Passive Transport
Concentration
Solute: A molecule or compound that is being dissolved in a solution. Common examples include sugar, salt, oxygen (O₂), and carbon dioxide (CO₂). Solutes can vary greatly in size and chemical structure, influencing their behavior in a solvent.
Solvent: The substance that dissolves the solute. Water is the most common solvent in biological systems, known as the "universal solvent" due to its ability to dissolve a wide variety of substances.
Concentration: Refers to the amount of solute present in a specific volume of solvent. It is commonly expressed in terms of grams per liter (g/L), moles per liter (Molarity, M), or percentage solutions.
Passive Transport: A method of transporting molecules across a membrane without the use of energy (ATP).
Forms of Passive Transport:
Diffusion: The process whereby molecules move from an area of higher concentration to an area of lower concentration until equilibrium is reached. This process is fundamental for gas exchange in respiratory systems, such as the transfer of oxygen to cells and carbon dioxide out of cells.
Osmosis: A specific type of diffusion that involves the movement of water molecules through a semipermeable membrane, from a region of higher water concentration (or lower solute concentration) to a region of lower water concentration (or higher solute concentration).
Concentration Gradient: Refers to the difference in solute concentrations across a membrane. Molecules tend to travel down this gradient, moving from areas of higher to lower concentration.
Energy Requirements:
Molecules traveling against the concentration gradient require energy input, as they are moving toward an area of higher concentration.
This energy is often supplied by ATP during active transport processes.
Equilibrium: A state achieved when the concentration of solutes is uniform throughout a space, leading to no net movement of molecules across a membrane.
Types of Solutions:
Hypotonic Solution: A solution where the concentration of solute outside the cell is lower than inside. Water moves into the cell, potentially causing it to swell and reach turgor pressure until equilibrium is reached.
Hypertonic Solution: In this solution, the concentration of solute is higher outside the cell than inside. Water moves out of the cell to balance solute levels, leading to cell shrinkage or plasmolysis.
Turgor Pressure: The pressure exerted by water inside the cell against the cell wall, crucial for maintaining plant structure and rigidity. Without adequate turgor pressure, plants wilt.
Plasmolysis: Occurs in plant cells in a hypertonic solution when water leaves the cell, causing the cell membrane to detach from the cell wall, leading to a flaccid state.
Cytolysis: Happens when a cell is placed in a hypotonic solution; water influx causes the cell to swell and may eventually burst due to excessive internal pressure.
Isotonic Solution: A condition in which the concentration of solute molecules outside the cell is equal to that inside. Here, water moves into and out of the cell at equal rates, maintaining cell size and shape without net gain or loss of water.
Facilitated Diffusion: A special case of passive transport where molecules move across a membrane with the help of specific carrier proteins. This mechanism is vital for transporting larger or polar molecules that cannot diffuse freely through the lipid bilayer.
Understanding these concepts of concentration and transport is integral to fields such as biology, chemistry, and medicine where fluid balance and molecular transport are crucial for life processes.