Measurement of Cell Number

Microscopic Counts The number of cells in a population can be measured under a microscope by counting cells placed in special counting chambers. There are two types of chambers used for counting cell number in liquid samples  

hemocytometer. a blood cell counting chamber for use with organisms of 3 pan in diameter or larger. 

Petroff-Hausser counting chamber, for use primarily with bacteria. Both chambers have a special square grid marked on the surface of 

Dead cells cannot usually be distinguished from live cells. 

Small cells are difficult to see under the microscope and can be missed when counting. 

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Figure 2. Effect of butamiphos on cell division of Chlorella grown in synchronized culture. Butamiphos in methanol was added to the culture after 6 h. Aliquots were taken for the measurement of cell number and packed cell volume at various time intervals. The dark period was between the 18th and the 24th h. Key O, untreated control and butamiphos-treated (30 /jM).

With recent developments in analytical instrumentation these criteria are being increasingly fulfilled by physicochemical spectroscopic approaches, often referred to as whole-organism fingerprinting methods.910 Such methods involve the concurrent measurement of large numbers of spectral characters that together reflect the overall cell composition. Examples of the most popular methods used in the 20th century include pyrolysis mass spectrometry (PyMS),11,12 Fourier transform-infrared spectrometry (FT-IR), and UV resonance Raman spectroscopy.16,17 The PyMS technique... 

The study of peptidergic neurons requires a number of special tools. These tools include methods to detect the neuropeptides both in cells and after release, the enzymes specific to their biosynthesis and their cognate receptors. Since the actions of peptides require secretion, measurements of cell content (e.g. immunostaining) can be deceptive, with a decrease in content reflecting increased release. 

Despite displaying a fair predictive value, the tier 1 assay is based on simple cytotoxicity measurement of cell lines, not primary cells, which may have lost a number of primitive characteristics. Therefore, the trust level of this assay to embrace a wide range of predictable events is not as high as it is for the CFU assay. It is then advisable to confirm some key findings of the tier 1 stage, by the more elaborated and more validated CFU assay [43 9]. 

Ozkaya (76) studied conceptual difficulties experienced by prospective teachers in a number of electrochemical concepts, namely half-cell potential, cell potential, and chemical and electrochemical equilibrium in galvanic cells. The study identified common misconceptions among student teachers from different countries and different levels of electrochemistry. Misconceptions were also identified in relation to chemical equilibrium, electrochemical equilibrium, and the instrumental requirements for die measurement of cell potentials. Learning difficulties were attributed mainly to failure of students to acquire adequate conceptual understanding, and the insufficient explanation of the relevant... 

Similar to what was shown for growth, some models establish a linear relationship between the specific death rate (kj) and an autoinhibitory product synthesis (Lee et al., 1995). This autoinhibitory product is represented by the expression Xv/D, where Xv is a viable cells concentration, measured in terms of cell number per volume, and D is the specific feed rate that plays the part of substrate supply to the culture. By setting kj/px as a function of Xt/D (where Xt is a total cell concentration) it is possible to build up a more robust model that can fit a larger amount of experimental data (Equation 56) (Zeng et al., 1998). 

Thus, emf measurements of cells with transference yield transference numbers. 

Determination of Transference Numbers.—Since activity coefficients can be derived from e.m.f. measurements if transference numbers are known, it is apparent that the procedure could be reversed so as to make it possible to calculate transference numbers from e.m.f. data. The method employed is based on measurements of cells containing the same electrolyte, with and without transference. The e.m.f. of a concentration cell without transference E) is given by equation (11), and if the intermediate electrodes are removed so as to form a concentration cell with transference, the e.m.f., represented by Et, is now determined by equation (25), provided the transference numbers may be taken as constant within the range of concentrations in the cells. It follows, therefore, on dividing equation (25) by (11), that... 

A large number of measurements of cells of the types described, containing different halides, have been made by Harned and his collaborators over a series of temperatures from 0 to 50° the excellent agreement between the results obtained in different cases may be taken as... 

The Coulter principle was patented in 1949 [2] and described in 1956 [3] as a method for counting and sizing blood cells. Kubitschek [4,5] introduced modifications which permitted the counting of bacterial cells, and pointed out that the method could be applied to the measurement of cell volumes as well as number counting. Modified instruments were soon developed with which particles could be sized as well as counted. In 1998 the company was acquired by Beckman and renamed Beckman Coulter. 

To measure performance, to achieve reproducibility or to make comparative studies, a means of quantifying the cell population is needed. Classically, direct counts of cell numbers using a microscopic counting chamber (haemocytometer), usually in conjunction with a vital stain (e.g. Trypan blue) to distinguish viable and non-viable cells, is used. However, all vital stains are subjective and cannot give absolute values, and cell numbers take no account of differences in cell size/mass. The method is simple, quick and cheap, and requires only a small fraction of the total cells from a cell suspension. 

Steady state is achieved when cell (as measured by cell number, biomass, DNA or protein content) and metabolite (e.g. glucose, lactate, ammonia, amino acids, product) concentrations remain stable over a period of time. The attainment of steady state should be confirmed by measuring several parameters, because the stability of a single parameter (e.g. cell number) is not necessarily indicative of a steady state. 

The presence and distribution of phytoplankton in the sea is determined primarily by the abundance of chlorophyll. Although this is not a direct measure of the number of cells, because they contain different amounts of chlorophyll under different conditions, it is the most rapid and widely used method of identifying the presence of photosynthetic organisms. Because the color of the ocean can be determined by satellites, it is possible to determine the global content of chlorophyll in the sea over one optical depth, about the first 30 m of surface waters. 

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