question_answer 50)

  Both animals and plants grow. Why do we say that growth and differentiation in plants is open and not so in animals? Does this statement hold true for sponges also?

Answer:

                Growth and differentiation in plant and animals can be explained as follows

Growth in Plants

Growth in Animals

Plant growth is indeterminate, i.e., cells can divide and enlarge continuously for life time. Growth is open due to presence of rneristematic cells which keep dividing, i.e., growing and replacing new organs. Structure in plants at tips or meristematic zones is never complete, owing to open ended tips or apices. Plant growth is in a modular fashion, i.e., grows longitudinally, laterally and in girth.

Animal growth is determinate i.e., till finite period, they mature and stop growing externally. Cell division is distributed through-out the body of organism to replace old and damaged cells, rather localised at specific regions. After a specific time period i.e., embryonic, the growth rate is reduced in juvenile phase and ceases in maturity.

Sponges are exception to this They show open growth as every cell of their body can give rise to an individual and their growth and differentiation is continuous is their life cycle,