7-3 movement through the membrane a. the cell membrane is semipermeable - only certain molecules can...
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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