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1. In order for a cell to actively transport a substance across its cell membrane, there needs to be a protein pump embedded in the cell membrane and the energy (ATP) needed to make it run.
2. Diffusion simply means the movement of a substance from an area of high concentration to low concentration. Osmosis is the diffusion of water, specifically. If in order for a molecule to diffuse across a cell membrane it needs a protein to act as a tunnel, it is referred to as facilitated diffusion.
3. The process of endocytosis is active transport because energy is required to change the shape of the cell in order to engulf a food particle.
4. A cell living in hypotonic conditions must deal with osmosis occurring into the cell.
5. The paramecium would suddenly be in hypertonic conditions, which means water would diffuse out of the cell (and the cell would most likely die).
6. Ys = -iCRT
i = 2 (because NaCl will break up into Na+ and Cl- in solution)
C = 0.23 M
R = 0.00831 liter MPa/mole K
T = temperature in kelvins (20°C + 273 = 293)
Y s = -iCRT = -(2)(.23M)(0.00831 liter MPa/mole K)(293)
Y s = - 1.1 MPa
7. Facilitated diffusion would help the passive movement of glucose molecules into the cell. Facilitated diffusion provides a tunnel through which the glucose molecules could diffuse.
8. It is bad to disrupt a cell’s chemical gradients because the cell would no longer be able to do work. For example, if there were no longer hydrogen ion gradients in a mitochondrion, the cell would no longer be able to generate ATP.
9.
a. A plant cell floating in pure water: hypotonic.
b. A protist cell normally living in a freshwater lake transferred to a marine environment: hypertonic.
c. A bacterium in a solution that has the same water potential as inside the bacterial cell: isotonic.
10. Some cells that live in hypotonic conditions have evolved to rely on an organelle called a contractile vacuole to pump out the extra water that diffuses inward.
11. The overall water potential is the sum of the solute potential plus the pressure potential: Y = Ys + Yp
Yp = 0 (because it is in an open container)
Y s = -2.0 MPa
Therefore, overall Y = -2.0 MPa
12. a. When a cell releases carbon dioxide from cellular respiration, it diffuses from the cell because the concentration of carbon dioxide in the surrounding environment is lower than that inside the cell.