Answer
1. Barriers: Physical and chemical barriers are the first lines of defense. A physical barrier is the skin while an example of a chemical barrier is the mucus.
2. Immune system: This is the second line of defense. It fights against the invading pathogens.
3. Antibodies: These are the third line of defense. They recognize the invading pathogens from previous attack and fight against them.
Work Step by Step
Three lines of defense are as follows:
1. Barriers: Physical and chemical barriers are the first lines of defense. A physical barrier is the skin while an example of a chemical barrier is the mucus.
2. Immune system: This is the second line of defense. It fights against the invading pathogens.
3. Antibodies: These are the third line of defense. They recognize the invading pathogens from previous attack and fight against them.
