The Cell Membrane -...
Transcript of The Cell Membrane -...
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Summary Section 2 – pages 175-178
Why cells must control materials
The cell membrane is the boundary between the cell and its environment.
Living cells must
maintain homeostasis
for survival.
The Cell Membrane
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Summary Section 2 – pages 175-178
It is the cell membrane’s job to:
• allow waste and other products to leave the cell.
• remove excess amounts of nutrients
• allow a steady supply of nutrients to come into the cell
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Summary Section 2 – pages 175-178
The cell membrane is selectively permeable
-- allows some molecules in while keeping others out.Plasma
Membrane
Water
O2
CO2
Glucose
(sugar) Toxins, viruses…
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Structure of the Cell Membrane
The cell membrane is composed of 2 layers of phospholipids back-to-back.
Phospholipids are lipids (fat) with a phosphate attached to them.
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Structure of a Phospholipid:
Glycerol Backbone
Two Fatty Acid Chains
Phosphate Group
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Summary Section 2 – pages 175-178
Makeup of the phospholipid bilayer
The phosphate group creates a polar and a nonpolar end, which allows for formation of a cell membrane
Phosphate Group
Hydrophilic = “loves water”
Hydrophobic –
“hates” water
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Makeup of the phospholipid bilayer
The fluid mosaic model describes the plasma membrane as a flexible boundary of a cell. The phospholipids move within the membrane.
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Summary Section 2 – pages 175-178
Other components of the plasma membrane:
Proteins – on the surface of the c.m. allow needed substances or waste materials to move through
Ex.1 Receptors – bind to hormones and trigger the c.m. to respond (ex. Insulin allows in sugar)
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• Ex. 2. Channel proteins – form channels
for specific ions or molecules to travel
through the c.m.
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• Diffusion = movement of particles from an area of higher concentration to an area of lower concentration.
• Concentration gradient = unequal distribution of particles
Diffusion and Osmosis
“Things flow from high to low”
Think of a hill
(steep grade)
• osmosis =diffusion of water across a selectively permeable membrane – EGG Lab
More
less
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• passive transport – move particles down a concentration gradient, uses no energy
Concentration gradient
Plasma membrane
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active transport - Move Particles UP a
concentration gradient, Uses ENERGY
Active Transport
Cell membrane
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Passive vs active transport
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Solution = Water + ____
Isotonic
Hypotonic
Hypertonic
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A Cell in Isotonic Solution
CELL
20% NaCL80% H2O
20% NaCL80% H2O
The cell is at _______________.equilibrium
ENVIRONMENT
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Cell in Hypotonic Solution
CELL
15% NaCL85% H2O
20% NaCL80% H2O
Environment
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Cell in Hypertonic Solution
CELL
15% NaCL85% H2O
5% NaCL95% H2O
ENVIRONMENT
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Isotonic Solution
NO NET MOVEMENT OF
H2O (equal amounts entering & leaving)
Hypotonic Solution
Cell will Burst
Hypertonic Solution
Cell will Shrivel
copyright cmassengale
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osmosis
Inside cell
Environment
outside the
cell
% salt
% water
% salt
% water
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Cell membrane
Crossword Creation• Start with a key
• Put your words in a crossword pattern
• Number across and down
• Write the clues
• Create a blank crossword
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Front Back
SS O T O N I C
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across down
1.
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Answer keyBlank crossword
across down
1.
2.
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1.
2.
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Endocytosis-move things into the cell
(Pinocytosis and Phagocytosis)
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Pinocytosis – “Cell drinking”
Most common form of endocytosis.
Takes in dissolved molecules as a vesicle.
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Phagocytosis
The cell does this to engulf large particles
such as food, bacteria, etc. into vesicles
“Cell Eating”
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Paramecium vs Amoeba
Amoeba vs Paramecium
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Molecules are moved out of the cell by vesicles
that fuse with the plasma membrane.
Exocytosis- moving things out of the cell
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Section 1 Check
Question 1
B. endocytosisA. active transport
The diffusion of water across a selectively permeable membrane is called __________.
Water molecule
Sugar moleculeSelectively permeablemembrane
C. exocytosis D. osmosis
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The answer is D, osmosis. Regulating the water flow through the plasma membrane is an important factor in maintaining homeostasis within the cell.
Water molecule
Sugar moleculeSelectively permeablemembrane
Before osmosis After osmosis
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What is the expected result of having an animal cell in a hypertonic solution?
Question 2
D. The cell retains its normal shape.
C. The cell swells up.
A. The cell shrivels up.
B. The plasma membrane shrinks away from
the cell wall.
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The answer is A. In a hypertonic solution, cells experience osmosis of water out of the cell. Animal cells shrivel because of decreased pressure in the cells.
H2O
H2O
Water moleculeSugar molecule
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A grocer mists the celery display with water to keep it looking fresh. What type of solution is the celery now in?
Question 3
D. exotonic
C. hypertonic
B. hypotonic
A. isotonic
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The answer is B. Plant cells contain a rigid cell wall and do not burst even in a hypotonic solution.