Cell membrane of plant cell: definition and structure

Cell membrane of plant cell

Introduction

The world is full of diversity where plants and animals are living together. A cell is the basic unit of life for all living things on this earth. Among all these living things, plants are a large group of the whole living world. The structure and function of the cell membrane of the plant cell are discussed below.

All living things on earth are made up of countless cells. Just as all animals on earth are made up of many cells, so the body of a plant is made up of various cells. The cell is the basic unit of the plant body (2) & (1).

The cells present in the body of a plant are the unit that carries information about plant structure, metabolic activity, and heredity. Plant cells are the unit of plant life. Plant cells are both unicellular and multicellular.

  • Acetabularia is the largest unicellular plant cell that is visible to the naked eye.
  • The bark fibers of the ramie tree are the largest multicellular plant cell.
  • The length of this multicellular plant cell is about 55 cm.
  • Plant cells do not have microvilli.
  • Plant cells are of a eukaryotic type. That means the plant cells have specific parts such as cell wall, cell membrane, well-formed nucleus, various cell organelles, and cytoplasm.
  • Plants produce food in the process of photosynthesis by these cell organelles.

 

Definition of cell membrane

The protoplasm of every plant cell that is covered by a fine, elastic, and semipermeable membrane from the outside is called the cell membrane. This is the second covering of plant cells.

The next part of the cell wall is the cell membrane it is a living part. It is a fine layer made up of lipoproteins. This membrane is bi-layer. It separates the cell wall of the plant cell from the cytoplasm. So it is also called cytomembrane.

Another name for the membrane of the plant cell is plasma membrane or plasmalemma or biomembrane. Inside the cell is a medium that is said to be responsible for life. This medium is protoplasm. The protoplasm is the basic of life. Main function is to protect the plant cell and protoplasm (3) & (4).

Location of cell membrane

A two-layered cell membrane is present in plant cells like animal cells. Membrane means screen. Just as the screen prevents harmful substances from entering the outside, therefore it also protects the protoplasm of the plant cell from the outside.

Like all living cells, the plant cells have a cell membrane. This membrane is located in the middle of the protoplasm and cell in plant cells (5).

Facts

There are some facts about the cell membrane of plant cells.

  • It is a major part of the plant cell that is a living part.
  • Membrane of plant cells has two phospholipids layers.
  • An inert cell wall is attached to the outer surface of the cell membrane of a plant cell.
  • The cell membrane of a plant cell is a very delicate, resilient, and semi-permeable membrane.
  • It is an elastic single membrane made up of protein and lipids.
  • Plant cells have an elastic and inert cell wall on the outside of the cell membrane that protects. Due to the presence of this cell wall, the plant cell can withstand the pressure of the water inside. So if the cell is submerged in water, it does not swell and does not rupture (7) & (9).

Structure of cell membrane

The cell membrane is a thin three-layer membrane (8). A plant membrane is made up of two phospholipid layers called lipid bilayers. Globular protein molecule is scattered between these lipid layers. These globular proteins are able to move through the liquid lipid layer. Lipid molecules are also able to change their position (3).

There are two types of proteins in the membrane of plant cells. Some proteins partially or completely break down two lipid layers. These are called internal proteins or membrane proteins. Other proteins are loosely attached to the outer or inner lipid layer or membrane, called external or marginal proteins.

Each phospholipid layer of the plant membrane contains two molecules of fatty acids and one molecule of phosphate (7). Thickness of the membrane of the plant cell is about 75 Å. The structure of the membrane of a plant cell is liquid.

There are many tiny holes in the plant membrane. The diameter of these vesicles is 10 to 50 Å. The membrane contains some amount of water. But the amount of water is not high in the plant membrane. It contains about 25% water (3) & (8).

Chemical structure

The cell membrane is a significant part of the plant cell. It provides the distinction between intracellular and extracellular environments. This membrane of plant cells are made up of lipids, proteins, and carbohydrates (3).

Besides, there are also some amounts of polysaccharides, RNA, DNA, etc. inside the plant membrane. Besides this, it is composed of about 30-45% lipids, about 50-60% of proteins, and also some amount of carbohydrates (5 to 10%).

30-45% of lipids contain phospholipids and cholesterol molecules. And 50- 60% of proteins include lipoproteins, glycoproteins, enzymatic proteins, carrier proteins, structural proteins, etc (6).

There are three types of lipids observed in the membrane of plant cells. These are galactolipid, phospholipids, and cholesterol. The presence of three main types of proteins can be observed in the membrane of plant cells. These are integral protein, peripheral protein and lipid saturated protein.

The oligosaccharide molecules located on the outside of the membrane combine with proteins and lipids to form glycoproteins and glycolipids. Membrane of plant cells is elastic due to the presence of proteins. Lipids form the basis of the membrane of plant cells (1).

And the proteins present in the membrane is to provide mechanical energy and help in the transport of some materials in the plant cell (3) & (7).

The function of the cell membrane

  • It protects the other organelles inside the plant cell.
  • This is semi-permeable, so this membrane allows certain substances to enter.
  • The function of the membrane is to protect the protoplasm of the cell from external injury and give shape to the cell (3).
  • It helps the entry of liquid food into the cell through the vesicle.
  • This living membrane controls the exchange of various organic and inorganic substances inside or outside the cell.
  • The membrane of plant cells also participates in protein synthesis with the help of ribosomes (8).
  • Plant cells move various objects through the membrane.
  • This membrane protects the inner object of the plant cell from external adverse conditions.
  • There are many types of enzymes that participate in some physiological processes of the plant body.
  • It has a role in interconnection, growth, and movement.
  • Plays a major role in the diffusion and osmosis of the plant cells.
  • The membrane helps in the entering of solid food into the plant cell in the process of phagocytosis (1) & (6).

Reference

  1. Unified botany- S. B. Agarwal

 

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