Question

Which of the following biological membranes is semipermeable? (a) Fish and animal bladders (b) Egg membrane (c) Plasma membrane of cell (d) All of these

Short answer

All of the listed membranes, fish and animal bladders, egg membrane, and plasma membrane of cell, are semipermeable; therefore, the correct answer is (d) All of these.

Step-by-step solution

Definition of a Semipermeable Membrane

A semipermeable membrane is a type of biological or synthetic membrane that allows certain molecules or ions to pass through it by diffusion and occasionally specialized facilitated diffusion. This type of membrane is selective in its permeability to substances.

Identify the Semipermeable Membranes

We need to examine each option and determine if it fits the definition of a semipermeable membrane: (a) Fish and animal bladders have tissues that contain semipermeable membranes that regulate the passage of substances. (b) Egg membranes are known to allow certain molecules like water and gases to pass through while blocking others, making them semipermeable. (c) The plasma membrane of a cell is quintessentially semipermeable, as it regulates the movement of substances in and out of the cell.

Determine the Correct Answer

Considering that all the given options (fish and animal bladders, egg membrane, and plasma membrane of cell) have properties that classify them as semipermeable membranes, the correct answer is thus (d) All of these.

Key concepts

Diffusion

Diffusion is a key process that can be described as the movement of molecules from an area of higher concentration to an area of lower concentration, without the requirement of energy input. It's one of the fundamental mechanisms by which substances move in nature, and it's pivotal in the context of biological systems. For example, oxygen diffusing into cells or carbon dioxide moving out are crucial processes for life.

Imagine a scenario where you open a bottle of perfume in a room. Initially, the fragrance particles are highly concentrated around the bottle's opening, but over time they spread out evenly throughout the room. This is diffusion in action. In biology, similar principles govern how substances move across semipermeable membranes, such as the plasma membrane of cells. Understanding diffusion is essential for grasping the workings of biological systems, as it underlies many physiological and cellular processes.

Plasma Membrane of Cell

The plasma membrane of a cell, often referred to as the cell membrane, acts as the gatekeeper to the cell's interior. It's a critical structure that defines the boundary of the cell while controlling the passage of materials in and out. Biologically, plasma membranes are composed of a phospholipid bilayer with embedded proteins, cholesterol, and glycolipids that contribute to its fluidity and function.

The plasma membrane's selective permeability is essential for maintaining homeostasis within the cell. Certain molecules, such as oxygen and carbon dioxide, can freely diffuse through the plasma membrane due to their small size and nature. Conversely, ion channels and transport proteins assist larger or hydrophilic molecules in crossing the membrane selectively, ensuring that the internal environment of the cell remains regulated. The complexity of the plasma membrane permits the cell to interact with its environment and respond appropriately to changes.

Biological Membranes

Biological membranes encompass a variety of membranes found within and around biological cells. They include not only the plasma membrane but also intracellular membranes such as those surrounding organelles like mitochondria and the endoplasmic reticulum. These membranes, similar to the plasma membrane, are semipermeable and serve critical functions, ranging from compartmentalization within cells to the exchange of materials and information with the external environment.

All biological membranes share a common structure: they're composed of a lipid bilayer and associated proteins that dictate their specific functions. The fluid mosaic model is a widely accepted description of membrane dynamics, which posits that membranes are fluid structures with proteins that float among the lipids. These biological barriers are not just static entities; they are dynamic and play active roles in cellular processes such as signal transduction, energy harvesting, and the synthesis of important biological molecules. By studying these membranes, we gain insights into the complex nature of life and how cells harness and maintain the delicate balance necessary for survival.