Unit 2 Quiz Flashcards (Passive/Active Transport and Tonicity)

Substances that can pass through the membrane easily

Small, nonpolar, hydrophobic molecules

• ex. hydrocarbons

Substances that can’t pass through the membrane easily

Large, polar, hydrophilic molecules/ions

• ex. sugars/waters

Passive Transport

Transport of molecules that doesn’t require energy from the cell because a solute is moving with/down its concentration or electrochemical gradient.

• involved in the import of materials and export of waste

Diffusion

A spontaneous process resulting from the constant motion of molecules

• Substances move from a high to a low concentration

• Move down the concentration gradient

• Molecules diffuse directly across the membrane

• Different rates of diffusion for different molecules

Osmosis

The diffusion of water down its concentration gradient across a selectively permeable membrane.

• It can also be thought of as the diffusion of water from areas of low solute concentration to areas of high solute concentration.

Facilitated Diffusion

Diffusion of molecules through the membrane via transport proteins

• Increased rate of diffusion for small ions, water, carbohydrates

• Each transport protein is specific for substances it can facilitate the movement of (Channel and Carrier proteins).

Channel Proteins

Provide a channel for molecules and ions to pass

• The channel is hydrophilic

• Mainly are gated channels

• Only allow passage when there is a stimulus

• Aquaporins: Specific channel protein for water

Carrier Proteins

Undergo conformational changes for substances to pass

Active transport

Transport of a molecule that requires energy (ATP) because it moves a solute against its concentration gradient.

• Pumps

• Cotransport

• Exocytosis

• Endocytosis

Adenosine Triphosphate (ATP)

• ATP can transfer the terminal (outermost) phosphate group to the transport protein, which changes the shape (conformational change) of the transport protein to better move a substance

• ADP means a phosphate group was used in ATP (Can come back in cellular respiration).

Pumps

Maintain membrane potential

Membrane Potential

Unequal concentrations of ions across the membrane result in an electrical charge/electrochemical gradient.

• The cytoplasm is relatively negative in comparison to the extracellular fluid energy stored in electrochemical gradients

Electrogenic Pumps

Proteins generate voltage across membranes, which can be used later as an energy source for cellular processes.

• Voltage is a force that prompts electron movement

Sodium Potassium Pump

Animal cells will regulate their relative concentrations of NA+ and K+

• 3 NA+ get pumped out of the cell

• 2 K+ get pumped into the cell

• Results in a +1 net charge to the extracellular fluid

• NA+ and K+ are used for nerve signals

Proton Pump

An integral membrane protein that builds up a proton gradient across the membrane

• Used by plants, fungi, and bacteria

• Pumps H+ out of the cell

Cotransport

The protein-mediated coupling of a favorable movement of one substance with an unfavorable movement of another substance.

• Uses the energy stored in electrochemical gradients (generated by pumps) to move substances against their concentration gradient.

• Favorable movement: downhill diffusion

• Unfavorable movement: uphill diffusion

• Plants use cotransport for sugars and amino acids (ex., sucrose-H+)

• Sucrose can travel into a plant cell against its concentration gradient ONLY if it is coupled with H+ that is diffusing down its concentration gradient

How are large molecules transported?

Endocytosis and Exocytosis

Exocytosis

The secretion of molecules via vesicles that fuse to the plasma membrane

• vesicles can fuse to the membrane by forming a bilayer

• Once fused, the contents of the vesicle are released to the extracellular fluid

• Ex. nerve cells releasing neurotransmitters

Endocytosis

The uptake of molecules from vesicles fused with the plasma membrane (Opposite of exocytosis)

• Phagocytosis

• Pinocytosis

• Receptor-Mediated

Phagocytosis

When a cell engulfs particles to be later digested by lysosomes

• The cell surrounds the particle with pseudopodia

• Packages particles into a food vacuole

• The food vacuole fuses with a lysosome to be digested

Pinocytosis

A cell takes in dissolved molecules in a protein-coated vesicle

• The protein coat helps to mediate the transport of molecules

Receptor-mediated Endocytosis

Specific uptake of molecules via solute binding to receptors on the plasma membrane.

• Allows the cell to take up large quantities of a specific substance

• When solutes bind to the receptors, they cluster in a coated vesicle to be taken into the cell.

Tonicity

The ability of an extracellular solution to cause a cell to gain or lose water.

• Depends on the concentration of solutes that cannot pass through the cell membrane

Osmoregulation

The cell’s ability to regulate its solute concentrations and maintain water balance

• Animal cells will react differently from cells with cell walls, like plants, fungi, and some protists

Isotonic Solution

• Cells have no net movement of water

• The concentration of nonpenetrating solutes inside the cell is equal to that outside of the cell

• Water diffuses into the cell at the same rate water moves out of the cell

Hypertonic Solutions

• Cells lose water to their extracellular surroundings

• The concentration of nonpenetrating solutes is higher outside of the cell

• Water will move to the extracellular fluid

• Cells shrivel and die

Hypotonic Solution

• Cells gain water

• The concentration of nonpenetrating solutes is lower outside of the cell

• The cell will gain water

• Animal cells swell and lyse

• Plant cells work optimally (turgor pressure is supported)

Water Potential

A physical property that predicts the direction water will flow

• Includes the effects of solute concentration and physical pressure

Water will flow from areas of…

• Higher water potential in areas of low water potential

• Low solute to areas of high solute concentration

• High pressure over areas of low pressure

High water potential: Low solutes/high pressure

Low water potential: High solutes/low pressure

Electrochemicals

Form of energy (ions)