Active Transport Review

Using the diagram showing three labeled membrane transport proteins (A, B, C), match each label to the correct mechanism: sodium–potassium pump, proton pump, cotransport. Provide the mapping for A, B, and C.

• Proton pump

• B

• Sodium–potassium pump

• A

• Cotransport

• C

Define active transport.

• Movement of molecules across the cell membrane against their concentration gradient using cellular energy

• Random movement of molecules until equilibrium without any energy input

• Bulk flow of water through channels driven by osmotic pressure only

• Movement of molecules down their concentration gradient by simple diffusion

Tags

NGSS.HS-LS1-3

Why is ATP required for active transport?

• ATP hydrolysis releases energy that transport proteins use to move molecules against their concentration gradients

• ATP binds to solutes to make the membrane more permeable, allowing passive diffusion

• ATP lowers external solute concentrations so diffusion can proceed without resistance

• ATP directly stores ions inside the lipid bilayer until they leak through

Predict the impact on the flow of molecules across a membrane if ATP hydrolysis (the breakdown of ATP into ADP and inorganic phosphate, releasing energy) is inhibited.

• Transport against concentration gradients would be greatly reduced or cease, leading to ion imbalances and decreased nutrient uptake

• Passive diffusion would increase dramatically, compensating fully for the loss of active transport

• Membrane permeability to all molecules would increase, causing higher rates of active transport

• Cotransport rates would increase while ATP-dependent pumps continue at normal levels

Describe how proton pumps contribute to the establishment and maintenance of membrane potential.

• They actively move H+ out of the cell using ATP, creating a proton gradient

• The resulting gradient produces a difference in charge across the membrane (membrane potential)

• They equalize ion distributions on both sides of the membrane, neutralizing any charge difference

• By sustaining the proton gradient, they help maintain the membrane potential over time

Using the figure, explain how cotransport facilitates the movement of sucrose across the membrane.

• A sucrose–H+ cotransporter uses the energy stored in the H+ gradient to move sucrose into the cell against its gradient

• Sucrose diffuses through the lipid bilayer independently of any ion gradients

• Sucrose export occurs via the Na+/K+ pump whenever ATP is abundant

• The proton pump directly binds sucrose and transports it by itself without using a gradient

Discuss the role of sodium–potassium pumps in neurons and how they contribute to changes in membrane potential.

• They move 3 Na+ out of the neuron and 2 K+ into the neuron per cycle, using ATP

• Their ion movements create a net negative charge inside the neuron relative to the outside, contributing to the resting membrane potential

• They directly depolarize the membrane during action potentials by allowing Na+ influx through the pump

• They are essential for restoring and maintaining ion gradients that underlie action potentials

In developing countries, contamination of food and water from cholera is a serious problem. Cholera is caused by Vibrio cholerae and releases a toxin that attaches to the lining of the digestive system, causing the release of sodium and chloride ions into the intestinal lumen (space inside the intestines). Based on this information, how does the release of sodium and chloride ions lead to a loss of water from the body?

• It raises the osmolarity of the intestinal lumen, pulling water from body tissues into the lumen by osmosis and increasing water loss in diarrhea

• It lowers the osmolarity of the intestinal lumen, drawing water into the bloodstream and reducing water loss

• It activates aquaporins to pump water directly into the blood vessels

• It converts the ions into water, increasing total body fluid

Tags

NGSS.HS-LS1-3

Intestinal cells possess sodium–glucose cotransporters. Why do doctors administer a sodium–glucose solution to patients recovering from cholera?

• The cotransporters use sodium to bring glucose and sodium into intestinal cells, promoting osmotic water reabsorption

• The solution directly kills Vibrio cholerae in the intestinal lumen

• The solution increases chloride secretion to flush out the toxin

• The solution blocks neuronal exocytosis to reduce gut motility

Tags

NGSS.HS-LS2-3

The image illustrates a portion of a neuron with membrane-bound vesicles releasing their contents into the extracellular space. Identify the cellular process occurring in this image.

• Exocytosis of neurotransmitters

• Endocytosis

• Facilitated diffusion through ion channels

• Phagocytosis