Selective Permeability

Definition

Selective permeability refers to the property of cell membranes that allows certain molecules or ions to pass through while restricting others. This characteristic is essential for maintaining homeostasis within the cell, enabling it to control its internal environment by regulating what enters and exits. The structure of the cell membrane, particularly the phospholipid bilayer and embedded proteins, plays a crucial role in this selective process.

5 Must Know Facts For Your Next Test

1. Selective permeability is crucial for nutrient uptake and waste removal, allowing cells to maintain a balanced internal environment.
2. The fluid mosaic model describes how proteins and lipids can move within the membrane, facilitating selective interactions with different substances.
3. Small nonpolar molecules like oxygen and carbon dioxide can easily cross the membrane, while charged ions and large polar molecules require specific transport mechanisms.
4. Active transport is a process that allows cells to move substances against their concentration gradient, utilizing energy in the form of ATP.
5. The degree of selective permeability can vary between different cell types and conditions, impacting cellular functions and responses.

Review Questions

• How does selective permeability contribute to maintaining homeostasis in cells?
  • Selective permeability helps maintain homeostasis by regulating which substances can enter or exit a cell. This regulation ensures that essential nutrients are absorbed while harmful substances are kept out. Additionally, it allows waste products to be removed efficiently, thereby supporting the overall health and function of the cell. By controlling the internal environment, cells can respond effectively to changes in their surroundings.
• Discuss how the structure of the cell membrane facilitates selective permeability.
  • The structure of the cell membrane, primarily composed of a phospholipid bilayer and various embedded proteins, plays a vital role in selective permeability. The hydrophobic core of the bilayer restricts the passage of polar and charged molecules, while embedded transport proteins provide specific pathways for these substances to cross. This structural arrangement allows the membrane to selectively permit certain ions and molecules while denying others access based on size, charge, and polarity.
• Evaluate the impact of changes in selective permeability on cellular function and overall physiology.
  • Changes in selective permeability can significantly impact cellular function and overall physiology. For example, if a cell's membrane becomes more permeable than normal, it may lead to an influx of excess ions or nutrients, disrupting homeostasis and potentially causing cellular damage or death. Conversely, reduced permeability could impair nutrient absorption or waste removal, leading to toxicity or nutrient deficiencies. Understanding these effects helps explain various physiological conditions and diseases linked to membrane integrity and function.

Related terms

Phospholipid Bilayer: A double layer of phospholipids that forms the fundamental structure of the cell membrane, with hydrophilic heads facing outward and hydrophobic tails facing inward.

Transport Proteins: Proteins embedded in the cell membrane that assist in the movement of substances across the membrane, including channels and carriers.

Osmosis: The diffusion of water across a selectively permeable membrane from an area of lower solute concentration to an area of higher solute concentration.