Ch. 7 - Membrane Structure and Function

Problem 4

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Chapter 7, Problem 4

Which of the following processes includes all the others? a. osmosis b. diffusion of a solute across a membrane c. passive transport d. transport of an ion down its electrochemical gradient

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Identify the general process: Passive transport is a type of transport that does not require energy to move substances across cell membranes. It relies on the natural motion of particles and includes several specific types of movement.

Understand osmosis: Osmosis is a specific type of passive transport that involves the movement of water molecules across a semipermeable membrane from an area of lower solute concentration to an area of higher solute concentration.

Understand diffusion of a solute across a membrane: This is another specific type of passive transport where solute particles move from an area of higher concentration to an area of lower concentration across a membrane.

Understand transport of an ion down its electrochemical gradient: This process involves the movement of ions across a membrane from an area where they are more concentrated to an area where they are less concentrated, following both concentration gradient and electrical gradient. This is also a form of passive transport.

Conclude the inclusive process: Since osmosis, diffusion of a solute, and transport of an ion down its electrochemical gradient are all specific examples of substances moving across cell membranes without the expenditure of energy, they are all included under the broader category of passive transport. Therefore, the answer is c. passive transport.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Passive Transport

Passive transport is a biological process that allows substances to cross membranes without the need for energy input. It relies on the concentration gradient, where molecules move from areas of higher concentration to areas of lower concentration. This category includes processes like diffusion and osmosis, making it a fundamental concept in cellular biology.

Diffusion

Diffusion is the movement of molecules from an area of higher concentration to an area of lower concentration, driven by the kinetic energy of the molecules. This process continues until equilibrium is reached. In biological systems, diffusion is crucial for the transport of gases, nutrients, and waste products across cell membranes.

Osmosis

Osmosis is a specific type of diffusion that refers to the movement of water molecules through a selectively permeable membrane. Water moves from an area of lower solute concentration to an area of higher solute concentration, aiming to equalize solute concentrations on both sides of the membrane. This process is vital for maintaining cell turgor and overall homeostasis.

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Osmosis

Related Practice

In what way do the membranes of a eukaryotic cell vary? a. Phospholipids are found only in certain membranes. b. Certain proteins are unique to each membrane. c. Only certain membranes of the cell are selectively permeable. d. Only certain membranes are constructed from amphipathic molecules.

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Textbook Question

According to the fluid mosaic model of membrane structure, proteins of the membrane are mostly a. spread in a continuous layer over the inner and outer surfaces of the membrane. b. confined to the hydrophobic interior of the membrane. c. embedded in a lipid bilayer. d. randomly oriented in the membrane, with no fixed inside-outside polarity.

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Textbook Question

Which of the following factors would tend to increase membrane fluidity? a. a greater proportion of unsaturated phospholipids b. a greater proportion of saturated phospholipids c. a lower temperature d. a relatively high protein content in the membrane

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Textbook Question

Based on Figure 7.18, which of these experimental treatments would increase the rate of sucrose transport into a plant cell? a. decreasing extracellular sucrose concentration b. decreasing extracellular pH c. decreasing cytoplasmic pH d. adding a substance that makes the membrane more permeable to hydrogen ions

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Textbook Question

DRAW IT An artificial 'cell' consisting of an aqueous solution enclosed in a selectively permeable membrane is immersed in a beaker containing a different solution, the 'environment,' as shown in the accompanying diagram. The membrane is permeable to water and to the simple sugars glucose and fructose but impermeable to the disaccharide sucrose. a. Draw solid arrows to indicate the net movement of solutes into and/or out of the cell. b. Is the solution outside the cell isotonic, hypotonic, or hypertonic? c. Draw a dashed arrow to show the net osmosis, if any. d. Will the artificial cell become more flaccid, more turgid, or stay the same? e. Eventually, will the two solutions have the same or different solute concentrations?

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