3.2.3 Transport across the cell membrane Flashcards
Q: What is the basic structure of all cell membranes in eukaryotic cells?
A: The basic structure of all cell membranes, including cell-surface membranes and the membranes around organelles, is the same and is described by the fluid-mosaic model.
Q: What components are included in the fluid-mosaic model of membrane structure?
A: The fluid-mosaic model includes phospholipids, proteins, glycoproteins, glycolipids, and cholesterol.
Q: How are phospholipids arranged in the cell membrane, and what is their role?
A: Phospholipids are arranged in a bilayer, with hydrophobic tails facing inward and hydrophilic heads facing outward. This arrangement forms a barrier that selectively allows substances to enter or exit the cell
Q: What is the function of proteins in the cell membrane?
A: Membrane proteins function as channels, carriers, receptors, and enzymes, facilitating the movement of substances across the membrane and playing roles in cell signaling.
Q: What roles do glycoproteins and glycolipids play in the cell membrane?
A: Glycoproteins and glycolipids are involved in cell recognition, signaling, and interactions with the extracellular environment.
Q: How does cholesterol affect the cell membrane?
A: Cholesterol is present in the cell membrane where it restricts the movement of other molecules, adding stability to the membrane and making it less permeable to very small water-soluble molecules.
Q: What is simple diffusion, and what limits it across the phospholipid bilayer?
A: Simple diffusion is the passive movement of molecules from an area of high concentration to an area of low concentration. It is limited by the hydrophobic core of the phospholipid bilayer, which restricts the movement of polar and large molecules.
Q: How does facilitated diffusion differ from simple diffusion?
A: Facilitated diffusion involves the movement of molecules across the membrane through specific carrier proteins or channel proteins, allowing substances that cannot directly diffuse through the bilayer to move across the membrane passively.
Q: What is osmosis, and how is it explained in terms of water potential?
A: Osmosis is the passive movement of water molecules across a semi-permeable membrane from an area of higher water potential to an area of lower water potential.
Q: Describe the process of active transport across cell membranes.
A: Active transport is the movement of molecules or ions against their concentration gradient, requiring energy from the hydrolysis of ATP. It involves carrier proteins that change shape to move substances across the membrane.
Q: What is co-transport, and how is it illustrated by the absorption of sodium ions and glucose in the mammalian ileum?
A: Co-transport is a type of active transport where two substances are simultaneously transported across a membrane by one protein. In the mammalian ileum, sodium ions move down their concentration gradient into the cell, while glucose is transported against its concentration gradient using the energy from sodium’s movement.
Q: How are cells adapted for rapid transport across their membranes?
A: Cells may be adapted by increasing the surface area of the membrane or by increasing the number of protein channels and carrier molecules in the membrane, facilitating faster transport of substances.
Q: How does surface area affect the rate of movement across cell membranes?
A: An increased surface area provides more space for molecules to pass through, enhancing the rate of diffusion or transport across the membrane.
Q: How do the number of channel or carrier proteins affect transport rates across membranes?
A: A greater number of channel or carrier proteins increases the rate at which specific molecules can be transported across the membrane.
Q: What effect do gradients of concentration or water potential have on the rate of movement across membranes?
A: Steeper concentration or water potential gradients result in a faster rate of diffusion, osmosis, or active transport across membranes.
