3.5 Passive Transport
3 min read•june 18, 2024
is the movement of molecules across cell membranes without using energy. It relies on concentration gradients and the membrane's . and are two types of .
and are key processes in passive transport. affects cell shape and function, with , , and solutions impacting water movement. Membrane properties play a crucial role in regulating molecular passage.
Passive Transport
Passive transport across membranes
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- Passive transport moves molecules across cell membranes without using cellular energy ()
- Relies on the kinetic energy of molecules and the selective permeability of the
- Molecules move down their from high to low concentration areas (diffusion)
- Types of passive transport include simple diffusion and facilitated diffusion
- Simple diffusion: Small, nonpolar molecules (, ) move directly through the
- Facilitated diffusion: Larger or polar molecules (, ) move through specific protein channels or carriers embedded in the membrane
Diffusion vs osmosis in cells
- Diffusion is the movement of molecules from high to low concentration areas
- Occurs with any type of molecule (gases, ions, small polar or nonpolar molecules)
- Does not require a
- Examples: Oxygen and carbon dioxide diffusing across cell membranes
- Osmosis is a special type of diffusion involving water molecules moving across a semipermeable membrane
- Water moves from high water concentration (low concentration) to low water concentration (high solute concentration) areas
- The semipermeable membrane allows water to pass through but not larger molecules (ions, proteins)
- Osmosis maintains cell volume and in plant cells
Tonicity effects on cells
- Tonicity is the relative concentration of solutes in a solution compared to inside a cell
- solution: Equal solute concentration inside and outside the cell; no net water movement
- Hypotonic solution: Lower solute concentration outside the cell; water moves into the cell, causing swelling or (bursting)
- Hypertonic solution: Higher solute concentration outside the cell; water moves out of the cell, causing shrinking or
- Cell shape and function are affected by changes in tonicity
- Animal cells:
- In a hypotonic environment, animal cells swell and may lyse due to excessive water intake
- In a hypertonic environment, animal cells shrink as water moves out, leading to crenation
- Plant cells:
- In a hypotonic environment, plant cells become turgid (swollen and firm) due to water influx, which is essential for plant structure and growth
- In a hypertonic environment, plant cells undergo , where the cell membrane pulls away from the cell wall as water moves out, leading to wilting
- Animal cells:
Membrane properties and transport
- Cell membranes have both and regions
- Hydrophobic tails of phospholipids face inward, creating a barrier to polar molecules
- Hydrophilic heads of phospholipids face outward, interacting with the aqueous environment
- play a crucial role in facilitating the movement of specific molecules across the membrane
- Passive transport continues until is reached, where the concentration of molecules is equal on both sides of the membrane
Key Terms to Review (32)
Amino acids: Amino acids are organic compounds that serve as the building blocks of proteins, consisting of a basic amino group, an acidic carboxyl group, and a distinctive side chain that determines the characteristics of each amino acid. They play essential roles in various biological processes, including metabolism and the structure and function of proteins, which are crucial for life.
ATP: ATP, or adenosine triphosphate, is the primary energy carrier in all living organisms. It serves as a molecular currency, transporting chemical energy within cells for metabolism and cellular processes, linking various biological activities including movement, biosynthesis, and transport mechanisms.
Carbon dioxide: Carbon dioxide (CO₂) is a colorless, odorless gas that is a natural component of Earth's atmosphere. It plays a crucial role in various biological processes, particularly in the processes of photosynthesis and respiration, where it acts as a key reactant and product. Additionally, carbon dioxide is involved in climate regulation and is a significant greenhouse gas that traps heat in the atmosphere.
Cell membrane: The cell membrane is a biological barrier that surrounds the cell, consisting primarily of a phospholipid bilayer with embedded proteins. It plays a crucial role in maintaining the integrity of the cell by regulating the movement of substances in and out, contributing to cell communication and signaling, and facilitating cellular interactions.
Concentration gradient: A concentration gradient refers to the difference in the concentration of a substance across a space. In biological systems, this concept is crucial for understanding how substances move, especially during passive transport, where molecules move from an area of higher concentration to an area of lower concentration without the need for energy input. This natural movement helps maintain homeostasis in cells by allowing them to regulate the internal concentrations of various substances.
Crenation: Crenation is the process by which red blood cells shrink and develop a notched or scalloped appearance due to the loss of water when placed in a hypertonic solution. This phenomenon illustrates the effects of osmosis on cell volume, as water moves out of the cell to balance solute concentrations. Crenation is important for understanding how cells react to their environment, particularly in terms of fluid movement across cell membranes.
Diffusion: Diffusion is the process by which molecules spread from areas of high concentration to areas of low concentration, resulting in an even distribution of substances. This passive movement occurs naturally and is crucial for various biological processes, particularly in the functioning of cells and their interactions with their environment.
Equilibrium: Equilibrium refers to a state in which opposing forces or influences are balanced. In biological systems, particularly in passive transport, equilibrium describes the condition where the concentration of a substance is uniform throughout a space, resulting in no net movement of that substance across membranes. This balance is crucial for maintaining homeostasis within cells and organisms, ensuring that essential substances are evenly distributed.
Facilitated diffusion: Facilitated diffusion is a passive transport mechanism that allows specific molecules or ions to cross a biological membrane with the assistance of specialized proteins. This process occurs down the concentration gradient, meaning substances move from areas of higher concentration to lower concentration, without the use of cellular energy. It plays a crucial role in maintaining cellular homeostasis, especially in eukaryotic cells where the lipid bilayer can be selectively permeable.
Facilitated transport: Facilitated transport is a type of passive transport where molecules move across the cell membrane through protein channels or carriers. It does not require energy because it relies on the concentration gradient.
Glucose: Glucose is a simple sugar and an important carbohydrate that serves as a primary source of energy for living organisms. It plays a crucial role in cellular respiration, where it is metabolized to produce ATP, the energy currency of cells, linking it to processes like glycolysis and photosynthesis.
Hydrophilic: Hydrophilic refers to substances that have an affinity for water, meaning they are able to interact and form hydrogen bonds with water molecules. This property is crucial for biological processes, as it influences how molecules interact with each other in aqueous environments, affecting solubility, transport, and cellular functions.
Hydrophobic: Hydrophobic refers to the property of molecules that repel water, meaning they do not easily dissolve in or mix with water. This characteristic is vital in biology as it influences the structure and function of cells, especially in the formation of cell membranes and the behavior of proteins. Hydrophobic interactions are critical in maintaining the integrity of cellular structures and contribute to various processes like passive transport across membranes.
Hypertonic: A hypertonic solution is one that has a higher concentration of solutes compared to another solution, typically referring to the environment outside a cell. In biological contexts, when a cell is placed in a hypertonic solution, water moves out of the cell to balance solute concentrations, leading to cell shrinkage or crenation. This movement of water occurs through osmosis, which is a key aspect of passive transport in cellular processes.
Hypotonic: Hypotonic refers to a solution that has a lower concentration of solutes compared to another solution, usually referring to the fluid inside a cell. When a cell is placed in a hypotonic solution, water moves into the cell through osmosis, causing the cell to swell and potentially burst. This process is vital for understanding how cells interact with their environment and maintain homeostasis.
Isotonic: Isotonic solutions have the same solute concentration as the cell's cytoplasm. Water moves in and out of the cell at equal rates, maintaining cell size.
Isotonic: Isotonic refers to a solution that has the same solute concentration as another solution, typically a cell's cytoplasm. This balance allows for no net movement of water across the cell membrane, maintaining cell size and function. The concept is crucial in understanding how cells interact with their environment through processes like passive transport.
Lysis: Lysis is the process of breaking down or disintegration of a cell, typically through the rupture of its membrane. This event can occur naturally, such as during cell death, or be induced by external factors like viral infections or osmotic pressure. The consequences of lysis can lead to the release of cellular contents into the surrounding environment, impacting neighboring cells and overall tissue health.
Osmolarity: Osmolarity is the measure of solute concentration per unit volume of solution, expressed as osmoles of solute per liter. It is crucial for understanding how water moves across cell membranes during passive transport.
Osmosis: Osmosis is the passive movement of water molecules through a selectively permeable membrane from an area of lower solute concentration to an area of higher solute concentration. This process is vital for maintaining cellular functions and homeostasis, as it directly influences how cells manage their internal environments, their shape, and their ability to maintain balance with their surroundings.
Oxygen: Oxygen is a colorless, odorless gas that is essential for the survival of most living organisms, playing a crucial role in cellular respiration and energy production. In biological systems, oxygen acts as an electron acceptor in metabolic processes, facilitating the release of energy from organic molecules. Additionally, it is vital for photosynthesis, where it is produced as a byproduct during the conversion of sunlight into chemical energy.
Passive transport: Passive transport is the movement of molecules across a cell membrane without the need for energy input from the cell. This process relies on the natural motion of particles and occurs along the concentration gradient.
Passive Transport: Passive transport is the movement of molecules across a cell membrane without the need for energy input, relying on the natural concentration gradient. This process is crucial for maintaining cellular homeostasis, allowing cells to acquire essential nutrients and eliminate waste efficiently. It encompasses various mechanisms that facilitate the movement of substances based on their concentration differences, ensuring that cells function optimally.
Phospholipid bilayer: The phospholipid bilayer is a fundamental structure of cell membranes, consisting of two layers of phospholipids with hydrophilic (water-attracting) heads facing outward and hydrophobic (water-repelling) tails facing inward. This arrangement creates a semi-permeable membrane that separates the interior of the cell from the external environment, playing a crucial role in maintaining cellular integrity and function.
Plasmolysis: Plasmolysis is the process in which cells lose water in a hypertonic solution, leading to the contraction of the cell membrane away from the cell wall. This occurs when the surrounding solution has a higher concentration of solutes than the inside of the cell, causing water to move out through osmosis. The result is a significant change in cell turgor pressure, affecting the cell's structure and function.
Selective permeability: Selective permeability is the property of a biological membrane that allows certain molecules to pass through while blocking others. This feature is crucial for maintaining the internal environment of cells, enabling them to regulate the entry and exit of substances essential for cellular function and homeostasis.
Semipermeable membrane: A semipermeable membrane is a biological barrier that allows certain molecules or ions to pass through while blocking others, maintaining the distinct composition of different environments. This selective permeability is crucial for processes like passive transport, where substances move across the membrane without the need for energy. The membrane's structure, typically composed of a lipid bilayer with embedded proteins, plays a key role in its ability to control the flow of materials.
Simple diffusion: Simple diffusion is the passive movement of molecules from an area of higher concentration to an area of lower concentration without the need for energy input. This process occurs across a semipermeable membrane and is driven by the concentration gradient, allowing substances to move freely until equilibrium is reached. It plays a vital role in various biological processes, including nutrient absorption and waste removal in cells.
Solute: A solute is a substance that is dissolved in a solvent to form a solution. In biological systems, solutes can be ions, molecules, or gases that are distributed within cells and fluids.
Tonicity: Tonicity refers to the ability of a solution to affect the volume and pressure of a cell by osmosis, depending on the concentration of solutes in the solution compared to that inside the cell. It is essential for understanding how cells interact with their environment, as it determines whether water will move into or out of the cell, influencing cellular function and homeostasis.
Transmembrane Proteins: Transmembrane proteins are integral membrane proteins that span across the lipid bilayer of a cell's plasma membrane. These proteins play crucial roles in various cellular processes, including transport, communication, and signaling by providing pathways for substances to enter or exit the cell and allowing cells to interact with their environment.
Turgor pressure: Turgor pressure is the internal pressure exerted by the fluid (typically water) inside a plant cell against its cell wall, which helps maintain the cell's shape and rigidity. This pressure plays a crucial role in keeping plants upright and is a result of the osmotic movement of water into the cell, causing it to swell. When turgor pressure is adequate, it ensures that the plant remains turgid, supporting various physiological processes.