Question 1
What is the prime difference between male and female gametes in anisogamous species?
A.
Male gametes contain more stored food than female gametes.
B.
Female gametes are produced by meiosis, but male gametes are produced by mitosis.
C.
The female gamete contributes no genetic material to the zygote.
D.
The male gamete travels to the female gamete and is usually smaller.
Question 2
What condition gives asexual reproduction a relative advantage over sexual reproduction?
A.
Gametes from two parents fuse to restore the diploid chromosome number.
B.
The environment is changing rapidly and new allele combinations are needed.
C.
Offspring require recombination to break up parental combinations of alleles.
D.
One parent is well adapted to a stable environment and produces genetically identical offspring.
Question 3
During a typical menstrual cycle, high oestradiol concentration just before ovulation has what effect?
A.
It inhibits LH secretion and directly triggers menstruation.
B.
It causes the corpus luteum to secrete progesterone before ovulation.
C.
It stimulates LH secretion by positive feedback, producing the LH surge.
D.
It prevents follicle development by destroying the dominant follicle.
Question 4
Why are artificial doses of FSH used during in vitro fertilization treatment after the normal cycle has been suppressed?
A.
To stimulate many follicles to develop so that more eggs can be collected.
B.
To harden the zona pellucida before sperm are added.
C.
To make the embryo implant before transfer to the uterus.
D.
To prevent all follicles from developing before egg collection.
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Question 5
What sequence triggers the onset of puberty in humans?
A.
FSH from the gonads stimulates the pituitary to release oestradiol and testosterone.
B.
Decreased LH release directly stimulates the gonads to stop producing sex hormones.
C.
Increased GnRH release stimulates pituitary FSH and LH release, increasing gonadal steroid sex hormones.
D.
Increased progesterone from the placenta stimulates GnRH release from the ovaries.
Question 6
What is the role of the cortical reaction after the first sperm fuses with a human egg?
A.
It modifies the zona pellucida so additional sperm cannot bind and pass through.
B.
It releases enzymes from the sperm acrosome to digest a path through the zona pellucida.
C.
It stimulates meiosis in the testes to produce more sperm.
D.
It causes the egg nucleus to leave the egg and fuse with the sperm tail.
Question 7
What characterizes the blastocyst stage before implantation?
A.
A hollow structure with an outer cell layer, a fluid-filled space and an inner cell mass.
B.
A layer of endometrium that later develops into the embryo.
C.
A mature follicle that releases an egg from the ovary.
D.
A solid mass of identical cells that implants in the oviduct.
Question 8
In a diploid organism, the chromosome number is maintained across generations during sexual reproduction.
Define a zygote.
[1]
Outline the role of meiosis in the sexual life cycle.
[2]
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Question 9
After a human sperm fuses with the egg cell membrane, what event contributes paternal nuclear DNA to the first embryonic mitosis?
A.
The whole sperm cell remains intact inside the egg until the first cell division is complete.
B.
The sperm nucleus enters, nuclear membranes dissolve and both chromosome sets attach to one spindle.
C.
The sperm mitochondria remain active and replicate with the egg mitochondria.
D.
The sperm tail enters the egg and forms the first mitotic spindle.
Question 10
In a self-incompatible flowering plant, pollen from the same plant lands on its stigma. What response promotes genetic variation?
A.
Pollen germination or pollen tube growth is inhibited when compatibility alleles are shared.
B.
Ovules develop into seeds without fertilization by male gametes.
C.
Seed dispersal is blocked until pollen from another species arrives.
D.
The pollen tube grows faster because the pollen and stigma are genetically similar.
Question 11
What is a key difference between spermatogenesis and oogenesis in humans?
A.
Spermatogenesis uses mitosis only, while oogenesis uses both mitosis and meiosis.
B.
Oogenesis produces four equal functional eggs from each primary oocyte.
C.
Spermatogenesis produces one large sperm with abundant cytoplasm per meiosis.
D.
Spermatogenesis usually produces four sperm, while oogenesis usually produces one egg and polar bodies.
Question 12
What feature of the placenta allows exchange between the mother and foetus while their blood normally remains separate?
A.
The placenta prevents diffusion of small molecules such as oxygen and carbon dioxide.
B.
Foetal tissues exchange materials only with the amniotic fluid and not with maternal blood.
C.
Maternal blood and foetal blood mix directly inside one shared capillary network.
D.
Placental villi provide a large surface area with foetal capillaries separated from maternal blood by a barrier.
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Question 13
A population of small aquatic organisms lives in a pond that remains stable for many years but occasionally dries for a season.
State one difference between asexual reproduction and sexual reproduction.
[1]
Explain why asexual reproduction can be advantageous in a stable environment.
[2]
Suggest why sexual reproduction may be advantageous after the pond environment changes.
[1]
Question 14
The diagram shows part of the human male reproductive system. Structures I and II are indicated by leader lines.
Identify structure I.
[1]
State the function of structure I.
[1]
Outline the role of the glands indicated by structure II in reproduction.
[1]
Question 15
In an IVF treatment cycle, drugs are used before eggs are collected from the ovaries.
State what is meant by in vitro fertilization.
[1]
Explain why normal secretion of reproductive hormones is first suppressed in IVF treatment.
[1]
Outline how artificial hormones increase the chance of obtaining eggs for IVF.
[1]
Question 16
Puberty begins when hormone secretion patterns change during childhood.
State the hormone released in increased pulses by the hypothalamus at the onset of puberty.
[1]
Outline how this change leads to increased production of steroid sex hormones.
[2]
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Question 17
The diagram shows an insect visiting a flower. Arrows indicate the path taken by the insect to reach nectar.
State the function of the anther in the flower shown.
[1]
Using the diagram, explain two features that increase the chance of insect pollination.
[2]
Distinguish pollination from fertilization in this flower.
[1]
Question 18
Early epidemiological studies found lower coronary heart disease incidence among people using hormone replacement therapy, but later randomized controlled trials found a small increase in risk. What conclusion is best supported?
A.
The early correlation did not prove causation because socioeconomic status was a confounding variable.
B.
Hormone replacement therapy prevents coronary heart disease whenever users have high socioeconomic status.
C.
Randomized controlled trials are weaker than epidemiological correlations for testing cause and effect.
D.
The coronary heart disease risk was measured by monoclonal antibodies binding to hCG.
Question 19
The graph shows relative concentrations of four hormones during one menstrual cycle. The curves are labelled A, B, C and D.
Identify the hormone represented by the curve with the sharp mid-cycle surge.
[1]
Explain how oestradiol can cause the surge identified in part (a).
[2]
State the role of progesterone in the uterine cycle after ovulation.
[1]
Question 20
A hermaphroditic insect-pollinated flower is shown. Anthers and stigma are positioned so that a visiting insect brushes against them.
Distinguish pollination from fertilization in flowering plants.
[2]
Explain how the insect and the flower can both benefit from this interaction.
[2]
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Question 21
Spermatogenesis and oogenesis are both forms of gametogenesis in humans.
State two cell division processes involved in both spermatogenesis and oogenesis.
[2]
Compare the products of one primary spermatocyte with the products of one primary oocyte.
[2]
Question 22
Only one sperm normally contributes chromosomes to a human embryo.
Define polyspermy.
[1]
Explain the role of the acrosome reaction in fertilization.
[1]
Explain how the cortical reaction prevents polyspermy.
[2]
Question 23
The diagram shows an early human embryo several days after fertilization as it reaches the uterus.
State one structural feature of a blastocyst.
[1]
Outline how the early embryo forms a blastocyst after fertilization.
[1]
Explain what occurs during implantation.
[2]
Question 24
The diagram shows a pregnancy test strip after urine has moved along it. The control band and test band positions are indicated.
State the hormone detected by pregnancy test strips.
[1]
Outline the source and early role of this hormone in pregnancy.
[2]
Explain the function of the control band on the test strip.
[1]
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Question 25
A population of yeast was grown for many generations either by asexual reproduction or by sexual reproduction. The environment was kept constant at first and then changed by raising the temperature.
State which type of reproduction produced the larger population before the temperature was changed.
[1]
Describe how the relative success of the two lineages changed after the temperature was raised.
[2]
Suggest why sexual reproduction gave an advantage after the environment changed.
[1]
Question 26
The graph shows relative concentrations of four hormones during a typical menstrual cycle, together with changes in thickness of the endometrium.
Day / d | LH / a.u. | FSH / a.u. | Oestradiol / a.u. | Progesterone / a.u. | Endometrium thickness / mm |
|---|---|---|---|---|---|
0 | 2 | 6 | 2 | 1 | 2 |
5 | 2 | 4 | 4 | 1 | 4 |
10 | 3 | 3 | 9 | 1 | 8 |
12 | 4 | 3 | 12 | 1 | 10 |
13 | 5 | 4 | 14 | 1 | 11 |
14 | 15 | 6 | 13 | 1 | 11 |
16 | 4 | 3 | 8 | 4 | 12 |
21 | 2 | 2 | 5 | 9 | 14 |
26 | 1 | 2 | 3 | 10 | 15 |
28 | 1 | 4 | 2 | 2 | 4 |
Identify the event in the ovarian cycle that coincides with the LH surge.
[1]
Explain how oestradiol is involved in producing the LH surge.
[2]
Explain why menstruation begins when progesterone concentration falls near the end of the cycle.
[1]
Question 27
The diagram summarizes hormone treatment during one IVF cycle and the mean number of mature follicles observed at different stages.
State the purpose of suppressing normal pituitary hormone secretion at the start of IVF treatment.
[1]
Describe the effect of artificial FSH treatment shown in the data.
[1]
Explain why progesterone may be given after embryo transfer.
[2]
Question 28
The graph shows changes in hormone secretion during the onset of puberty in a typical male body.
Describe the sequence of hormonal changes shown in the graph.
[2]
Explain how the increase in GnRH can lead to developmental changes associated with puberty.
[2]
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Question 29
The diagram compares gametogenesis in typical male and female human bodies.
Compare the number of functional gametes produced from one primary spermatocyte and one primary oocyte.
[1]
Explain why the egg has much more cytoplasm than a sperm cell.
[2]
State one process shown in both spermatogenesis and oogenesis.
[1]
Question 30
The diagram shows the principle of a urine pregnancy test that detects hCG using monoclonal antibodies.
Interpret the result when both the test band and control band are coloured.
[1]
Explain the purpose of the control band.
[1]
Explain why monoclonal antibodies are suitable for detecting hCG in this test.
[2]
Question 31
Early epidemiological studies found a negative correlation between use of hormone replacement therapy (HRT) and incidence of coronary heart disease (CHD). Later randomized controlled trials found a small increase in CHD risk among HRT users.
State why the early epidemiological evidence alone did not establish that HRT protects against CHD.
[1]
Explain how socioeconomic status could account for the early observation.
[2]
Suggest why randomized controlled trials provide stronger evidence about the effect of HRT on CHD risk.
[1]
Question 32
Researchers investigated fruit production in a hermaphroditic flowering plant. Pollen from different sources was placed on stigmas, and pollen tube growth and fruit set were recorded.
Pollen source | Mean pollen tube length after 24 h / mm | Fruit set (out of 20) |
|---|---|---|
Self pollen | 0.0 | 0 |
Pollen from another plant | 12.0 | 18 |
Identify the treatment that provides evidence for successful cross-pollination.
[1]
Using the data, explain why this plant can be described as self-incompatible.
[2]
Explain how self-incompatibility can increase genetic variation in offspring.
[1]
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Question 33
Students investigated dispersal of winged seeds by dropping seeds from different heights in still air and measuring the horizontal distance travelled from the release point.
Identify the independent variable and the dependent variable in this investigation.
[2]
Describe the relationship shown by the data.
[1]
Suggest two variables that should be controlled to make the investigation valid.
[2]
Question 34
Eggs were exposed to sperm under different experimental conditions. The percentage of eggs showing polyspermy and the extent of zona pellucida hardening were recorded.
Describe the relationship between zona pellucida hardening and polyspermy shown in the data.
[1]
Explain the role of the acrosome reaction before sperm membrane fusion with the egg.
[2]
Explain how the cortical reaction prevents polyspermy.
[2]
Question 35
The diagram and data summarize exchange of substances across placental villi during pregnancy.
Measure | Value |
|---|---|
Villi per 1 mm² placental tissue / count | 150 |
Total villus surface area in 1 placental tissue / | 48 |
Placental barrier thickness / m | 1.0 |
Maternal concentration / a.u. | 100 |
Foetal concentration / a.u. | 30 |
Maternal concentration / a.u. | 35 |
Foetal concentration / a.u. | 70 |
Maternal glucose concentration / a.u. | 6 |
Foetal glucose concentration / a.u. | 4 |
Maternal urea concentration / a.u. | 1 |
Foetal urea concentration / a.u. | 3 |
State one structural feature of placental villi that increases exchange.
[1]
Using the diagram, identify one substance moving from the mother to the foetus and one substance moving from the foetus to the mother.
[2]
Explain why maternal and foetal blood normally remain separate in the placenta.
[2]
Question 36
A freshwater invertebrate can reproduce asexually when water temperature and food availability remain stable. Under crowding or seasonal change, it produces haploid gametes and reproduces sexually.
Compare asexual and sexual reproduction in this invertebrate.
[3]
I.
Explain why meiosis and fertilization are both needed in the sexual life cycle.
[2]
II.
Discuss why the relative advantage of sexual reproduction changes when the environment becomes unpredictable.
[2]
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Question 37
The diagram shows the human male-typical reproductive system.
I.
Identify the structure that stores and matures sperm before ejaculation.
[1]
II.
Explain the roles of two accessory glands in producing semen.
[2]
Draw a labelled diagram of the human female-typical reproductive system and annotate two structures with their functions.
[3]
Explain why the position of the testes in the scrotum is important for reproduction.
[2]
Question 38
The diagram shows events following contact between a human sperm and an egg.
I.
State the prime difference between male and female gametes in anisogamy.
[1]
II.
Explain how this difference affects the numbers and food reserves of gametes produced.
[2]
Explain the events in human fertilization from membrane fusion to formation of two diploid nuclei.
[4]
Question 39
The graph shows changes in hypothalamic, pituitary and gonadal hormone secretion during the onset of puberty.
I.
State the hormone from the hypothalamus that triggers the increase in pituitary gonadotropins.
[1]
II.
Explain the sequence of endocrine events that leads from this hormone to changes associated with puberty.
[2]
Compare the roles of LH and FSH in typical male and typical female bodies during puberty.
[2]
Suggest why very low GnRH secretion in early childhood prevents reproductive maturity.
[2]
Question 40
Early observational studies and later randomized controlled trials investigated hormone replacement therapy (HRT) and risk of coronary heart disease (CHD). Socioeconomic status was also recorded.
Study design | Group | CHD incidence / cases per 1000 women | Mean socioeconomic score / a.u. |
|---|---|---|---|
Observational study | HRT users | 18 | 78 |
Observational study | Non-users | 31 | 57 |
Randomized controlled trial | HRT | 27 | 66 |
Randomized controlled trial | Placebo | 25 | 65 |
Compare the conclusion suggested by the observational studies with the conclusion from the randomized controlled trials.
[2]
Explain how socioeconomic status could act as a confounding variable in the observational studies.
[2]
Evaluate why the randomized controlled trials provide stronger evidence for the effect of HRT on CHD risk.
[1]
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Question 41
The graph shows changes in the concentrations of four hormones during a 28-day menstrual cycle.
I.
Deduce the approximate time of ovulation from the graph.
[1]
II.
Explain the role of LH at this time.
[2]
Explain how oestradiol can produce both negative and positive feedback during the cycle.
[3]
Suggest why menstruation occurs if no embryo implants.
[2]
Question 42
A plant species has hermaphroditic flowers. Each flower produces pollen and contains ovules. Botanists observe that fruit set is higher when insects visit flowers on different plants.
I.
Explain why reproduction in a hermaphroditic flower is still sexual reproduction.
[2]
II.
Distinguish pollination from fertilization in flowering plants.
[1]
Explain how two features of insect-pollinated flowers increase the probability of cross-pollination.
[2]
Evaluate the importance of mechanisms that promote cross-pollination in maintaining vigour in this species.
[3]
Question 43
A student investigates dispersal of winged seeds by releasing seeds from different heights in still air and measuring the horizontal distance travelled.
I.
Distinguish seed dispersal from pollination.
[1]
II.
Identify the independent and dependent variables in the investigation.
[2]
Evaluate two aspects of experimental design that would improve confidence in the conclusion.
[2]
Explain how germination uses structures and reserves in the seed after dispersal to a suitable site.
[2]
Question 44
The diagrams summarize gametogenesis in typical male and typical female human bodies.
I.
Identify two processes that occur in both spermatogenesis and oogenesis.
[2]
II.
State the ploidy of mature sperm and mature eggs.
[1]
Compare and contrast the outcomes of spermatogenesis and oogenesis.
[3]
Explain how differences in cytoplasm allocation relate to early development and reproductive strategy.
[2]
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Question 45
During an IVF procedure, many sperm are placed near each egg. Only one sperm normally contributes a nucleus to the embryo.
I.
Define polyspermy.
[1]
II.
Explain why polyspermy would usually prevent viable embryo development.
[2]
Explain the roles of the acrosome reaction and cortical reaction in allowing fertilization by one sperm only.
[4]
Question 46
A fertility clinic monitors early embryo development after fertilization and before embryo transfer to the uterus.
I.
Describe the first mitotic division after fertilization.
[2]
II.
Explain why early embryonic cells become smaller during the first divisions.
[1]
Explain how the structure of a blastocyst is related to implantation.
[3]
Suggest why the endometrium must be maintained before implantation can succeed.
[2]
Question 47
The diagram shows part of a human placenta with maternal blood spaces and foetal capillaries inside villi.
I.
Identify two substances that normally move from the mother to the foetus through the placenta.
[2]
II.
State one waste product that moves from the foetus to the mother.
[1]
Explain how placental villi and the placental barrier allow exchange without mixing maternal and foetal blood.
[3]
Discuss how hormonal control maintains pregnancy and later allows childbirth.
[2]
Question 48
Early observational studies reported that people using hormone replacement therapy had a lower incidence of coronary heart disease. Later randomized controlled trials found a small increase in coronary heart disease risk among people assigned to hormone replacement therapy.
Study | Group | SES index | CHD cases / 1000 |
|---|---|---|---|
Observational | HRT users | 78 | 18 |
Observational | Non-users | 60 | 24 |
RCT | HRT | 69 | 20 |
RCT | Placebo | 69 | 19 |
I.
Distinguish correlation from causation using the HRT observations.
[2]
II.
Identify the confounding variable proposed to explain the early epidemiological result.
[1]
Explain why randomized controlled trials provide stronger evidence about the effect of HRT on CHD risk.
[2]
Evaluate the conclusion that HRT protects against coronary heart disease.
[2]
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