▶️ Answer/Explanation
Detailed solution
(a) (i) Reasons bacteria are useful in biotechnology:
- They have a rapid reproduction rate. Bacteria reproduce asexually via binary fission very quickly (often every 20 minutes), allowing for the mass production of a product in a short time.
- They have the ability to make complex molecules.
- (Alternative point): They contain plasmids (circular DNA), which are easily modified and transferred from one cell to another.
(a) (ii) Ways genetic modification improves crop plants:
- Herbicide resistance: Crops can be modified to withstand weed-killers, allowing farmers to spray fields to kill weeds without harming the crop (e.g., Roundup Ready crops).
- Pest/Insect resistance: Crops can produce their own toxins (e.g., Bt toxin) that kill specific pests, reducing the need for chemical pesticides.
- Increased yield: Modification can lead to larger fruits, faster growth, or resistance to environmental stress like drought.
- Improved nutritional qualities: Crops can be fortified with vitamins (e.g., Golden Rice, which is enriched with Vitamin A precursor).
(b) (i) Conclusions from the graph:
The correct statements based on Fig. 7.1 are:
- At \(\text{pH } 10\), enzyme B is more active than enzyme A. (\(\checkmark\))
Reasoning: Looking at the x-axis at \(10\), the line for Enzyme A is at \(0\), while the dashed line for Enzyme B is at approx \(12\) units. - Enzyme A has a maximum activity of \(33\) arbitrary units. (\(\checkmark\))
Reasoning: The peak of the solid line (Enzyme A) is at \(\text{pH } 5.5\). The y-axis value is \(3\) small squares above \(30\). Since \(5\) squares = \(5\) units, the value is \(33\). - The largest difference in activity between enzyme A and enzyme B is at \(\text{pH } 5\). (\(\checkmark\))
Reasoning: At \(\text{pH } 5\), Enzyme A is at \(30\) units and Enzyme B is at \(0\) units. The difference is \(30\). At any other pH, the gap between the lines is smaller than this.
Why the others are incorrect:
- “Enzyme A and enzyme B are not active at \(\text{pH } 4\)”: Incorrect. Enzyme A is active (value approx \(18\)).
- “Enzyme B has a greater maximum activity than enzyme A”: Incorrect. Peak A is \(33\), Peak B is \(30\).
- “Enzyme A shows activity over a pH range of \(6\) to \(10\)”: Incorrect. It loses activity before \(10\), and starts well before \(6\).
(b) (ii) Washing powder selection:
- Enzyme: B
- Reason: At \(\text{pH } 9\) (the pH of the washing powder), only Enzyme B is active. Enzyme A has denatured and has zero activity at this pH. Alternatively, Enzyme B’s optimum is closer to \(\text{pH } 9\).