6. The Membrane

Active Transport

Primary Active Transport vs Secondary Active transport

Which of the following cannot pass through the membrane without the help of a membrane protein?
a. carbon dioxide;
b. water;
c. oxygen;
d. charged molecules

Which of the following defines the type of transport by the sodium-potassium pump?

transmembrane pumps; an electrochemical gradient

The force driving simple diffusion is ________, while the energy source for active transport is ________.

Secondary Active Transport

Many species of animals on islands are larger than related species on the mainland. Scientists hypothesize that this phenomenon, called island gigantism, evolved in response to the scarcity of competitors and predators on islands. Reduced competition and predation allows species to exploit more resources and frees them from the need to hide in small refuges.

On a trip to the Galápagos Islands, you overhear a group of tourists refer to tortoises as “cold blooded.” Explain why this word is not accurate to describe a giant tortoise.

Sodium Potassium Pump

Primary active transport establishes a concentration gradient, but secondary active transport doesn’t

Secondary active transport uses the concentration gradient established by primary active transport

Primary active transport moves one molecule, but secondary active transport moves two

How are primary and secondary active transport related?

A Level Biology Revision "Cotransport (AQA)"

MEMBRANE TRANSPORT

Active transport can use ATP as its energy source and ensures that there is no voltage across the cell membrane.

No. Although active transport can use ATP, cells usually have a membrane potential.

Active transport moves solutes down their concentration gradients and always uses ATP as the source of energy to do this.

No. If solutes were moving down their gradients, there would be no need for active transport. Also, there are other sources of energy for active transport.

Active transport uses channel proteins and ensures that the interior of the cell is always positive compared to the exterior of the cell.

No. Active transport uses transport proteins called pumps; generally, the interior of the cell is maintained at a voltage slightly negative compared to that of the exterior of the cell due to the sodium-potassium pump.

The source of energy for active transport of a solute up its gradient can be ATP or a concentration gradient of a second solute. This second gradient of solutes maintains no net difference in voltage across the membrane.

No. Although ATP or a concentration gradient of solute can drive active transport, the driving gradient of solutes does not maintain membrane voltage at zero.

The sodium-potassium pump hydrolyzes ATP and results in a net positive change outside the cell membrane.

Consider the characteristics of active transport.

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?

Transports 3 potassium ions out of a cell and 2 sodium ions into a cell and produces a molecule of ATP.

Transports 3 sodium ions out of a cell and 2 potassium ions into a cell using energy from ATP hydrolysis.

Transports 3 potassium ions out of a cell and 2 sodium ions into a cell using energy from ATP hydrolysis.

Transports 3 sodium ions out of a cell and 2 potassium ions into a cell and generates an ATP in each cycle.

BioFlix: Active Transport

Electrogenic pumps pump sodium out of the cell and potassium into the cell.

No. This statement describes the electrogenic pump in animal cells, but the electrogenic pump in plants, fungi, and bacteria pumps protons out of the cell.

Electrogenic pumps can pump a large variety of solutes across a membrane against their concentration gradient.

No. Electrogenic pumps are limited to a few solutes, primarily protons in plants, bacteria, and fungi and sodium-potassium in animal cells.

Electrogenic pumps result in a cell with an interior that is positively charged relative to the outside the cell.

No. In cells, the membrane potential that develops is always negative on the inside, positive on the outside.

Electrogenic pumps result in a cell with a high internal concentration of protons.

No. The electrogenic pumps found in plants, fungi, and bacteria move protons out of the cell.

Electrogenic pumps create a voltage difference across the membrane.

Consider the common properties of electrogenic pumps.

Which of the following correctly describes a general property of all electrogenic pumps?

Primary Active Transport

Sodium and glucose move together into the cell via facilitated diffusion.

No. Because glucose is moving up its concentration gradient, some energy is required in this process.

To pump glucose up its concentration gradient, sodium moves down its concentration gradient.

No. Although this is true, there is a better answer.

The distribution of sodium ions across the membrane forms an electrochemical gradient that drives this mechanism.

Sodium and glucose move together into the cell via facilitated diffusion, and to pump glucose up its concentration gradient, sodium moves down its concentration gradient.

No. Although the movement of sodium down its gradient powers the movement of glucose up its gradient, the two solutes are moving in the same direction, so a symporter is being used.

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.

Consider the nature of the gradient being described and also the mechanisms to move solutes that exploit the directionality of this gradient.

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?

Primary Active Transport: Na+/K+ Pump

A Level Biology Revision "Active Transport"

Which of the following forms of membrane transport require specific membrane proteins?
a. diffusion;
b. exocytosis;
c. facilitated diffusion;
d. active transport;
e. facilitated diffusion and active transport

Protons cannot move through membrane transport proteins.

No. The movement of protons down their electrochemical gradient through cotransport proteins is the energy that drives active transport of most solutes in plants and bacteria.

Protons are freely permeable through the phospholipid bilayer, so no transport protein is needed for protons.

No. Protons are charged and do not move passively through phospholipid bilayers.

In the absence of sucrose, the ATP-powered proton pump does not function, so there is no proton gradient.

No. The ATP-dependent proton pump is always on in plant cells to power the active transport of many compounds.

Protons, unlike other substances, do not diffuse down their electrochemical gradient.

No. Diffusion of protons down their electrochemical gradient is the energy that powers all cotransport systems in plants and bacteria.

The movement of protons through the cotransport protein cannot occur unless sucrose moves at the same time.

Consider the energy requirements of cotransport.

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?

Cell Membrane Transport - Transport Across A Membrane - How Do Things Move Across A Cell Membrane

Cotransport involves the hydrolysis of ATP by the transporting protein.

No. Cotransport proteins do not hydrolyze ATP; rather, they use the energy of gradients created by the ATP-dependent pumps.

A cotransport protein is most commonly an ion channel.

No. Cotransport proteins are always carrier proteins.

The sodium-potassium pump is an example of a cotransport protein.

No. The sodium-potassium pump is an example of an ATP-dependent ion pump, not of a cotransport protein.

In cotransport, both solutes that are being transported are moving down their chemical gradients.

No. In cotransport, one solute is moving down its electrochemical gradient and this energy is used to move the second solute against its electrochemical gradient.

Cotransport proteins allow a single ATP-powered pump to drive the active transport of many different solutes.

Consider the role of cotransport proteins in active transport of solutes.

Which of the following statements about cotransport of solutes across a membrane is correct?

Active Transport Example 1

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