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Movement of Substances Into & Out of Cells

____________________ passes freely through most membranes, but other molecules rely on help from __________________ in the plasma membrane to get through.


________________________ - The mixing of two substances by the random motion of molecules.

Molecules diffuse from a region of ________________ concentration to a region of ________________ concentration until both kinds of molecules are evenly dispersed.


________________________ - The diffusion of water across a membrane.

As water enters a cell by osmosis, the water molecules move from an area of ______________ concentration to an area of _________________ concentration.

Cells also contain _________________, ___________________, and other substances. Therefore, the concentration of water outside the cell is usually greater than inside the cell. Cells are continually gaining water by osmosis.

______________________________ - The force created when water enters a cell, causing it o swell. (ex: air inflating a balloon)

If osmotic pressure is very _______________, it can cause a cell to _______________.

_____________________ have cell walls to support their cells and prevent them from bursting.



 (fig 4-7)




Many organisms, such as a single-celled paramecium, have organelles that _______________ excess water out of the cell.


Channels & Pumps Provide Selective Transport of Materials

______________________ & _____________________ are too ____________________ to pass through gaps in phospholipids. Some of these molecules are also _________________ and can’t pass through ______________________ regions of a lipid bilayer.


_____________________________ - The transport of specific substances (polar molecules, ions) across a membrane by means of protein channels & pumps.


Two types:

The cell DOES NOT ____________________________ to transport these substances into or out of the cell. Ions move along a _____________________ gradient. Potassium (K+) ions help maintain the proper balance of electrical charges inside and outside of the cell.


(fig 4-8b)


Cell uses _________________ to change the shape of the __________________________ and allow molecules (sugars, amino acids) _______________ the cell.

Example: Na+/K+ Pump:
Moves Na+ out of cells
Moves K+ into cells

This flow of ions is vital for restoring a balance needed to keep a nerve cell functioning.


(fig 4-9)


Example: Proton Pump:

Pumps protons out of the cell…protons accumulate outside of the cell, and diffuse back into the cell through channel proteins.

This is important in ________________________________ because the proton pumps depend on chemical, or light energy.

In ____________________, proton pumps enable cells to convert light energy chemical energy.

In ____________________, proton pumps enable you too transform energy from food energy you can use.


Defective Channel Proteins Can be Lethal

_____________________________ - a genetic disease involving a defective chloride protein channel. Because cells are unable to export chloride ions, high levels of chloride salt exist in cells. This salt draws water out of mucus in the lungs, causing it to thicken. These patients have trouble clearing this mucus out of their lungs, and they end up with infections and difficulty breathing. They usually live to be in their thirties.


Moving Large Particles

________________________ - Arm-like extensions of the cell reach out to surround & engulf particles that are too large to pass through the plasma membrane.


________________________ - Material within sacs inside the cell is discharged from the cell. Secretions and wastes are released from the cell.

 (fig 4-10)


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