Flowering will take place in a short day plant only when:
1. days are shorter than nights.
2. days are shorter than a certain critical value.
3. nights are shorter than a certain critical value.
4. nights are longer than a certain critical value.

A short day plant is exposed to a flash of red light followed by a flash of far-red light given during the middle of the night. The expected effect is that this will:
1. cause increased flower production.
2. have no effect upon flowering.
3. inhibit flowering.
4. stimulate flowering.

An incandescent light bulb has a high output of red light. Which of the following plant process will be least promoted by it:
1. photosynthesis.
2. seed germination.
3. phototropism.
4. flowering.

The level of the biologically active ${\mathrm{P}}_{\mathrm{fr}}$ form of phytochrome will be reduced by all the following except:
1. exposure to far-red light
2. exposure to red light
3. long dark period
4. destruction of phytochrome

You want to induce opening of stomata in a plant that are otherwise closed during the night. The color of light that you should use would be?
1. red
2. far-red
3. blue
4. red followed by far-red

Let us say, a short day plant requires a critical night length of 14 hours for flowering. In which of the following scenarios will flowering be inhibited in such a plant?
1. 9 hours light/15 hours dark
2. 4 hours light/20 hours dark
3. 7hours light/2 hours dark/light flash/15 hours dark
4. 8 hours light/8 hours dark/light flash/8 hours dark

Etiolated seedlings become normal when exposed to:
1. Blue light
2. Green light
3. Red light
4. Far red light

Light passing through the green leaves of canopy trees above a seed:
1. stimulates its germination
2. inhibits its germination
3. does not affect its germination
4. causes abnormal germination in the seed

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

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