(i) Plants retain the capacity for unlimited growth
throughout the life due to the presence of meristems at certain locations in their body.
The cells of such meristems have the capacity to divide and self perpetuate. The product however, soon loses the capacity to divide and
such cells make up plant body.
(ii) This form of growth where in new cells are always being added to the plant body by the activity of the meristem is called the open form of growth.
(iii) The cells divided from root apical and shoot apical meristems and cambium differentiate the
. nature to perform specific functions. It is called differentiation.
(iv) Differentiation in plants is open because cells/ tissues arising out of the same meristems have different structures at maturity. The final structure at maturity of cell tissue is also determined by the location of the cell within.
(B) (i) A long day plant require the exposure to
light for a period exceding a well-defined critical duration while short day plant must be exposed to light for a period less than this critical duration before the flowering is initiated in them. It means that not only the duration of light period but the duration of dark period is also of equal importance.
(ii) Hence, flowering depends not only a combination of ligt and dark exposure but also their relative durations.
(iii) That is why, both a short day and a long day plant produce flower simultaneously in a given place
(C) (i) No, a defoliated plant would not respond
to photoperiodic cycle. Because the site of perception of light, dark duration are the leaves.
(ii) There is a hormonal substance (S) present in leaves which are responsible for flowering. This hormonal substance migrates from leaves to shoot apices for inducing flowering only when the plants are exposed to the necessary photoperiod.