Question

Read the given statements and select the correct option. statement 1: Ethylene is a gaseous hormone. statement 2: Ethylene causes climacteric ripening of fruits (a) Both statements 1 and 2 are correct and statement 2 is the correct explanation of statements 1. (b) Both statements 1 and 2 are correct but statement 2 is not the correct explanation of statements 1. (c) statements 1 is correct and statements 2 are incorrect . (d) Both statements 1 and 2 are incorrect and

Short answer

Both statements 1 and 2 are correct; however, statement 2 is not the correct explanation of statement 1. The correct option is (b).

Step-by-step solution

Verifying Statement 1

Analyze the first statement: 'Ethylene is a gaseous hormone.' To verify its accuracy, refer to scientific texts or reputable sources which elaborate on plant hormones and their states. Ethylene is indeed known to be a gaseous plant hormone.

Verifying Statement 2

Review the second statement: 'Ethylene causes climacteric ripening of fruits.' This requires validating the role of ethylene in fruit ripening. Ethylene is recognized for its role in the climacteric ripening process of many fruits, which is an increase in the rate of respiration as the fruit ripens.

Relation between Statement 1 and Statement 2

Determine if statement 2 is a correct explanation for statement 1. Since statement 2 provides information about the function of ethylene, but statement 1 simply categorizes it as a gaseous hormone, statement 2 is not directly explaining why ethylene is gaseous. Therefore, while both statements are correct, statement 2 does not serve as an explanation for statement 1.

Key concepts

Gaseous Plant Hormones

Plant hormones, also known as phytohormones, play a crucial role in regulating growth, development, and responses to environmental stimuli in plants. Among the five major categories of plant hormones are the gaseous plant hormones, of which ethylene is a prime example.

Ethylene stands out from other plant hormones such as auxins, gibberellins, cytokinins, and abscisic acid due to its gaseous state at biological temperatures. This unique feature allows it to easily diffuse through the air and plant tissues, making it incredibly effective in signaling changes over long distances within plant parts.

Importance of Gaseous State

One of the benefits of being a gaseous hormone is the ability of ethylene to act on various parts of a plant swiftly and uniformly. This is particularly essential during the stress response, where ethylene can be released by one part of the plant and promptly perceived by another, guiding the developmental adjustments needed to cope with the challenge.

Climacteric Ripening of Fruits

Ripening of fruits is a complex biological process that involves a variety of biochemical and physiological changes. It can be categorized into two types: climacteric and non-climacteric ripening.

Climacteric fruits exhibit a marked increase in respiration rate accompanied by ethylene production during ripening. Examples of climacteric fruits include apples, bananas, and tomatoes. Contrarily, non-climacteric fruits, like grapes, citrus, and strawberries, do not show this surge in respiration or ethylene release; they ripen without the dramatic changes seen in their climacteric counterparts.

Role of Ethylene in Climacteric Ripening

In climacteric fruits, ethylene acts as an essential hormone that signals the beginning of the ripening process. This gaseous hormone is both a byproduct of the ripening process and a catalyst that accelerates it, creating a positive feedback loop. It promotes the breakdown of cell walls, conversion of starches to sugars, and development of characteristic colors and flavors.

Role of Ethylene in Fruit Ripening

The role of ethylene in fruit ripening is pivotal and multifaceted, encompassing a range of biochemical processes. As fruits enter the ripening stage, ethylene synthesis surges, acting as a signaling molecule that triggers various ripening-related genes.

A Cascade of Ripening Events

Once synthesized, ethylene initiates a cascade of events such as increasing cellular respiration, enhancing the conversion of starches into sugars (which sweetens the fruit), softening the fruit texture by altering cell wall components like pectin, and developing the volatile compounds that contribute to the fruit’s aroma and flavor.

Softening of the fruit is an especially important aspect, as it makes the fruit more appealing for consumption by various organisms, which in turn helps in seed dispersal. Ethylene’s influence on pigmentation also plays a role in signaling ripening; it can help to degrade chlorophyll and promote the accumulation of carotenoids, which contribute to the color changes in the ripening fruit. Ethylene is thus not only critical for the ripening process but also for the reproductive success of many plants.