All of the following defend the eyes EXCEPT:
a. tears.
b. lysozyme.
c. several corneal epithelial layers.
d. a hard external layer encasing the entire eyeball, including the cornea.
e. lactoferrin.

Verified step by step guidance

1. Identify the function of each option in the context of eye defense.
2. Option a: Tears - Understand that tears help to wash away debris and contain antimicrobial substances.
3. Option b: Lysozyme - Recognize that lysozyme is an enzyme found in tears that breaks down bacterial cell walls.
4. Option c: Several corneal epithelial layers - Note that these layers provide a physical barrier to pathogens.
5. Option d: A hard external layer encasing the entire eyeball, including the cornea - Consider whether such a structure exists and its role in eye defense.

Key Concepts

Tears

Tears are a crucial component of the eye's defense system. They provide lubrication, wash away debris, and contain antimicrobial substances that help prevent infections. The presence of tears is essential for maintaining eye health and protecting against environmental threats.

Lysozyme

Lysozyme is an enzyme found in various bodily fluids, including tears, that plays a significant role in the immune defense of the eyes. It works by breaking down the cell walls of certain bacteria, thereby inhibiting their growth and helping to prevent infections.

Corneal Structure

The cornea is the transparent front part of the eye, composed of several layers of epithelial cells that provide a barrier against pathogens. Its structure is vital for protecting the inner components of the eye while also allowing light to enter, making it essential for vision and defense.