Question

decide whether each function is carried out by lipids, proteins, or carbohydrates in the cell membrane.
allow the cell to be recognized by other cells
give the membrane its flexibility
pump large molecules across the membrane

Explanation:

• Carbohydrates: In the cell membrane, carbohydrates are often attached to lipids (glycolipids) or proteins (glycoproteins). These carbohydrate - containing molecules are crucial for cell - cell recognition. For example, in the immune system, cells recognize "self" and "non - self" based on these carbohydrate - protein or carbohydrate - lipid complexes.
• Lipids: The lipid bilayer (mainly phospholipids) provides the basic structure of the cell membrane. Cholesterol (a type of lipid) is also present in the membrane. Cholesterol helps to maintain the fluidity (flexibility) of the membrane. At moderate temperatures, it restricts the movement of phospholipids, preventing the membrane from becoming too fluid. At low temperatures, it prevents the membrane from becoming too rigid by disrupting the regular packing of phospholipids.
• Proteins: There are different types of membrane proteins. Integral proteins can span the membrane and act as pumps. For example, the sodium - potassium pump (an integral membrane protein) actively transports sodium and potassium ions across the cell membrane. This is a form of active transport where large molecules (in the context of ion transport, ions are considered as molecules in terms of membrane transport) are moved against their concentration gradient.

Answer:

Function	Lipids	Proteins	Carbohydrates
Give the membrane its flexibility	✔
Pump large molecules across the membrane		✔