Name ____________________________ Date ______________ Period ________
Biology
Unit 5 – Cancer, Background Paper 5-2
Cell Structure – Cell Membrane
Cells are typically called the building blocks of life. Every
living thing that we have so far encountered exhibits a structure
composed of groupings of cells. Cells were first observed in the
1600’s due to advances in optics that made the first microscopes
Early Microscope
possible. Cell theory was proposed in the mid
1800’s based on microscopic observations of
cells. Cell theory simply states that all living
things are made of cells. With this simple
statement researchers went on to describe cells
and discover what they were composed of. Since
the cell theory was first put forth much has been learned about the way life is
First Cell Drawing
constructed.
Robert Hooke
Those first cork cells seen by Robert Hooke showed little detail. All he
could see was the outer layer surrounding the cell. In animals that outer layer is
called the plasma membrane and is made of a double layer of fats and phosphate molecules. These
molecules arrange themselves much like the bubbles that form in your sink when you wash dishes.
This layered cell membrane is described as a phospholipid bilayer 1. This describes the fact that it is
made up of joined phosphate and lipid (fat) molecules arranged
in two layers. This cell membrane is far from being a simple bag
to hold the contents of the cell in. It is nearly fluid in nature and
allows some small molecules, such as water and oxygen, to slip
through its structure while excluding other. The phosphate head
is attracted to water (hydrophilic), while the fatty tails repel
water (hydrophobic). This property of the plasma membrane
forces it to self organize into the bilayer when place in water.
The tails pointed toward each other so as to avoid the water
while the phosphate
heads align themselves
Proteins
so as to be in contact with the water. Placed throughout the
cell are various proteins that serve as gatekeepers to the
interior of the cell for molecules too large to slip between
the bilayer such as neurotransmitters. Membrane proteins
also serve as signals to the immune system and hook cells
together.
1
www.sirinet.net
Background5-2,CellMembrane2012
Text 2012
Greg Ballog
Page 1
Name ____________________________ Date ______________ Period ________
Title of Reading: 5-2 Cell Structure – Cell Membrane
Points Earned
1 2 3 4 5 6 7
Concept Map of Reading (3 points)
Main Idea
A) What one question do I have about this article?
1 Point
A&B
B) Show or describe the reading to a parent or guardian (Name ___________________).
What comments or questions did they have concerning the reading?
(Biology Homework Time __________)
Background5-2,CellMembrane2012
Text 2012
Greg Ballog
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Answers
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