The subject of carrots wasn’t something the pupils had come across before in their science lessons, so the question asking why carrots don’t increase in mass when they’re boiled, threw a lot of them.
Within hours after the exam finished at 4pm on Tuesday 15 May, many teens started tweeting about how puzzled they were by the question, with some adding that this was not in their revision guide.
So would you know the answer?
Students told HuffPost UK that the second part of the question asked why carrots change mass in sugar solution.
We asked Roberts Zivtins, a former science teacher and current PhD student, from Royston, Hertfordshire, why the question sparked so much confusion. “A question asking why osmosis didn’t happen is admittedly a hard question because it’s the opposite of what students might expect - it really tests students’ understanding of concepts rather than just rote learning of definitions and relying on one classic example,” he explains to HuffPost UK.
So how does osmosis work?
Zivtins explains: “Osmosis is the process by which water moves across a partially permeable cell membrane, either into or out of a cell. The water will diffuse from the region of low solute concentration (think weak squash) to high solute concentration (strong squash). The example of osmosis usually given to students is the movement of water into or out of potato cells.
“If you put a potato into water, there is a relatively high solute concentration inside the potato, and a low solute concentration outside the potato so water will diffuse into the potato and gain mass.
“If you put a potato in very salty water, there is a high solute concentration outside the potato (compared to inside the cell), so water will diffuse out of the potato and actually lose mass.
“The same is probably true of carrot. When put in sugar water, there is a higher concentration of solutes outside of the carrot, so it won’t gain mass, if anything it would be reasonable to expect it to lose mass.”