Biology
Name:
Per:
Cell Membrane DBQ
And Close Read
1. Read the 4 documents. Circle any unknown words and put a ? in the margin
2. Re-read the 4 documents. Underline and unknown phrases, put ?? in margin
3. With an understanding of the circled and underlined phases, please answer the
questions.
Document 1: From Webster’s Dictionary
per·me·able
adjective \ˈpər-mē-ə-bəl\
: allowing liquids or gases to pass through
im·per·me·able
adjective \(ˌ)im-ˈpər-mē-ə-bəl\
: not allowing something (such as a liquid) to pass through
semi·per·me·able
adjective
:partially but not freely or wholly permeable; specifically: permeable to some usually small
molecules but not to other usually larger particles <a semipermeable membrane>
1. Please compare and contrast the three terms in Document 1.
Document 2: Campbell, Neil. Biology
The Davson- Danielli Model:
Several models for the cell membrane have been proposed. The Davson- Danielli Model was
widely accepted from 1935 to about 1970. The model states that the cell membrane is
composed of a lipid bilayer sandwiched between two protein layers.
2. Draw a version of the cell membrane according to the Davson- Danielli Model.
Document 3: Nowicki , Stephen. Biology
The Fluid Mosaic Model describes the arrangement of molecules that make up the cell
membrane. This model of the cell membrane structure takes its name from two characteristics.
First the cell membrane is flexible, not rigid. The phospholipids are arranged in a bilayer and
each layer can move from side to side and slide past each other. Second, there are a variety of
molecules studding the membrane such as proteins and cholesterol. Some proteins are
embedded through both layers of lipids and some proteins go through just one layer.
3. Draw a version of the cell membrane according to the Fluid Mosaic Model.
Document 4: Albert Towle, Modern Biology
Small non polar molecules can easily enter the cell by slipping past the phospholipids. Other
larger polar molecules cannot slip through the lipids and must use a protein as a channel to
enter or leave the cell.
4. Given that the cell membrane is selectively permeable (semipermeable), which model would
be more appropriate. Why? Explain why the other model does not work and why. Use evidence
from Documents 2, 3 and 4.