Tissues, Cells, Organs & Biomolecules: Structure and Function

Tissues: Types, Structure and Function

Tissue: a group of cells that assemble and function together. Between cells is the intercellular substance (extracellular matrix). Cells can be closely packed together or separated by this intercellular material.

Epithelial Tissue

Epithelial (covering) tissues form protective layers such as skin (the outer layer). They also form mucous membranes that line internal cavities and surfaces, and they include secretory tissues (glands). Epithelial tissues are made of crowded cells with little intercellular substance and may be arranged in one or several layers.

Nervous Tissue

Nervous tissue consists of neurons and supporting cells. It transmits nerve impulses and is responsible for coordination, sensation, and the relationship of the organism with its environment.

Connective Tissue

Connective tissue unites, supports, and sustains organs. Examples include:

• Bone: supports other body parts and provides the skeletal function.
• Cartilage: provides support and protection in specific structures.
• Adipose (fat): energy reserves and mechanical/thermal protection.
• Blood: transports substances throughout the body.

Muscular Tissue

Muscular tissue enables movement. Main types:

• Skeletal (striated): voluntary movements; typically fast and controlled.
• Smooth: involuntary; slow and sustained contractions (e.g., in internal organs).
• Cardiac: involuntary muscle of the heart responsible for its contractions.

Cells: Prokaryotes and Eukaryotes

Some organisms are prokaryotes (no true nucleus). These cells have a plasma membrane and often a cell wall; many are unicellular. Example: bacteria. Prokaryotes lack a membrane-bound nucleus and their genetic material is not enclosed within one.

Eukaryotes have a true nucleus where chromosomes are contained. Eukaryotic organisms can be unicellular or multicellular and include animal and plant cells. Basic cellular structures include the plasma membrane, cytoplasm, and nucleus.

Organs and Organ Systems

Organs are structures consisting of one or more tissues that perform specific functions, for example: heart, nose, eye, tongue. Apparatuses or organ systems are formed by groups of organs working together.

Examples of organ systems (apparatus):

• Circulatory system
• Digestive system
• Reproductive system
• Excretory system
• Respiratory (breathing) system

Biomolecules: Functions and Examples

Biomolecules are molecules found in all organisms:

• Carbohydrates: sugars and polysaccharides that provide energy.
• Lipids (fats): energy reserves; provide mechanical and thermal protection.
• Proteins: large molecules formed by amino acids. Functions include transport, regulation, structural support, and contraction.
• Nucleic acids: very large molecules formed by nucleotides. Function: store and transmit genetic information.
• Water: a solvent and reaction medium. Functions: allows biochemical reactions, has a high specific heat, and helps regulate temperature.
• Minerals: support skeletal structures and are involved in cellular activity, membrane function, and impulse conduction.

All these components and structures contribute to the activity of cells, tissues, organs, and systems in living organisms.