Video Transcript
Nitella is a genus of algae
that grows while submerged in water. The graph shows a comparison
between the cells of a species of Nitella and the surrounding water. What conclusions can be made using
this data? (A) The membranes of these
Nitella cells have been damaged, so all ions are moving freely in and out
of the cells. (B) The membranes of these
Nitella cells allow chlorine and potassium through, but not calcium or
sodium. (C) The membranes of these
Nitella cells are not permeable to any of the ions in the graph. (D) The membranes of these
Nitella cells are only permeable to magnesium, calcium, and sodium
ions. Or (E) the membranes of these
Nitella cells are selectively permeable to all ions in the graph.
To answer this question, let’s
first look at how algae, like organisms that belong to the Nitella genus,
obtain ions.
Much like plants, algae must absorb
many of their required nutrients, such as mineral ions, from their surroundings. As most algae are aquatic, this
means that they take in nutrients from the surrounding water.
Now let’s take a closer look at the
graph that has been provided to us by the question. We can see that it shows the
concentration of five different mineral ions: chlorine, potassium, magnesium,
calcium, and sodium. The concentration of each of these
ions is much higher in the Nitella cells, represented by the red bars, than
in the surrounding water, represented by the blue bars. This suggests that the algae have
taken up these ions from their environment via active transport.
Active transport is the process by
which molecules move against, or up, a concentration gradient from an area of low
concentration to an area of comparatively high concentration across a selectively,
or partially, permeable membrane. This process is described as active
as it requires an input of energy from the organism itself. This is because the ions are moving
in an opposite direction to how they would naturally spread out by diffusion.
As we have seen that the
concentration of all of these ions is higher in the Nitella cells than in the
surrounding water, we can deduce that the answer to this question is (E). The membranes of these
Nitella cells are selectively permeable to all ions in the graph.
