"To meet grading criterion P3 learners must be able to identify all of the named muscles in the content and describe the function of the muscular system. Learners must also be able to describe the sliding filament theory in order to demonstrate an understanding of muscle movement"

BTEC ND in Sport Specification (2007).

Describe = paint a picture with words.

Major muscles: location; biceps; triceps; deltoids; pectorals; rectus abdominis;
quadriceps (rectus femoris, vastus lateralis, vastus medialis, vastus intermedius);
hamstrings (semimembranosus, semitendinosus, biceps femoris); gastrocnemius;
soleus; tibialis anterior; erector spinae; teres major; trapezius; latissimus dorsi;
obliques; gluteus maximus.

Not sure how your tutor is grading you so thats as much info as I can give you.