CBSE 12th Biotechnology Question Paper 2022 (Set 1)

(a) Regulation of pH is important for mammalian cells in culture because: 1. Enzymes and metabolic reactions in cells work properly only within a narrow pH range. 2. Even slight changes in pH can damage cells, inhibit growth, or lead to cell death. (b) Bicarbonate $CO_2$ buffering system works as follows: $\mathrm{CO_2 + H_2O \rightleftharpoons H_2CO_3 \rightleftharpoons H^+ + HCO_3^-}$ If acidity increases, bicarbonate ions combine with excess $H^+$ to form carbonic acid, helping raise pH. If alkalinity increases, carbonic acid dissociates to release $H^+$, helping lower pH. Thus, it maintains a stable pH in culture.

RefSeq (Reference Sequence) is a curated, non-redundant database of DNA, RNA and protein sequences maintained by NCBI. Significance: 1. It provides a standard reference sequence for a gene or genome, so researchers can compare new sequences accurately. 2. It helps in identifying genes, predicting protein products, and studying mutations and variations.

Chemostat and turbidostat are both continuous culture systems, but they differ in the factor that controls growth. In a chemostat, the rate of growth is controlled by keeping one nutrient in limiting amount and maintaining a constant dilution rate. In a turbidostat, the turbidity (cell density) of the culture is kept constant by automatically adjusting the inflow of fresh medium, so nutrients are usually not limiting.

A farmer can eliminate emasculation in maize by using male sterility. In male-sterile plants, pollen is not produced, so self-pollination is prevented and emasculation is unnecessary. Yes, normal pollen formation can be ensured at the onset of the breeding season by restoring fertility through suitable hybridisation or by growing fertile lines/maintainers, so that pollen-producing plants are available when required.

The graph shows a batch culture, in which the microbial population increases through the lag, log, stationary and decline phases in a closed system.