**(a)** Just one daughter cell divides following mitotic cell division in arithmetic growth, whereas the other differentiates and develops. For example, the elongation of roots at a constant rate. A linear curve is obtained by plotting the length of the organ against time. Mathematically, it is written as: -

L_{t }= L_{O }+ rt

Hence, t L is length at time ‘t’, 0 L is the length at time zero and r is the growth rate or elongation per unit time.

**b. Geometric growth :-** In most systems, the initial growth is slow and is referred to as the lag phase, and after that, it increases rapidly at an exponential rate and is referred to as the log or exponential phase. In this case, both progeny cells that result from mitotic cell division retain the capacity to divide and continue to do so. However, when nutrition availability is limited, growth slows and eventually stops, resulting in a stationary phase. A sigmoid curve can be seen on the graph of geometric growth.

**c. Sigmoid growth curve :- **A sigmoid curve is a characteristic property of a living organism growing in its natural habitat. The lag phase, the log phase or exponential phase of rapid growth, and the stationary phase are the three phases of this curve. Exponential growth can be expressed as:

W_{1} = W_{0} e^{rt}

W_{1} = final size

W_{0} = initial size of the period

r=growth rate

t=time growth

e=base of natural logarithms

**d. Absolute and relative growth rates :-** The measurement and the comparison of total growth per unit time are called the absolute growth rate. The relative growth rate is the rate at which a particular system grows per unit time on a common basis, e.g., per unit initial parameter.

What would be expected to happen if:

**(a)** GA_{3} is applied to rice seedlings

**(b)** dividing cells stop differentiating

**(c)** a rotten fruit gets mixed with unripe fruits

**(d) **you forget to add cytokinin to the culture medium

Would a defoliated plant respond to a photoperiodic cycle? Why?

Which one of the plant growth regulators would you use if you are asked to:

**a.** Induce rooting in a twig

**b.** Quickly ripen a fruit

**c.** Delay leaf senescence

**d.** Induce growth in axillary buds

**e.** Bolt a rosette plant

**f.** Induce immediate stomatal closure in leaves.

‘Both a short-day plant and a long-day plant can flower simultaneously in a given place’. Explain

‘Both growth and differentiation in higher plants are open’. Comment.