2.4. Passive and active transport, water potential Flashcards
What is the function of a PM (what does it maintain)? What are the two types of transport across it?
it acts as an effective barrier between aqueous solutions - it holds useful substances inside of the cell and prevents potentially harmful substances from entering it - it maintains homeostasis by controlling transport in and out of the cell.
- active and passive transport
What are the types of passive transport?
diffusion (simple and facilitated) and osmosis
Define diffusion. What are the two types of diffusion?
the net movement of particles from a region of their higher to a region of their lower concentration
simple and facilitated
Define simple and facilitated diffusion.
simple: diffusion of small, hydrophobic substances across a “bare” phospholipid layer - O2, CO2, ethanol, water (to some extent)
facilitated: diffusion of big, hydrophilic substances across the membrane through protein channels - glucose, amino acids, proteins, starch, sodium ions, water (mostly) – direction of movement cannot be controlled
Define concentration gradient.
the existence of the difference in concentrations of a specific particle of two different areas separated by a plasma membrane. The speed at which diffusion occurs depends on the difference between concentrations (how steep the concentration gradient is)
Define osmosis. How is it avoided in organ transportation?
the facilitated diffusion of water molecules across a semi-permeable membrane – the diffusion of water across the membrane from a region of lower solute concentration (hypotonic) to a region of higher solute concentration (hypertonic)
- by placing the donor organs inside isotonic solutions (0.9% NaCl or 5% glucose solution)
How does a cell keep control over diffusion?
the specific diameter size and the chemical properties of channels ensure that only one type of substance can pass through them
What is aquaporin? What does it increase? Where can it be found?
protein channel transporting water molecules
- only water can pass through due to the specific diameter size and chemical properties of its wall
- greatly increase membrane permeability to water molecules and they can be found in kidney cells and plant root cells
How are particles transported through protein pumps (describe the process)?
The solute enters the protein pump (carrier protein) and E from ATP changes the pump’s conformation so that its opening is on the other side of the membrane. The pump then goes back to its initial conformation spontaneously (no E/ATP required).
What is a solvation process?
when solvent (water) molecules surround and interact with solute particles (remove them from the crystal grid)
What is the Na/K pump called and why?
an exchange transporter/antiporter because it transports Na and K ions in the opposite directions
What is a resting potential? What is an action potential?
- unequal distribution of charges on opposite sides of the membrane while the cell is at rest
action potential – new distribution of charges across the membrane once the Na+ channels opened and let the ions inside (the membrane is still electrically polarized)
When is the resting potential of a neuron zero and why?
When the cell is dead, there is no ATP produced, so there is no source of E for the pump to perform its function and the membrane polarity goes to zero mV.
What is a nerve impulse?
the change of polarity of the membrane
What is indirect active transport? Explain with the sodium-glucose example.
Sodium-glucose cotransporters move Na+ and glucose together into the cell. First, Na+ moves down its C gradient, releasing ATP in the process. Glucose uses this ATP to move against its C gradient. This type of transport depends on the Na+ pump to pump ions back out and maintain the sodium gradient. This happens in the kidneys during the reabsorption of glucose and in the absorption of glucose from digested foods by the small intestine epithelial cells.
