Common Test 1 (sec 3 - 2007)(marking Scheme)

Section A

:

Multiple-Choice Questions (10 marks)

Choose the most suitable answer and write the corresponding letter (A, B, C or D) in the answer table provided on page 5. Question Answer Section B

1 C :

2 D

3 A

4 B

5 D

6 A

7 D

8 D

9 C

10 D

Short-Structured Questions (30 marks)

Answer the following questions in the spaces provided. 11. The figure shows a cell observed under a light microscope.

F

E (a) State the functions of structures A, C and F.

[3]

A: Provides mechanical support for the plant (turgor) / Prevents overexpansion of plant cell when placed in water. Accept any possible answers [1]; C: Site of photosynthesis [1]; F: Control of substances entering or leaving the plant cell [1]. (b) What substance is A made of? [1] Cellulose [1]. (c) Name a membrane network present in the cell. Briefly state the function of this membrane network. [2] Golgi apparatus / Rough endoplasmic reticulum / Smooth endoplasmic reticulum [1]; Stores and modifies substances made by the ER / packages substances in vesicles for secretion out of the cell (Golgi apparatus); Transports proteins made by ribosomes to the Golgi apparatus (Rough ER); Synthesize substances like fats and steroids / converts harmful substances into harmless materials (smooth ER) [1].

2

(d) Structure D is used for food storage. What type of food is found in D? [1]

Starch [1].

(e) What is the function of the mitochondrion?

[1]

Releases energy for use in cellular respiration [1]. (f) What is the most important function of E?

[1]

Contains genetic information which is essential for cell division / Controls cell activities such as cell growth and repair of worn-out parts [1]. [Total: 9] 12.

In an experiment, a crystal of potassium permanganate was placed in a beaker of water at room temperature (25°C) and the setup was observed at intervals of 15 minutes. The same experiment was repeated for water at 60°C. Table 1.1 shows the results of the experiment. Time (minutes) 0 15 30 45 60

Percentage (%) of water coloured at temperature of 25°C 60°C 0 0 10 20 30 60 80 100 100 100 Table 1.1

(a) Plot the results of the experiment on the graph paper provided, labelling each axes clearly. [3]

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Correct axes used (labeled with units) [1]; Correct plotting of 2 sets of data points and 2 smooth curves drawn [2].

(b) Name the process by which the molecules of potassium permanganate were able to spread out in the water. What is the evidence that this process is taking place? [2] Diffusion [1]; At higher temperatures, water takes a shorter time to become coloured as higher temperature provides more kinetic energy to the molecules hence faster movement [1]. (c) What is the aim of this experiment? What is the conclusion that can be made from this experiment? [2] Aim: To find out if temperature had any effect on the rate of diffusion [1]; Conclusion: Higher temperature results in faster diffusion [1]. [Total: 7] 13.

A cork borer was used to obtain five cylinders of sweet potato as shown in Figure 1.2. Figure 1.2 2 mm The cylinders were placed in sugar solutions of different concentrations. After 2 hours, the cylinders were removed, gently blotted dry and their lengths measured again. The results are recorded in Table 1.3.

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Table 1.3 Solution A B C D E

Original length (mm) 20 20 20 20 20

Final length (mm) 15 25 17 22 20

(a) What process is being investigated here?

[1]

Osmosis [1]. (b) Briefly explain when the cylinders will (i) Increase in length,

[1]

When more water is entering the cells due to a higher water potential outside the cell to a region of lower water potential inside the cell [1]; (ii) Decrease in length,

[1]

When more water is leaving the cells due to a higher water potential inside the cell to a region of lower water potential outside the cell [1];

(iii) Remain unchanged in length.

[1]

When the external sugar solution has the same concentration / water potential as the cell sap of the potato [1]. (c) List the solutions in increasing order of concentration based on the results in Table 1.3. [1] B, D, E, C, A [Total: 5]

5

14.

Fig 1.4 shows the effect of increasing substrate concentration on the rate of a particular reaction in the presence and absence of an enzyme.

Fig 1.4

(a)

Explain why there is a difference in the rates of reaction between the following ranges of substrate concentrations. (i)

Between points A to C and between points B to D.

[3]

Between A and C, the rate of reaction increases much more compared to that between B and D over the same range of substrate concentration [1]; This is due to the presence of enzymes, which lower the activation energy required to start the chemical reaction [1]; Resulting in a greater increase in rate of reaction for the interval between point A to point C than between points B to D [1]. (ii)

Beyond point C and beyond point D.

[3]

Beyond point C, rate of reaction does not increase any further [1]; Because at any given instant, all the enzyme molecules are being made use of / enzyme molecules are saturated [1]; However, beyond point D, rate of reaction still increases since there is more substrate present within the same volume and the chances of the substrates reacting are much higher resulting in an increase in the rate of reaction [1]. (b)

Explain what is meant by the active site of an enzyme. The region of the enzyme where the substrate fits snugly into the enzyme so that a reaction can be initiated [1].

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[1]

(c)

Name the limiting factor in this experiment. How can the rate of reaction be made to increase again? Explain your answer. [2] Enzyme concentration [1]; To increase the rate further, enzyme concentration could be increased by increasing amount of enzyme present + to make more active site available [1]. [Total: 9]

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