Chapter 37, Problem 1TY

Summary Introduction

Introduction: An organism’s response to an external or an internal stimulus is known as its behavior. Plant movement is one of the examples of plant behavior. The plants respond to light, gravity, and sometimes touch. Chemical signals which are transported within the body of a plant are known as plant hormones. Plant hormones are employed to provide a response to a stimulus.

Answer to Problem 1TY

Correct answer: Auxin, cytokinin, and gibberellin are some of the examples of plant hormones. Hence, the correct answer is option c.

Explanation of Solution

Reason for correct answer:

Some of the examples of plant hormones are auxins, cytokinins, gibberellins. Auxins are known as the master plant hormones. They influence the structure, development, and behavior of the plant in many ways. They induce vascular tissue development, mediate phototropism, promote the formation of adventitious roots, establish apical-basal polarity, and stimulate fruit development. The cell division and the aging of the cells are promoted with the help of cytokinins. Seed germination and flowering are promoted with the help of gibberellins.

Option c. is given as “auxin, cytokinin, and gibberellin”.

Auxin, cytokinin, and gibberellin are employed to provide a response to a stimulus, thus referred to as plant hormones. Hence, the correct answer is option c.

Reasons for incorrect answer:

Option a. is given as, “cyclic AMP, IP3, and calcium ions”.

Cyclic AMP, IP3, and calcium ions are examples of secondary messengers that are employed to transmit messages in plant cells. Their primary responsibility is to transmit messages from various receptors and they are not referred to as plant hormones. Hence, option a. is incorrect.

Option b. is given as, “calcium, CDPKs, and DELLA proteins”.

CDPKs are involved in influencing cellular responses and are known as effector molecules. CDPKs turn off transcription of particular genes. DELLA proteins are involved in restricting cell division in the presence of gibberellin. These are not involved in responding to a stimulus, therefore they are not considered as plant hormones. Hence, option b. is incorrect.

Option d. is given as, “cryptochrome, phototropin, and phytochrome”.

Cryptochrome, phototropin, and phytochrome are involved in assisting a plant’s response to light. Cryptochromes are involved in assisting the growth of young seedlings. Plants respond to blue light with the help of phototropin. The receptor absorbing visible light of red and far-red light wavelengths is known as phytochrome. They are light receptors and not plant hormones. Hence, option d. is incorrect.

Option e. is given as, “statoliths, pulvini, and aerenchyma”.

Statoliths assist the root to grow downward by sensing gravity. Pulvini help plant cells in responding to touch. Aerenchyma refers to the spongy tissues that contain air spaces. It is found mainly in aquatic plants. Aerenchyma allows gas exchange and provides buoyancy. Therefore, these are not considered as plant hormones. Hence, option e. is incorrect.

Hence, the options a., b., d., and e. are incorrect.

Conclusion

Thus, auxin, cytokinin, and gibberellin are referred to as plant hormones.