Cell Organelles and Membrane Transport Mechanisms

Classification of Cell Organelles

Organelles without membrane: The cell wall, ribosomes, and cytoskeleton are non-membrane-bound cell organelles. They are present both in the prokaryotic cell and the eukaryotic cell.

Single membrane-bound organelles: Vacuole, lysosome, Golgi apparatus, and endoplasmic reticulum are single membrane-bound organelles present only in a eukaryotic cell.

Double membrane-bound organelles: Nucleus, mitochondria, and chloroplast are double membrane-bound organelles present only in a eukaryotic cell.

Let us learn more in detail about the different cell organelles in brief.

Key Cell Organelles and Their Functions

Plasma Membrane

The plasma membrane, also called the cell membrane, is the membrane found in all cells that separates the interior of the cell from the outside environment.

Cytoplasm

Cytoplasm is a thick solution that fills each cell and is enclosed by the cell membrane.

The Nucleus

The nucleus controls and regulates the activities of the cell (e.g., growth and metabolism) and carries the genes, which are structures that contain the hereditary information.

Endoplasmic Reticulum (ER)

In biology, the Endoplasmic Reticulum (ER) is a continuous membrane system that forms a series of flattened sacs within the cytoplasm of eukaryotic cells and serves multiple functions.

Rough Endoplasmic Reticulum

The Rough Endoplasmic Reticulum (RER) is a membranous organelle that functions to produce proteins with the help of ribosomes located on the membrane surface.

Smooth Endoplasmic Reticulum

The Smooth Endoplasmic Reticulum (SER) functions in many metabolic processes. It synthesizes lipids, phospholipids (as found in plasma membranes), and steroids.

Mitochondria

Mitochondria are called the powerhouses of the cell as they produce energy-rich molecules for the cell. The mitochondrial genome is inherited maternally in several organisms. It is a double membrane-bound, sausage-shaped organelle found in almost all eukaryotic cells.

Ribosomes

Ribosomes are non-membrane-bound and important cytoplasmic organelles found in close association with the endoplasmic reticulum.

Mechanisms of Cell Membrane Transport

Cellular transport is categorized into three main types:

• Active Transport
• Passive Transport
• Bulk Transport

Active Transport

In cellular biology, active transport is the movement of molecules across a cell membrane from a region of lower concentration to a region of higher concentration—moving against the concentration gradient.

Bulk Transport

Like the active transport processes that move ions and small molecules via carrier proteins, bulk transport is an energy-requiring (and, in fact, energy-intensive) process. The different modes of bulk transport include:

• Phagocytosis
• Pinocytosis
• Receptor-mediated endocytosis
• Exocytosis

Passive Transport

Passive transport involves the movement of substances from a higher to a lower concentration without the expenditure of energy.

Osmosis

Osmosis is the movement of water molecules or a solvent from a region of low solute concentration towards a region of high solute concentration through a semi-permeable membrane.

Diffusion

Diffusion can be described as the process of movement of molecules from a region of higher concentration to a region of lower concentration, allowing the entry and exit of substances in and out of cells.