Video Transcript
The diagram shows a simplified outline of a root hair cell and the movement of
calcium ions from the soil into it. What process is being shown by the movement of calcium ions in the diagram? (A) Active transport, (B) diffusion, (C) osmosis, (D) biosynthesis, or (E)
chemosynthesis.
Mineral ions are essential for many different plant functions. For example, calcium ions play an important structural role in plant cell walls and
cell membranes. Generally, plants absorb these ions through their roots from soil, and many plants
have specialized root hair cells to aid in this absorption. There are two main ways that root cells can take up these ions from soil: either
passively or actively.
When a particular ion is in a higher concentration in the soil than in the root hair
cell, it will passively move down its concentration gradient into the root without
requiring any extra input of energy from the plant itself. This process is called diffusion. The ion continues to passively spread out by diffusion until there is an
approximately equal concentration of this particular ion in both areas.
Alternatively, if the concentration of this ion is higher in the root hair cell than
in the soil, as we have illustrated in this pink diagram on the right, the uptake of
this particular ion must be done actively. This process is called active transport. Active transport requires an input of energy to move ions from an area of low
concentration in the soil to an area of high concentration in the root hair
cell.
The question asks us to determine the process being shown by the movement of calcium
ions in the diagram provided to us in the image on the far left. We can see that calcium ions, which are represented as red circles, are in a far
higher concentration in the soil than they are in the root hair cell.
As the arrows show calcium ions moving into the root hair cells from the soil from an
area of high to low concentration, we can work out the correct answer to this
question. We know that moving particles from an area of high to low concentration does not
require an input of energy, so it is a passive process. Therefore, the correct answer to this question is (B) diffusion.
