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IB Biology Unit 6 Physiology practice questions answers (from IB past exams)

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(Plus up to [2] for quality)

5 max

5 max

8 max

[20]

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Spermatogenesis

Oogenesis

number of gametes
produced

many / millions per day

one per
month/menstrual
cycle/28 days / about
400 eggs per life time;

products of meiosis

four / equal division of the
cytoplasm / no polar bodies

one / unequal division of
the cytoplasm / polar
bodies;

start of process

at puberty

begins during fetal
development;

duration of production

throughout adult life

ends at menopause;

timing of release

produced continuously /
released during ejaculation

released at ovulation / in
the middle of the
menstrual cycle;

both spermatogenesis and oogenesis involve meiosis;
both produce haploid cells/nuclei;
both occur in gonads

occurs in testes

occurs in ovaries;
5 max

(b)

meiosis;
independent assortment/random orientation of bivalents/pairs of
chromosomes/homologous chromosomes;
in metaphase I;
223/2n possible combinations (where n is the haploid number of
chromosomes);
crossing over / recombination of linked genes;
during prophase I;
can occur anywhere along a chromosome;
random orientation of chromatids (in metaphase II);
(gene) mutations may occur;

(c)

drugs used to (down-)regulate/stop the menstrual cycle;
hormones/FSH injected to stimulate many follicles to develop;
HCG injected to cause the follicles to mature;
eggs are harvested/extracted from the follicles/ovaries;
semen/sperm sample produced/collected;
semen is processed to concentrate it / sperm screened/given a
swim-up test;
semen/sperm mixed with eggs/oocyte / in a dish/in glass;
fertilization occurs;
embryos/blastocyst placed in uterus/oviduct (using a catheter/

5 max

long plastic tube);
Do not accept fertilized egg or zygote
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(Plus up to [2] for quality)

8 max
[20]

3
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(b)

(c)

α cells (of pancreas) produce glucagon;
glucagon promotes release of glucose/breakdown of glycogen by
liver cells;
glucagon secreted when blood glucose levels are low / raises blood
glucose levels;
β cells (of pancreas) produce insulin;
insulin promotes glucose uptake/storage of glycogen by liver/body/
muscle cells;
insulin secreted when blood glucose levels are high / lowers blood
glucose levels;
negative feedback mechanism;
Do not accept answers implying that insulin or glucagon catalyse
glucose-glycogen conversions directly
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5 max

urine of diabetics contains glucose;
whereas urine of non-diabetics contains no glucose;
glomerular filtrate contains glucose / glucose filtered out;
glucose (normally) reabsorbed from filtrate/into blood;
through wall of / in the proximal convoluted tubules;
blood glucose concentration higher than normal in diabetics;
reabsorption not completed / pumps cannot reabsorb all glucose in
diabetics;
glucose in urine can be detected using test strips;
type I diabetes is lack of insulin secretion / lack of β cells;
type II diabetes is body cells not responding to insulin / not
absorbing glucose;

8 max

(Plus up to [2] for quality)
[20]

5
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head and midpiece/mid-section/body;
tail/flagellum; (at least four times length of the head and containing fibres)
acrosome; (shown as distinct structure near front of head)
nucleus; (occupying more than half the width or length of head)
mitochondria; (as repetitive structures inside membrane of mid piece)
centriole; (between head and midpiece)
(plasma) membrane; (shown as single line covering whole cell)
microtubules; (in 9 plus 2 array)
5 max
[5]

6
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head and midpiece/mid-section/body;
tail/flagellum; (at least four times length of the head and containing fibres)
acrosome; (shown as distinct structure near front of head)
nucleus; (occupying more than half the width or length of head)
mitochondria; (as repetitive structures inside membrane of mid piece)
centriole; (between head and midpiece)
(plasma) membrane; (shown as single line covering whole cell)
microtubules; (in 9 plus 2 array)
4 max
(b)

(c)

FSH promotes development of a new follicle;
also leads to the production of estrogen;
estrogen brings about repair and growth of uterine lining;
estrogen causes negative feedback of FSH;
estrogen brings about LH production;
LH stimulates follicle growth;
LH triggers ovulation;
estrogen contributes to the proliferative phase of the uterine cycle /
triggers LH surge;
progesterone contributes to the secretory phase of the uterine cycle/
maintains uterus lining;
lowered level of progesterone (due to degeneration of corpus luteum)
leads to menstruation;
cause: [4 max]
AIDS caused by HIV;
penetrates (T) lymphocytes;
(envelope) (glyco)protein and cell receptors involved;
reverse transcrip
tase enables DNA (reject DNA transformed

to be produced from viral RNA;
into RNA)

number of lymphocytes reduced over years;
results in lower immunity;
other illnesses develop (as result of lower immunity);
AIDS is the observed syndrome when final stages of infection
develop / OWTTE;
transmission: [3 max]
HIV transmitted through blood/sexual contact/body fluids/placenta/
childbirth/breastfeeding;
distribution/transmission uneven around the world;
transmission risk increased depending on society’s traditions/beliefs/
behaviour;
(rare minority of) individuals do not have cell receptors and do not
develop AIDS;
condoms/latex barriers only protection against transmission through
sexual contact;

6 max

social implications: [3 max]
treatment expensive;
discrimination against victims;
moral obligation of wealthy countries to help poorer countries;
economic consequences / loss of wage earners etc
...
(b) oogenesis is process by which female gametes/eggs are produced;
begins during fetal development;
oogonia/large number of cells formed by mitosis;
oogonia/cells enlarge/undergo cell growth/become primary oocytes;
begin first meiotic division but stop in Prophase I;
until puberty;
(at puberty) some follicles develop each month in response to FSH;
(primary oocyte) completes first meiotic division;
forms two cells of different/unequal sizes / unequal distribution
of cytoplasm;
(creating a) polar body;
polar body eventually degenerates;
larger cell/secondary oocyte proceeds to meiosis II;
stops at prophase II;
meiosis II completed if cell is fertilized;
ovum and second polar body formed;

(c)

To award full marks, discussion must contain both pro and con
considerations
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6 max

(Plus up to [2] for quality)
[17]

8
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(a) Award [1] for each structure clearly drawn and correctly labelled
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6 max

(c)

transfer of foods/nutrients/glucose from mother to fetus;
fetal gas exchange/transfer of oxygen from mother to fetus;
transfer of excretory products/CO2 from fetus to mother;
transfer of antibodies/hormones from mother to fetus;
secretion of estrogen/progesterone;
from approximately 12 weeks / when ovary/corpus luteum stops secretion;
disc shaped structure;
connected to the fetus by an umbilical cord;
embryonic tissue invades/grows into the uterine wall;
placental villi increase the surface area (for exchange);
fetal capillaries in placenta/placental villi;
inter-villous spaces/sinuses through which mother’s blood flows;
small distance between fetal and mother’s blood/narrow placental barrier;
Allow reference to embryo instead of fetus throughout
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(a)

(b)

(c)

Award [1] for each structure clearly drawn and correctly labelled
...

right and left ventricles — not connected shown larger than atria;
right and left atrium — not connected, thinner walls than ventricles;
right ventricle has thinner walls than left ventricle / vice versa;
atrio-ventricular valves / tricuspid and bicuspid valves — shown between
atria and ventricles;
aorta and pulmonary artery — shown leaving the appropriate ventricle
with semilunar valves shown;
pulmonary vein and vena cava — shown entering appropriate atrium;
Vessels must join unambiguously to correct chamber
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(a)

Award [1] for each structure clearly drawn and correctly labelled
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(c) process of water balance is called osmoregulation;
water passes into the kidney tubules by ultrafiltration;
water is reabsorbed in the proximal convoluted tubule;
water reabsorbed into blood from the (descending limb) of the
loop of Henle;
process by osmosis;
transport of salts into the medulla of kidney;
changes salt concentration so water is reabsorbed;
ADH released into blood when water is required;
ADH causes concentrated urine / no/low ADH causes dilute urine;
this causes more reabsorption of water from the collecting duct;
excess water is released as urine;

urine concentration depends on the body’s need for water;
drinking a lot gives dilute urine;

9 max

(Plus up to [2] for quality)
[11]

13
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(a)

(b)

Award [1] for each of the following clearly drawn and correctly labelled
...
(a) Award [1] for each structure correctly drawn and labelled

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