Biology Chapter: Solutions and Membrane Transport

Solutions and Osmosis

• A hypotonic solution causes a cell to swell due to a lower concentration of dissolved particles outside than inside the cell.
• An isotonic solution maintains a cell's shape as the concentration of dissolved particles is equal inside and outside the cell.
• A hypertonic solution results in a cell shrinking because the concentration of dissolved particles is higher outside the cell.

Membrane Transport Mechanisms

• Osmosis is the diffusion of water molecules across a semipermeable membrane.
• Active transport involves moving particles against their concentration gradient, requiring energy.
• Passive transport includes mechanisms like diffusion and facilitated diffusion, where particles move from higher to lower concentration without energy.
• Channel proteins provide pathways for particles to diffuse across the plasma membrane, while carrier proteins change shape to transport specific molecules.

Types of Transport Processes

• Endocytosis refers to the process where a cell takes in materials via vacuole formation; phagocytosis and pinocytosis are two types of endocytosis.
• Exocytosis is when a cell expels waste material from a vacuole.
• Facilitated diffusion is a form of passive transport utilizing transport proteins.

Water Movements in Cells

• In a hypotonic solution, water enters the cell, increasing turgor pressure and causing plant cells to become rigid.
• In a hypertonic solution, water exits the cell, leading to cell shrinkage and wilting in plants due to loss of turgor pressure.
• Osmotic pressure is the force exerted by water on the cell membranes, influencing cell volume.

Concentration and Solvent

• Concentration signifies the ratio of solute (dissolved substance) to solvent (dissolving medium, primarily water).
• The universal solvent is water, which effectively dissolves most substances.
• Percent concentration of solvent can be calculated by subtracting the percent concentration of solute from 100%.

Cell Membrane Structure and Function

• The cell membrane regulates movement of dissolved molecules and separates the cell from surroundings.
• It contains lipid molecules forming a lipid bilayer and assembles as a mosaic structure through various proteins.
• Organisms like fungi, plants, and bacteria possess a cell wall, which provides support and protection.

Diffusion and Equilibrium

• Diffusion is the movement of particles from an area of higher concentration to an area of lower concentration, not requiring energy.
• Equilibrium occurs when particles are evenly distributed throughout a space.
• If a membrane is permeable to a substance, that substance can diffuse across it.

Effects of Osmotic Pressure

• Cells in freshwater are hypertonic and experience a net movement of water into them, which may cause them to swell or burst without the restraining effect of a cell wall.
• Plant and bacteria cells resist bursting due to osmotic pressure thanks to their cell walls, which provide structural integrity.

Test your knowledge on solutions, osmosis, and membrane transport mechanisms. This quiz covers hypotonic, isotonic, and hypertonic solutions, as well as the different transport processes in cells. Challenge yourself and reinforce your understanding of cellular processes!