Symmetry in Living Things - Finite Mathematics Study Guide
Definitions and Types of Symmetry in Organisms
Symmetry in living things is a fundamental biological and mathematical concept explored within Finite Mathematics 1. All living organisms, including vertebrates and invertebrates, exhibit specific body plans categorized by their symmetrical arrangements. Marine invertebrates, in particular, frequently display radial symmetry as a core feature of their physical design.
Bilateral symmetry is defined as a body plan in which an organism can be divided into exactly two equal mirror-image halves by a single line or plane, known as the mid-plane, passing down the middle of the body. This is the most common form of symmetry found in complex land-dwelling animals and humans. Radial symmetry, conversely, is a body plan where an organism can be divided into similar parts around a central point or axis by many different lines or planes. This form of symmetry is common in organisms that interact with their environment from all directions.
Symmetry as an Evolutionary Adaptation
The presence of symmetry in the natural world is not accidental; it is rooted in the principles of preservation and reproduction. At the heart of why living things display symmetry is the need to pass on traits that are biologically useful to future generations. This process is known as evolutionary adaptation. The specific form of symmetry preserved and reproduced within a species is the one that best supports the organism's survival and matches the demands of its specific environmental niche.
Radial Symmetry in Marine Invertebrates: Jellyfish and Starfish
Jellyfish and starfish are classic examples of organisms that utilize radial symmetry to thrive in marine environments. This adaptation is primarily driven by their feeding habits. These animals feed on plankton, which are microorganisms that float and occupy a three-dimensional space in the water. Because plankton are distributed both horizontally and vertically within a defined volume of water, it is biologically advantageous for jellyfish and starfish to grow radially to maximize their capture area.
In jellyfish, tentacles grow radially from the central bell. These biological structures are designed to capture plankton from any direction and move them toward the mouth, which is located at the center and underside of the jellyfish bell. Similarly, a starfish's mouth is located in the center of its body. The radial symmetry of these marine creatures is an adaptation specifically evolved to respond to the distribution of food sources in the ocean.
Bilateral Symmetry in Plant Life and Photosynthesis
In the plant kingdom, bilateral symmetry is a critical feature of leaves. A leaf is designed with a midrib that serves as the axis of reflection, creating two symmetrical halves. This specific symmetry helps the leaf absorb sunlight evenly across its surface, thereby maximizing its exposure to radiant energy, which is essential for photosynthesis.
Beyond energy absorption, bilateral symmetry also results in the even distribution of stomata across the leaf surface. Stomata are microscopic pores responsible for gas exchange, allowing the plant to take in carbon dioxide () and release oxygen () into the atmosphere. This even distribution ensures that respiration and the exchange of gases occur efficiently throughout the entire structure of the leaf.
Bilateral Symmetry in Insects and Complex Animals
Bilateral symmetry is a requirement for the survival and efficiency of many flying and terrestrial organisms. Flying insects, for example, must be perfectly symmetrical to ensure they can fly evenly and efficiently through the air. Symmetry is also a functional requirement for their respiratory processes, aiding in the balance and movement necessary for survival.
Insects, birds, reptiles, mammals, and humans all display bilateral symmetry because they inherited this specific design from a common ancestor. Symmetry is ubiquitous in the world of living things because it provides the structural and functional advantages necessary for organisms to survive, move, and interact with their surroundings successfully.
The Biological and Cellular Origins of Symmetry
The macroscopic symmetry observed in large organisms begins at the microscopic level with cellular reproduction. Somatic cells, which are the primary cells that form the body of an organism, reproduce through a process called mitosis. During mitosis, a cell divides into two or more daughter cells. Because these daughter cells are exact copies of the parent cell and share the identical biological design, the result is a uniform distribution of structures that ultimately manifests as the symmetry seen in the fully grown organism.