Download General Biology Notes 9 The Cell Membrane (pages 204, 205, 208

General Biology
Notes 9 The Cell Membrane (pages 204, 205, 208 – 213)
I. The Cell Membrane
A. Every cell has a _____________ ______________, which is a layer made mostly of a special type
of lipid, that forms a boundary between the inside and the outside of the cell
1. __________________ also are surrounded by membrane
B. The cell membrane has several _________________…
1. It controls what ___________ and leaves the cell
2. It receives signals from and sends signals to surrounding cells or the surrounding
_______________________
3. Helps maintain the cell size and _____________
C. In order to fulfill its functions, the cell membrane must be _________________ in water (so it
doesn’t dissolve) but it must be willing to __________________ with water, (so it doesn’t
separate from water like _________ does)
D. The membrane is able to have both of these characteristics (insoluble but associates with water)
because it is primarily composed of a special type of molecule called a ____________
1. Phospholipids have a __________________ head; because the head is charged it likes
_______________ (hydrophilic)
2. Phospholipids have a tail, made of fatty acid chains, that is ______________ (also called
nonpolar); because they are not charged they dislike water (_________________)
E. In a watery environment phospholipids will form a _____________________ ________________
1. Two layers of the lipids joined neutral tail to tail, with the _____________ portion of the
molecule facing outwards from the cell or inwards, where there are watery environments
F. The membrane is also composed of proteins and to a lesser extent carbohydrates
1. Proteins
a. Many types of proteins aid in ________________ of substances across the membrane
(see II C below)
b. Some proteins stick out from the membrane into the surrounding environment and
help the cell sense ______________ in the environment and help the cell to
____________________ with other cells
2. ________________________ in the membrane are also used in cellular communication
II. Movement across the membrane
A. The cell membrane is designed so that it allows certain things to pass through, while restricting
the passage of other things
1. This property is called ___________________ ________________________
Please turn over
B. Some small molecules, such as H2O, O2 and _______ can freely pass through the membrane
1. These molecules are ________________ enough to squeeze between the much bigger
phospholipids of the membrane
2. Free movement between the phospholipids, from an area of high concentration to an area
of low concentration, is called ___________ ______________
3. To understand how passive transport works, one must understand the process of ________
a. Diffusion is the natural tendency of solutes to move from an area where they are
_______________ concentrated to an area where they are less _________________
b. This is a very important process because, as we will see, it is largely responsible for
getting __________ and _____________ into the cell, and getting ______________
(including CO2) out
C. ________________ are also found in the membrane forming holes and gates, which open and
close when needed
1. ________________ and larger molecules (for example _______________________ or
amino acids) cross the membrane through these gates or holes
a. Movement from an area of high concentration to an area of low concentration through
these proteins is called _______________ __________________
b. Proteins can also use energy to move substances from where they are in low
concentration to where they are in high concentration; this is called
________________ _______________
III. Water and the membrane
A. Water movement by itself is important because cells must stay ___________________, but there
are also times when cells must export water
1. Water moves by _____________________
2. The special situation of water moving across a permeable barrier (a ________________) by
diffusion is called _______________
a. Water flows according to ________________, from areas where it is _______________
concentrated to areas where it is in __________ concentration
b. What determines water concentration is solute concentration
i. Where __________ are in high concentration ___________ is in low
concentration, and vice versa
i. Example
- solute concentration inside the cell is 50 micrograms/1000 ml
- solute concentration outside of the cell is 25 micrograms/1000 ml
- where solute is low (25<50) water is high, so water will flow _______________
the cell
3. Since water concentration in part determines solute concentration, water also influences
the ____________________ _______________ and _____________________
______________ of solutes