Biology February 24, 2014

Copy and answer the following EQ into your science journal.

EQ: How does the structure of the cell membrane aid in its functions of

equilibrium?

It helps cells to maintain homeostasis by controlling what is allowed in and out of the

cell.

Word of the DaySemipermeable

A barrier that permits the passage of some substances but not others.

Here is what is going on this week

• Your workbook, Ch 7 pp 71-84 is due today!

• Prefix/Suffix quiz part 2 on Friday

• Complete the lab in your workbook pp 35-40.

Tonicity

Tonicity is a measure of the

osmotic pressure gradient of two

solutions separated by a

semipermeable  membrane

Diffusion is the movement of molecules from a high concentration to a low concentration.

Examples-• Spraying air freshener in a room• The odour of food cooking diffuses throughout

the kitchen and spreads into the next room.

• Osmosis- It is the diffusion of water through a semipermeable membrane from a more dilute solution to a more concentrated solution.

Examples:• Absorption of water by plant roots. • Reabsorption of water by the nephron in

kidneys • Absorption of water by the alimentary canal

— stomach, small intestine and the colon.

Equilibrium• To regulate internal conditions in order to

stay healthy and functioning, regardless of the outside changing conditions.

There are 3 types of situations in which this could vary:

Hypotonic Isotonic Hypertonic

There are 3 types of situations in which this could vary:

1. Hypertonic• In HYPERTONIC solutions, water moves

out of the cell.• Hypertonicity causes cells to shrink.• Plants cells lose water and start to wilt.• The process of water moving out of a cell

is called plasmolysis.• More H2O moves out of the cell.

2. Isotonic• Water DOES or DOES NOT stop moving.• Cells reach a point called Dynamic

Equilibrium in isotonic solutions.• Equal amounts of water are found inside

and outside of the cell.• H2O moves in and out of the cell

equally.

3. Hypotonic• In HYPOTONIC solutions, water moves

into a cell.• Animal cells increase in size and burst or

lyse in these solutions• Bursting of cells is called cytolysis.• Plant cells need this tonicity to be at

homeostasis.• Turgor pressure results from water inside

a plant cell pushing the cell membrane out against the plant’s cell wall.

• More H2O moves into of the cell.

Cells in Solution Models• Each cell has a 10%, or 6% NaCl (salt)

solution in an ENVIRONMENT with either a 3%, 10% or15% salt solution.

• COLOR the cell yellow and the environment light blue.

• Using RED, draw arrows showing the direction of movement of water into or out of the cell. 10%

NaCl

15% NaCl