Chapter 5 Flashcards
(18 cards)
Animal cells are surrounded by _________ fluid. This fluid is ________ to the cytosol.
a. phospholipid; isotonic
b. plasma; hypertonic
c. interstitial; isotonic
d. interstitial; hypotonic
c
Which of the following cannot enter a cell by simple diffusion?
a. water
b. sugar
c. estrogen
d. oxygen
b
Glycoproteins are important for
a. binding hormones.
b. cell recognition by the immune system.
c. forming ion channels.
d. active transport through the membrane.
b
Diffusion
a. is always facilitated.
b. occurs by active transport.
c. is increased when temperature increases.
d. requires aquaporin proteins.
c
Which of the following is not true of endocytosis?
a. It is a form of passive transport.
b. It includes pinocytosis.
c. It can occur in coated pits.
d. It is used by Amoeba to feed on Paramecium.
a
Membranes consist of a bilayer of ________. The five major categories of protein within the bilayer are ________, _________, _______, _________, and _________ proteins.
phospholipids; receptor, recognition, enzymes, attachment and transport
A membrane that is permeable to some substances but not to others is described as being _______. The movement of a substance through a membrane down its concentration gradient is called _________. When applied to water, this process is called _________. Channels that are specific for water are called _________. The process that moves substances through a membrane against their concentration gradient is called _______.
selectively permeable; diffusion; osmosis; aquaporins and active transport
Facilitated diffusion involves either _________ proteins or _________ proteins. Diffusion directly through the phospholipid bilayer is called ________ diffusion, and molecules that take this route must be soluble in _________ or be very small and have no net electrical charge.
channel, carrier; simple and lipids
After each molecule, place the two-word term that most specifically describes the process by which it moves through a plasma membrane. Carbon dioxide: ________ ; ethyl alcohol: __________ ; a sodium ion: ________ ; glucose: _________.
simple diffusion, simple diffusion, facilitated diffusion and facilitated diffusion
The general process by which fluids or particles are transported out of cells is called _________. Does this process require energy? _________. The substances to be expelled are transported within the cell in membrane-enclosed sacs called ________.
exocytosis; yes and vesicles
Describe and diagram the structure of a plasma membrane. What are the two principal types of molecules in plasma membranes, and what is the general function of each?
See Figure 5-1 for a diagram of the plasma membrane. The plasma membrane can be described as a fluid mosaic, referring to the fluidity of the phospholipid bilayer and the mosaic of different proteins it contains. The two types of molecules are phospholipids and proteins. The function of the phospholipid bilayer is to isolate the cell from its surroundings. The proteins of the membrane allow selective interactions with the environment.
Sketch the configuration that 10 phospholipid molecules would assume if placed in water. Explain why they arrange themselves this way.
The phospholipid molecules would form a droplet with all their tails in the center and their heads facing the water. This is because the heads are polar (hydrophilic) and attracted to polar water molecules, whereas the tails are hydrophobic and not attracted to water.
What are the five categories of proteins commonly found in plasma membranes, and what is the function of each one?
The five categories of proteins found in the plasma membrane are (1) enzymes, which promote chemical reactions without being changed themselves; (2) recognition proteins, which serve to identify the cell; (3) transport proteins, which are used to regulate the movement of water-soluble molecules or ions through the plasma membrane; (4) receptor proteins, which respond to molecules in the extracellular fluid, such as hormones; and (5) attachment proteins, which anchor the plasma membrane to the cytoskeleton inside, to the extracellular matrix outside, or to adjacent cells.
Define diffusion and osmosis. Explain how osmosis helps plant leaves remain firm. What is the term for water pressure inside plant cells?
Diffusion is the net movement of molecules in a fluid from regions of high concentration to regions of low concentration. Osmosis is the diffusion of water though selectively permeable membranes. Plant leaves are supported by the turgor pressure produced when plant cell vacuoles take in water by osmosis. Turgor pressure “inflates” plant cells, supporting them.
Define hypotonic, hypertonic, and isotonic. What would be the fate of an animal cell immersed in each of these three types of solution?
The terms hypotonic, hypertonic, and isotonic describe relative concentrations of solutes when one solution is compared to another solution separated by a membrane that is selectively permeable to water. A hypotonic solution has a lower solute content, a hypertonic solution has a higher solute content, and an isotonic solution has the same solute content as the compared solution. Water will move by osmosis through the membrane from a hypotonic solution into a hypertonic solution. If an animal cell is placed into a solution hypotonic to the cell’s cytoplasm, water will enter the cell by osmosis and may eventually cause the cell to burst. A hypertonic solution causes water to leave a cell and will cause an animal cell to shrivel. An isotonic solution results in no net loss or gain of water by a cell, because both the cytoplasm and the extracellular solution contain the same concentration of solutes.
Describe the following types of transport processes in cells: simple diffusion, facilitated diffusion, active transport, pinocytosis, receptor-mediated endocytosis, phagocytosis, and exocytosis.
Simple diffusion is the diffusion of water, dissolved gases, or lipid-soluble molecules through the phospholipid bilayer of a membrane. Facilitated diffusion is the diffusion of molecules through a membrane, assisted by membrane transport proteins. Active transport is the movement of small molecules and ions through membrane proteins, using cellular energy, usually in the form of ATP. Pinocytosis is the introduction of extracellular fluid into a cell by a small piece of the plasma membrane that dimples inward and pinches off, forming a vesicle. Receptor-mediated endocytosis moves specific molecules into a cell when the particular molecule binds to receptor proteins on the plasma membrane, and the membrane is pinched off, forming a sac that contains the imported molecule. Phagocytosis is the movement of large food particles or whole organisms into a cell by extensions of the plasma membrane called pseudopods that encircle an extracellular particle and form a vesicle. In exocytosis, vesicles fuse with the plasma membrane, expelling the contents outside the cell.
Name the protein that allows facilitated diffusion of water. What experiment demonstrated the function of this protein?
Aquaporin allows facilitated diffusion of water. Peter Agre and associates inserted an unknown membrane protein from red blood cells into frog eggs (which are not very permeable to water) and found that the frog eggs with the protein took up water rapidly and burst in hypotonic solutions, whereas those without the protein were unchanged.
Imagine a container of glucose solution, divided into two compartments (A and B) by a membrane that is permeable to water and glucose but not to sucrose. If some sucrose is added to compartment A, how will the contents of compartment B change? Explain.
Glucose will diffuse from compartment A into compartment B, and water will follow by osmosis. The result will be greater (but equal) concentrations of glucose in both compartments and the same amount of water in both compartments.
