Download S10 8.1 notes - Cochrane High School

Sci 10. Ch 8
Cell Membranes
CELL MEMBRANES ARE PHOSPHOLIPID BILAYERS
MADE OF A DOUBLE LAYER OF PHOSPHOLIPIDS WHICH HAVE A HYDROPHOBIC
FATTY ACID TAIL AND A HYDROPHILIC HEAD
They also contain
a) carbohydrate chains for cell to cell communication. These chains are attached to both lipids and
proteins of the cell membrane.
b) peripheral (surface) and integral proteins (spans the membrane). These proteins are crucial for
transport of substances into and out of the cell.
c) cholesterol maintains proper membrane flexibility, and also is crucial for cell signaling and nerve
conduction.
3 jobs of the cell membrane
1. THE CELL MEMBRANE PROTECTS THE CELL ORGANELLES It’s a barrier: it keeps
_____________________________________ out, keeps __________________ in.
2. THE CELL MEMBRANE HELPS WITH CELL ORGANIZATION.
Organizes by surrounding and packaging materials into vesicles (i.e. lysosomes, endoplasmic
reticulum, golgi apparatus). Organizes complex cellular chemical reactions like photosynthesis in the
chloroplasts and cellular respiration in the mitochondria.
3. THE CELL MEMBRANE REGULATES WHAT GOES IN AND OUT OF THE CELL.
a. Cell membrane is semipermeable: it is a selective filter that only lets certain substances in and out
of cell.
b. Regulates by particle size –molecules like oxygen and water are so small they can diffuse across the
cell by slipping between the phospholipid molecules.
c. Large or charged molecules can only be transported across the cell membrane by the membrane
proteins.
d. The cell is an OPEN SYSTEM (substances can enter and leave the cell).
CELL MEMBRANE : FLUID MOSAIC MODEL
The fluid mosaic model is used to describe cell membranes.
All of the different molecules in the membrane = mosaic. The mosaic pieces are continually moving.
This fluidity allows lipids, proteins, and carbohydrates to move within the membrane to where
they are needed and it gives the membrane flexibility.
cell membrane is a fluid mosaic
http://www.youtube.com/watch?v=Rl5EmUQdkuI&feature=fvwrel : basic membrane
stucturehttp://www.youtube.com/watch?v=GW0lqf4Fqpg&feature=related : shows membrane
proteins receiving communications from hormones and sending this information inside the cell
so it can carry out the instructions from the hormones.
 Identify by number in the diagram be the following structures (see pg. 293 in text)
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phospholipid bilayer
filaments of cytoskeleton (draw in)
peripheral protein
integral protein
cholesterol
Exterior of the cell
Interior of the cell
Hydrophobic tails (lipids)
Hydrophilic heads (phosphate)
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Layer 1
Layer 2
glycolipid (carbohydrate chain
attached to membrane lipid) (draw in
and label)
glycoprotein (carbohydrate chain
attached to cell membrane protein).
(draw in and label)
 Learning Check! Test yourself!
http://www.biology4kids.com/extras/quiz_cellmemb/index.html
 ASSIGNMENT: Answer the following questions:
1) Which of the following are open systems?
a) a school cafeteria
b) a sealed glass jar
c) a cell
d) a plant vacuole
e) a closed metal box
2) Beet root cells can be used to study the effects of different solvents on membrane
permeability. As each solvent dissolves the cell membrane, coloured pigments inside the cells
leak out, tinting the solution. Slices of beet root were placed in three different solutions for 10
min. A special device was then used to measure the absorbance (measure of pigment
concentration) in each solution, as shown below.
Alcohol
Absorbance for each alcohol
concentration
(%)
Methanol
Ethanol
Propanol
0
250
250
250
20
300
270
262
40
500
350
299
60
625
453
366
80
625
630
500
100
625
628
600
a) Identify the manipulated, responding and control variables in this experiment.
b) At lower concentrations, which alcohol was most damaging to beet cell membranes?
c) Which alcohol appears to affect beet cell membranes the most? Explain how you arrived
at your conclusion.
3) List 3 common household items that contain or have features of a semi-permeable
membrane. Explain how the semi-permeability of each item relates to its function.
4) What would happen to a cell if its cell membrane were permeable rather than semipermeable?