AP Bio Unit 2: Module 10-12

Concentration gradient

difference in concentration of molecules across a space; the natural expected way for molecules to move from high concentration to low in order to create dynamic equilibrium

Simple diffusion

a type of passive transport of small molecules without an aid (O2, CO2, N2, and only small amounts of H2O)

What is the driving force of simple diffusion?

concentration gradient, molecules naturally move from an area of high concentration to low concentration until dynamic equilibrium is reached

What kind of transport goes against the concentration gradient?

active transport, uses ATP

What is active transport?

movement against the concentration gradient, meaning molecules go from an area of low concentration to high concentration; this requires energy (ATP) and usually involves a transport protein. WILL NOT reach dynamic equilibrium

What is passive transport?

movement of molecules across a membrane without using ATP, going from high concentration to low concentration (concentration gradient)

What is facilitated diffusion?

passive transport where molecules move down their concentration gradient (high → low) through transport proteins in the cell membrane, without using energy (ATP).

What do facilitated diffusion and active transport have in common?

they are both a kind of facilitated transport; meaning they transport large, polar, and charged molecules that require facilitation, or help of channel proteins to cross the membrane.

What is exocytosis?

process by which cells release molecules, or waste, into the extracellular space, by fusing a vesicle with the cell membrane and pushing the contents out the cell, requires the input of ATP (exo→outside)

What is endocytosis?

process by which cells take in molecules into the intracellular space, by forming a vesicle inside the cell, requires the input of ATP (endo→inside)

What is phagocytosis?

a type of endocytosis where a cell surrounds and ingests large particles, like food or bacteria (even dead cells), forming a vesicle to digest them (sometimes called cellular eating)

Process of diffusion

the passive movement of molecules from an area of high concentration to an area of low concentration due to their random motion, until equilibrium is reached.

How does facilitated diffusion by channel proteins differ from facilitated diffusion by carrier protein?

Facilitated diffusion by channel proteins uses pores or tunnels in the membrane that allow the molecule or ions to pass quickly by concentration gradient, while by carrier proteins involves the protein changing shape to bind and transport the molecule across the membrane.

What is the important difference between phagocytosis and endocytosis?

Phagocytosis is a specific type of endocytosis in which the cell engulfs large particles or microorganisms, while endocytosis is the broader process of bringing substances into the cell by forming vesicles from the plasma membrane.

When can something pass through the membrane without proteins?

when it is small, nonpolar, or lipid-soluble, allowing it to diffuse directly through the phospholipid bilayer by simple, passive diffusion.

ex: H2O, CO2, O2

Hypotonic solution?

less solute, more water outside the cell; water will move inside the cell bc of the concentration gradient, can swell + burst (turgid)

Isotonic solution?

same amount of solute, same amount of water; water’s net movement is equal and cell is at dynamic equilibrium (flaccid)

Hypertonic solution?

more solute, less water outside the cell; water will move outside the cell bc of concentration gradient, causes cell to shrink (plasmolyzed)

What is osmosis?

the passive diffusion of water molecules across a selectively permeable membrane from an area of high water potential (low solute concentration) to an area of low water potential (high solute concentration) until dynamic equilibrium is reached

How is the process of osmosis?

water molecules move through the cell membrane (often through aquaporins) from the side with more free water molecules (lower solute concentration) to the side with fewer free water molecules (higher solute concentration). this movement continues passively, without energy, until the concentrations of water and solute reach equilibrium on both sides.

What is the difference between osmosis and diffusion?

diffusion is the passive movement of any type of molecule, while osmosis is a specific type of diffusion that involves the movement of water molecules across a selectively permeable membrane from high to low concentration

If the plasma membrane becomes hypotonic compared with the blood cells, what would be the effect?

this means the outside has more water than the inside, therefore the water will move into the cell by osmosis, causing the cell to swell and possibly burst

What is turgor pressure?

the force the water exerts back on the cell wall, exerted by water osmosis into the cell (specifically in the vacuole) pushing on the cell wall

Why is turgor pressure essential for plant life?

because it keeps cells rigid, allowing plants to stand upright, maintain structure, and support growth. without it, cells lose water, the plant wilts, and necessary functions are disrupted.

What is osmotic pressure?

the amount of force applied to a solution that prevents solvent from moving across a semipermeable membrane

What is water potential?

(symbol: Ψ) is a measure of the water's tendency to move from one location to another due to energy differences, such as those created by solutes or pressure. it is calculated by combining the solute potential (influenced by the concentration of dissolved substances) and the pressure potential (physical pressure) of the water system. 

What is osmoregulation?

the biological process where organisms maintain a stable internal balance of water and salts, known as homeostasis, to ensure proper cell function. vital for survival, allowing organisms to adapt to different environments by controlling water and electrolyte concentrations despite external changes.

ex. freshwater fish must prevent too much water from entering their bodies, while saltwater fish need to avoid excessive water loss.