bacterium

n. (pl. bacteria) a unicellular, prokaryotic microorganism, that is, an organism whose chromosome is not contained in a nuclear envelope. Bacteria are considered to represent an earlier stage in the evolution of life than eukaryotes (organisms whose chromosomes are contained in nuclear envelopes, i.e., all organisms except bacteria). In humans, many bacteria cause disease (e.g., tetanus, syphilis, tuberculosis), whereas others are beneficial (e.g., preventing the growth of harmful microbes in the large intestine and enhancing the immune response). —bacterial adj.

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Psychology term of the day

February 25th 2025

group

n. any collection or assemblage, particularly of items or individuals. For example, in social psychology the term refers to two or more interdependent individuals who influence one another through social interactions that commonly include structures involving roles and norms, a degree of cohesiveness, and shared goals. Such social groups thus are contrasted with aggregations. Similarly, in animal behavior, a group refers to an organized collection of individuals that moves together or otherwise acts to achieve some common goal (e.g., protection against predators) that would be less effectively achieved by individual action, and in research, it denotes a collection of participants who all experience the same experimental conditions and whose responses are to be compared to the responses of one or more other collections of research participants.