Q20 - Osmolality and Sperm Motility Initiation

Theoretical 1 Real exam question - full text reproduced under IBO's CC BY-NC-SA 4.0 license

Comparative Osmoregulation & Excretion Reproductive Physiology

Spermatozoa motility is essential for the fertilization of an oocyte. In most animals, including fish, spermatozoa are immotile in the male reproductive organ (testis or sperm duct). Spermatozoa motility is triggered after being ejaculated into the female reproductive tract (in animals with internal fertilization) or after it is released into the aquatic environment (in animals with external fertilization). Ionic composition and osmolality of freshwater, seawater, and seminal plasma of pike (Esox lucius), sturgeon (Acipenser ruthenus), and cod (Gadus morhua) are shown in the table. Pike and sturgeon spawn in freshwater, and cod spawns in seawater.

Figure 1. Figure 1.

Using the information and data, determine which of the statements are true or which are false.

A. Sperm motility in pike and cod become triggered in a hypo-osmotic and hyper-osmotic environment, respectively.

B. Under physiological condition, osmolality is the main factor that inhibits sperm motility initiation in sturgeon.

C. Sperm motility in sturgeon become triggered after discharged into a hypo-osmotic environment with lower K+ ions.

D. Environmental osmolality is a key signal to trigger sperm motility initiation after release from reproductive system into aquatic environment in marine fish

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Question reproduced from IBO 2018, Theoretical Paper 1, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)