A: Integral proteins that penetrate the hydrophobic core of the lipid bilayer and peripheral proteins that are loosely bound to the surface of the membrane.
Q: What is the diffusion of water across a slectively permeable membrane called?
A: Osmosis
Q: How do large molecules such as proteins and polysaccharides generally cross the membrane?
A: They cross the membrane in bulk by mechanisms that involve packaging in vesicles.
1. Cellular membranes are fluid mosaics of lipids and proteins.
2. Membrane structure results in selective permeability.
3. Passive transport is diffusion of a substance across a membrane with no energy invetment.
4. Active transport uses energy to move solutes against their gradients.
5. Bulk transport across the plasma membrane occurs by exocytosis and endocytosis.
Figure 7.13
The water balance of living cells
If a solution is hypotonic, the water will move to a higher concentration of solute, into the cell, therefore there is a great possibility that the cell will eventually swell and lyse (burst). Instead, if the solution is hypertonic, which means that the solution has a greater concentration than the cell, the cell will lose water and give it to the solution, which causes the cell to shrivel and probably die.
Isotonic is when there is no net movement and the two concentrations are equal.
This chapter is about the cellular membranes, their structures and functions. The Plasma membrane is the membrane at the boundary of the cell and functions as a selective barrier for the passage of materials in and out of cells. The membrane is composed of phospholipids and proteins. It's known as the phopholipid bilyaer with the hydrophilic heads and hydrophobic tails. These keep the fluidity. Because the phospholipid bilayer is hydrophobic, hydrophilic materials cannot cross so easily.
Then there are diffusion, osmosis and facilitated diffusion. Diffusion is the net movement of atoms, ions or molecules down a concentration gradient and osmosis is the diffusion of water. Facilitated diffusion is the passive transport aided by proteins.
Key terms
Osmosis: the diffusion of water across a selectively permeable membrane is called osmosis.
Isotonic: the isotonic to the cell means a cell without a wall, like an animal cell is immersed in an environment.
Hypertonic: when animal cell is immersed in a solution, it means hypertonic which the cell will lose water to its environment, shrivel and probably die.
Passive transport: the diffusion of a substance across a biological membrane is called passive transport.
Plasmolysis: as the plant cell shrivels, its plasma membrane pulls away from the wall, this phenomenon called plasmolysis.
Hypotonic: if we place the cell in a solution that is hypotonic to the cell, water will enter the cell faster than it leaves, and the cell will swell and lyse like an overfilled water ballon.
Active transport: to pump a solute across a membrane against its gradient requires work; the cell must expend energy, therefore, this type of membrane traffic is called active transport.
Facilitated diffusion: many polar molecules and ions impeded by the lipid bilayer of the membrane diffuse passively with the help of transport proteins that span the membrane. This phenomenon is called facilitated diffusion.
Peripheral proteins: they are not embedded in the lipid bilayer at all; they are appendages loosely bound to the surface of the membrane, often to exposed parts of integral proteins.
Integral proteins: they penetrate the hydrophobic core of the lipid bilayer.
http://www.youtube.com/watch?v=sdiJtDRJQEc&feature=related
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