Biology Chapter 3.3 and 3.5 Flashcards

Passive Transport

• Passive transport is the movement of molecules across cell membranes without the need for energy input.

Diffusion

• Diffusion is the spontaneous movement of fluid particles from high to low concentration, moving down a concentration gradient.
• No energy is required for diffusion, occurring through random kinetic movement.
• Net diffusion ceases when concentrations on both sides are equal, reaching equilibrium where diffusion of one compound is independent of others.

Factors Affecting Diffusion

• Factors influencing diffusion include the direct passage through the lipid bilayer and the diffusion of hydrophilic molecules across the plasma membrane.

Osmosis

• Osmosis refers to the passive transport of water, specifically the diffusion of water across a semi-permeable membrane from high to low concentration.
• Plasma membranes are permeable to water but not to solute; water moves from dilute to concentrated solutions.

Solution Types

• Solutions are classified into three types relative to cells: hypertonic, hypotonic, and isotonic.
  • Hypertonic Solution: Higher concentration of dissolved particles outside the cell, causing water to move out, resulting in cell shrinkage.
  • Hypotonic Solution: Lower concentration of dissolved particles outside the cell, causing water to move in and potentially making the cell expand or burst.
  • Isotonic Solution: Solute concentration is equal inside and outside the cell, resulting in no net water movement.

Effects of Osmosis on Cells

• Water movement into a cell can exert pressure on the plasma membrane, and in animal cells, it may lead to expansion and bursting.
• Organisms with cell walls, like plants, do not burst due to osmosis as the rigid wall resists the pressure from the cell membrane pushing against it.

Plant Responses to Water Availability

• A lack of water causes plants to wilt, referred to as plasmolysis. Rehydration restores turgidity, raising the leaves back up.

Facilitated Diffusion

• Facilitated diffusion allows larger, membrane-insoluble compounds (e.g., sugars, amino acids) to diffuse down a concentration gradient without energy use.
• It is highly selective and involves the binding of the substance to membrane proteins, changing the protein's shape to facilitate transport.

Characteristics of Facilitated Diffusion

• It is reversible; molecules can enter and exit the cell via the transport protein.
• An example includes glucose transport, where glucose binds to the protein, alters its shape, and is released into the cell.

Active Transport

• Active transport moves substances across membranes with an energy cost, typically against their concentration gradient.
• Energy is required to overcome both concentration and electrochemical gradients or to allow the passage of larger or charged particles through the membrane.

Test your knowledge of diffusion, osmosis, active transport, and endocytosis with these flashcards. Each card features key terms and definitions to help you understand passive transport mechanisms in cells. Perfect for students aiming to master these concepts in biology.