortical granules involved in the acrosome reaction at
fertilization.
• Follicular cells found round the outside are the follicle.
11.4 S.2 Annotation of diagrams of mature sperm and egg to indicate functions

43. 11.4 U.3 Fertilization in animals can be internal or external
• Sexual Reproduction – Frogs
External fertilization

44. Fertilization = sperm + egg
External Fertilization
• Egg shed by female, fert. by male
in water
• Environmental cues / courtship
behavior
• Large # gametes  low survival
• Eg. fish, amphibians
Internal Fertilization
• Sperm deposited in female
reprod. tract
• Cooperative behavior
• Dry environment
• Fewer gametes, fewer zygotes
 greater survival
External Devel.
•Tough eggshell
•Eg. reptiles, birds,
platypus
Internal Devel.
•High parental care
•Eg. placentals,
sharks, some reptiles
11.4 U.3 Fertilization in animals can be internal or external

45. Fertilization
11.4 U.4 Fertilization involves mechanisms that prevent polyspermy

48. a) The cumulus is a thick loose grouping of cells in a
gelatinous matrix. The sperm cell must penetrate
this mass to reach the zona pellucida, a
glycoprotein matrix surrounding the egg plasma
membrane.
b) Contact between the zona pellucida and proteins
in the sperm cells membrane trigger a the
acrosome reaction.
c) The acrosome vesicle fuses with the sperm plasma
membrane and releases enzymes that digest a
path through the zona pellucida.
d) The membrane of the sperm cell and the ovum fuse
together. This causes a prominent raising of the
egg membrane. At the same time this results in a
release of Ca2+
from the endoplasmic reticulum.
(e) The cortical vesicle fuse with the plasma membrane
releasing enzymes that destroy the sperm binding
proteins on the zona pellucida. This prevents
polyspermy. The release of Ca2+
also activate
meiosis and prepare the cell for completion of

50. 6.6 A.2 William Harvey’s investigation of sexual reproduction in deer
• Embryogenesis an early theory of
egg development proposed by
Aristotle. His idea called the Seed
and soil theory, believed that males
produce seed, females form an egg
which mixes with menstrual blood
to develop into a fetus inside the
mother
• William Harvey tested this idea by
shooting deer during mating season
• He discovered that it took months
for the fertilized egg to develop in
the uterus.
• This help debunk the idea of
Spontaneous generation and lead to
a better understanding of
embryology.
(1578-1657)

51. Human embryonic development
•Conception: in oviduct
•Implantation: in uterus
•Hormones:
– Human Chorionic Gonadotropin (hCG): maintain
estrogens in early pregnancy; pregnancy test
•Human gestation (pregnancy) = 40 weeks
•Egg lodged in oviduct = ectopic (tubal) pregnancy
11.4 U.5 Implantation of the blastocyst in the endometrium is essential for the continuation of pregnancy
.

52. Zygote the fused sperm and egg cell. This cell undergoes rapid
mitotic cell division, but these do not increase the size of the
zygote
Morula Cleavage produces a solid sphere of cells, still
surrounded by zona pellucida.
Blastocyst At 4.5 to 5 days, cells have developed into a hollow
ball of cells. At this stage the cell enters the uterus.

53. From ovulation to implantation
Cleavage starts
Fertilization occurs
Uterus
Ovulation
Ovary
Endometrium
The blastocyst implants
Cleavage continues
Formation of Zygote

54. Implantation of blastocyst
Blastocyst
Endo-
metrium
Cavity
Inner cell mass
Trophoblast
Early Postfertilization Events

55. 11.4 U.6 HCG stimulates the ovary to secrete progesterone during early pregnancy.
Human Chorionic Gonadotrophin
(HCG)
a) The fertilized egg has developed into a
blastocyte that will implant into the
endometrium
b) Implantation of the blastocyst which
begins to secrete human chorionic
gonadotrophin (hCG)
c) hCG passes into the maternal blood. The
concentration doubles every 2-3 days and
reaches a peak at 8-10 wk's.
d) The hCG targets the ovary and the corpus
luteum.
e) The corpus luteum secretes progesterone
and estrogen at high levels .
f) The estrogen and progesterone continue
to inhibit FSH and LH secretion from the
pituitary.
g) The progesterone's prevent the
breakdown of the endometrium and so
the embryo can continue its development
into a fetus

56. Human Chorionic Gonadotrophin (HCG)

57. Placenta
The placenta grows from the embryonic tissue. It attaches to the
endometrium of the uterus. Unlike other mammals the human placenta
is invades the endometrium very deeply.

58. Functions of the placenta:
1. Transfer gases
2. Transport nutrients
3. Excretion of wastes
4. Hormone production –
temporary endocrine organ –
estrogen and progesterone
5. Formation of a barrier –
incomplete, nonselective –
alcohol, steroids, narcotics,
anesthetics, some antibiotics
and some organisms can cross
11.4 U.7 The placenta facilitates the exchange of materials between the mother and fetus.

59. 11.4 U.8 Estrogen and progesterone are secreted by the placenta once it has formed.
As the placenta forms and grows, it develops the ability to produce
hormones. Between weeks 6-9 of pregnancy, the placenta takes over
from the ovaries as the main producer of progesterone and estrogen,
vital to the establishment of pregnancy.
Progesterone also has many functions during mid to late pregnancy,
including:
• Preventing the muscles of the womb contracting until the onset
of labor
• Preventing lactation until after pregnancy
• Strengthening the muscles of the pelvic wall in preparation for
labor
Estrogen the placenta produces several distinct estrogens
• Stimulate growth of the myometrium and oxytocin receptors,
thereby preparing the uterus for parturition.
• Stimulate mammary gland development.

60. 11.4 U.9 Birth is mediated by positive feedback involving estrogen and oxytocin.
Estrogen

61. 6.6 A.1 The use in IVF of drugs to suspend the normal secretion of hormones, followed by the use of artificial doses of
hormones to induce superovulation and establish a pregnancy.

62. Ethical Issues with in vitro fertilization
Advantages of IVF: there are as many reasons for this treatment as
there are people seeking this treatment. As examples
•Over comes infertility
•Allow families for people who must be sterilized e.g..
radiography/chemo therapy cancer patients
Disadvantages of IVF:
•What happens to unwanted embryo's
•What happens to orphaned embryo's
•Should infertility be by-passed

63. 11.4 A.1 The average 38-week pregnancy in humans can be positioned
on a graph showing the correlation between animal size and the
development of the young at birth for other mammals.
• Altricial "requiring nourishment“, refers to a pattern of growth and development
in organisms which are incapable of moving around on their own soon after
hatching or being born
• Precocial refers to species in which the young are relatively mature and mobile
from the moment of birth or hatching. These are usually have large body masses.
Correlation between maximum lifespan (tmax) and typical adult body mass (M) using all species (n = 1,701)