Question

A mass of dividing, undifferentiated cells in a tissue culture is called __________.
A. A Shield
B. A Callus
C. An Embryoid
D. An Aggregate
E. A Plasmodium

Answer 1

Plant species representing all major land plant groups are capable of producing callus in tissue culture. A callus cell culture is usually sustained on the gel medium. The callus induction medium consists of agar and a mixture of macronutrients and micronutrients for the given cell type.

Complete step by step answer: Plant callus is a growing mass of unorganized plant parenchyma cells. In living plants, callus cells are those cells that cover a plant wound. In biological research and biotechnology, callus formation is induced from plant tissue samples (explants) after surface sterilization and plating onto tissue culture medium in vitro. Plant callus is usually derived from somatic tissues. The tissues used to initiate callus formation depends on plant species and which tissues are available for explant culture. The cells that give rise to callus and somatic embryos usually undergo rapid division or are partially undifferentiated such as meristematic tissue. Specific auxin to cytokinin ratios in plant tissue culture medium give rise to an unorganized growing and dividing the mass of callus cells. Callus cultures are often broadly classified as being either compact or friable. Friable calluses fall apart easily and can be used to generate cell suspension cultures. Callus can directly undergo direct organogenesis and/or embryogenesis where the cells will form an entirely new plant.
Hence, the correct answer is option B.

Note: Plant calluses derived from many different cell types can differentiate into a whole plant, by a process called regeneration, It involves addition of plant hormones to the culture medium. This ability is known as totipotency. Regeneration of a whole plant from a single cell allows transgenics researchers to obtain whole plants which have a copy of the transgene in every cell.