VJC 2021 Prelim P4 Suggested Answer

1 Victoria Junior College Biology Department 2021 Prelim Paper 4 Suggested Answer Marking abbreviations: A: Accept R: Reject BOD: benefit of doubt AW: alternative wording AVP: Any valid point NAQ: not answering question Question 1 (a) (i) Suggest why betalain molecules cannot pass from vacuoles of plant cells into the cytoplasm. [2] 1. betalain molecules are polar / charged / hydrophilic; 2. (so) will not be able to diffuse through hydrophobic core of phospholipid bilayer or hydrophobic ‘tails’ of phospholipids; 3. membrane lack membrane proteins / carriers / channels / pumps to transport betalain across membrane; Or 4. betalain molecules are too large; 5. (so) will not be able to diffuse, through hydrophobic core of phospholipid bilayer / AW ; A ref. to hydrophobic ‘tails’ of phospholipids Note: mark will only be awarded once for either points 1 or 4. The second mark is awarded for the explanation which must be related to the first point (i.e. point 1 or 4) that student gave. (ii) Why were beetroot discs washed several times before they were used? [1] • The surface of the beetroot discs is covered by pigments and hence affecting the accuracy of the data collected; Or • Wash away the leaked pigments from cut/ damaged cells so that the leakage of pigment later can be attributed to the effects of alcohol; (iii) State the concentrations of alcohol that you will use in your investigation. [1] • at least five different concentrations of alcohol at regular intervals, including 0% e.g. 0, 20, 40, 60, 80, 100% / 0, 25, 50, 75, 100% R: 10x, 5x, 2x dilution factors, i.e., serial dilution (iv) Use the space provided below to show, in a suitable format, how you prepared the solutions of alcohol. [4] Concentration of alcohol/ % Volume of 100% alcohol / cm3 Volume of distilled water / cm3 Total volume / cm3 0 0.0 0.0 10.0 5.0 10.0 5.0 20 2.0 1.0 8.0 4.0 10.0 5.0 40 4.0 2.0 6.0 3.0 10.0 5.0 60 6.0 3.0 4.0 2.0 10.0 5.0 80 8.0 4.0 2.0 1.0 10.0 5.0 100 10.0 5.0 0.0 0.0 10.0 5.0

2 Marking points: 1. A complete lined table, with independent variable on left-most column; 2. Correct column headings with appropriate units + No units in the body of the table; 3. [Precision] Recording of volume; 4. [Calculation] Correct calculation; Allow error from (iii) carried forward (ECF) here. Calculation is based on the alcohol concentration indicated. (v) State and explain a step that you can take in the preparation of the discs to ensure that you obtained valid results in this investigation. [2] • step taken on preparing discs, e.g. use a cutter with a fixed dimension of 4 mm / measure and discard poorly cut discs; ignore simple use of ruler and scalpel • to ensure constant thickness/ surface area of discs; OR • discs washed, until no trace of pigment / same number of times (minimum of four) or discs handled carefully so not, punctured / damaged; • ensuring no furt