BiologyChapter 1: Cells and Sub-Cellular Organelles
1.5 Cell Wall and Plasma Membrane
Plasma Membrane:
Explanation level
Introduction
The cell is the basic unit of life. Every cell has an outer boundary that separates its internal environment from the external environment. This boundary is called the plasma membrane. Many cells also have an additional outer covering called the cell wall. Together, these structures control what enters and leaves the cell and provide protection and support.
Definition
Plasma Membrane: The plasma membrane is the outer living boundary of the cell. It is also called the cell membrane. It controls the passage of materials into and out of the cell.
Cell Wall: The cell wall is an extracellular component formed exterior to the membrane. It is present in plant cells, prokaryotes, fungi, and some protists, but animal cells do not have a cell wall.
Plasma membrane = the living boundary of every cell.
Cell wall = a non-living, rigid outer covering found in some cells (not animal cells).
Core Concept
Cell Wall
The cell wall is present in plant cells, prokaryotes, fungi, and some protists.
Animal cells do not have a cell wall. This is probably due to their locomotor mode of life.
The chemical composition of the cell wall differs:
Plant cell wall = made of cellulose
Prokaryotic cell wall = made of peptidoglycan
Fungal cell wall = made of chitin
The cell wall is an extracellular structure secreted by the cell.
It is porous and allows free passage of water and dissolved materials.
The plant cell wall consists of three main layers: primary cell wall, middle lamella, and secondary cell wall.
Plasma Membrane
The plasma membrane is found in all living prokaryotic and eukaryotic cells.
It is the boundary of the protoplasm and most organelles.
It controls the passage of materials into and out of the cell.
It is about 7 nm thick.
It is described by the Fluid Mosaic Model.
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