Question

Examples of plant hormones include a. cyclic AMP, IP \(y\), and calcium ions. b. calcium, CDPKs, and DELLA proteins. c. auxin, cytokinin, and gibbercllin. d. cryptochrome, phototropin, and phytochrome. statoliths, pulvini, and aerenchyma.

Short answer

c. auxin, cytokinin, and gibberellin.

Step-by-step solution

Identification of Plant Hormones

It's important to know what plant hormones are. Plant hormones, or phytohormones, are chemical substances produced naturally in plants to regulate growth or other physiological functions. They include auxins, cytokinins, and gibberellins, among others.

Examine Each Option

Next, examine each option and identify whether the substances listed in each one are examples of plant hormones or not.

Selection of the Correct Choice

After examining each option, it can be determined that 'c. auxin, cytokinin, and gibberellin' are all examples of plant hormones. Those are the names of some of the key hormones that control various aspects of plant growth and development. Therefore, option c is the correct answer.

Key concepts

Auxin

Auxin is a crucial plant hormone essential for various growth processes. Found mainly in shoot tips, young leaves, and seed embryos, auxin regulates cell elongation, which is vital for plant growth.
Its presence ensures the plant grows towards light, a phenomenon known as phototropism. Auxin does this by accumulating on the shaded side of a plant, causing cells there to lengthen and bend towards the light.
Additionally, auxin plays an important role in:

• Root development: promoting formation of new roots
• Fruit development: helping fruits to grow uniformly
• Apical dominance: inhibits lateral bud growth, encouraging a single stem growth

Auxin demonstrates the complexity of plant hormonal control by influencing many developmental processes simultaneously.

Cytokinin

Cytokinins are another group of plant hormones that primarily promote cell division in plant roots and shoots. Unlike auxin, cytokinins are synthesized chiefly in roots and transported upwards through the plant.
They work alongside auxin to control various physiological processes including:

• Cell division and growth: essential for tissue formation and repair
• Delay of leaf senescence: keeping leaves green and functional longer
• Breaking seed dormancy: encouraging germination under appropriate conditions

Cytokinins also impact nutrient mobilization, encouraging the plant to redistribute valuable nutrients leading to healthier growth. The balance and interaction between cytokinins and auxins are critical in maintaining overall plant form and function.

Gibberellin

Gibberellins are a family of plant hormones that play a significant role in promoting growth and development in plants. They are known for their ability to stimulate stem elongation, seed germination, and flowering.
Gibberellins are primarily found in young tissues and seeds, and are involved in several key processes such as:

• Breaking seed dormancy: assisting seeds to sprout by weakening the seed coat
• Stem and leaf expansion: aiding in the rapid growth of stems and lengthening of internodes
• Inducing flowering: especially crucial in certain plants that require gibberellins to flower

The action of gibberellins allows plants to adapt their growth according to environmental conditions, showcasing their vital role in agricultural productivity and horticulture.