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IB Biology Notes
SL & HL
Assessment Statements covered: 9
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6, 11
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3 Reproduction in Angiospermophytes
9
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1 Draw and label a diagram showing the structure of a dicotyledonous animal-pollinated
flower
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The image above is a WALLFLOWER
9
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2 Distinguish between pollination, fertilization and seed dispersal
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3
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The named seed should be non-endospermic
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Vicia faba – broad bean seed

9
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4 Explain the conditions needed for the germination of a typical seed
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Water – seed is hydrated so that embryo is enabled to be physiologically active
Oxygen – aerobic cell respiration to generate ATP
Suitable temperature – optimum temperature for enzymes involved in mobilization of stored food
reserves, the translocation of organic solutes in the phloem and synthesis of intermediates for cell

growth and development
External
Water uptake – hydration of the cytoplasm of
cells of embryo
Ambient temperature – within optimum range for
enzyme reaction

Internal
Overcoming dormancy
Production of gibberellic acid GA by embryo
cells to initiate biochemical changes, leading to
production of hydrolytic enzymes for
mobilization of stored food

Oxygen – to sustain aerobic cell respiration
9
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5 Outline the metabolic processes during germination of a starchy seed
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This stimulates
the production of amylase, which catalyses the breakdown of starch to maltose
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No further details are expected
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2
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4
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6
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3
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Limit this to the conversion of Pr (red absorbing) to Pfr (far-red absorbing) in red or white light, the
gradual reversion of Pfr to Pr in darkness, and the action of Pfr as a promoter of flowering in long-day
plants and an inhibitor of flowering in short-day plants
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6 Reproduction
6
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1 Draw and label diagrams of the adult male and female reproductive systems
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Do not include any histological details, but include
the bladder and urethra
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6
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FSH
LH
Estrogen
Progesterone
Menstrual cycle: 1-14 days follicular phase; 14-28 days luteal phase
1
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2
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Estrogen:
a
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In the pituitary gland, estrogen inhibits further secretion of FSH, which prevents
the possibility of further follicles being stimulated to develop – negative
feedback
3
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The
high and rising level of estrogen suddenly stimulates the secretion of LH as well as FSH
(to a lesser extent)
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LH also stimulates conversion of the vacant follicle into a corpus luteum
4
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Progesterone:
a
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In pituitary gland, it inhibits further secretion of LH and FSH – negative
feedback
5
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Low levels of FSH and LH
allow the corpus luteum to degenerate
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If the egg is fertilized, then the developing embryo itself becomes an endocrine gland,
secreting a hormone (HCG) and maintains corpus luteum for 16 weeks
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6
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6
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4 List three roles of testosterone in males
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GenChaSex
6
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5 Outline the process of in vitro fertilization (IVF)
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Normal menstrual cycle steps are blocked temporarily
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3
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5
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7
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Synthetic FSH is injected – ovaries are stimulated to develop many egg cells – superovulation
Male partner provides semen sample
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Checked by microscopic examination to ensure
fertilization
Zygotes then incubated at body temperature for 2-3 days
Microscopic examination to confirm that embryos have reached 4- to 8-cell stage
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6
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Aim 8: There is great variation between human societies around the world in the views held on IVF
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There is little evidence to suggest that children born
as a result of standard IVF protocols are different in any way from children conceived naturally
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TOK: There are potential risks in the drug treatments that the woman is given, and there are concerns
about the artificial selection of sperm and the injection of them into the eggs that occurs with some IVF
protocols
...

11
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4
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Interstitial cells (Leydig cells) are in the connective tissue between the seminiferous tubules in the
testes – endocrine glands that secrete testosterone
Germinal epithelium cells are attached to the basement membrane (the first layer after the membrane)
one cell thick
Sertoli cells are slightly bigger where the spermatocytes and spermatids are lodged in – dependent on
until they mature into spermatozoa (sperms)
Histology of the testis (uploaded as a separate document)
11
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2 Outline the processes involved in spermatogenesis within the testis, including mitosis, cell
growth, the two divisions of meiosis and cell differentiation
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Spermatogonia ! primary spermatocytes ! secondary spermatocytes ! spermatids ! spermatozoa
Germinal epithelium cells (undifferentiated stem cells) of the semniferous tubule (2n) become the
spermatogonia through differentiation
Differentiation of germinal epithelium cells (2n) ! spermatogonia (2n) ! mitosis ! growth and
maturation ! primary spermatocyte (2n) ! meiosis I ! secondary spermatocytes (n) ! meiosis II !
spermatids (n) ! spermatozoa

11
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3 State the role of LH, testosterone and FSH in spermatogenesis
...
4
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Histology of an ovary
Germinal epithelium – which lines the outer surface of the ovary, divides by mitotic cell division to
form numerous oogonia
Primary follicles – oogonia cells migrate into the connective tissue of the ovary where they grow and
enlarge to form oocytes, each oocyte becomes surrounded by layers of follicle cells called primary
follicles
11
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5 Outline the processes involved in oogenesis within the ovary, including mitosis, cell
growth, the two divisions of meiosis, the unequal division of cytoplasm and the degeneration of
polar body
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Oogenesis begins in the ovaries of the fetus before birth, but the final development of oocytes is only
completed in adult
...
Very many degenerate, a process that continues throughout life
...

Germinal epithelium cells in embryo ! differentiation ! oogonia in fetus through mitosis ! growth
and development becomes primary follicle (“bigger”) until prophase I at birth ! puberty ! meiosis I
is completed becomes secondary oocyte (suspended at prophase II) ! ovulation of secondary oocyte
! if fertilization, meiosis II completes ! ootid (male and female nuclei)
1
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3
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5
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7
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4
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From head to tail: acrosome – plasma membrane – nucleus – centriole – middle piece with
mitochondria – tail

A mature secondary oocyte
Zona pellucida (jelly coat) is glycoprotein
11
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7 Outline the role of the epididymis, seminal vesicle and prostate gland in the production of
semen
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4
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Timing of the formation

Number of gametes

Spermatogenesis
Spermatogonia formed from the
time of puberty, throughout
adult life
Meiosis I and II go to
completion during sperm
production
Millions of sperms are formed
daily

Oogenesis
Oogonia formed in the
embryonic ovaries, long before
birth
Meiosis II reaches prophase and
then stops until a male nucleus
enters the secondary oocyte,
triggering completion of meiosis
II
From puberty, a few primary
oocytes undergo meiosis I to
become secondary oocytes each
month
...

Most fail to develop further –
they degenerate
Fertilized ovum is non-motile
and becomes lodged in the
endometrium of the uterus
where cell divisions lead to
embryo formation

Comparison Table
11
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9 Describe the process of fertilization, including the acrosome reaction, penetration of the
egg membrane by a sperm and the cortical reaction
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2
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4
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6
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8
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Fertilization occurs in the first one third of the oviduct
Sperm passes between the follicle cells and arrives at the jelly coat surrounding the secondary
oocyte
‘Capacitation’: changes to the surface of the head of the sperm, releasing the hydrolytic
enzymes packaged in acrosome
The zona pellucida is hydrolyzed
3 actin filaments cause protrusion of membrane which attaches to a protein receptor on
vitelline membrane (specificity) – only same species
Plasma membranes of secondary oocyte and sperm fuse
Sperm is engulfed, which triggers meiosis II in oocyte
Membrane becomes depolarized (influx of Na+) – fast block to polyspermy (within 1 – 3 sec)
Cortical reaction – slow block to polyspermy
a
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Causes exocytosis of cortical granules into the pre-vitelline space
c
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Zone pellucida is chemically altered thus no more sperm can enter (hardened)

11
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10 Outline the role of HCG in early pregnancy
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4
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Limit this to several mitotic divisions resulting in a hollow ball of cells called the blastocyst
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2
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4
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Division of zygote into a mass of daughter cells is called cleavage
NO CHANGE in mass or size
The embryo reaches the uterus in a ball of blastomeres
Then blastocyst forms – blastomeres and blastocoel (cytoplasm inside)
Day 6 – 14: implantation – blastocyst embeds in the endometrium
a
...
Chorionic villi receive nutrients from endometrium

11
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12 Explain how the structure and functions of the placenta, including its hormonal role in
secretion of estrogen and progesterone, maintain pregnancy
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4
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Embryonic details of the fetus and the structure of amniotic membranes are not required
...
4
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11
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15 Outline the process of birth and its hormonal control, including the changes in
progesterone and oxytocin levels and positive feedback
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2
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4
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6
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Just before birth, levels of progesterone fall sharply
Progesterone inhibits contractions and secretion of oxytocin
Oxytocin is thus released, relaxing the elastic fibers that join the bones of the pelvic girdle –
aids dilation of the cervix for the head
Oxytocin stimulates rhythmic contractions of the muscles of the uterus wall – this contraction
is controlled by positive feedback – as contraction occurs, more release of oxytocin
This results in powerful intermittent waves of contraction
Decreased stretching of cervix breaks the positive feedback cycle
Falls in levels of estrogen and progesterone allow pituitary to release prolactin – milk



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