movement of substances (chapter 2) -o level pure bio

diffusion

the net movement of particles from a region of higher concentration to a region of lower concentration down a concentration gradient until equilibrium is reached.

concentration gradient

difference in concentration between 2 regions.

factors that affect the rate of diffusion

-surface area-to-volume ratio

-concentration gradient

-diffusion distance

osmosis

net movement of water molecules from a region of higher water potential to a region of lower water potential through a partially permeable membrane down a water potential gradient.

water potential

a measure of the tendency of water molecules to move from one place to another.

plant cell in solution of higher water potential

-water molecules will move into the cell via osmosis from a region of higher water potential to a region of lower water potential.

-the vacuole increases in size and the plant cell expands. the cell does not burst as it is protected by the inelastic cell wall.

-the cell is said to become turgid.

plant cell in an area of lower water potential

-water molecules move from a region of higher water potential to a region of higher water potential via osmosis from the cell’s vacuole out of the cell into the solution.

-cell becomes flaccid

-vacuole becomes smaller and cytoplasm shrinks away from the cell wall. (plasmolysis)

-cell is said to be plasmolysed

animal cell in solution of lower water potential

-water from the cell moves out of the cell into the solution from an area of higher water potential to an area of lower water potential via osmosis.

-cell shrinks and spikes appear on the cell

-this process is called crenation

-cell will eventually die if it remains crenated

animal cell in solution of higher water potential

-water molecules leave the cell and enter the solution by osmosis from a region of higher water potential to a region of lower water potential

-cell expands and bursts

importance of turgor in plants

turgor pressure in the cells of the plant help to keep non-woody plants firm and erect. when there is a high rate of water loss from cells, they lose their turgidity and wilt.

- also why you should not put too much fertiliser into soil as it will lower the water potential of the soil and water from the plants will move out of the cell instead.

active transport

cellular energy is used to move particles of a substances across a membrane against its concentration gradient from a region of lower concentration to higher concentration.

uses energy from respiration, hence it only occurs in living cells.