Answer #1:
Gram-positive bacteria have a thick peptidoglycan layer and no outer lipid membrane whilst Gram-negative bacteria have a thin peptidoglycan layer and have an outer lipid membrane.
Answer #2:
Gram-positive bacteria have lots of peptidoglycan in their cell wall which allows them to retain crystal violet dye, so they stain purple-blue. Gram-negative bacteria have less peptidoglycan in their cell wall so cannot retain crystal violet dye, so they stain red-pink.
