In which of the following yam tissues will osmosis occur?

Analyze the question: Osmosis is the movement of water from a region of higher water potential to one of lower water potential through a selectively (semi-) permeable membrane. So we need the yam tissue whose cell membranes are still alive and intact.

Concept: Cell membranes only act as selectively permeable membranes when the cells are alive. Heat (boiling, roasting) denatures the proteins in the membrane, killing the cells and destroying selective permeability. Once that happens, the membrane becomes freely permeable and osmosis can no longer take place.

Going through the options:

• A. Boiled and peeled: The cells are dead and the membranes are denatured, so there is no osmosis.
• B. Raw and peeled: The cells are alive and their membranes are intact. Peeling removes the outer protective layer, which exposes living cells directly to the surrounding solution, so osmosis occurs readily.
• C. Boiled and unpeeled: The cells are dead, so there is no osmosis. The peel does not change this.
• D. Roasted and peeled: Heat has killed the cells, so there is no osmosis.

Answer: Only the raw yam still has living cells with selectively permeable membranes, so the correct option is B (Raw and peeled).

Exam tip: In questions like this, remember "no life, no osmosis". Any tissue that has been boiled, roasted or otherwise heated cannot carry out osmosis. This also appears in experiments with potato or yam cylinders in sugar solution, where boiled tissue shows no change in mass or length.