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

Verified step by step guidance

1. Identify the mechanism of sucrose transport: Sucrose transport into plant cells typically involves a cotransporter protein that uses the proton gradient (H+ ions) across the membrane. This gradient is maintained by the active transport of H+ ions out of the cell, creating a higher concentration of H+ outside the cell compared to inside.
2. Analyze the options: a) Decreasing extracellular sucrose concentration would lower the gradient for sucrose entry, thus reducing transport. b) Decreasing extracellular pH means increasing H+ concentration outside, enhancing the proton gradient, which could increase the driving force for the cotransporter. c) Decreasing cytoplasmic pH would reduce the proton gradient across the membrane, likely reducing sucrose transport. d) Adding a substance that increases membrane permeability to H+ ions would dissipate the proton gradient, reducing the energy source for sucrose transport.
3. Evaluate the impact of decreasing extracellular pH: By increasing the concentration of H+ ions outside the cell (decreasing pH), the proton gradient across the membrane is enhanced. This increased gradient can provide more energy for the H+/sucrose cotransporter to function, thereby increasing the rate of sucrose transport into the cell.
4. Conclude the most effective treatment: Based on the mechanism of sucrose transport involving a proton gradient, the treatment that would most likely increase the rate of sucrose transport into a plant cell is decreasing the extracellular pH.
5. Eliminate other options: Treatments such as decreasing extracellular sucrose concentration, decreasing cytoplasmic pH, and making the membrane more permeable to hydrogen ions would not increase the rate of sucrose transport based on their effects on the proton gradient and sucrose concentration gradient.

Key Concepts

Sucrose Transport Mechanisms

Sucrose transport in plant cells primarily occurs through active transport and facilitated diffusion. Active transport requires energy to move sucrose against its concentration gradient, often coupled with the movement of protons (H+) into the cell. Understanding these mechanisms is crucial for analyzing how changes in concentration gradients or membrane permeability can affect sucrose uptake.

Concentration Gradients

A concentration gradient refers to the difference in the concentration of a substance across a space. In the context of sucrose transport, a higher extracellular sucrose concentration compared to the cytoplasm can drive the movement of sucrose into the cell. Manipulating these gradients, such as by decreasing extracellular sucrose concentration, can significantly influence transport rates.

Membrane Permeability

Membrane permeability is the ability of substances to pass through a cell membrane. Factors that affect permeability include the lipid composition of the membrane and the presence of specific transport proteins. Increasing membrane permeability to hydrogen ions can enhance the electrochemical gradient, facilitating the co-transport of sucrose into the cell, thereby increasing its transport rate.