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Biology
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7-3 Cell Boundaries
7-3 Cell Boundaries
EQ Identify the main function of the cell membrane and the cell wall.
Explain osmosis.
Photo Credit: © Quest/Science Photo Library/Photo Researchers, Inc.
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7-3 Cell Boundaries
All cells are surrounded by a thin, flexible barrier known as the cell membrane.
Many cells also produce a strong supporting layer around the membrane known as a cell wall.
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Cell Membrane
Cell Membrane
The cell membrane regulates what enters and leaves the cell and also provides protection and support.
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Cell Membrane
Cell Membrane
Outside of cell
Carbohydrate chains
Proteins
Cell membrane
The cell membrane regulates what enters and leaves the cell.
Inside of cell (cytoplasm)
Protein channel
Lipid bilayer
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Cell Walls
Cell Wall
Cell walls are found in plants, algae, fungi, and many prokaryotes.
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7. Diffusion Through Cell Boundaries
Particles in a solution tend to move from an area where they are more concentrated to an area where they are less concentrated.
This process is called diffusion.
When the concentration of the solute is the same throughout a system, the system has reached equilibrium.
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8. Diffusion Through Cell Boundaries
Diffusion is the process by which molecules of a substance move from areas of higher concentration to areas of lower concentration. Diffusion does not require the cell to use energy.
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9. Selectively permeable membrane
Osmosis
How Osmosis Works
Dilute sugar solution (Water more concentrated)
Concentrated sugar solution (Water less concentrated)
Sugar molecules
Osmosis is the diffusion of water through a selectively permeable membrane. In the first beaker, water is more concentrated on the right side of the membrane. As a result, the water diffuses (as shown in the second beaker) to the area of lower concentration.
Movement of water
Selectively permeable membrane
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Osmosis
Water tends to diffuse from a highly concentrated region to a less concentrated region.
If you compare two solutions, three terms can be used to describe the concentrations:
hypertonic (“above strength”).
hypotonic (“below strength”).
isotonic (”same strength”)
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Osmosis
Osmotic Pressure 
Osmosis exerts a pressure known as osmotic pressure on the hypertonic side of a selectively permeable membrane.
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12. Facilitated Diffusion
Glucose molecules
Facilitated Diffusion
During facilitated diffusion, molecules, such as glucose, that cannot diffuse across the cell membrane’s lipid bilayer on their own move through protein channels instead.
Protein channel
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Active Transport
Active Transport
Sometimes cells move materials in the opposite direction from which the materials would normally move—that is against a concentration difference. This process is known as active transport.
Active transport requires energy.
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Active Transport
Molecular Transport
Molecule to be carried
Active Transport
Active transport of particles against a concentration difference requires transport proteins and energy.
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Active Transport
Endocytosis and Exocytosis 
Endocytosis is the process of taking material into the cell.
Two examples of endocytosis are:
phagocytosis
pinocytosis
During exocytosis, materials are forced out of the cell.
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Organization of Cells
Cell—}Tissues---} Organs---} Organ Systems---}Organism
Tissue is a group of cells that perform a particular function
Organ system is a group of organs that work together
Cell having different functions is called cell specialization
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