Glycoproteins and glycolipids display carbohydrate chains at the cell surface, enabling recognition, adhesion, signalling, and immune compatibility between neighbouring cells.
Glycoproteins are membrane proteins with exposed carbohydrate chains whose shapes act as cell-surface identity and recognition markers.
A receptor, antibody or neighbouring cell can bind a matching carbohydrate pattern. This supports self/non-self recognition, cell adhesion and signalling; the membrane anchor presents the marker in the correct location.
ABO blood-group antigens are cell-surface carbohydrate patterns carried on glycoproteins and glycolipids. Type A and B cells display different terminal sugars; type O lacks those A/B additions, affecting antibody compatibility.
If red cells bearing an unfamiliar A or B antigen meet matching antibodies in incompatible plasma, antibody cross-linking can cause agglutination.
Recognition is specific to molecular shape and a compatible binding partner. Do not describe ABO identity as a free sugar floating outside the cell or as the protein sequence alone.
B1.1 becomes easy when every answer follows structure -> property -> function. Carbon skeletons and functional groups create molecular diversity. Condensation builds larger molecules and hydrolysis breaks them. Alpha-glucose stores energy as starch and glycogen; beta-glucose forms strong cellulose. Surface carbohydrates enable recognition. Lipids are hydrophobic, triglycerides store energy, phospholipids self-assemble into bilayers, and steroids cross membranes because they are mostly non-polar.