Levels of Organization in Living Systems

This page depicts the hierarchical organization of living systems, from cells to organs and organ systems. Cells are the basic units of life, which combine to form tissues. Tissues then organize into organs, which work together as organ systems to perform complex functions in organisms.

Definition: An organ system is a group of organs that work together to perform specific functions in an organism.

Enzymes: Biological Catalysts

Enzymes are specialized proteins that act as biological catalysts, speeding up chemical reactions in living organisms. Key features of enzymes include:

• Specific active sites that bind to particular substrates
• Ability to accelerate reaction rates
• Formation of enzyme-substrate complexes during reactions

The diagram illustrates the lock-and-key model of enzyme action, showing how the substrate fits into the enzyme's active site to form products.

Vocabulary: The active site is the region of an enzyme where the substrate binds and the reaction occurs.

Cell Wall and Vacuole: Plant Cell Specializations

Two structures unique to plant cells are the cell wall and the large central vacuole:

Cell Wall:

• Provides structure and support to the cell
• Offers protection and is made of cellulose
• Found only in plant cells

Vacuole:

• Contains cell sap to maintain cell turgor
• Helps in storage and waste management
• Present only in plant cells

Vocabulary: Turgor is the state of fullness or tension in plant cells caused by the pressure of the cell contents against the cell wall.

Specialized Cells: Adaptations for Specific Functions

Specialized cells are cells that have adapted to perform specific functions within an organism. An example of a specialized cell is the sperm cell, which has adapted for its reproductive function:

• Long tail for swimming to the egg
• Head containing enzymes to penetrate the egg

Example: A sperm cell's streamlined shape and powerful tail enable it to navigate through the female reproductive tract to reach and fertilize the egg.

Nerve Cell: Specialized for Signal Transmission

Nerve cells, or neurons, are specialized for transmitting electrical impulses throughout the body:

• Long and thin structure with branched ends
• Connects to other cells to pass on electrical impulses

Vocabulary: Neurons are the basic functional units of the nervous system, responsible for transmitting information as electrical and chemical signals.