▶️ Answer/Explanation
(a) Cell membrane and cytoplasm (or ribosomes or DNA).
Explanation: Both animal and bacterial cells share these fundamental structures. The cell membrane controls what enters and exits the cell, while the cytoplasm is the jelly-like substance where metabolic reactions occur. Ribosomes are present in both for protein synthesis, and DNA carries genetic information in both cell types.
(b) Any three from: rapid reproduction rate, reproduce asexually, small size, simple growth requirements, ability to make complex molecules, few ethical concerns, presence of plasmids, same genetic code as other organisms.
Explanation: Bacteria are extremely useful in biotechnology due to several key characteristics. Their rapid reproduction allows quick production of desired products. Asexual reproduction ensures genetic consistency. Their small size means they can be grown in large quantities in small spaces. They have simple nutritional needs, often just requiring basic nutrients. Many bacteria naturally produce complex molecules like enzymes. There are fewer ethical concerns compared to using animal or human cells. Plasmids make genetic modification easier, and their universal genetic code means genes from other organisms can be expressed in bacteria.
(c)(i) X placed between 0-8 hours.
Explanation: The lag phase is the initial period where bacteria are adjusting to their environment, synthesizing enzymes and preparing for growth, before population numbers begin to increase significantly.
(c)(ii) Y placed between 18-24 hours.
Explanation: The stationary phase occurs when birth rate equals death rate, resulting in no net population growth. This typically happens when resources become limited.
(c)(iii) 12 hours.
Explanation: At 24 hours the population is at its peak (about 10 million cells/cm³). By 36 hours it has halved to about 5 million cells/cm³, so the halving time is 12 hours.
(c)(iv) The population enters death phase where death rate exceeds birth rate, decreasing due to limited resources, increased competition, waste buildup, or other unfavorable conditions.
Explanation: After 24 hours, the bacterial population begins to decline. This death phase occurs because essential nutrients become depleted, waste products accumulate to toxic levels, and competition for remaining resources intensifies. The environment becomes increasingly hostile, causing more cells to die than are being produced through reproduction.
(c)(v) To maximize enzyme activity while preventing denaturation.
Explanation: Enzymes function best at their optimum temperature. At this temperature, they have sufficient kinetic energy for frequent collisions with substrates, forming many enzyme-substrate complexes. The active site maintains its correct shape for substrate binding. Temperatures above the optimum would cause denaturation (permanent shape change), while lower temperatures would reduce reaction rates.
(c)(vi) To make proteins/enzymes/nucleic acids.
Explanation: Amino acids are the building blocks of proteins, which bacteria need for growth, enzyme production, and cellular structures. Providing amino acids in the growth medium allows for efficient protein synthesis without requiring the bacteria to produce all amino acids from scratch, thus supporting faster growth and higher yields of desired products.
