Question

The callus is defined as ______________________.
A. Decaying cells
B. Differentiated cells
C. Sterile mass of cells
D. Undifferentiated mass of the cell

Answer 1

Hint: It is used in tissue culture technique.
The cells used in this technique are taken from parts of a plant known as explants.

Complete answer:
Callus is the unorganized and actively dividing the mass of cells that are maintained in tissue culture. It is a highly meristematic group of cells that has a high amount of cytoplasm, this is to facilitate increased cell division. The cells also have high numbers of Golgi apparatus, endoplasmic reticulum, and other cell organelles due to its high rate of metabolism.
It is treated with growth hormones like auxins to allow rapid cell division, differentiation, and development.
Callus when treated with auxins, promotes the formation of roots. When it is treated with cytokinin, it stimulates cell maturation, differentiation, and ultimately promotes the development of the stem.

So, the correct answer is “Option D”.

Additional Information:
The explant is a small part of a plant. This may be a root tip or a shoot tip having growing points and increased meristematic activity that is used for tissue culture technique. Callus, on the other hand, is an unorganized and undifferentiated mass of cells formed from the explant when it is kept in a nutrient medium.
Explants used in the tissue culture experiments need to be pathogen-free to produce sterile and safe plants. For the production of a pathogen-free plant, the explant must include the use of cells having a high meristematic activity such as the cells of the apical meristem, axillary bud, and leaf primordial.

Note: Embryos, however, cannot be used as explants to obtain such pathogen-free plants because they are likely to be affected by pathogens.
Tissue culture is the growth and propagation of tissues/ cells in an artificial medium. This technique is also known as micropropagation. This is typically facilitated by the use of a liquid, semi-solid, or solid growth mediums such as broth or agar.