thin, flexible, cell membrane
All cells are surrounded by a _________ and __________ barrier known as the ____________ _____________.
strong, cell wall
Many cells also produce a ____________ supporting layer around the membrane known as the _________ ______________.
what enters and leaves the cell and also provides protection and support.
The cell membrane regulates
a double-layered sheet called a lipid bilayer.
What is the composition of nearly all cell membranes?
The lipid bilayer gives cell membranes a _____________ structure that forms a _____________ between the cell and its surroundings.
protein molecules embedded in the lipid bilayer, some of which have carbohydrate molecules attached to them.
What do most cell membranes contain?
The ___________ ____________ regulates movement of dissolved molecules from the liquid on one side of the membranes to the liquid on the other side.
The _____________ of a solution is the mass of a solute in a given volume of solution, or ________/_________.
more concentrated, less concentrated
Particles in a solution tend to move from an area where they are _______ ____________ to an area where they are ________ ________________.
process by which molecules tend to move from an area where they are more concentrated to an area where they are less concentrated
Diffusion depends on _________ particle movements. Therefore, substances diffuse across membranes without requiring the cell to use _____________.
Water tends to _____________ from a highly ________________ region to a less concentrated region.
is the more dilute (less concentrated) solution when compared across a membrane.
A "hypotonic" solution
Osmosis exerts a pressure known as osmotic pressure on the ____________ side of a selectively ________________ membrane.
Because the cell is filled with salts, sugars, proteins, and other molecules, it will almost always be ______________ to fresh water.
pressure, into, volume
If a cell is hypertonic the osmotic ___________ should produce a net movement of water _________ the cell. As a result, the ____________ of the cell will increase until the cell becomes swollen or bursts.
Cell membranes have protein _____________ that act as _____________, making it easy for certain molecules to cross.
the movement of specific molecules across cell membranes trough protein channels.
Facilitated diffusion is
Facilitated diffusion will only occur if there is a ____________ concentration of the particular ______________ on one side of a cell membrane as compared to the other side.
when cells move materials in the opposite direction from which the materials would ordinarilly move- or against the concentration difference.
Active transport is
In active transport, small molecules and ________ are carried across membranes by ____________ in the membrane.
____________ molecules and even __________ clumps of material may undergo active transport by means of the cell membrane.
the process of taking material into the cell by means of infoldings, or pockets, of the cell membrane.
What is endocytosis?
The pocket breaks loose from the outer portion of the cell membrane and forms a ___________ within the cytoplasm.
extensions of cytoplasm surround a particle and package it within a food vacuole. The cell then engulfs it.
tiny pockets form along the cell membrane, fill with liquid, and pinch off to form vacuoles within the cell.