When might a cell need to use active transport?

Active transport is the mediated process of moving particles across a biological membrane against a concentration gradient. If the process uses chemical energy, such as from adenosine triphosphate (ATP), it is termed primary active transport. Secondary active transport involves the use of an electrochemical gradient. Active transport uses energy, unlike passive transport, which does not use any energy

Specialised trans-membrane proteins recognize the substance and allows it access (or, in the case of secondary transport, expend energy on forcing it) to cross the membrane when it otherwise would not, either because it is one to which the lipid bilayer of the membrane is impermeable or because it is moved against the concentration gradient. The last case, known as primary active transport, and the proteins involved in it as pumps, uses the chemical energy of, usually, ATP. The other cases, which usually derive their energy through exploitation of an electrochemical gradient, are known as secondary active transport and involve pore-forming proteins that form channels through the cell membrane.

Sometimes one substance is transported in one direction at the same time as another substance is being cotransported in the other direction. This is called antiport. Symport is the name if two substrates are being transported in the same direction across the membrane. Antiport and symport are associated with secondary active transport, meaning that one of the two substances are transported against their concentration gradient utilizing the energy derived from the transport of the second substance (mostly Na+, K+ or H+) down its concentration gradient.

When particles are being moved from areas of low concentration to areas of high concentration (i.e., against the concentration gradient) then specific carrier proteins in the membrane are required to move these particles. The carrier proteins bind to specific molecules (e.g., glucose) and transport them into the cell where they are released. Because energy is required for this process, it is known as active transport. Examples of active transport include when sodium is transported out of the cell and potassium into the cell by the sodium-potassium pump. Active transport often takes place in the internal lining of the small intestine.

Plants need to absorb mineral salts from the soil, but these salts are in very dilute solution. Active transport enables these cells to take up salts from this dilute solution against the concentration gradient.

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RE:

When might a cell need to use active transport?

whats an example and describe it

When diffusion cannot occur due to the lack of a favourable concentration gradient, active transport is used. An example of this is in the villi of the small intestine.

Although a steep concentration is usually mantained to facilitate the diffusion of glucose into the blood stream, if one has eated food containing a lot of carbohydrates and sugar, the concentration of glucose may be higher in the blood stream than in the villi. Thus, active trasnport will occur with the carrier proteins transporting glucose molecules from the villi into the capillaries lining it.

Hope that answered your question! :D

If the cell needs to go up a concentration gradient (basically this means that you are going from lower to higher concentration), then it takes energy. Think of how water can't flow up a stream, it can only flow down with the current. It would take energy of some kind to move it up!

The sodium potassium pump would be an example, as KI is moved in and Na is moved out of the cell. If water were being moved into the cell and washing it throughout, as in diffusion, it wouldn't require energy.

Cells use osmosis to take in water and diffusion to take in other substances, but this only works if the substances they're taking in are travelling from their area of higher concentration (say a high concentration of glucose molecules outside the cell) to the area of lower concentration (a low concentration of glucose molecules inside the cell.) So a cell will use active transport to take in a substance which is at higher concentration inside the cell than outside. I think glucose fits for this example, as does lactose molecules.

An example is a sodium-potassium pump.

The pump, with bound ATP, binds 3 intracellular Na+ ions.

ATP is hydrolyzed, leading to phosphorylation of the pump at a highly conserved aspartate residue and subsequent release of ADP.

A conformational change in the pump exposes the Na+ ions to the outside. The phosphorylated form of the pump has a low affinity for Na+ ions, so they are released.

The pump binds 2 extracellular K+ ions. This causes the dephosphorylation of the pump, reverting it to its previous conformational state, transporting the K+ ions into the cell.

The unphosphorylated form of the pump has a higher affinity for Na+ ions than K+ ions, so the two bound K+ ions are released. ATP binds, and the process starts again.

Example endocytosis is used to bring antibodies into the cell

ATP, sodium potassium pump, uses ATP to transfer K inside and Na out

When they are making proteins

The mRNA is transported from the nucleus to the ribosomes

When it needs materials 😛👏🏽👏🏽👏🏽👏🏽👏🏽