BSCI170: Passive and Active Transport

notes from 10/20 + 10/15

What are the functions of the central vacuole in plant cells?

• regulates transport of water

• maintains cell wall rigidity bc when it inflates with water, it puts pressure on the walls

Passive Transport: characteristics

• naturally occurring

• no energy needed

• most direct forms of transport are passive

• used for small, nonpolar molecules

Passive Transport: Types of Passive Transport 

• Diffusion

  • Simple diffusion

  • Facilitated diffusion

What is diffusion?

Movement of area from high concentration to area of low concentration until equilibrium is reached

What is a concentration gradient?

difference in concentration of a solute across a region

• things move down a concentration gradient

What is simple diffusion

diffusion that transports small, nonpolar molecules through the cell membrane

What is facilitated diffusion

diffusion that transports polar, charged molecules w/ the help of transport proteins

• faster than simple diffusion

Types of transport proteins?

• Channel protein

• Carrier protein

What is a channel protein? Examples?

channel for small nonpolar molecules to go through

• specific for one type of ion/molecule

• ex. aquaporins for water, ion channels (either open 24/7 or gated) for ions

What are the types of gated channels?

• Ligand

• Voltage

What is a ligand channel?

type of gated channel protein that opens and closes in response to binding a specific ligand/chemical signal

What is a voltage channel?

type of gated channel protein that opens and closes in response to a change in voltage

What are carrier proteins?

binds w/ molecules and changes shape to push polar molecules through

Types of carrier proteins and their function

• Uniporter: carries 1 specific molecule

• Symporters: carries 2 different molecules in the same direction

• antiporters: carries 2 different molecules in different directions

What affects diffusion rate?

• extent of concentration gradient: the difference in concentration

• mass of molecules: heavier molecules move slower

• temperature: high temp leadsto faster movement

• solvent density: more dense = slower

• solubility: nonpolar molecules diffuse faster than polar ones

• surface area: more surface area = faster

• distance: greater distance = slower

What is osmosis?

diffusion of water from an area of low concentration to an area of high concentration

• water is inversely proportional to concentration of solute; more solute = less water, less water = more solute

What is osmolarity?

total solute concentration

What is tonicity, and what are the types of tonicity?

how a solute and osmosis affects a cell volume by describing the concentration in/out of a cell

• hypotonic

• hypertonic

• isotonic

Isotonic

solute concentration is the same in and out of the cell. no net movement of water

Hypotonic

solute concentration is less on the outside. net water movement into the cell

• cell can burst

Hypertonic

solute concentration is more on the inside, net water movement out of the cell

• cell shrinks and dies

What is active transport

molecules move from an area of low concentration to an area of high concentration

• goes against the concentration gradient, which is why it needs energy

Types of Active Transport and their Characteristics

• Primary active transport: uses ATP hydrolysis (breaks ATP to gain energy)

• Secondary active transport: doesn’t directly use ATP; uses the energy of one molecule moving down to move another molecule down