#Question id: 14276
#Section 5: Bioprocess Engineering and Process Biotechnology
Nicotiana tabacum cells are cultured to high density for production of polysaccharide gum. The reactor used is a stirred tank, containing initially 100 litres medium. The maximum specific growth rate of the culture is 0.18 d-1 and the yield of biomass from substrate is 0.5 g g-l. The concentration of growth-limiting substrate in the medium is 3% (w/v). The reactor is inoculated with 1.5 g l- 1 cells and operated in batch until the substrate is virtually exhausted; medium flow is then started at a rate of 4 l d-1. Fed-batch operation occurs under quasi-steady-state condition. The fermenter is available 275 d per year with a downtime between runs of 24 h. How much plant cell biomass is produced annually? ___________________
#Question id: 14235
#Section 5: Bioprocess Engineering and Process Biotechnology
Nutrient medium is to be heated from 10⁰C to 28⁰C is a single-pass countercurrent shell-and-tube heat exchanger before being pumped into a fed-batch fermenter. Medium passes through the tubes of the exchanger; the shell-side fluid is water which enters with flow rate 3 x 10^4 kg h^- 1 and temperature 60⁰C pre-heated medium is required at a rate of 50 m^3 h^-1. The density, viscosity and heat capacity of the medium are the same as water; the thermal conductivity of the medium is 0.54 Wm^- 1 ⁰C^ - 1. It is proposed to use 30 steel tubes with inner diameter 5 cm; the tubes will be arranged in line. The pipe wall is 5-mm thick; the thermal conductivity of the metal is 50 Wm^- 1 ⁰C^ - 1. The maximum linear shell-side fluid velocity is estimated as 0.15 m s^-1. Determine the heat-transfer area. ____________
#Question id: 2074
#Section 2: General Biology
In some cells, there are many ion electrochemical gradients across the plasma membrane even though there are usually only one or two proton pumps present in the membrane. The gradients of the other ions are most likely accounted for by:
#Question id: 3857
#Section 3: Genetics, Cellular and Molecular Biology
The CAAT box is usually located near the position:
#Question id: 1985
#Section 2: General Biology
Which of the following is the last line of defense against an extracellular pathogen?