Question

49.
part a
which of the following describes the plasma membrane?
○ a double layer of protein enclosing the plasma
○ a single - layered membrane that surrounds the nucleus of the cell
○ a membrane composed of tiny shelves or cristae
○ a phospholipid bilayer surrounding the cell

50.
part a
which of the following would not be a constituent of a plasma membrane?
○ glycoproteins
○ messenger rna
○ phospholipids
○ glycolipids

51.
part a
which of the following is a component of the plasma membrane that creates a physical barrier between the inside and the outside of
the cell?
○ proteins
○ cholesterol
○ water
○ phospholipids

Explanation:

Question 49

To determine the correct description of the plasma membrane, we analyze each option:

• Option 1: The plasma membrane is not a double layer of protein enclosing the plasma. The main component is phospholipids, not just protein.
• Option 2: The nuclear membrane surrounds the nucleus, not the plasma membrane. The plasma membrane surrounds the cell.
• Option 3: Cristae are structures in mitochondria, not related to the plasma membrane's structure.
• Option 4: The plasma membrane is a phospholipid bilayer that surrounds the cell, which is the correct description.

To find what is NOT a constituent of the plasma membrane, we examine each option:

• Option 1: Glycoproteins are present in the plasma membrane (involved in cell recognition, etc.).
• Option 2: Messenger RNA (mRNA) is involved in protein synthesis in the cytoplasm/nucleus and is not a constituent of the plasma membrane.
• Option 3: Phospholipids are the main structural component of the plasma membrane (form the bilayer).
• Option 4: Glycolipids are present in the plasma membrane (involved in cell recognition, etc.).

To identify the component that creates a physical barrier between the inside and outside of the cell in the plasma membrane:

• Option 1: Proteins in the plasma membrane are involved in transport, signaling, etc., but do not form the main physical barrier.
• Option 2: Cholesterol in the plasma membrane helps with fluidity, not the main physical barrier.
• Option 3: Water is not a component that creates the physical barrier of the plasma membrane.
• Option 4: Phospholipids form a bilayer that acts as a physical barrier, preventing free movement of many substances between the inside and outside of the cell.

Answer:

a phospholipid bilayer surrounding the cell

Question 50