Eleventh grade
Section review 1
1. Diffusion eventually leads to equilibrium, which occurs when the concentration gradient of
molecules is the same throughout a space.
2. Diffusion is the movement of molecules from an area of higher concentration to an area of lower
concentration; osmosis is the diffusion of water from an area of higher concentration to an area of
lower concentration across a membrane.
3. The external solution is hypotonic to the cytosol.
4. Carrier proteins bind to molecules on the side of the cell membrane, the proteins change shape,
and then the proteins release the molecules on the other side of the membrane.
5. Both processes can help substances move down their concentration gradients from one side of
the cell membrane to the other and without an input of energy by cells. Both processes also involve
membrane proteins.
6. The solutes in the sea water would make the ingested solution more concentrated
Section review 2
1. Passive transport moves substances down their concentration gradient and, therefore, does not
require an input of energy from the cell. Active transport moves substances up their concentration.
2. Carrier proteins bind to specific molecules on one side of the membrane and move them up their
concentration gradient to the other side of the membrane.
3. Transferring a phosphate group from ATP to the carrier protein supplies the energy that drives
the sodium potassium pump.
4. Pinocytosis moves solutes or fluid into cells; phagocytosis moves particle or whole cells into
cells.
5. In exocytosis, vesicles fuse with the cell membrane and release their contents outside the cells.
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6. The concentration of sodium and potassium inside and outside the muscle cells are important in
the regulation of contraction. These concentrations differ when a muscle is relaxing or contracting.
Contraction: potassium concentrations are higher outside the cell than inside the cell.
Relaxation: the potassium concentrations are higher inside the cell than outside the cell.
The muscle cell needs some kind of active transport to pump the potassium ions back into the cell.
This is wat the sodium-potassium pump does. This pump is driven by ATP and exchanges a
sodium ion from inside the cell with a potassium ion outside the cell.