Biology 5090 · O Level · Biological molecules

Biological molecules — practice question

Carbohydrates occur in a range of plant organs as starch and as sugars, for example glucose and maltose. A student chose to check two different plant organs, a potato and an apple, for starch and sugar. The student did the starch test on pieces of potato and apple. Fig. 1.1 shows how the plant pieces looked before the test and after the test.
(a(i))[2]

Suggest a suitable reagent for the starch test and explain how it should be applied. You do not need to give any possible results.

(a(ii))[4]

Use Fig. 1.1 to write in Table 1.1 what you see after the test and what conclusion you can make.

(b(i))[2]

Describe how you would maintain the test-tubes at the required temperature for ten minutes.

(b(ii))[1]

After ten minutes, the student looked at the test-tubes. The apple mixture was red, and the potato mixture was blue. State the conclusions that can be drawn from these results. apple [BLANK] potato [BLANK]

(b(iii))[3]

Suggest why it was necessary to: - use a $1\text{ cm} \times 1\text{ cm} \times 1\text{ cm}$ cube for each plant organ - chop each cube into small pieces - crush the small pieces and mix them with water.

(b(iv))[1]

Explain why the tile, cutting device and stirring rod had to be cleaned after they had been used on the potato.

(c)[4]

Describe how you would test the apple for protein, and state the observations if protein was present and if protein was absent. test [BLANK] protein present [BLANK] protein not present [BLANK]

Worked solution & mark scheme

This 17-mark question has a full step-by-step worked solution and mark scheme. One marking point: sample should be cut / crushed

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