Lecture 10 Study Guide

Question 1

Define osmosis. Why does water move towards high solute concentration?

Answer 1

osmosis: the diffusion of water across a selectively permeable membrane

because there is less water in high solute concentration so the water diffuses to reach equilibrium

Question 2

Distinguish between solute, solvent and solution.

Answer 2

solute: substance dissolved in a substance
solvent: the liquid in which the solute is dissolved to form a solution
solution: homogenous mixture containing two or more substances

Question 3

List three factors that affect the rate of diffusion.

Answer 3

1. concentration gradient
2. medium of diffusion
3. density of diffusing substance

Question 4

Define plasmolysis. Why is it found only in plant and bacterial cells?

Answer 4

plasmolysis: when a plant cell shrivels up and the plasma membrane pulls away from the cell wall

it only happens in plants and bacteria because plants and bacterial are the cells with cell walls

Question 5

State the specific membrane transport proteins that transport the following molecules:
Water down a concentration gradient:
Small non-polar molecules down the concentration gradient:
Polar molecules down a concentration gradient:
Ions down a concentration gradient:
Large macromolecules down a gradient:
Na+/K+ against the concentration gradient:
Amino acids and sugars against a concentration gradient (in plants):

Answer 5

water: aquaporins
small non-polar: simple diffusion
polar molecules: facilitated diffusion
Ions: ion channels
large molecules: facilitated diffusion
Na+/K+: sodium potassium pump
amino acids and sugars: active transport

Question 6

Define the term ‘ligand’

Answer 6

small signaling molecule that is not transported but triggers ion channels to open

Question 7

Describe 4 main types of ion channels and how they function.

Answer 7

Ligand Gated Ion Channels: signaled by ligands to open
Voltage gated ion channels: opens in response to change in charge
Mechanical Gated Ion Channel: opens in response to a physical stimulus
Light Gated ion channel:sensitive to visible wavelengths and light

Question 8

State the range of voltages found across membranes in cells.

Answer 8

-50 to -200 minivolts

Question 9

Define the following terms:
Membrane potential
Electrochemical gradient
Electrogenic pump
Proton pump
Co-transport

Answer 9

membrane potential: the voltage across a membrane
electrochemical gradient: combination of forces on ions (chemical & electrical forces)
electrogenic pump: a transport protein that generates voltage across a membrane
proton pump: the main electrogenic pump of plants, fungi, and bacteria
co-transport: a transport protein can could the “downhill” diffusion of the solute to the “uphill” transport of a second substance against its own concentration gradient

Question 10

Distinguish between endocytosis and exocytosis using specific examples of each.Which of these methods involve fusion of a vesicle at the plasma membrane? Which of these methods involve the formation of a vesicle at the plasma membrane?

Answer 10

Endocytosis: cell takes in molecules and particulate matter by forming new vesicles from the plasma membrane (ex: human cells use receptor mediated endocytosis to take in cholesterol for membrane synthesis)
exocytosis: the process in which cells secrete certain molecules by fusion of vesicles to the plasma membrane (ex: many secretory cells use exocytosis to export products)

Question 11

Distinguish between phagocytosis, pinocytosis, and receptor-mediated endocytosis.

Answer 11

phagocytosis: a cell engulfs a particle
pinocytosis: a cell continuously gulps droplets of extracellular fluid into tiny vesicles, formed by its infoldings of the plasma membrane
receptor mediated endocytosis: specialized type of pinocytosis that enables the cell to acquire bulk quantities of specific substances