Q1. Explain how auxins help a plant grow towards light. Give an example from daily life.
Answer:
Auxins are mainly produced at the tips of shoots in plants.
When light falls on one side of a plant, the other side has more auxin.
This uneven distribution causes cells on the darker side to grow longer, so the shoot bends towards the light.
This process is called phototropism.
Gardeners often use this knowledge to turn cuttings towards a window to encourage straight, healthy growth.
Thus, auxins play a vital role in directing plant growth towards sunlight, which is important for photosynthesis.
Q2. Describe how gibberellins are used to improve the yield and quality of crops.
Answer:
Gibberellins stimulate stem elongation and seed germination in plants.
In crops like sugarcane, gibberellins help increase the length of internodes (the parts between the leaves), leading to higher yields.
Applying gibberellins to grapevines results in larger, seedless grapes with more space between them.
In brewing, gibberellins are sprayed on barley to speed up germination for malting.
Dwarf varieties of rice become tall and healthy if treated with gibberellins.
These uses show how plant hormones can directly benefit agriculture and food industries.
Q3. What role do cytokinins play in delaying the ageing of plant leaves? Provide examples of their application.
Answer:
Cytokinins are hormones that promote cell division and delay senescence (ageing) in leaves.
When sprayed on leafy vegetables like lettuce, they keep the leaves fresh and green for a longer time.
Cytokinins are used in laboratory tissue cultures to encourage the growth of new shoots from plant tissues.
They also balance growth with auxins so that plants have a healthy ratio of roots and shoots.
In natural conditions, coconut water, rich in cytokinins, helps young plants grow faster.
Therefore, cytokinins are valuable for prolonging the shelf-life and quality of vegetables.
Q4. How does abscisic acid help plants survive drought conditions?
Answer:
Abscisic acid (ABA) acts as a growth inhibitor and helps plants during dry conditions.
When there is water scarcity, ABA increases in leaves and signals the stomata to close.
Closed stomata reduce water loss by evaporation, helping the plant save water.
ABA also puts seeds and buds into dormancy, stopping their growth until water becomes available.
This hormone can help desert plants and crops survive during dry periods.
Without ABA, plants would lose much more water and not survive a drought.
Q5. A farmer wants his cuttings of rose plants to root faster. Which plant hormone should he use and why?
Answer:
The farmer should use auxins, as they promote root formation in plant cuttings.
Synthetic auxins like IAA, IBA, or NAA are often used as rooting powders.
When applied to the base of stem cuttings, they stimulate the development of new roots quickly.
This helps the cutting to absorb water and nutrients from the soil faster.
Using auxins increases the success rate of plant propagation through cuttings.
Thus, auxins make it easier for the farmer to grow more rose plants efficiently.
High Complexity (Analysis & Scenario-Based)
Q6. Imagine a tomato plant is producing fruit that drops before it is mature. Which hormone imbalance is likely, and how can it be corrected?
Answer:
The tomato plant may have low auxin levels.
Auxins normally help to prevent premature fruit drop by strengthening the bond between the fruit and the plant.
When auxin is lacking, fruits may fall off before ripening.
To fix this, synthetic auxins (like NAA) can be sprayed on the plant to hold the fruits longer until they mature.
This application is common in orchards and helps increase the harvested yield.
Proper hormonal balance is therefore crucial for quality fruit production.
Q7. If a plant in a greenhouse remains short with stunted stems, which hormone would you recommend applying? What changes would you expect after applying it?
Answer:
The plant likely needs more gibberellins, which encourage stem elongation.
After applying gibberellins, the plant's stems would grow longer and stronger, overcoming the “dwarf” appearance.
Leaves might also spread out better, improving photosynthesis.
The plant may also flower and bear fruit more normally.
This is often done with certain commercial crops, like rice and peas, to achieve a desired height and structure.
Thus, gibberellin application helps recover proper growth and productivity in greenhouse plants.
Q8. Analyse how both auxins and cytokinins interact to determine whether a plant tissue will develop roots or shoots during tissue culture.
Answer:
In tissue culture, the ratio of auxins to cytokinins is key for plant development.
If there is more auxin than cytokinin, the tissue will mainly form roots.
If there is more cytokinin than auxin, the tissue will produce shoots and buds.
A balanced amount of both leads to the growth of a complete plantlet with roots and shoots together.
Scientists use this property to propagate plants in the lab, quickly multiplying desired varieties.
Controlling these hormones allows mass production of healthy, uniform plants.
Q9. A sudden environmental change causes all the leaves of a tree to drop early in autumn. Explain the likely role of abscisic acid in this process.
Answer:
Abscisic acid (ABA) is responsible for promoting leaf abscission (fall).
If environmental stress occurs, such as unexpected cold or drought, ABA levels rise in the plant.
Higher ABA signals the plant to shut down growth and shed leaves to reduce water loss.
This is a protective response so the tree can survive harsh conditions with less water loss.
The process of leaves dropping, or abscission, is mostly controlled by ABA in response to stress.
Thus, ABA helps plants adapt to and survive sudden environmental stress.
Q10. Consider a scenario where a batch of barley grains does not sprout evenly during malting. Based on your knowledge, suggest a plant hormone treatment to solve this.
Answer:
The problem lies in uneven seed germination.
Gibberellins are known to stimulate and synchronize seed germination in grains like barley.
Treating the barley batch with gibberellins will ensure that most seeds sprout at the same time.
This is important in malting (for making beer), where even sprouting ensures uniform quality.
Using gibberellin hormone in this way is a common practice in the food-processing industry.
This solution shows how plant hormones have practical uses beyond just field agriculture.
