Crossing Membranes Flashcards
What keeps molecules moving when they are in a gas or a liquid?
Kinetic energy
What is a passive process?
Relies on the kinetic energy that mols have (diffusion)
What is equilibrium?
no overall movement of mols in one direction, no net movement, after diffusion mols are distributed evenly
What is the rate of diffusion affected by?
Diffusion increased if: Increased temp = more KE, concentration gradient steeper, stirring liquid/air currents in gas, greater SA to diffuse across, thinner membrane, small mols/ions
How do lipid based mols diffuse across the membrane?
membrane made of phospholipids so fat-soluble mols can pass through, down concentration gradient, steroid hormones
How do small ions/mols pass across the membrane membrane?
CO2 and O2 small enough to pass through bilayer between phospholipid mols, water mols small enough can pass even though some are polar (charged)
How do large/charged mols pass across the membrane?
sodium ions or glucose mols cant pass: need protein mols to help via facilitated diffusion
What are channel proteins?
forms pores in membrane, shaped to allow one ion to pass through, many are gated (open or closed)
What are carrier proteins?
Shaped so a specific mol can fit into them, when fitted the protein changed shape to allow mols to pass to other side of membrane
Why is active transport necessary?
Need to move mols against concentration gradient like Mg ions from soil into plant for chlorophyll, helps us adsorb glucose from intestines
How do protein pumps differ when used in active transport?
they carry specific mols across, use ATP, carry mols in opposite direction to concentration gradient, much faster than diffusion rate, mols accumulated inside/outside cells
What is an example of active transport?
Muscle fibres only contract if calcium ions present, when muscle stimulated, Ca ions released from membrane bound stores (endoplasmic reticulum), then need to be pumped rapidly back into store by Ca ion pumps
What is endocytosis?
Large quantities of material being moved into the cell
What is exocytosis?
Large quantities of material being moved out of the cell
How is bulk transport possible in cells?
Membranes can easily fuse, separate and pinch off, requires ATP which is used to move vesicles
