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Ch. 7 - Membrane Structure and Function
Campbell - Campbell Biology 12th Edition
Urry12th EditionCampbell BiologyISBN: 9785794169850Not the one you use?Change textbook
All textbooksUrry 12th EditionCh. 7 - Membrane Structure and FunctionProblem 6
Chapter 7, Problem 6

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.
Diagram of a cell in a beaker showing solute concentrations and membrane permeability for osmosis study.
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?

Verified step by step guidance
1
Examine the diagram to identify the solutes present inside and outside the artificial cell. Note that the membrane is permeable to water, glucose, and fructose, but not to sucrose.
Determine the concentration gradient for each permeable solute (glucose and fructose) across the membrane. Solutes will move from areas of higher concentration to areas of lower concentration.
Draw solid arrows on the diagram to indicate the net movement of glucose and fructose based on their concentration gradients. If glucose is more concentrated inside the cell, draw an arrow pointing outwards, and vice versa for fructose.
Assess the tonicity of the solution outside the cell by comparing the total solute concentration inside and outside the cell. If the external solution has a higher solute concentration, it is hypertonic; if lower, hypotonic; if equal, isotonic.
Draw a dashed arrow to represent the net movement of water (osmosis) based on the tonicity assessment. Water will move towards the area with higher solute concentration. Determine if the cell will become more flaccid (losing water), more turgid (gaining water), or stay the same, and predict whether the solute concentrations will eventually equalize.

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Key Concepts

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

Selective Permeability

Selective permeability refers to the ability of a membrane to allow certain molecules or ions to pass through it while blocking others. In the context of the artificial cell, the membrane permits the passage of water, glucose, and fructose but restricts sucrose, influencing the movement of solutes and water between the cell and its environment.
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Osmosis

Osmosis is the movement of water across a selectively permeable membrane from a region of lower solute concentration to a region of higher solute concentration. This process aims to equalize solute concentrations on both sides of the membrane, affecting the cell's turgidity and the net movement of water in the artificial cell scenario.
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Tonicity

Tonicity describes the relative concentration of solutes in two solutions separated by a membrane, determining the direction of water movement. Solutions can be isotonic, hypotonic, or hypertonic, affecting whether the artificial cell becomes more turgid, flaccid, or remains unchanged based on the solute concentration gradient between the cell and its environment.
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Related Practice
Textbook Question

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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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

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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