diffusion and active transport Flashcards
what factors affect diffusion
size of gradient
membrane surface area
permeability of membrane (high lipid solubility, small molecules, thickness)
O2, CO2, fatty acids, steroid hormones
what does the rate of facilitated diffusion depend on
Number of carriers in membrane
Affinity — same both sides
Concentration of substance to be transported
describe facilitated diffusion
a way for certain molecules to move across a cell membrane without using energy. Instead of passing directly through the membrane, these molecules travel through carrier proteins. This helps substances like glucose or ions move more easily.
what type of transport opposes electrochemical gradient
active transport with ATP
what is secondary active transport
Uses a gradient created by active transport
E.g. Na+/K+/ATPase pump.
what is phosphorylation
adding a phosphate group to a molecule, usually a protein or ADP to make ATP
what is the ratio in a sodium pump
3:2 ratio of Na+ out to K+ in
(3 sodium out and 2 potassium in)
describe cotransport
Both substances move in the same direction across the membrane.
Example: Sodium-Glucose Transporter (SGLT) in the intestines, where Na⁺ moves into the cell and brings glucose with it.
describe countertransport
Substances move in opposite directions across the membrane.
Example: Sodium-Calcium Exchanger (NCX), where Na⁺ moves into the cell while Ca²⁺ is pumped out.
what is the resting membrane potential of a cell
negative 70milivolts
(inside of cell has a negative potential compared to outside cell)
why does the separation of opposite charges across plasma membrane occur
Due to differences in concentration and permeability of key ions
what is the significance of membrane potential?
Lose positive charge every time so it keeps membrane potential negative
what are examples of passive membrane transport
carriers and channels
(facilitated diffusion, ion channels)
what is an example of active membrane transport
pumps
describe the graph for concentration gradient
straight diagonal line
is facilitated diffusion passive or active
passive
what are the steps of facilitated diffusion
- molecule needs to enter cell and comes near a special transport protein in the membrane
- The molecule binds to the carrier protein, which is specifically shaped to recognize and transport it
- The carrier protein changes its shape (conformational change), allowing the molecule to pass through.
- Once the shape changes, the molecule is released on the other side of the membrane, into the cell.
- The carrier protein resets to its original form, ready to transport another molecule.
describe Diffusion through Ion Channels
a type of passive transport that allows specific ions (like Na⁺, K⁺, and Cl⁻) to move across the cell membrane through specialized protein channels.
- both end of channel are open
- each channel is specfic to a certain ion
- no energy required
what is the sodium potassium pump (Na⁺/K⁺ ATPase)
an active transport mechanism that moves sodium (Na⁺) out of the cell and potassium (K⁺) into the cell using ATP.
what are the steps of the sodium potassium pump
- Three Na⁺ (sodium) ions from inside the cell bind to the pump.
- ATP is used, and a phosphate group attaches to the pump (phosphorylation), causing a shape change (Resting state is pump is open on inside, so changes it to be open on outside)
- The shape change moves the Na⁺ ions out of the cell.
- Two K⁺ (potassium) ions from outside bind to the pump.
5.The phosphate group is removed, returning the pump to its original shape. - The two K⁺ ions are released inside the cell, and the cycle repeats.
why is ATP needed in the sodium potassium pump
sodium and potassium are moving aganist gradient
why is the sodium potassium pump crucial
Helps maintain cell potential and fluid balance
what is used to record cell membrane potential
a microelectrode
what is the Electrical Driving Force
the force exerted on charged particles (ions) due to the difference in electrical charge across the cell membrane.
- Opposite charges attract (positive ions move toward negative areas, and vice versa).
- Like charges repel (positive ions move away from positive areas, and vice versa).
- EDF influences the movement of ions independent of their concentration gradient.
what are the names of positive and negative charged particles
anions - negative
cations - positive
is extracellular fluid positively and negatively charged
cations > anions
Net positive
is intracellular fluid positive and negatively charged
Anions > cations
net negative
Name three cations found in the body fluids and state whether their concentration is higher inside or outside of the cell.
Sodium (Na⁺) – Higher concentration outside the cell (extracellular fluid).
Potassium (K⁺) – Higher concentration inside the cell (intracellular fluid).
Calcium (Ca²⁺) – Higher concentration outside the cell (extracellular fluid).
Name three anions found in the body fluids and state whether their concentration is higher inside or outside of the cell.
Chloride (Cl⁻) – Higher outside the cell (extracellular fluid).
Bicarbonate (HCO₃⁻) – Higher outside the cell (extracellular fluid).
Phosphate (HPO₄²⁻ / H₂PO₄⁻) – Higher inside the cell (intracellular fluid).
Name 5 transport methods by which molecules can cross the cell membrane.
simple diffusion
facilitated diffusion
active transport
Endocytosis & Exocytosis
osmosis
