Homeostasis – Process by which organisms maintain a relatively stable internal environment; All...
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Transcript of Homeostasis – Process by which organisms maintain a relatively stable internal environment; All...
Homeostasis
Homeostasis – Process by which organisms maintain a relatively stable internal environment; All organisms have ranges that are tolerated (i.e. pH and temperature) Example - Paramecium
contain contractile vacuoles that collect and remove excess water, thereby helping to achieve homeostasis
Cell Membrane Composed of a double-layered sheet
called the lipid bilayer which includes:1. Two layers of lipids (phosphate group + two
fatty acids) Creates a strong barrier that is flexible
2. Proteins that are embedded in the bilayer Some form channels and pumps that help to
move material across the cell membrane
3. Carbohydrate molecules that are attached to the proteins
Allows individual cells to identify one another
Understanding Concentration
Concentration - the mass of solute in a given volume of solution, or mass/volume
Example: 12 grams of salt in 3 liters of water
Concentration = 12 g/3 L (4 g/L) If you had 12 grams of salt in 6 liters of water
concentration = 12 g/6 L (2 g/L)
***The 1st solution is 2X as concentrated as the 2nd.
Passive Transport vs. Active Transport
Passive transport – Transport of materials from a higher to lower concentration. Energy is not required for this to occur.
Active transport – Transport of materials from a lower to higher concentration. Energy is needed for this to occur.
high
low
Weeee!!!
high
low
This is gonna
be hard work!!
Passive Transport
Three Types of Passive Transport:1. Diffusion - Transport of substances2. Osmosis – Transport of water3. Facilitative Diffusion – Transport with
the help of carrier proteins (for molecules too large to pass through the membrane without help)
Diffusion Diffusion - Process by
which molecules tend to move from an area where they are more concentrated to an area where they are less concentrated when the concentration
of a solute is the same throughout a solution it has reached equilibrium
View Diffusion
http://www.indiana.edu/~phys215/lecture/lecnotes/diff.html
Diffusion (Continued) Because diffusion depends upon random
particle movements, substances diffuse across membranes without requiring the cell to use energy.
Even when equilibrium is reached, particles of a solution will continue to move across the membrane in both directions.
Particles are always in motion!
Some Membrane Terms
Many substances can diffuse across biological membranes, but some are too large or too strongly charged to cross the lipid bilayer.
If a substance is able to diffuse across a membrane, the membrane is said to be permeable to it.
A membrane is impermeable to substances that cannot pass across it.
Most biological membranes are selectively permeable, meaning that some substances can pass across them and others cannot.
Osmosis
Water passes easily across most membranes, but most solute does not.
Osmosis - Diffusion of water through a selectively permeable membrane High to low concentration
There are more sugar molecules on the right. That means that the concentration of water is lower on the right than the left.
The membrane is permeable to water but not to sugar. As a result, there is a net movement of water from the area of high concentration to the area of low concentration.
Osmosis Terms
Water will tend to move across the membrane to the left until equilibrium is reached. Isotonic - when the concentration of two
solutions is the same Hypotonic - when comparing two solutions,
the solution with the lesser concentration of solutes
Hypertonic - when comparing two solutions, the solution with the greater concentration of solutes
Osmotic Pressure
For organisms to survive, they must have a way to balance the intake and loss of water.
Osmosis exerts a pressure known as osmotic pressure on the hypertonic side of a selectively permeable membrane. Osmotic Pressure - The force exerted by
osmosis that “pushes” water through a selectively permeable membrane to make the concentration of solutes the same on both sides.
Turgor Pressure Turgor Pressure - The
force behind the cell walls of plants, which allows them to keep their shape. Very similar to osmotic
pressure, but occurs in plants.
When the cells contents press the plasma membrane against the cell wall and the cell wall in turn presses against the membrane
Osmotic and Turgor Pressure Causes….
The cell is filled with salts, sugars, proteins, and other molecules. If placed in a hypertonic solution.
Cell will shrink or become shriveled (plasmolysis)
Water moves out of cell. If placed in a hypotonic solution
Cell will be swell or become enlarged. Cytolysis occurs when a cell ruptures
or lyses. Water moves into the cell.