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Cell Boundaries
Every living cell exists in liquid environment.
There is liquid on the inside and outside of a cell.
One of the most important functions of the cell membrane is to regulate the movement of molecules from one side membrane to the other side.
Semi-Permeable Membrane
Smaller molecules can pass through.
Larger molecules cannot.
Diffusion Movement particles from high to low
concentration. Diffusion will occur until equlibrium is reached. This process does NOT require cellular energy
(ATP).
Osmosis
Diffusion of water across cell membrane from high to low concentration.
Water molecules can very easily pass through cell membranes, because they are small.
Solution Concentrations The cytoplasm of a cell is solution of many
substances dissolved in water. A solution is mixture of two or more
substances. The substances dissolved in a solution are
called solutes. The concentration of solution refers to
amount of solute dissolved in liquid (solvent).
Solution Solute Solvent
Environment of the Cell The solution concentration outside
the cell will determine the direction water moves across the cell membrane.
The terms hypotonic, hypertonic, and isotonic are ADJECTIVES! They describe the environment of the cell!!!
Hypertonic Environments Low concentration of water/High
concentration solutes outside cell. Water diffuses out of the cell and
cell shrinks.
Hypotonic Environments High concentration of water/Low
concentration solutes outside cell. Cells swell with water and may explode.
Isotonic Environment
Equal concentration of water/solutes inside and outside the cell.
Water will move equally in/out cell.
96% Water, 4% salt
98% Water, 2% Salt
97% Water, 3% Salt
95% Water, 5% Salt
98% Water, 2% Salt
98% Water, 2% Salt
Osmotic Pressure
Water pressure that builds up inside a cell due to a hypotonic environment.
If pressure is too high, what could happen? Osmotic pressure in plants = turgor pressure. Cell Wall helps to with stand turgor pressure.
Plasmolysis- loss of water or “wilting” in plants
Facilitated Diffusion Some particles
are too large to pass through the membrane.
They need help from channel proteins.
This process does NOT require energy!
Glucose
ChannelProtein
Passive Transport
Particles moving from high to low concentration.
Doesn’t require energy.
Active Transport
Occasionally, particles need to move “against the concentration gradient.”
Particles moving from low to high concentration.
Requires energy (ATP).
Endocytosis Type of active transport. Process of taking in large amounts of food
or liquid by means of active transport. 1. Phagocytosis (cell eating) – Taking in large
clumps of food.2. Pinocytosis (cell drinking) – Taking in large
amounts of liquid.
Exocytosis Type of active
transport. Forcing contents
out of the cell. Method of removing
large amounts of waste from cell.