Cellular Organelles and Animal Tissues Explained
Endoplasmic Reticulum
A system of membranes in the cytoplasm that forms a complex network of tubules and sacs connected with the nuclear membrane. It may be free or associated with ribosomes. Functions include transport and storage of chemicals, synthesis of lipids (in the smooth endoplasmic reticulum) and proteins (in the rough endoplasmic reticulum), and destruction of toxic substances.
Ribosomes
Very small organelles consisting of RNA and proteins. Their function is protein synthesis.
Golgi Apparatus
A membranous organelle formed by the grouping of vesicles and flattened sacs. It is responsible for the preparation and cellular secretion of various substances.
Lysosomes
Spherical membrane vesicles that house digestive enzymes. They perform the digestion of large molecules, cellular renewal by destroying old organelles, and are involved in metabolism.
Vacuoles
Membranous vesicles of variable size and shape, most common in plant cells. They are responsible for storing substances.
Mitochondria
Organelles with an elongated shape, composed of a double membrane: an external smooth membrane and an internal membrane with folds called mitochondrial cristae. Their function is cellular respiration.
Chloroplasts
Organelles constituted by a double membrane enclosing a series of membranous sacs called thylakoids. The thylakoid membrane contains chlorophyll, a pigment that gives them their characteristic green color. Their function is photosynthesis.
Cytocenter
An organelle formed by two cylindrical structures called centrioles, arranged perpendicularly. Functions include cell division control and regulation of the movement of cellular components like cilia and flagella.
Porifera
These are primitive animals. Their body is made of a sac with numerous holes and a larger opening called an osculum. They possess cells called choanocytes, whose mission is to create water currents that traverse the body and flow out through the osculum. They lack a nervous system.
Flatworms
These organisms exhibit bilateral symmetry and are commonly called flatworms.
Nematodes
Worms with a cylindrical, unsegmented body. This group features a general body cavity that allows for the existence of hollow internal organs. They can be free-living or parasitic, including intestinal worms and trichina.
Annelids
Animals with a cylindrical body divided into rings. They exhibit metamerism, meaning organs are repeated in each ring. Some possess rigid structures, like bristles, used for locomotion. Leeches are an example.
Molluscs
Molluscs exhibit bilateral symmetry. Their body consists of:
- A visceral mass containing internal organs.
- A muscular foot on the ventral side.
- The mantle, a double dorsal fold.
- A paleal cavity between the mantle and visceral mass, often functioning as respiratory organs.
- A calcareous shell secreted by the mantle, which can have one or two valves.
There are three main classes of mollusks:
- Gastropods: Have a wide foot, a head with eye tentacles, and a single-valved shell. They can be terrestrial or aquatic.
- Bivalves (Lamellibranchs): Possess a hatchet-shaped foot, lack a distinct head, and have a two-valved shell. They are aquatic, including clams and mussels.
- Cephalopods: Have a well-developed foot with tentacles bearing suckers. The shell is internal or absent. They possess a siphon used for propulsion. They are marine, with octopuses being a prime example.
Connective Tissues
Connective tissues hold other tissues together and form the body’s supportive material. They are abundant in animals and are composed of cells (fibroblasts) and a large amount of intercellular substance, forming a matrix with fibers. The matrix consists of mucopolysaccharides, salts, and proteins, with consistency varying by tissue type. Fibers can be of three types:
- Collagen fibers: Resilient and flexible, arranged in bundles.
- Elastic fibers: Thinner than collagen fibers, providing elasticity to the tissue; composed of elastin.
- Reticular fibers: The finest and most intertwined in the matrix, formed by reticulin.
Structure of Connective Tissue: Cells are fibroblasts, which form the connective tissue. Elastic fibers provide elasticity. Reticular fibers form a fine network within the matrix.