All of the following protect the skin and mucous membranes from infection except:

• A. Cilia in the respiratory tract
• B. Lysozyme in tears and saliva
• C. Keratinized epithelial cells
• D. High concentration of glucose in sweat

Answer: (D)

Verified step by step guidance

1. Step 1: Understand the role of physical and chemical barriers in protecting the skin and mucous membranes from infection. These barriers prevent pathogens from entering the body.
2. Step 2: Identify the protective mechanisms listed: cilia in the respiratory tract help move mucus and trapped pathogens out; lysozyme in tears and saliva breaks down bacterial cell walls; keratinized epithelial cells form a tough, impermeable layer on the skin.
3. Step 3: Analyze the option 'High concentration of glucose in sweat' and consider whether glucose has any known antimicrobial properties or contributes to barrier defense.
4. Step 4: Recognize that glucose in sweat does not serve as a protective factor against infection; in fact, high sugar concentrations can sometimes promote microbial growth rather than inhibit it.
5. Step 5: Conclude that the correct answer is the option that does not protect against infection, which is the high concentration of glucose in sweat.