Transport Across The Cell Membrane Flashcards
What are the methods of cell membrane transport? 6
- Diffusion
- Facilitated diffusion
- Osmosis
- Active Transport
- Exocytosis
- Endocytosis
Define “diffusion”
The net movement of molecules/ions from a region of higher concentration to one of lower concentration
What particles can undergo diffusion (that is not facilitated)?
- Small uncharged particles
- Hydrophobic (lipid soluble) molecules
Why can CO2 still undergo unfacilitated diffusion even though it is polar?
Its small size means it can undergo rapid diffusion
When does diffusion occur?
When there is a difference in concentration between two areas (a concentration gradient)
What is the relationship between the steepness of a concentration gradient and the rate of diffusion?
The steeper the concentration gradient, the higher the rate of diffusion
What does diffusion continue until?
Equilibrium - when the particles of the substances are equally spread throughout the whole volume
How do particles diffuse directly across cell membrane?
They pass between the lipid molecules in the bilayer
Define “facilitated diffusion”
Molecules crossing the membrane with the aid of proteins
Does facilitated diffusion require energy?
No it is a passive process
What type of particles use facilitated diffusion?
Hydrophillic polar molecules/ions larger than CO2
Why can’t hydrophillic molecules dissolve through the bilayer?
They are insoluble in lipids as the hydrophobic tails of phospholipids form an impenetrable barrier
What are the two kinds of proteins used for facilitated diffusion?
- Carrier proteins
- Channel proteins
What are channel proteins?
Water filled pores in the membrane which polar/charged molecules/ions can diffuse through
How do different channel proteins facilitate diffusion for different polar molecules?
By having a specific shape that only permits the passage of a specific protein type
What are gated channels?
Types of channel proteins that can be opened/closed depending on the presence/absence of a signal
What kind of signals can open/close a gated channel?
- A specific molecule (e.g hormone)
- A change in potential difference across the membrane
What do carrier proteins do?
Move large molecules in or out of the cell down the concentration gradient
How do carrier proteins work? 4
- A large molecule attaches to a carrier protein in the membrane
- The protein changes shape
- Releases molecule on opposite side of the membrane
Define “passive transport”
Transport where no metabolic energy is needed for transport as it is driven by the concentration gradient itself
Define “osmosis”
The net movement of water molecules from an area of high water concentration to an area of low water concentration across a partially permeable membrane
What kind of process is diffusion and osmosis?
Passive - needs no ATP
What is active transport?
Movement against the concentration gradient using energy from the hydrolysis of ATP
How does active transport occur?
- Molecule attaches to carrier protein
- Protein changes shape
- Moves molecule across membrane
- Releases it on the other side
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