Chapter 7: Membrane structure and function
Biologists use the fluid mosaic model to describe membrane structure. Which statements about the fluid mosaic structure of a membrane are correct? Select the three correct statements.
- The diverse proteins found in and attached to membranes perform many important functions. - Because membranes are fluid, membrane proteins and phospholipids can drift about in the membrane. - The framework of a membrane is a bilayer of phospholipids with their hydrophilic heads facing the aqueous environment inside and outside of the cell and their hydrophobic tails clustered in the center.
Which statement about the sidedness of the plasma membrane is correct?
- The two lipid layers may differ in specific lipid composition. - Every integral membrane protein has a specific orientation in the plasma membrane. - The asymmetrical distribution of membrane proteins, lipids, and carbohydrates across the plasma membrane is determined as the membrane is being constructed. - Parts of proteins that are exposed on the cytoplasmic side of the endoplasmic reticulum are also exposed on the cytoplasmic side of the plasma membrane.
In the following reaction which of the molecules is the electron acceptor: CH4+O2→ CO2+H2O
02
The internal solute concentration of a plant cell is about 0.8 M. To demonstrate plasmolysis, it would be necessary to suspend the cell in what solution?
1.0 M
Green olives may be preserved in brine, which is a 30% salt solution. How does this method of preservation prevent microorganisms from growing in the olives?
A 30% salt solution is hypertonic to the bacteria, so they lose too much water and undergo plasmolysis.
Which of the following statements is not true of most cellular redox reactions?
A hydrogen atom is transferred to the atom that loses an electron.
The concentration of solutes in a red blood cell is about 2%, but red blood cells contain almost no sucrose or urea. Sucrose cannot pass through the membrane, but water and urea can. Osmosis would cause red blood cells to shrink the most when immersed in which of the following solutions?
A hypertonic sucrose solution
Which of the following would be least likely to diffuse through a plasma membrane without the help of a transport protein?
A large, polar molecule
Phospholipids can vary based on
A) Fatty acid chain length B) Fatty acid saturation or unsaturation
Which of the following characterizes the sodium-potassium pump?
A) Potassium ions are pumped into a cell against their gradient. B) Sodium ions are pumped out of a cell against their gradient.C) The pump protein undergoes a conformational change during the process.
The movement of a substance across a biological membrane down its concentration gradient (from high concentration to low) with assistance from a protein but no input of energy is known as
A) facilitated diffusion.
The phospholipid head is __________ and the fatty acid tails are ____________
A) hydrophilic; hydrophobic
Celery stalks that are immersed in fresh water for several hours become stiff. Similar stalks left in a 0.15 M salt solution become limp. From this we can deduce that the fresh water ________.
A) is hypotonic and the salt solution is hypertonic to the cells of the celery stalks
What kinds of molecules pass through a cell membrane most easily?
A) small and hydrophobic
Which of the following is a correct difference between active transport and facilitated diffusion?
Active transport requires an input of energy, and facilitated diffusion does not.
What property of dishwashing liquid (detergent) makes it useful to wash grease from pans?
Amphipathic nature
Which terms describe two atoms when they form a bond in which electrons are completely transferred from one atom to the other?
Anion and cation.
Diffusion occurs spontaneously with no energy input because
B) It increases entropy
The movement of a substance across a biological membrane against its concentration gradient with the help of energy input is
B) active transport.
In the process of osmosis, water moves across the cell membrane:
B) from an area of low total solute concentration, to an area of high total solute concentration
If placed in a hypertonic solution, an animal cell will:
B) lose water and shrivel
Cells A and B are the same size, shape, and temperature, but cell A is metabolically less active than cell B, and cell B is actively converting oxygen to water in cellular respiration. Oxygen will diffuse more rapidly into cell __________ because __________.
B; the diffusion gradient in cell B is steeper
Seawater is hypertonic to cytoplasm in vertebrate cells and in plant cells. If a red blood cell and a plant cell were placed in seawater, what would happen to the two types of cells?
Both cells would lose water; the red blood cell would shrivel, and the plant plasma membrane would pull away from the cell wall.
In the process of diffusion, solutes move
C) From an area of high concentration of that solute to an area of low concentration of that solute
The interior of the phospholipid bilayer is
C) hydrophobic
The movement of a substance across a biological membrane down its concentration gradient (from high concentration to low) with no assistance from a protein is known as
C) simple diffusion.
If placed in a hypotonic solution, an animal cell will:
C) swell and lyse
In the following reaction which of the molecules is the electron donor: CH4+O2→ CO2+H2O
CH4
Which of the following molecules is most likely to passively diffuse across the plasma membrane?
Carbon dioxide
Which of the following statements about cotransport of solutes across a membrane is correct?
Cotransport proteins allow a single ATP-powered pump to drive the active transport of many different solutes.
Individual phospholipids are held in the bilayer based on
D) Hydrophobic interactions
Which of the following correctly describes a general property of all electrogenic pumps?
Electrogenic pumps create a voltage difference across the membrane.
Which term describes the degree to which an element attracts electrons?
Electronegativity
A nursing infant is able to obtain disease-fighting antibodies, which are large protein molecules, from its mother's milk. These molecules probably enter the cells lining the baby's digestive tract via which process?
Endocytosis
Which of the following is not a function of membrane proteins?
Energy, carbon, and nitrogen storage
Which of the following is a function of membrane proteins?
Enzymatic activity Intercellular joining Transport Cell-cell recognition
Which of the following processes and organelles account for the replacement of lipids and proteins lost from the plasma membrane?
Exocytosis and smooth ER and rough ER
A cell has a membrane potential of -100 mV (more negative inside than outside) and has 1,000 times more calcium ions outside the cell than inside. Which of the following best describes a mechanism by which Ca2+ enters the cell?
Facilitated diffusion of Ca2+ into the cell down its electrochemical gradient
Which of these statements describes some aspect of facilitated diffusion?
Facilitated diffusion of solutes may occur through channel or transport proteins in the membrane.
Which of the following is false in regard to facilitated diffusion?
Facilitated diffusion requires the hydrolysis of ATP.
Gaseous hydrogen burns in the presence of oxygen to form water: 2H2 + O2 → 2H2 O + energy Which molecule is oxidized and what kind of bond is formed?
Hydrogen, polar
If a red blood cell is placed in a salt solution and bursts, what is the tonicity of the solution relative to the interior of the cell?
Hypotonic
Consider the currently accepted fluid mosaic model of the plasma membrane. Where in the plasma membrane would cholesterol most likely be found?
In the interior of the membrane
What kind of bond is formed when lithium and fluorine combine to form lithium fluoride?
Ionic
Which of the following statements about diffusion is true?
It is a passive process
Which of the following statements concerning carbohydrates associated with the plasma membrane is correct?
Membrane carbohydrates function primarily in cell-cell recognition.
Which of the following functions of membrane proteins is important in tissue formation during embryonic development in animals?
Membrane proteins with short sugar chains form identification tags that are recognized by other cells.
A selectively permeable membrane separates two solutions. Water is able to pass through this membrane; however, sucrose (a disaccharide) and glucose (a monosaccharide) cannot pass. The membrane separates a 0.2-molar sucrose solution from a 0.2-molar glucose solution. With time, how will the solutions change?
Nothing will happen because the two solutions are isotonic.
Consider the currently accepted fluid mosaic model of the plasma membrane. Where in the membrane would carbohydrates most likely be found?
On the outside (external) surface of the membrane
Which of the following particles could diffuse easily through a cell membrane?
Oxygen (O2)
Which of the following statements is true of the bonds in a water molecule?
Oxygen holds electrons more tightly than hydrogen does, and the net charge is zero.
Which of the following statements about passive transport is correct?
Passive transport permits the solute to move in either direction, but the net movement of solute molecules occurs down the concentration gradient of the molecule.
Which of the following statements about the role of phospholipids in the structure and function of biological membranes is correct? - Phospholipids are completely unable to interact with water. - Phospholipids form a structure in which the hydrophobic portion faces outward. - Phospholipids form a single sheet in water. - Phospholipids form a selectively permeable structure. - They are triacylglycerols, which are commonly available in foods.
Phospholipids form a selectively permeable structure.
Which of the following pairs correctly matches a membrane transport process to its primary function?
Pinocytosis: the uptake of water and small solutes into the cell by formation of vesicles at the plasma membrane
Which of the following enables a cell to pick up and concentrate a specific kind of molecule?
Receptor-mediated endocytosis
Which of the following is a reasonable explanation for why unsaturated fatty acids help keep the membrane more fluid at lower temperatures?
The double bonds form kinks in the fatty acid tails, preventing adjacent lipids from packing tightly
The plasma membrane is referred to as a "fluid mosaic" structure. Which of the following statements about that model is true? - The fluid aspect of the membrane is due to the behavior of phospholipids, and the mosaic aspect is due to the presence of carbohydrates. - The mosaic aspect of the membrane is due to the glycosylation of phospholipids on the cytoplasmic side of the membrane. - The fluid aspect of the membrane describes its structure at normal temperatures, and the mosaic aspect describes the behavior of the membrane as the temperature is lowered. - The fluid aspect of the membrane is due to the mobility of phospholipids, and embedded proteins account for the mosaic aspect. - Only phospholipids are capable of moving in the membrane.
The fluid aspect of the membrane is due to the mobility of phospholipids, and embedded proteins account for the mosaic aspect.
Which of the following statements is true for cell membranes
The membrane is a mixture of different phospholipids. Phospholipids can vary between the inner and outer layers and also within a layer.
Consider the transport of protons and sucrose into a plant cell by the sucrose-proton cotransport protein. Plant cells continuously produce a proton gradient by using the energy of ATP hydrolysis to pump protons out of the cell. Why, in the absence of sucrose, do protons not move back into the cell through the sucrose-proton cotransport protein?
The movement of protons through the cotransport protein cannot occur unless sucrose moves at the same time
Active transport requires an input of energy and can also generate voltages across membranes. Based on this information, which of the following statements is true?
The sodium-potassium pump hydrolyzes ATP and results in a net positive change outside the cell membrane.
According to the fluid mosaic model of cell membranes, which of the following is a true statement about membrane phospholipids?
They can move laterally along the plane of the membrane
Glucose can be moved into cells via an active transport mechanism when the concentration of glucose inside the cell is higher than the concentration of glucose outside the cell. This active transport mechanism moves glucose and sodium into the cell at the same time. The glucose moves up its gradient and the sodium moves down its gradient. Which of the following statements about this mechanism is accurate?
To pump glucose up its concentration gradient, sodium moves down its concentration gradient, and the distribution of sodium ions across the membrane forms an electrochemical gradient that drives this mechanism.
A single plant cell is placed in an isotonic solution. Salt is then added to the solution. Which of the following would occur as a result of the salt addition?
Water would leave the cell by osmosis, causing the volume of the cytoplasm to decrease.
Which of the following factors would tend to increase membrane fluidity?
a greater proportion of unsaturated phospholipids
Phospholipids vary in the small molecules attached to the phosphate group. The phospholipid shown in the figure has a _____________ attached to phosphate.
choline group
Which of the following is a CORRECT description of the role of cholesterol in the cell membrane
enables the membrane to stay fluid when cell temperature drops.
A phospholipid also has two "tails" made up of two ________ molecules, which consist of a carboxyl group with a long hydrocarbon chain attached.
fatty acid
Which of the following factors would tend to increase membrane fluidity?
high temperature
Because the phosphate group and its attachments are either charged or polar, the phospholipid head is _____________ which means it has an affinity for water.
hydrophilic,
Because the C-H bonds in the fatty acid tails are relatively nonpolar, the phospholipid tails are ___________ which means they are excluded from water.
hydrophobic,
Which of these can RAPIDLY pass directly through the phospholipids of the plasma membrane, without the help of a transport protein?
lipid soluble molecule
When molecules move down their concentration gradient, they move from where they are ___________ to where they are ____________
more concentrated to less concentrated
The following reaction is a(n) ______________: Na → Na+
oxidation
Diffusion across a biological membrane is called
passive transport
A phospholipid has a "head" made up of a glycerol molecule attached to a single ___________, which is attached to another small molecule.
phosphate group
The following reaction is a(n) ______________: Na + Cl → Na+ + Cl-
redox reaction
The following reaction is a(n) ______________: Cl → Cl-
reduction
Which of the following are NOT able to diffuse through the phospholipid bilayer of a cell membrane?
small ions
You are working on a team that is designing a new drug. For this drug to work, it must enter the cytoplasm of specific target cells. Which of the following would be a factor that determines whether the molecule selectively enters the target cells?
the similarity of the drug molecule to other molecules that are transported into the target cells
True or false? Osmosis is a type of diffusion.
true
True or false? The water-soluble portion of a phospholipid is the polar head, which generally consists of a glycerol molecule linked to a phosphate group.
true
