Question

The incorrect statement about the plasma membrane is
A. It serves as a selectively permeable barrier to the external environment.
B. It serves as a mediator between the internal and external environments
C. In eukaryotes, it contains the cytochrome chain of oxidative phosphorylation
D. It contains phospholipids as a structural compound
E. It contains proteins that in some cases span the membrane.

Answer 1

Hint: The plasma membrane is also known as the cell membrane. It is the membrane surrounding the cytoplasm in all living organisms. The membrane is made up of phospholipids and is selectively permeable.

Complete step by step answer: Cytochrome phosphorylation is the pathway that provides energy to eukaryotic organisms by synthesizing energy-rich molecules, i.e. ATP, but the cell plasma membranes are devoid of this process as it occurs in the membranes of organelles such as mitochondria in all eukaryotes and chloroplasts in autotrophs. The cell membranes of these organelles are modified for the purpose of oxidative phosphorylation.
Considering other options:
i. The plasma membrane acts as a barrier which is selectively permeable to certain substances only. Thereby, the flow of substances through it is highly regulated.
ii. The plasma membrane serves as a mediator between the environments both inside and outside the cell as it transports materials into and outside the cell.
iii. The cell membrane is made up of a phospholipid bilayer, made up of lipids with phosphorus moiety sticking out of the membrane. This membrane provides integrity to the cells.
iv. The membrane also consists of membrane proteins embedded on it. These proteins also help in the transport of substances to and from the cell and account for cell permeability.
Hence, the correct answer is option C.

Note: Phosphorylation is the process by which a cell acquires the energy for its further biologic processes. It involves the addition of a phosphate moiety to an organic molecule. The process of oxidative phosphorylation takes place in the inner mitochondrial membrane of the mitochondria.