Question

Which serves best as a semipermeable membrane? (a) copper ferrocyanide (b) vegetable membrane (c) animal membrane (d) cellophane

Short answer

Both vegetable membrane (b) and animal membrane (c) serve well as semipermeable membranes, but generally organic membranes like those from vegetables and animals are considered most effective.

Step-by-step solution

Understanding Semipermeable Membranes

A semipermeable membrane is a type of barrier that allows certain substances, commonly solvents such as water, to pass through while blocking other substances. It is used in processes like osmosis.

Analyzing the Options

We need to evaluate the given options to determine which one acts most effectively as a semipermeable membrane. Substances that are organic and have a cellular structure are generally good at being selectively permeable.

Determining the Best Semipermeable Membrane

(a) Copper ferrocyanide is not typically known for being semipermeable. (b) A vegetable membrane is organic and has a cellular structure suitable for selective permeability. (c) An animal membrane is also organic and known to possess semipermeable properties. (d) Cellophane is a synthetic product that can be made semipermeable through certain treatments, but typically it is not as effective as natural membranes. Among these, both vegetable and animal membranes are known to be good semipermeable membranes. If one must be chosen over the other, the context of use might determine the most appropriate choice, but both b and c are commonly accepted as effective semipermeable membranes.

Key concepts

Osmosis Process

The osmosis process is fundamental to life, playing a critical role in maintaining cell health and function. It's the movement of a solvent, usually water, across a semipermeable membrane from a region of low solute concentration to one of high solute concentration. This process aims to balance solute concentrations on the membrane's two sides.

Osmosis can be easily observed by placing a cell in a solution with a different concentration of solutes compared to the cell's interior. If the solution is 'hypertonic'—meaning it has a higher concentration of solutes—the cell will lose water and shrink. Conversely, a 'hypotonic' solution, with a lower solute concentration, will cause the cell to absorb water and swell. A solution that has the same solute concentration as the cell is called 'isotonic,' and in this situation, water moves in and out of the cell at equal rates, maintaining cell size and shape.

Simplifying Osmosis

Imagine a sponge in water. The sponge naturally absorbs water up to a point of equilibrium, where it can no longer take in water unless it is squeezed out. Cells work similarly; they absorb water but are regulated by their membrane's selective permeability, demonstrating the essence of the osmosis process.

Cellular Structures

Cellular structures are as diverse as life itself. However, all cells share a common feature: they are bounded by a plasma membrane. This membrane is not just a passive barrier; it's actively involved in transport processes, providing shape and protection, and facilitating communication between cells.

The membrane's architecture is crucial for its function. It typically consists of a phospholipid bilayer with various proteins embedded within it. This arrangement is often referred to as the 'fluid mosaic model' because it's fluid and the proteins create a pattern like a mosaic. The bilayer's 'fluidity' allows cells to be flexible, to interact with their environment, and to transport materials in and out.

Key Organelles

Inside the cell, organelles like the nucleus, mitochondria, and endoplasmic reticulum perform specialized roles, all working in unity for the health and survival of the cell. These structures are also bounded by membranes, underscoring the ubiquitous influence and importance of membranes in cellular function.

Selective Permeability

Selective permeability is the property of a membrane that allows it to decide which molecules can pass through and which cannot. This 'selectiveness' is essential for maintaining a stable internal environment within a cell or an organ.

Several factors contribute to this selective nature. The basic structure of membranes—comprised of the lipid bilayer—creates a barrier to water-soluble (hydrophilic) substances while allowing fat-soluble (hydrophobic) substances to pass more easily. Also, membrane proteins play a crucial role; they act as channels or carriers that specifically transport substances across the membrane.

How It Works

Pore-size on the membrane, and the size of the molecules trying to pass through, are important. Small, nonpolar molecules like oxygen and carbon dioxide can diffuse directly through the lipid bilayer, while larger or charged molecules require 'help' from membrane proteins. This regulation ensures that essential nutrients can enter cells while waste products can exit, and that the internal conditions necessary for cell survival are maintained against external fluctuations.