CHAPTER 2: MOVEMENT OF SUBSTANCES

2.1 What is diffusion?

Definition: Diffusion is the net movement of particles from a region of a higher concentration to a region of a lower concentration, down a concentration gradient.

FACTORS THAT AFFECT THE RATE OF DIFFUSION

• Diffusion distance

• Surface area-to-volume ratio

• Concentration gradient

2.2 What is osmosis?

Definition: 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

What will happen when a plant cell is placed in a solution of…

Higher water potential

• Cell sap has a lower water potential than solution outside

• Water molecules will enter the cell through the partially permeable cell membrane via osmosis

• The vacuoles increases in size and pushes the cytoplasm against the cell wall

• Does not burst due to cell wall

• The cell expands or swells and is said to become turgid

Lower water potential

• Cell sap has higher water potential than the outside

• Water molecules from the vacuoles and cytoplasm leave the cell through partially permeable cell membrane via osmosis

• The vacuoles decreases in size

• The cytoplasm shrinks away from the cell wall

• The shrinkage of cytoplasm and cell membrane from the cell wall is called plasmolysis

• The cell becomes flaccid or limp

What will happen when an animal cell is placed in a solution of…

Higher water potential

• Cytoplasm has a lower water potential than outside

• Water molecules enter the cell via osmosis

• Animal cell will swell and may even burst due to the lack of cell wall

Lower water potential

• Cytoplasm has a higher water potential than outside

• Water molecules move out of the cell via osmosis

• The cell shrinks and spikes appear on the cell surface

• This process is called cremation

• It will become dehydrated and eventually die