Life Science 7a Part Two
Highlighted=​ Terms/Concepts
Week Two
5.2
- Plasma membrane​: forms the cells outer boundary and separates the cells internal
environment from the outside environment, hydrophobic
- The plasma membrane obtains homeostasis by being ​selectively permeable​: ​lets
some molecules in and out freely, lets others in and out only under certain
conditions, and prevents other molecules from passing through at all.
- Diffusion ​is the movement of random molecules
- When a molecule moves by diffusion through a membrane protein and bypasses
the lipid bilayer, the process is called​ facilitated diffusion
- I​n the case of facilitated diffusion, the molecule moves through a membrane
transporter, whereas in the case of simple diffusion, the molecule moves directly
through the lipid bilayer.
- There are two types of membrane transporters: channel and carrier
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movement of molecules (the solutes) in water (the solvent)
Aquaporins: ​A protein channel that allows water to flow through the plasma
membrane more readily by facilitated diffusion.
Water itself also moves into and out of cells by passive transport. Although the
plasma membrane is hydrophobic, water molecules are small enough to move
passively through the membrane to a limited extent by simple diffusion.
The net movement of a solvent such as water across a selectively permeable
membrane such as the plasma membrane is known as ​osmosis
The “uphill” movement of substances against a concentration gradient requiring
an input of energy is called ​active transport
Active transport that uses the energy of ATP directly is called ​primary transport
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the sodium ions and potassium ions move in opposite directions. Protein
transporters that work in this way are referred to as antiporters. Other
transporters move two molecules in the same direction, and are referred to as
symporters or cotransporters
Secondary active transport​ uses the potential energy of an electrochemical
gradient to drive the movement of molecules; by contrast, primary active transport
uses the chemical energy of ATP directly.
A gradient that has both charge and chemical components is known as an
electrochemical gradient
Many cells use active transport to maintain their size
Changes in red blood cell shape due to osmosis. Red blood cells shrink, swell, or
burst because of net water movement driven by differences in solute
concentration between the inside and the outside of the cell.
Important Review Qs
Why does active transport require ATP?​An input of energy is needed to allow
the movement of molecules from an area of low concentration to one of
higher concentration.
Some plant cells take advantage of the high concentration of protons outside
the cell to move solutes, such as sucrose, across the plasma membrane into
the cell where the sucrose concentration is already relatively high. This type
of transport is an example of:secondary active transport.
The plasma membranes of some plant cells use transport proteins to move
protons out of the cell against their concentration gradient (from areas of
low proton concentration to areas of high proton concentration). This is an
example of:active transport.
Which of the following molecules does NOT easily diffuse across a plasma
membrane? large polar molecules