This video deals with how the immune system fights diseases.

This TED Ed video (3:58min) describes the function of cellular organelles and how they work together to allow a cell to fight a virus.

Aimed at slightly older students, this material is within the range of advanced Year 8 students (it mentions mRNA and enzymes very briefly), or it could be used as a summary of organelle functions.

Australian Curriculum v9 Codes: AC9S8U01 (Year 8), AC9S8U02 (Year 8)