Active transport
There are many occasions when cells need to take in substances which are only present in
small quantities around them.
If the substance has a lower concentration outside the cell than inside, then we would expect
the substance to diffuse out of the cell.
If the cell needs this substance, then it has to do something to make it go into the cell instead
of diffusing out of it. Cells can use energy to make substances move across their
membranes, up the concentration gradient.
This process is called active transport. The energy needed to do this is provided by
respiration.
Aerobic respiration, in mitochondria in the cell, releases energy for the cell to use. Some of
this energy is used for active transport, moving substances against their concentration
gradients.
In plants, for example, root hair cells take in nitrate ions from the soil.
The concentration of nitrate ions inside the root hair cell is usually
higher than their concentration in the soil.
 The diffusion gradient for the nitrate ions is out of the root hair, and
into the soil! But the root hair cells are still able to take nitrate ions in,
using active transport. Figure 3.14 shows how they do this.
There are special carrier proteins(carrier proteins (or protein carriers):
protein molecules in cell membranes that can use energy to change
shape and move ions or molecules into or out of a cell) in the cell
membrane of the root hair cells.
These proteins pick up nitrate ions from outside the cell, and then
change shape so that they push the nitrate ions through the cell
membrane and into the cytoplasm of the cell.
 Energy - provided by the mitochondria, which carry out aerobic
respiration is needed to produce the shape change in the carrier
protein.
https://youtu.be/tM0bGaaQ2jY?si=WoYBcXGXx2cYu_gd
Any questions?
Thank you