Question

Which of the following physiological effects plants by gibberellic acid? (a) Shortening of genetically tall plants. (b) Elongation of genetically dwarf plants. (c) Rooting in stem cuttings. (d) Yellowing of young leaves.

Short answer

The physiological effect of gibberellic acid on plants is (b) elongation of genetically dwarf plants.

Step-by-step solution

Understanding the Role of Gibberellic Acid

Gibberellic acid is a plant hormone that promotes cell elongation, growth, and development. It is particularly known for its role in affecting stem growth and seed germination.

Evaluating the Options

Option (a) is not correct because gibberellic acid generally promotes growth, not inhibition. Option (c) is associated with auxins, not gibberellins. Option (d) is not usually an effect of gibberellic acid but a symptom of deficiency in certain nutrients. Option (b) aligns with the known effects of gibberellic acid, which can cause elongation in certain dwarf plants, helping them to grow taller.

Determining the Correct Answer

Based on the known effects of gibberellic acid on plant growth, the most appropriate option is the one that matches the actions of gibberellins. In this case, it is option (b), the elongation of genetically dwarf plants.

Key concepts

Plant Hormones

Plant hormones, also known as phytohormones, play a critical role in regulating various aspects of growth and development within plants. These substances function as chemical messengers, orchestrating tasks from seed germination to fruit ripening, and everything in between.

Among the key plant hormones are auxins, cytokinins, ethylene, abscisic acid, and gibberellins. Each of these hormones has specific functions; for instance, auxins generally stimulate cell elongation and are involved in the formation of roots, cytokinins promote cell division, and ethylene is closely associated with the ripening of fruits. Gibberellins, such as gibberellic acid, are noteworthy for their role in overcoming seed dormancy, spurring stem elongation, and enhancing seed germination.

Gibberellic acid, in particular, causes significant effects on cell elongation, which leads us to understanding its impact when applied to dwarf varieties of plants. Its ability to stimulate elongation is utilized in agriculture to improve crop yields and manage the physical characteristics of certain plants.

Cell Elongation

Cell elongation is a critical process in plant growth, where cells increase in size, leading to the expansion of tissues and organs. This process is essential for plants to grow taller and for leaves to expand, allowing for more photosynthesis and ultimately, more energy for the plant.

One of the primary hormones responsible for this growth process is gibberellic acid. It works by stimulating the production of enzymes that break down the walls of plant cells, making them more flexible and capable of expanding. Gibberellins interact with other hormones and environmental cues to ensure that growth occurs at the ideal time and in the proper direction.

Students learning about plant physiology may find it useful to visualize the action of gibberellic acid as 'unlocking' the plant cells, allowing them to stretch and grow. This mechanism is critical not just in natural plant development but also in agricultural practices where controlling plant size and improving harvests is desired.

Dwarf Plants Growth

The growth of dwarf plants is a topic of major interest in both botany and agriculture. Dwarfing is often a genetic trait, where the plant naturally has a tendency to grow to a smaller size than standard varieties. However, the application of gibberellic acid can stimulate growth in these dwarf plants by promoting stem elongation.

Understanding the effect of gibberellic acid on dwarf plants helps us to see the potential benefits of using this hormone as a growth regulator. By inducing cell elongation, gibberellic acid can lead to a significant increase in the height of dwarf plants, which can be particularly useful in breeding programs and crop production. For instance, in trying to increase the yield of certain crops, farmers might apply gibberellic acid to naturally short plants to optimize the use of space and resources.

Educational exercises may improve by illustrating real-world examples where such treatments have resulted in tangible benefits, aiding students to grasp not just the scientific concept but also its practical application in the world of agriculture and horticulture.