1. Chapter 3 Movement of Substances

2. 3.1 Diffusion
Diffusion 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. 3.1.1 Concentration Gradient
Concentration Gradient is the difference in concentration between two regions
The steeper the gradient, the faster rate of diffusion it will occur.

4. 3.1.2 Diffusion across a membrane
Cell 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.

5. Osmosis
Osmosis 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.

6. Water Potential Hypertonic: Lesser water molecules
Hypotonic : More water molecules
Isotonic: Equal water molecules
Water potential is a measure of the tendancy of water to move from one place to another.
Dilute solution > Concentrated solution
When partially permeable membrane separates 2 solutions of different water potential, a water potential gradient is established.

7. Hypotonic – High Water Potential
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.

8. Hypertonic – 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.

9. Turgor Pressure in Plants
Maintaining shape of soft tissues in plants
To keep the plants firm and remains upright
Without turgor, plants will wilt
Opening 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.

10. Turgor Pressure in Plants
Exertion 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.

11. 3.3 Surface Area to Volume Ratio
Rate 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.

12. 3.4 Active Transport
Movement 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.

13. Movement of Substances
Diffusion
Refer to any substances
Membrane not required.
Osmosis
Refers to only water
Partially permeable required
Active Transport
Energy Required
Movement of substances is against concentration gradient