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A vitamin also called vitamin B1. Its active coenzyme form supports reactions in carbohydrate and amino acid metabolism; deficiency therefore affects energy-demanding tissues rather than representing a simple shortage of dietary energy.

The thyroid is an endocrine gland in the anterior neck. It produces thyroid hormones involved in metabolism and biological development. Its size and hormone output are different properties: a goitre names enlargement without specifying whether glandular secretion is high, low or normal.

Thyroid-stimulating hormone contributes to control of thyroid hormone secretion. Measuring the gland's dimensions and measuring circulating hormone concentrations therefore answer different physiological questions.

Tomi K. Baikie coauthored research on photosynthesis.^[ref]

Photosynthesis captures light energy and transforms it into chemical forms that a biological cell can use. In plants, algae and cyanobacteria, this supports carbon fixation: incorporation of carbon from carbon dioxide into chemical compounds used to build living material. Capturing light and incorporating carbon are distinct processes coupled through metabolism. See OpenStax Biology 2e, 8.1: overview of photosynthesis.

The trypan blue exclusion test reads cell membrane integrity through trypan blue exclusion. Prolonged dye exposure can itself increase staining.^[ref]

An unstained biological cell is dye-excluding at the time of this assay. That observation alone does not demonstrate future division, sustained metabolism or long-term renewal of a cell line. Conversely, a smaller unstained count can reflect both staining and loss of biological cells from the recovered preparation. Report the denominator and recovery procedure alongside the fraction.

A unicellular organism is an organism whose living body consists of one biological cell. That biological cell maintains itself, grows and participates in reproduction; it is not merely one specialized component of a larger body. Escherichia coli and ordinary free-living Saccharomyces cerevisiae illustrate prokaryotic and eukaryotic examples respectively. Cellular organization and the number of biological cells are separate questions. See Clark, Douglas and Choi, Biology 2e, 4.1: cells as units of organisms.

How can one biological cell do enough to sustain an organism? Its cell membrane retains useful material while membrane transport allows exchange; metabolism transforms nutrients and supplies usable energy; gene expression makes proteins needed to maintain and rebuild the machinery. These functions operate together inside the same boundary. In Saccharomyces cerevisiae, for example, glucose can support alcoholic fermentation and production of ATP, while the cell cycle and budding produce descendants. A single biological cell therefore combines chemical processing, regulated exchange and inherited organization. See Alberts et al., Molecular Biology of the Cell (2002): universal cellular machinery and the experimental accounts under Saccharomyces cerevisiae and yeast.

Being a unicellular organism does not mean isolated or independent of all other life. Unicellular organisms can interact and cooperate in groups. A biological colony describes association; clonal development describes descent; developmental integration describes coordination of the developing whole. Neither shared ancestry nor a visible clump alone establishes the latter. This distinction makes single-cell experiments easier to interpret: measuring the growth of one biological cell, the expansion of a group and the reproductive success of a reproducing cluster can answer different questions. See Queller and Strassmann, Beyond society: the evolution of organismality (2009): cooperation and the limits of simple organism criteria.

A vampire bat is a blood-feeding bat. Obtaining a specialized liquid food creates physiological and social challenges, making these animals useful for studying animal behaviour, metabolism and food sharing.

Vitamin B3 is the nutritional category including nicotinic acid and nicotinamide, compounds the body can use to make nicotinamide adenine dinucleotide and nicotinamide adenine dinucleotide phosphate. These coenzymes participate in metabolism, including transfer of reducing equivalents between reactions. Adequate dietary supply supports a reusable biochemical system rather than providing the bulk of the body's fuel.^[ref]

For example, an oxidized coenzyme can accept reducing equivalents in one reaction and transfer them in another. The coenzyme is regenerated during the cycle, so its importance is not measured by how much of it is burned for energy. Humans can also derive niacin equivalents from tryptophan; severe inadequacy is associated with pellagra.^[ref]

Can a gene from Schizosaccharomyces pombe replace a missing function in Saccharomyces cerevisiae? A modern laboratory project tested functional complementation of methionine synthesis. For each tested gene deletion, the investigators compared plasmids carrying the corresponding Saccharomyces cerevisiae gene, a candidate Schizosaccharomyces pombe gene, and an unrelated gene. The first was a positive scientific control; the last was a negative scientific control. The paper describes this design rather than publishing a complete set of individual growth measurements. ^[ref]

The recipient biological strains also lacked the ability to make uracil. The pYES2.1/V5-His plasmids carried URA3, a gene restoring that ability, and used the GAL1 gene promoter to control the inserted gene. Initial plates lacked uracil but supplied methionine: this selected biological colonies containing plasmids without requiring successful methionine synthesis. Subsequent plates lacking methionine tested the missing function, comparing galactose induction with glucose conditions. Thus selecting for a plasmid and testing its functional contribution were separate operations. ^[ref]

The apparatus can be simple and informative. In the associated protocol, replica plating uses a block covered with velveteen to transfer small samples of biological colonies from a master plate onto plates with different nutrient conditions. Orientation marks preserve correspondence between locations; gentle contact limits the transferred material. The specified replicas omit uracil and methionine with either inducing sugar or glucose, and include a fresh glucose plate supplying methionine. The readout is growth at corresponding locations, not a direct measurement of enzyme activity. ^[ref]

The scientific controls answer different objections. Growth on the methionine-supplied replica checks survival and transfer. Rescue by the native gene checks that this biological strain and assay can reveal functional complementation. The unrelated gene tests whether carrying a plasmid alone is sufficient. Comparing induction conditions checks dependence on gene expression, although changing the sugar also changes metabolism: it is not an isolated change of gene expression in every other respect.

If the candidate gene restores growth while those comparisons behave as intended, it supplies a function sufficient for the tested growth requirement in this recipient. Failure to rescue is less decisive: the candidate protein might not be produced, might be altered by its attached tag, or might not work in this cellular context. The investigators therefore also used Western blots to examine protein production. A detected protein still does not establish correct protein folding or catalytic activity. ^[ref]

Yujue Wang coauthored research on Pseudomonas aeruginosa.^[ref]

Pseudomonas aeruginosa is a bacterium with flexible central carbon metabolism. Its isocitrate branchpoint includes two regulated dehydrogenase routes and a glyoxylate shunt.