7-3 Movement through the Membrane

A. The cell membrane is semipermeable- only certain molecules can get

throughB. Passive transport: no energy required

1. Diffusion: the movement of molecules from a region of

high concentration to a region of low concentration

- continues until equilibrium is reached (equal concentrations on both sides of membrane)

- temperature affects diffusion:

higher = faster

- size of particles affects diffusion:

smaller = faster

2. Osmosis: the diffusion of water across a membrane from high

water concentration to low water concentration

Which way will the water move?97%

water

100% water

97% water

90% water

Which way will the water move?

This solution is hypertonic

- water diffuses out of the cell

95% water

90% water

95% water

98% water

This solution is hypotonic

- water diffuses into the cell

This solution is isotonic

- no net change95% water

95% water

3. Facilitated diffusion: uses protein channels to move molecules

from high concentration to low concentration

C. Active Transport: energy required

1. Carrier proteins may act as pumps

-example: sodium-potassium pump

a. Cells continually pump potassium ions into the

cell, and sodium ions out

b. Important for muscle contraction and nerve

impulse transmission

Na+

K+

2. Endocytosis: materials move into cell

a. Pinocytosis: membrane encloses a fluid droplet and brings it

inside the cell

b. Phagocytosis: membrane encloses a large particle and brings it inside the cell

3. Exocytosis: materials move outside the cell

- wastes and cell products may leave the cell this way

7-4 The Diversity of Cellular Life Unicellular organisms

– a cell is the entire organism– Do everything you would expect from a

living things– prokaryotic include bacteria– eukaryotic include algae

Multicellular– Organisms that contain many cells– Cells are specialized to perform particular

functions within the organism– Levels of organization

• Cells• Tissues• Organs• Organ systems