Questions & explanations
1. What is photoperiodism?
- Response of flowering to relative lengths of light and dark periods
- Response of plants to gravity
- Response of plants to touch
- Response of plants to temperature
Answer: Response of flowering to relative lengths of light and dark periods
Photoperiodism specifically refers to the physiological response of organisms, particularly plants, to the length of day or night. It is most commonly observed in the timing of flowering, where the relative lengths of light and dark periods determine when a plant will flower.
2. Which of the following is an example of a biennial plant that requires vernalisation?
- Spring wheat
- Winter wheat
- Rice
- Sunflower
Answer: Winter wheat
Winter wheat is a biennial or winter annual that requires a period of cold (vernalisation) to flower. Spring wheat, on the other hand, does not require vernalisation and can be planted in spring. Rice and sunflower are not typically vernalisation-requiring.
3. In photoperiodism, which period is more critical for flowering in short-day plants?
- Duration of the light period
- Duration of the dark period
- Total duration of light and dark combined
- Quality of light
Answer: Duration of the dark period
In photoperiodism, especially for short-day plants, the uninterrupted dark period is more critical than the light period. A brief interruption of the dark period with light can prevent flowering, demonstrating the importance of the dark period's duration.
4. Which type of plant flowers only when the day length is shorter than a critical length?
- Short-day plant
- Long-day plant
- Day-neutral plant
- Intermediate-day plant
Answer: Short-day plant
Short-day plants (SDP) require a day length shorter than a critical value to initiate flowering. They typically flower in autumn or spring when days are short. Long-day plants require longer days, and day-neutral plants are not influenced by day length.
5. Which statement correctly distinguishes photoperiodism from vernalisation?
- Photoperiodism involves response to temperature, while vernalisation involves response to day length
- Photoperiodism involves response to day length, while vernalisation involves response to low temperature
- Both are responses to day length
- Both are responses to temperature
Answer: Photoperiodism involves response to day length, while vernalisation involves response to low temperature
Photoperiodism is the response to relative lengths of light and dark periods (day length), whereas vernalisation is the promotion of flowering by exposure to low temperature. They are distinct processes that can interact in some plants.
6. Which pigment is primarily involved in photoperiodic perception in plants?
- Chlorophyll
- Carotenoid
- Phytochrome
- Cryptochrome
Answer: Phytochrome
Phytochrome is the photoreceptor pigment that detects red and far-red light and mediates photoperiodic responses. It exists in two interconvertible forms (Pr and Pfr) and plays a key role in measuring day length.
7. What is vernalisation?
- Promotion of flowering by exposure to low temperature
- Promotion of flowering by long days
- Promotion of flowering by short days
- Inhibition of flowering by low temperature
Answer: Promotion of flowering by exposure to low temperature
Vernalisation is the process by which exposure to prolonged cold temperature (typically winter) promotes flowering in some plants. It ensures that flowering occurs in favourable conditions, often after winter.
8. Which part of the plant perceives photoperiodic signals?
- Roots
- Stems
- Leaves
- Flowers
Answer: Leaves
Leaves are the primary site of photoperiodic perception. They detect changes in day length and produce a hormonal signal (florigen) that is transported to the shoot apical meristem to induce flowering.
9. The phenomenon of apical dominance in plants is primarily controlled by which plant hormone?
- Gibberellin
- Cytokinin
- Auxin
- Ethylene
Answer: Auxin
Auxin produced in the apical bud suppresses the growth of lateral buds, a phenomenon known as apical dominance. Cytokinins can overcome this effect, but auxin is the primary hormone responsible.
10. In agriculture, which plant hormone is commonly used to induce fruit ripening in climacteric fruits like bananas?
- Auxin
- Gibberellin
- Cytokinin
- Ethylene
Answer: Ethylene
Ethylene is used commercially to ripen fruits such as bananas, tomatoes, and apples. It triggers the ripening process by promoting the breakdown of starch to sugar and softening of the fruit.
11. Which of the following pairs of plant hormones show antagonistic effects?
- Auxin and gibberellin
- Gibberellin and cytokinin
- Abscisic acid and gibberellin
- Ethylene and abscisic acid
Answer: Abscisic acid and gibberellin
ABA promotes seed dormancy while gibberellins break dormancy; they have opposite effects on seed germination. Auxin and gibberellin often act synergistically in stem elongation.
12. Which of the following plant growth regulators is classified as a growth inhibitor?
- Auxin
- Gibberellin
- Cytokinin
- Abscisic acid
Answer: Abscisic acid
Abscisic acid (ABA) is a growth inhibitor that promotes stomatal closure, seed dormancy, and stress responses, while auxins, gibberellins, and cytokinins are growth promoters.