Which one of the following statement about human sperm is correct?

Question

Accepted Answer

The correct option is 3: The sperm lysins in the acrosome dissolve the egg envelope facilitating fertilization.

The acrosome is a highly specialised organelle that is essential for successful human fertilisation, classifying it as a modified lysosome derived from the Golgi apparatus. Its primary role is to act as a chemical warhead, storing a potent cocktail of hydrolytic enzymes often referred to as **sperm lysins**, including hyaluronidase and acrosin. When the capacitated sperm binds to the egg’s outermost layer, the zona pellucida, it triggers the **acrosomal reaction**. This reaction involves the fusion of the acrosomal membrane with the sperm's plasma membrane, leading to the exocytosis (release) of these stored enzymes. These enzymes then locally digest and break down the complex glycoprotein matrix of the egg’s protective envelopes (the corona radiata and the zona pellucida). This enzymatic action creates a clear path, or channel, for the sperm to penetrate the remaining layers and fuse with the egg's plasma membrane, which is the final step necessary for the pronuclei to combine and for fertilisation to occur.

The incorrect option is 1: Acrosome serves no particular function.
This is incorrect because the acrosome performs the singularly most important preparatory action for fertilisation: enzymatic penetration of the egg's protective layers. Without the release of acrosomal enzymes, the sperm would be physically unable to penetrate the thick, extracellular matrix of the zona pellucida and fertilise the ovum. Thus, the acrosome serves a highly specialised and crucial function in reproductive biology.

The incorrect option is 2: Acrosome has a conical pointed structure used for piercing and penetrating the egg resulting in fertilization.
While the overall sperm head is shaped to aid movement, the description of the acrosome as a pointed structure used for mechanical *piercing* is inaccurate. The acrosome's penetration mechanism is **enzymatic (chemical)**, not physical or mechanical. The acrosomal enzymes dissolve the egg coverings, allowing the sperm to pass through a digested path. The stiff, pointed structure mentioned is likely a reference to the overall shape of the sperm head, but it is the digestive action of the enzymes, not a physical stab, that facilitates entry.

The incorrect option is 4: Acrosome serve as a sensory structure leading the sperm towards the ovum.
This is incorrect because the acrosome is an enzyme storage and release organelle, not a sensory structure. The guidance of sperm towards the egg, known as **chemotaxis**, involves the detection of specific chemical signals released by the egg or its surrounding follicular cells, which is mediated by receptors on the sperm's membrane. The acrosome is activated and releases its contents *after* the sperm has already successfully reached and bound to the egg's surface, playing no role in the guidance or navigation process.