Notes on all hormones and reproductive processes in the syllabus for 6.6 and 11.4 in IB Biology - both SL and HL content, written as bullet point processes to easily follow for markschemes.
Outline the levels of each of the hormones that control the menstrual cycle immediately before
ovulation. [3 marks]
− FSH is released to trigger the development of an immature follicle
− the follicle produces oestrogen, uterine walls thicken as a result
− peaking oestrogen levels at day 12 increase levels of LH
− ovulation occurs at day 14, at the peak of LH levels
Outline the process of in-vitro fertilisation (IVF). [6 marks]
− IVF can only be done on selected candidates of a specific weight, age ranges, and other
criteria (eg. infertility)
− natural menstrual cycle is stopped by regulating LH and FSH
− superovulation is the process of overstimulating the reproductive system, so that multiple
eggs mature at the same time
− eggs are harvested
− sperm are then mixed with the eggs, and this can be done using ICSI, where a single sperm is
directly injected into the egg
− if fertilisation is successful, embryos will develop
− embryos can then be implanted into the uterus
Discuss the ethical issues surrounding IVF. [6]
− IVF can be beneficial because this allows infertile couples to have children, in some
countries, it could also benefit others, such as same-sex couples
− embryos can be screened for genetic disorders before being implanted
− successful embryos that are not implanted can be used for stem cell research, beneficial for
scientific research, as embryos are otherwise difficult to access
− limited access to IVF raises questions regarding medical justice (access to all, based on
clinical need, not ability to pay)
− success rate is quite low
− by choosing which embryos are implanted, we are essentially given the power to choose
who lives and who doesn’t
Fertilisation [8 marks]
− Sperm is attracted to egg by chemotaxis produced by the secondary oocyte
− The sperm passes through the follicle cells and binds to the zona pellucida
− The acrosome reaction occurs when protease is released from the acrosome and digests a
pathway through the zona pellucida
− Cortical reaction is the membrane fusion of the sperm and oocyte, cortical granules release
their contents
− The acrosome and cortical reactions prevent polyspermy
− The enzymes harden the zona pellucida
− Sperm nucleus enters cell, completing the second meiotic division
− Sperm and ovum fuse to form zygote
Pregnancy [8 marks]
− after fertilisation the zygote undergoes repeated mitosis
− after 4-5 days a blastocyst is formed
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