Cell Membrane
Differences in surface-to-volume ratios affect the capacity of a biological system to obtain resources and eliminate wastes.
Membranes allow cells to create and maintain internal environments that differ from external environments that differ from external environments.
The structure of the cell membrane results in selective permeability; the movement of molecules across them via osmosis, diffusion and active transport maintains dynamic homeostasis.
-The surface area of the plasma membrane must be large enough to adequately exchange materials.
-Smaller cells are better equipped for material exchange with their environments based on their larger surface area-to-volume ratio
Cell membranes separate the internal environment of the cell from the external environment. The specialized structure of the membrane, described in the fluid mosaic model, allows the cell to be selectively permeable, with dynamic homeostasis maintained by the constant movement of molecules across the membrane.
Passive Transport does not require the input of metabolic energy because spontaneous movement of molecules occurs from high to low concentrations; examples of passive transport are osmosis, diffusion, and facilitated diffusion.
- plays a primary role in the import of resources and the export of wastes
- membrane proteins play a role in facilitated diffusion of charged and polar molecules through a membrane
-glucose transport, Na+/K+ transport
(no particular membrane protein is required for teaching this concept)
- external environments can be hypotonic, hypertonic, or isotonic to internal environments of cells
Active transport requires metabolic energy and transport proteins to move molecules from low concentration to high concentration.
Active transport establishes concentration gradients vital for dynamic homeostasis, including sodium/potassium pumps in nerve impulse conduction and proton gradients in electron transport chains in photosynthesis and cellular respiration.
-active transport is a process where free energy (usually provided by ATP) is used by proteins embedded in
the membrane to "move" molecules and/or ions across the membrane and to establish and maintain
concentration gradients
-Membrane proteins are necessary for active transport.
The processes of endocytosis and exocytosis move large molecules from the external environment to the internal environment and visa versa, respectively.
-in exocytosis, internal vesicles fuse with the plasma membrane to secrete large macromolecules out of the cell.
-in endocytosis, the cell takes in macromolecules and particulate matter by forming new vesicles derived from the plasma membrane.
A. Cell membranes separate the internal environment of the cell from the external environment.
B. Selective permeability:
-Cell membranes consist of a structural framework if phospholipid molecules, embedded proteins, cholesterol, glycoproteins and glycolipids.
-Phospholipids give the membrane both hydrophilic and hydrophobic properties. The hydrophilic phosphate portions of the phospholipids are oriented toward the aqueous external or internal environments, while the hydrophobic fatty acid portions face eachother within the interior of the membrane itself.
-Embedded proteins can be hydrophilic, with charged and polar side groups, or hydrophobic, with nonpolar side groups.
-Small, uncharged polar molecules and small nonpolar molecules, such as N2, freely pass across the membrane. Hydrophilic substances such as large polar molecules and ions move across the membrane through embedded channel and transport proteins. Water moves across membranes and through channel proteins call aquaporins.
C. Cell wall provide a structural boundary, as well as a permeability barrier for some substances to the internal environments:
-Plant cell walls are made of cellulose and are external to the cell membrane.
-Other examples are cell walls of prokaryotes and fungi
SKILLS REQUIRED:
-Use calculated SA-to-V ratios to predict which cell/s would eliminate wastes or obtain nutrients faster via diffusion.
-Explain how cell size and shape affect the rate of nutrient acquisition and waste elimination.
-use representations and models to pose scientific questions about the properties of cell membranes and selective permeability based on molecular structure.
-construct models that connect the movement of molecules across membranes with membrane structure and function.
-use representations and models to analyze situations or solve problems qualitatively and quantitatively to investigate whether dynamic homeostasis is maintained by the active movement of molecules across membranes.
-represent graphically or model quantitatively the exchange of molecules between an organism and its environment, and the subsequent use of these molecules to build new molecules that facilitate dynamic homeostasis, growth and reproduction
Membranes allow cells to create and maintain internal environments that differ from external environments that differ from external environments.
The structure of the cell membrane results in selective permeability; the movement of molecules across them via osmosis, diffusion and active transport maintains dynamic homeostasis.
-The surface area of the plasma membrane must be large enough to adequately exchange materials.
-Smaller cells are better equipped for material exchange with their environments based on their larger surface area-to-volume ratio
Cell membranes separate the internal environment of the cell from the external environment. The specialized structure of the membrane, described in the fluid mosaic model, allows the cell to be selectively permeable, with dynamic homeostasis maintained by the constant movement of molecules across the membrane.
Passive Transport does not require the input of metabolic energy because spontaneous movement of molecules occurs from high to low concentrations; examples of passive transport are osmosis, diffusion, and facilitated diffusion.
- plays a primary role in the import of resources and the export of wastes
- membrane proteins play a role in facilitated diffusion of charged and polar molecules through a membrane
-glucose transport, Na+/K+ transport
(no particular membrane protein is required for teaching this concept)
- external environments can be hypotonic, hypertonic, or isotonic to internal environments of cells
Active transport requires metabolic energy and transport proteins to move molecules from low concentration to high concentration.
Active transport establishes concentration gradients vital for dynamic homeostasis, including sodium/potassium pumps in nerve impulse conduction and proton gradients in electron transport chains in photosynthesis and cellular respiration.
-active transport is a process where free energy (usually provided by ATP) is used by proteins embedded in
the membrane to "move" molecules and/or ions across the membrane and to establish and maintain
concentration gradients
-Membrane proteins are necessary for active transport.
The processes of endocytosis and exocytosis move large molecules from the external environment to the internal environment and visa versa, respectively.
-in exocytosis, internal vesicles fuse with the plasma membrane to secrete large macromolecules out of the cell.
-in endocytosis, the cell takes in macromolecules and particulate matter by forming new vesicles derived from the plasma membrane.
A. Cell membranes separate the internal environment of the cell from the external environment.
B. Selective permeability:
-Cell membranes consist of a structural framework if phospholipid molecules, embedded proteins, cholesterol, glycoproteins and glycolipids.
-Phospholipids give the membrane both hydrophilic and hydrophobic properties. The hydrophilic phosphate portions of the phospholipids are oriented toward the aqueous external or internal environments, while the hydrophobic fatty acid portions face eachother within the interior of the membrane itself.
-Embedded proteins can be hydrophilic, with charged and polar side groups, or hydrophobic, with nonpolar side groups.
-Small, uncharged polar molecules and small nonpolar molecules, such as N2, freely pass across the membrane. Hydrophilic substances such as large polar molecules and ions move across the membrane through embedded channel and transport proteins. Water moves across membranes and through channel proteins call aquaporins.
C. Cell wall provide a structural boundary, as well as a permeability barrier for some substances to the internal environments:
-Plant cell walls are made of cellulose and are external to the cell membrane.
-Other examples are cell walls of prokaryotes and fungi
SKILLS REQUIRED:
-Use calculated SA-to-V ratios to predict which cell/s would eliminate wastes or obtain nutrients faster via diffusion.
-Explain how cell size and shape affect the rate of nutrient acquisition and waste elimination.
-use representations and models to pose scientific questions about the properties of cell membranes and selective permeability based on molecular structure.
-construct models that connect the movement of molecules across membranes with membrane structure and function.
-use representations and models to analyze situations or solve problems qualitatively and quantitatively to investigate whether dynamic homeostasis is maintained by the active movement of molecules across membranes.
-represent graphically or model quantitatively the exchange of molecules between an organism and its environment, and the subsequent use of these molecules to build new molecules that facilitate dynamic homeostasis, growth and reproduction