Cellular Structures and Organelles: Functions Explained

Plasma Membrane

Structure

The plasma membrane is a flexible and deformable thin envelope that surrounds all cells.

Function

Its mission is to limit the cellular content, but it allows the passage of substances.

Cell Wall

Structure

The cell wall consists of cellulose fibers (a carbohydrate) that confer high resistance and prevent its distortion. This is why plant cells have fixed and often polyhedral forms. Sometimes, the cell wall is covered with a waxy substance that waterproofs it.

Function

It protects the cell and determines its shape, allowing the exchange of substances through pores.

Cytoplasm

The cytoplasm is the internal environment of the cell, where various organelles are suspended.

1. Hyaloplasm

   Structure

   The hyaloplasm is formed by a viscous fluid containing a large amount of dissolved substances in water and a multitude of fibrils.

   Function

   Some of the cell's chemical reactions take place within it. It also houses the other organelles.

2. Mitochondria

   Structure

   Mitochondria are more or less elongated organelles made of a double membrane and a liquid called mitochondrial matrix. The inner membrane folds inward like the fingers of a glove, constituting the mitochondrial cristae.

   Function

   Mitochondria are responsible for cellular respiration; that is, they are the powerhouses of eukaryotic cells, where energy contained in organic matter is released. The process can be outlined as follows:

3. Endoplasmic Reticulum

   Structure

   The endoplasmic reticulum is a network of tubes and membranous sacs that extends throughout the cytoplasm. There are two types:

   • The smooth endoplasmic reticulum, composed of tubes.
   • The rough endoplasmic reticulum, consisting of sacs whose walls have ribosomes attached.

   Function

   The smooth reticulum is responsible for the production of certain fats, while the rough reticulum stores and transports proteins.

4. Vacuoles

   Structure

   Vacuoles are more or less spherical membranous sacs. In animal cells, they are small, while in plant cells, there often exists a single large vacuole that fills most of the cell's interior.

   Function

   Animal vacuoles can have digestive or excretory functions, including expelling excess water.

5. Golgi Apparatus

   Structure

   The Golgi apparatus consists of a series of flattened sacs arranged over each other like a stack.

   Function

   Its mission is to produce and package substances from the endoplasmic reticulum, enclosing them inside vesicles.

6. Lysosomes

   Structure

   Lysosomes are spherical vesicles originating from the Golgi apparatus, which contain digestive enzymes.

   Function

   They are involved in cellular digestion.

7. Chloroplasts

   Chloroplasts are unique cell organelles found in plant cells.

   Structure

   They are oval-shaped and green.

   Function

   In chloroplasts, photosynthesis takes place. This process transforms inorganic matter into organic matter using solar energy.

8. Ribosomes

   Structure

   Ribosomes are very numerous and small organelles found scattered in the cytoplasm or attached to the wall of the rough endoplasmic reticulum.

   Function

   Their function is the synthesis of proteins.