▶️ Answer/Explanation
(a)(i)
Bacteria (or prokaryotes).
Explanation: Antibiotics are chemical substances that disrupt the metabolism or cell wall structure of bacteria. They are ineffective against viruses.
(a)(ii)
To limit resistance, antibiotics should be used only when essential/necessary (e.g., for confirmed bacterial infections, not viral ones) and the appropriate antibiotic should be selected. Other measures include completing the full course prescribed and restricting their use in agriculture.
Explanation: Overuse or misuse of antibiotics creates a selection pressure where only resistant bacteria survive and reproduce, spreading the resistance genes.
(b)(i)
Genus.
Explanation: In the binomial system ($Genus$ $species$), the first name indicates the genus (generic name) and starts with a capital letter.
(b)(ii)
Fungi (or Kingdom Fungi).
Explanation: The diagram (Fig 5.1) shows characteristic fungal features: a cell wall made of chitin, hyphae (filamentous structures), and spores for reproduction.
(c)(i)
Acceptable answers include: insulin, mycoprotein, ethanol (alcohol), amino acids, or enzymes.
Explanation: Fermenters are used to grow microorganisms like genetically modified bacteria (for insulin) or fungi (for mycoprotein) on a large scale.
(c)(ii)
Oxygen.
Explanation: Penicillium is an aerobic fungus. It requires oxygen for aerobic respiration to generate the energy needed for growth and penicillin production.
(c)(iii)
Key conditions and control methods include:
- Temperature: Controlled using a water jacket (or water bath). The respiration of the fungus releases heat, so cold water is circulated to cool the tank and keep the temperature at the optimum for enzyme activity.
- pH: Controlled by adding buffers (or acids/alkalis). Metabolic activity can change pH, so it is monitored to ensure it stays at the optimum for enzymes.
- Nutrient supply: Essential nutrients (glucose/amino acids) are added to provide energy and raw materials for growth.
- Agitation/Mixing: Controlled by a stirrer (or paddles). This ensures that oxygen and nutrients are equally distributed throughout the mixture and prevents the fungus from settling.
- Hygiene: The fermenter is sealed and steam-cleaned to prevent contamination by other microorganisms.
(d)
Yeast.
Explanation: Yeast carries out anaerobic respiration (fermentation). In bread-making, the $CO_2$ produced makes the dough rise. In biofuel production, the ethanol produced is harvested as fuel.