Active transport occurs against the electrochemical gradient. It needs energy to move molecules from the lower concentration side to the higher concentration side. <em>The mode of transport is </em><u><em>active transport. </em></u>
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There are three main different types of transport across the membrane
- Simple diffusion ⇒ <em>Does not need energy to occur</em>
- Facilitated transport ⇒ <em>Does not need energy to occur</em>
- Active transport ⇒ <em>Needs </em><em>energy </em><em>to occur</em>
Active transport is the transport of molecules that move <em>against the </em><em>electrochemical gradient</em>, so it does <em>need energy </em><em>to happen</em>.
Molecules move from the lower concentration side to the higher concentration side of the membrane.
Carrier proteins are in charge of active transport. The needed energy might proceed from the ATP molecules or the membrane's electric potential.
In the exposed example, a scientist wants to determine how substance L enters a cells in a culture.
- The cells maintain a <u>120 mM </u><u>intracellular concentration</u><u> </u>of substance L.
- Varying external concentrations of substance L (10 to 100 mM) in culture medium (Table 1).
Table 1. Rate of entry of substance L into mammalian cells in culture
<em><u>External concentration of substance(mM) Rate of entry of substance L </u></em>
10 5%
20 25%
30 45%
40 65%
50 80%
60 90%
70 95%
80 100%
90 100%
100 100%
<em>Now, we need to identify the most likely </em><em>mode of transport </em><em>across the </em><em>membrane </em><em>for substance L, and explain how information provided helps determine the most likely mode of transport.</em>
We know that the intracellular concentration is 120mM.
As we can see, this concentration exceeds all of the culture media concentrations. Yet, the substance keep moving into the cell.
As the concentration inside the cell is always higher than the concentration outside, we can assume that this is <u>not passive transport </u>because the molecule transport is going against its concentration gradient.
Hence, the remaining option is <u>active transport.</u> And as said before, we can see it because the substance keeps crossing the membrane toward the cell interior despite its concentration being higher in the interior of the cell than in the exterior.
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