The fact that various plant hormones can have different effects at different concentrations can explain:
1. Need of photoperiodism for flowering in plants.
2. Plant hormones being needed in vary high amounts.
3. Antagonism between auxin and cytokinin in the control of apical dominance.
4. Cell elongation stimulation in apical meristems and inhibition axillary buds by auxins.

Hyponastic response in submerged plants may be due to auxin and:
1. ABA
2. Ethylene
3. Cytikinin
4. Gibberellins

The ‘triple response to mechanical stress’ is related to the plant growth regulator:
1. Ethylene
2. ABA
3. Auxin
4. Cytokinin

To render the cells of abscission layer more sensitive to ethylene, an aging leaf produces less and less:
1. Cytokinin
2. Auxin
3. Gibberellin
4. ABA

The newly discovered PGR brassinosteroids have effects qualitatively similar to:
1. Auxins
2. Gibberellins
3. Cytokinins
4. Ethylene

The plant hormones that are produced by wounded plants and play a key role in controlling plant defences against herbivores as well as responsible for enchanting fragrance of jasmine are:
1. Brassinosteroids
2. Strigolactones
3. Jasmonates
4. Auxins

The most important colors in regulating photomorhogenesis in plants are:
1. Violet and Yellow
2. White and Black
3. Green and Orange
4. Red and Blue

Blue light photoreceptors in plant do not regulate:
1. Phototropism
2. Light induced opening of stomata
3. Light induces slowing of hypocotyls elongation
4. Seed germination

The biologically active form of the phytochrome is:
1.${\mathrm{P}}_{\mathrm{r}}$
2. ${\mathrm{P}}_{\mathrm{fr}}$
3. Both
4. None

When lettuce seeds illuminated by red light are then exposed to far red light:

1. ${\mathrm{P}}_{\mathrm{r}}$ is converted to ${\mathrm{P}}_{\mathrm{fr}}$ and germination is inhibited
2. ${\mathrm{P}}_{\mathrm{r}}$ is converted to ${\mathrm{P}}_{\mathrm{fr}}$ and germination is initiated
3. ${\mathrm{P}}_{\mathrm{fr}}$ is converted to ${\mathrm{P}}_{\mathrm{r}}$ and germination is inhibited
4. ${\mathrm{P}}_{\mathrm{fr}}$ is converted to ${\mathrm{P}}_{\mathrm{r}}$ and germination is initiated