Difference Between Tonoplast and Plasma Membrane

The key difference between tonoplast and plasma membrane is that tonoplast is the membrane that encloses the central vacuole of a plant cell while the plasma membrane is the membrane that encloses the cytoplasm of a cell.

A cell is the basic structural and functional unit of living organisms. Some organisms are unicellular, while many are multicellular. A cell has different components. The cell membrane, cytoplasm, cellular organelles, vacuoles and tonoplast are several such components. The cell membrane is the boundary of the cell that separates the cell plasma from its exterior environment. However, plant cells have a cell wall exterior to the cell membrane. Tonoplast is the membrane that encloses the vacuole of the cell, especially in a plant cell. In other words, it is the vacuolar membrane of a plant cell. Both tonoplast and plasma membrane allow water and solutes to move across them.

CONTENTS

1. Overview and Key Difference
2. What is Tonoplast 
3. What is Plasma Membrane
4. Similarities Between Tonoplast and Plasma Membrane
5. Side by Side Comparison – Tonoplast vs Plasma Membrane in Tabular Form
6. Summary

What is Tonoplast?

Plant cells have a big vacuole in the center of the cell, and it is responsible for the turgor pressure. Therefore, vacuole maintains the turgor pressure in plants in order to maintain a rigid plant structure. Tonoplast is the special type of membrane that surrounds the central vacuole of a plant cell. It is also known as the vacuolar membrane.

Since only plant cells have a tonoplast, tonoplast is a unique structure to plants. It is a semi-permeable membrane which allows selected types of ions and substances to pass through it in and out. By acting as a barrier between the cytoplasm and the contents of the vacuole, it maintains a proper balance of nutrients and ions inside and outside of the vacuole. There are proton pumps such as proton-ATPase and proton-pyrophosphatase located in the tonoplast. These proton pumps help to regulate turgor pressure.

What is Plasma Membrane?

Plasma membrane or cell membrane is the biological membrane that encloses the cytoplasm of a cell. It separates the interior of the cell from the outside environment. By acting as a barrier between the interior and exterior of the cell, it protects the cell interior. In addition to protection, the plasma membrane also facilitates the signal transduction and cellular transport of ions and other substances. The plasma membrane is a semi-permeable membrane which allows selected substances to enter and exit the cell. The movement of molecules across the membrane can occur passively or actively.

Structurally, the plasma membrane is composed of a lipid bilayer. It also has proteins on the surface, spanned across the membrane and attached from the inner surface. In addition to phospholipids and proteins, plasma membrane has cholesterol and carbohydrate molecules. Fluid mosaic model is the model that describes the structure of the plasma membrane containing a mosaic of components. Cholesterol molecules contribute to the fluidity of the membrane.

What are the Similarities Between Tonoplast and Plasma Membrane?

• Tonoplast and plasma membrane are membranes that enclose vacuole and cytoplasm, respectively.
• Both are semi-permeable membranes.
• Tonoplast and plasma membrane are composed of a lipid bilayer.

What is the Difference Between Tonoplast and Plasma Membrane?

Tonoplast is the semi-permeable membrane that encloses the central vacuole in a plant cell while the plasma membrane is a semi-permeable phospholipid bilayer that encloses the cytoplasm of all cells. So, this is the key difference between tonoplast and plasma membrane. Thus, the tonoplast separates the content of vacuole from the cytoplasm while plasma membrane separates the external environment from the cytoplasm.

Moreover, tonoplast is unique to plant cells, but the plasma membrane is seen in all types of cells. Functionally, tonoplast maintains turgor pressure, and it regulates the movement of ion in and out the vacuole. Meanwhile, cell membrane controls the movement of substances in and out of cells, participates in cell adhesion, ion conductivity and cell signalling and serves as the attachment surface for several extracellular structures. So, this is the functional difference between tonoplast and plasma membrane.

Below infographic summarizes the difference between tonoplast and plasma membrane.

Summary – Tonoplast vs Plasma Membrane

Tonoplast is the membrane that surrounds the central vacuole of a plant cell. But, the plasma membrane is the membrane that surrounds the cytoplasm of all cells. This is the key difference between tonoplast and plasma membrane. However, both tonoplast and plasma membrane are phospholipid bilayers. They act as semi-permeable membranes and allow the movement of selected ions and molecules to enter inside and outside from them.

Reference:

1. “Components And Structure | Boundless Biology”. Courses.Lumenlearning.Com, 2020, Available here.
2. “Tonoplast: Definition & Function”. Study.Com, 2020, Available here.

Image Courtesy:

1. “Plant cell structure svg vacuole” By Mariana Ruiz LadyofHats, labels by Dake modified by smartse – (Public Domain) via Commons Wikimedia
2. “Cell membrane detailed diagram 4” By derivative work: Dhatfield (talk)Cell_membrane_detailed_diagram_3.svg: *derivative work: Dhatfield (talk)Cell_membrane_detailed_diagram.svg: LadyofHats Mariana Ruiz – Cell_membrane_detailed_diagram_3.svg, (CC BY-SA 3.0) via Commons Wikimedia