Chapter 3 Chapter 3

Movement of SubstancesMovement of Substances

3.1 Diffusion3.1 DiffusionDiffusion is the net movement of

particles from a higher concentration region to a region of lower concentration.

After diffusion, overall concentration remains the same

Only happens in substance in gaseous or liquid state

3.1.1 Concentration Gradient3.1.1 Concentration GradientConcentration Gradient is the

difference in concentration between two regions

The steeper the gradient, the faster rate of diffusion it will occur.

3.1.2 3.1.2 Diffusion across a membraneDiffusion across a membraneCell Surface Membrane

◦Partially permeable surface◦Allow some substances to pass through

but not others◦Only small particles can pass through and

not others.◦Unicellular organism like amoeba get

oxygen and removes carbon dioxide by diffusion through the cell surface membrane.

OsmosisOsmosisOsmosis is the net movement of water

molecules from a region of higher water potential to a region of lower water potential through a partially permeable membrane.

Allow some substance to pass through but not other.

Water PotentialWater PotentialHypertonic: Lesser water moleculesHypotonic : More water moleculesIsotonic: Equal water moleculesWater potential is a measure of the

tendancy of water to move from one place to another.

Dilute solution > Concentrated solutionWhen partially permeable membrane

separates 2 solutions of different water potential, a water potential gradient is established.

Hypotonic – High Water Hypotonic – High Water PotentialPotential

Plant Cell Animal Cell-Water enters cell by osmosis.- Plant cell expands and become swollen/turgid causing the cell to be turgor (filled with water)-Pressure exerted by water on cell wall is call turgor pressure

- Cell expands and will eventually burst.

Hypertonic – Low Water PotentialHypertonic – Low Water Potential

Plant Cell Animal Cell-As cell loses water, vacuole decrease in size-Shrinkage of cytoplasm and cell membrane from cell wall is known as plasmolysis-Tissues of plant become flaccid-Plasmolysed cell can be restored to its original state.

-Shrink in size and become spiky Crenation- Cell become dehydrated and eventually die.

Turgor Pressure in PlantsTurgor Pressure in PlantsMaintaining shape of soft tissues in plantsTo keep the plants firm and remains uprightWithout turgor, plants will wiltOpening of flowers, moving of leaves and

opening/closing of guard cells are results of changes in turgor pressure

Plant requires turgor to keep them upright.Cutting stem of plant exposes inner cortex

cells.

Turgor Pressure in PlantsTurgor Pressure in PlantsExertion of cortex cells prevented by

epidermal cells which are prevented by cuticle layer

Cutting releases this restraint exerted by epidermis, thus cortex expands & cause strip to curl outwards.

3.3 Surface Area to Volume 3.3 Surface Area to Volume RatioRatioRate of movement of a substance across

the surface of a cell depends on how big the area of cell membrane is.

The greater the area of cell surface membrane per unit volume, the faster the rate of diffusion of a substance for a given concentration gradient.

Increase rate of diffusion, there must be presence of many small cells instead of one big cell.

3.4 Active Transport3.4 Active TransportMovement of molecule from a region of

low concentration to a region of high concentration against a concentration gradient.

Energy is required.Only occurs in living cells as living cell

respire.For example:

◦ Absorption of dissolved minerals by root hairs◦ Absorption of glucose and amino acids by cells in

small intestine.

Movement of Substances