D3.1 Reproduction

Question 1

D3.1.1—Differences between sexual and asexual reproduction

Answer 1

Include these relative advantages: asexual reproduction to produce genetically identical offspring by
individuals that are adapted to an existing environment, sexual reproduction to produce offspring with
new gene combinations and thus variation needed for adaptation to a changed environment.

Question 2

D3.1.2—Role of meiosis and fusion of gametes in the sexual life cycle

Answer 2

Students should appreciate that meiosis breaks up parental combinations of alleles, and fusion of gametes
produces new combinations. Fusion of gametes is also known as fertilization.

Question 3

D3.1.3—Differences between male and female sexes in sexual reproduction

Answer 3

Include the prime difference that the male gamete travels to the female gamete, so it is smaller, with less
food reserves than the egg. From this follow differences in the numbers of gametes and the reproductive
strategies of males and females.

Question 4

D3.1.4—Anatomy of the human male and female reproductive systems

Answer 4

Students should be able to draw diagrams of the male-typical and female-typical systems and annotate
them with names of structures and functions.

Question 5

D3.1.5—Changes during the ovarian and uterine cycles and their hormonal regulation

Answer 5

Include the roles of oestradiol, progesterone, luteinizing hormone (LH), follicle-stimulating hormone (FSH)
and both positive and negative feedback. The ovarian and uterine cycles together constitute the
menstrual cycle.

Question 6

D3.1.6—Fertilization in humans

Answer 6

Include the fusion of a sperm’s cell membrane with an egg cell membrane, entry to the egg of the sperm
nucleus but destruction of the tail and mitochondria. Also include dissolution of nuclear membranes of
sperm and egg nuclei and participation of all the condensed chromosomes in a joint mitosis to produce
two diploid nuclei

Question 7

D3.1.7—Use of hormones in in vitro fertilization (IVF) treatment

Answer 7

The normal secretion of hormones is suspended, and artificial doses of hormones induce superovulation

Question 8

D3.1.8—Sexual reproduction in flowering plants

Answer 8

Include production of gametes inside ovules and pollen grains, pollination, pollen development and
fertilization to produce an embryo. Students should understand that reproduction in flowering plants is
sexual, even if a plant species is hermaphroditic

Question 9

D3.1.9—Features of an insect-pollinated flower

Answer 9

Students should draw diagrams annotated with names of structures and their functions.

Question 10

D3.1.10—Methods of promoting cross-pollination

Answer 10

Include different maturation times for pollen and stigma, separate male and female flowers or male and
female plants. Also include the role of animals or wind in transferring pollen between plants.

Question 11

D3.1.11—Self-incompatibility mechanisms to increase genetic variation within a species

Answer 11

Students should understand that self-pollination leads to inbreeding, which decreases genetic diversity
and vigour. They should also understand that genetic mechanisms in many plant species ensure male and
female gametes fusing during fertilization are from different plants.

Question 12

D3.1.12—Dispersal and germination of seeds

Answer 12

Distinguish seed dispersal from pollination. Include the growth and development of the embryo and the
mobilization of food reserves.

Question 13

D3.1.13—Control of the developmental changes of puberty by gonadotropin-releasing hormone and
steroid sex hormones

Answer 13

Limit to the increased release of gonadotropin-releasing hormone (GnRH) by the hypothalamus in
childhood triggering the onset of increased luteinizing hormone (LH) and follicle-stimulating hormone
(FSH) release. Ultimately the increased sex hormone production leads to the changes associated with
puberty

Question 14

D3.1.14—Spermatogenesis and oogenesis in humans

Answer 14

Include mitosis, cell growth, two divisions of meiosis and differentiation. Students should understand how
gametogenesis, in typical male and female bodies, results in different numbers of sperm and eggs, and
different amounts of cytoplasm.

Question 15

D3.1.15—Mechanisms to prevent polyspermy

Answer 15

The acrosome reaction allows a sperm to penetrate the zona pellucida and the cortical reaction prevents
other sperm from passing through.

Question 16

D3.1.16—Development of a blastocyst and implantation in the endometrium

Answer 16

Students are not required to know the names of other stages in embryo development

Question 17

D3.1.17—Pregnancy testing by detection of human chorionic gonadotropin secretion

Answer 17

Include the production of human chorionic gonadotropin (hCG) in the embryo or developing placenta and
the use of monoclonal antibodies that bind to hCG.

Question 18

D3.1.18—Role of the placenta in foetal development inside the uterus

Answer 18

Students are not required to know details of placental structure apart from the large surface area of the
placental villi. Students should understand which exchange processes occur in the placenta and that it
allows the foetus to be retained in the uterus to a later stage of development than in mammals that do not
develop a placenta.

Question 19

D3.1.19—Hormonal control of pregnancy and childbirth

Answer 19

Emphasize that the continuity of pregnancy is maintained by progesterone secretion initially from the corpus luteum and then from the placenta, whereas the changes during childbirth are triggered by a
decrease in progesterone levels, allowing increases in oxytocin secretion due to positive feedback.

Question 20

D3.1.20—Hormone replacement therapy and the risk of coronary heart disease

Answer 20

NOS: In early epidemiological studies, it was argued that women undergoing hormone replacement
therapy (HRT) had reduced incidence of coronary heart disease (CHD) and this was deemed to be a causeand-effect relationship. Later randomized controlled trials showed that use of HRT led to a small increase
in the risk of CHD. The correlation between HRT and decreased incidence of CHD is not actually a causeand-effect relationship. HRT patients have a higher socioeconomic status, and this status has a causal
relationship with lower risk of CHD.