Problem 14 - Biology: Concepts and Applications

Question

Match the observation with the hormone.. ____ethylene ____ cytokinin ____ auxin ____gibberellin ____ abscisic acid a. Your cabbage plants bolt (they form elongated flowering stalks) b. The philodendron in your room is leaning toward the window. c. The last of your apples is getting really mushy. d. The seeds of your roommate's marijuana plant do not germinate no matter what he does to them. e. Lateral buds on your Ficus plant are sprouting branch shoots.

Step-by-Step Solution

Answer

a: gibberellin, b: auxin, c: ethylene, d: abscisic acid, e: cytokinin.

Step 1: Match 'a' with the Hormone

Observe the phenomenon described: "Your cabbage plants bolt (they form elongated flowering stalks)". This is related to the growth phenomenon involving stem elongation and flowering, commonly regulated by the hormone gibberellin. Thus, match 'a' with gibberellin.

Step 2: Match 'b' with the Hormone

The phenomenon: "The philodendron in your room is leaning toward the window" is known as phototropism, where plants grow toward light. Auxin is the hormone that facilitates this process by accumulating on the shaded side to promote growth. Therefore, match 'b' with auxin.

Step 3: Match 'c' with the Hormone

"The last of your apples is getting really mushy" refers to the ripening and over-ripening process in fruits, primarily governed by ethylene. Ethylene accelerates the ripening which results in softening. Hence, match 'c' with ethylene.

Step 4: Match 'd' with the Hormone

The observation "The seeds of your roommate's marijuana plant do not germinate no matter what he does to them" involves seed dormancy, which is enforced or prolonged by the hormone abscisic acid. Therefore, match 'd' with abscisic acid.

Step 5: Match 'e' with the Hormone

"Lateral buds on your Ficus plant are sprouting branch shoots" suggests promoting lateral growth or branching, a process facilitated by cytokinins. Cytokinins stimulate cell division and shoot formation. Thus, match 'e' with cytokinin.

Key Concepts

Ethylene

Ethylene is a key player in the process of fruit ripening. Known as a plant hormone, ethylene is actually a gas. It is often referred to as the "aging hormone" because it accelerates various processes in the plant's life cycle. You might recognize the effects of ethylene when a piece of fruit becomes soft and mushy. This happens because ethylene signals the breakdown of cell walls and the conversion of starches to sugars. It is also involved in leaf abscission, the process where leaves drop from a plant. Other roles of ethylene include:

• Regulating leaf and flower senescence.
• Inducing flowering in some plants.
• Facilitating adventitious root formation.

Understanding ethylene's roles can help in agricultural practices, like controlling the timing of fruit ripening for market readiness.

Cytokinin

Cytokinins are essential plant hormones known for their role in promoting cell division and growth. They are primarily synthesized in the roots and travel upwards through the plant, encouraging shoot growth by stimulating the production of new cells. This is why you might notice more branching or a bushier appearance when cytokinins are active. Some other functions include:

• Delaying leaf aging by reducing chlorophyll degradation.
• Influencing nutrient allocation by modifying the plant's response to nutrient deficiencies.
• Working in tandem with auxins to regulate plant growth and development.

In practical terms, gardeners often use cytokinins to encourage lateral bud growth and enhance overall plant structure.

Auxin

Auxin is pivotal in plant growth and development, largely facilitating cell elongation. The behavior of phototropism, where a plant grows towards light, is significantly influenced by auxin. When light hits a plant, auxin collects on the shaded side, causing those cells to elongate and the plant to bend toward the light. Besides phototropism, auxin is also responsible for:

• Establishing pattern formation during embryogenesis.
• Regulating fruit development under certain conditions.
• Promoting root formation on cuttings and in tissue culture.

Auxin's influence on growth patterns and directionality makes it a powerful tool in agriculture and horticulture.

Gibberellin

Gibberellins are a group of plant hormones that play a crucial role in various growth processes. They are perhaps best known for their influence on stem elongation and bolting, the rapid growth of a flowering plant's stalk. Farmers often utilize gibberellin to manipulate the growth phases in crops for more efficient production. They also:

• Break seed dormancy and encourage germination.
• Boost flowering and fruit formation in some types of plants.
• Influence leaf and stem expansion, leading to larger and healthier foliage.

Manipulating gibberellin levels can be a strategic component in agriculture to enhance plant size and fruit yield.

Abscisic Acid

Abscisic acid (ABA) is often associated with stress responses in plants, helping them adapt to adverse conditions. One of its primary roles is to enforce seed dormancy, helping seeds remain dormant until conditions are just right for germination. This hormone is quite versatile, with functions including:

• Regulating guard cells during water deficiency, thereby controlling the opening and closing of stomata.
• Influencing root architecture and growth under stress conditions.
• Modulating plant responses to environmental factors like drought and high salinity.

Through its regulatory actions, ABA helps ensure plant survival during challenging environmental scenarios. Understanding ABA can significantly impact crop management and conservation efforts.