(a) A phase of growth which is maximum and fastest is exponential phase.

(b) Apical dominance as expressed in dicotyledonous plants is due to the presence of more auxins in the apical bud than in the lateral ones.

(c) In addition to auxin, a cytokinin must be supplied to culture medium to obtain a good callus in plant tissue culture.

(d) Leaves of vegetative plants are the sites of photoperiodic perception.

(a) Gibberellic acid increases the yield of sugarcane.

(b) Cytokinin spray on plants promote lateral shoot growth.

(c) The effect of ethylene on potato causes its sprouting.

(d) ABA - Abscissic acid inhibit the seed germination.

Growth is dependent on three factors - initial size $\left(W_0\right)$, rate of growth $(r)$ and time interval (+) for which the rate of growth is retained.

Where,

$$ \begin{aligned} W_1 & =W_0 e^{r t} \\ W_1 & =\text { final size }, \\ W_0 & =\text { Initial size }, \\ r & =\text { growth rate, } \\ t & =\text { time, } \\ e & =\text { base of natural logarithim. } \\ 19 & =5 \times(2.7)^{r \times 7} \\ \frac{19}{5} & =(2.7)^{r \times 7} \\ 3.8 & =(2.7)^{r \times 7} \end{aligned}$$

$$ \begin{aligned} &\begin{aligned} \log 3.8 & =r \times 7 \times \log (2.7) \\ 0.5798 & =r \times 7 \times 0.4314 \\ \frac{0.5798}{7 \times 0.4314} & =r=0.1907 \\ \text { Relative growth rate } & =\frac{\text { Growth in given time period }}{\text { Measurement at start of time period }} \\ & =\frac{19}{5}=3.8 \mathrm{~cm} \end{aligned}\\ &\text { Thus absotule growth rate is } 0.1907 \text { while relative growth rate is } 3.8 \mathrm{~cm} \end{aligned}$$