Passive, active, and bulk transport

What are the 3 types of transport?

passive, active, and bulk transport

What is a concentration gradient?

• Integral proteins

small nonpolar molecules do not need integral proteins

What is passive transport?

• Movement of molecules across cell membrane that does not require energy

• simple diffusion, facilitated diffusion, and osmosis

What is active transport?

• Energy (ATP) is required

• ATP is used to pump nutrients across cell membranes

• Against the concentration gradient

What is diffusion?

A process where molecules move from a high concentration to a low concentration along the concentration gradient until equilibrium is achieved

What is simple diffusion?

• Small, non-polar (O₂ and CO₂) and uncharged polar (glycerol) molecules can freely pass through the bilayer

• Follows the concentration gradient

• Does not require energy or transport proteins

What is facilitated diffusion?

• Small polar (Na⁺, Cl^-, K⁺, Ca²⁺) and large (glucose) molecules enter/exit the cell with the assistance of transport and carrier proteins

• Follows the concentration gradient

• No energy required

What is osmosis?

• The process by which water enters and exits the cell

• Water follows the concentration gradient of other solutes via an integral protein (aquaporines)

  • Travels from a low solute concentration to a high solute concentration until equilibrium is reached

• Osmosis is a vital fluid control process (e.g. blood and urine balance)

• No energy is required, but transport proteins are needed

What is tonicity?

The ability of an extracellular solution to make water enter or exit a cell by osmosis

What are the 3 osmotic conditions of the solution surrounding the cell?

Hypertonic, isotonic, and hypotonic solutions

What happens to a cell (animal and plant) when it is in a hypotonic solution?

• A hypotonic solution is an unsaturated solution

• Net inflow of water

  • More water enters the cell because there is a greater solute concentration in the internal environment

• In animal cells, this results in lysis, where the cell membrane ruptures

• In plant cells, this results in turgor pressure (cells are turgid), the ideal state in which the vacuole is filled.

What happens to a cell (animal and plant) when it is in an isotonic solution?

• An isotonic solution is a mostly balanced solution

• No net flow of water

  • Water exits and enters the cell at a steady rate to adjust until equilibrium between the solute in the internal and external environment is reached

• In animal cells, this is the ideal state

• In plant cells, this results in a flaccid cell

What happens to a cell (animal and plant) when it is in a hypertonic solution?

• A hypertonic solution is a highly oversaturated solution

• Net outflow of water

  • More water exits the cell because there is a greater solute concentration in the external environment

• In animal and plant cells, this is not ideal as it results in:

  • Shrivelled animal cells

  • Plasmolyzed plant cells

What is bulk transport?

• Allows for very large molecules (hormones, polysaccharides, etc) to enter and exit the cells

• Uses vesicles and ATP

What are the 2 types of bulk transport?

endocytosis and exocytosis

What is exocytosis?

• Moving materials into cells

What are the 3 types of endocytosis?

phagocytosis, pinocytosis, receptor mediated endocytosis

What is phagocytosis?

• Cell eating

• The cell moves around the particle and surrounds it

• For larger molecules

• Used by white blood cells and amoeba

What is pinocytosis?

• Cell drinking

• The cell pinches inward to “swallow” the contents

• For smaller molecules dissolved in water or liquids

• Same process as phagocytosis except the cell is moving liquids such as water

What is receptor-mediated endocytosis (RME) or carrier-mediated endocytosis?

• Specialized system

• Transport of certain important molecules or ions into the cell

• Molecules bind to receptors on the cell membrane before being internalized

• e.g. moving cholesterol into the cell (hypercholesterolemia) or iron carried through the blood tightly bound to transferrin protein

What is exocytosis?

• Moving materials out of the cell

• The reverse of pinctosis

• The vesicle (originally from the Golgi apparatus) fuses with the membrane and expels the contents

• e.g. hormones

What is the endomembrane system?

Series of membrane-bound organelles used to produce, package, process and ultimately export cellular materials

What are the two types of active transport?

primary and secondary active transport

What is primary active transport?

• Using ATP, carrier proteins pump substances across a membrane from an area of low concentration to an area of high concentration

• e.g. Na⁺ and K⁺ in neve cells

What is secondary active transport?

• When ions (like H⁺ and Cl^-) create electrochemical gradients, which are used to fuel active transport of other substances against the gradient

• Also key for the generation of ATP

• e.g. hydrogen-sucrose pump in plants

What is ATP?

• Adenosine triphosphate

• Molecule that carries energy in the cell

• When the cell needs energy, ATP is broken down via hydrolysis reaction by removing a phosphate group and releasing the energy to where it is needed in the cell