Biology: Osmosis

Created on 25/9/24.

Osmosis

The movement of water molecules across a semi-permeable membrane from a region of high water concentration to a region of lower water concentration.

Diffusion

The movement of molecules from a region of high concentration to a region of lower concentration.

Give two examples of diffusion

1.) Water entering xylem of a leaf.

2.) Gas exchange in capillaries in the lungs.

What is osmosis known as

A special type of diffusion.

Membranes can be

1.) Impermeable

2.) Semi or selectively permeable

3.) Permeable

Impermeable

Substances can’t pass through.

Semi or selectively permeable

Allows some, but not all substances to pass through.

Permeable

Substances can pass through.

Turgor/Turgor pressure

The pressure the cytoplasm and vacuole exert on the cell wall of a plant.

What does turgor do for plants

Gives more strength to plants with no wood.

Turgid cell

When the cell is enlarged and swollen with water.

Plasmolysis

The movement of the cell membrane away from the cell wall.

What does plasmolysis do for plants

Causes plants to wilt

What is tonicity

Refers to the solute concentration.

Isotonic

Same solute concentration in solution as in the cytoplasm.

Water enters and leaves at same rate.

Hypotonic

Lower solute concentration in solution than in the cytoplasm.

Water enters cell.

Hypertonic

Higher solute concentration in solution than in the cytoplasm.

Water leaves the cell.

Effect of hypotonicity on animal and plant cell

Animal cell: Cell swells and bursts

Plant cell: Makes cell turgid

Effect of hypertonicity on animal and plant cell

Animal cell: Cell shrivels and bursts

Plant cell: Cell is plamolysed

Effect of isotonicity on plant cell

Cell is flaccid (flabby).

Crenation

Cells shriveling and dying when water leaves.

Which cell is turgid?

A

Explain in detail what has happened to cell B

The cell membrane moved away from the cell wall due to a loss of water.

Active transport

The movement of molecules (usually ions) from a region of lower concentration to a region of higher concentration (opposite of diffusion and energy is required).