Problem 15 - Biology Concepts and Applications

Question

Match the observation with the main hormone. ________ethylene ________cytokinin ________auxin ________gibberellin ________abscisic acid ________nitric oxide a. Your cabbage plants bolt (they form elongated flowering stalks). b. The potted plant in your room is leaning toward the window. c. Lateral buds are sprouting. d. The seeds of your roommate's marijuana plant do not germinate no matter what he does to them. e. The last of your apples is getting really mushy. f. Your lettuce plants develop brown spots on their leaves.

Step-by-Step Solution

Answer

a. Gibberellin, b. Auxin, c. Cytokinin, d. Abscisic acid, e. Ethylene, f. Nitric oxide.

Step 1: Identify the Hormone Functions

First, let's determine the primary functions of the given hormones. Ethylene is involved in fruit ripening. Cytokinin promotes cell division and growth, especially in lateral buds. Auxin facilitates phototropism, causing plants to grow toward light. Gibberellin is crucial for stem elongation and seed germination. Abscisic acid is known for inhibiting growth and promoting dormancy. Nitric oxide can induce browning and cell death in stressed leaves.

Step 2: Match Observations to Functions

Next, we'll match the observations with the known functions of the hormones. Consider each observation and pair it with the hormone whose function it aligns with.

Step 3: Match Hormones to Observations

a. Gibberellin: Your cabbage plants bolt (elongate flowering stalks). b. Auxin: The potted plant leans toward the window (phototropism). c. Cytokinin: Lateral buds are sprouting (growth and development). d. Abscisic acid: Seeds do not germinate (inhibits germination). e. Ethylene: Apples become mushy (fruit ripening). f. Nitric oxide: Lettuce leaves develop brown spots (stress response, cell death).

Key Concepts

Ethylene

Ethylene is a gaseous plant hormone that plays a crucial role in various stages of a plant's life cycle. It is best known for its role in fruit ripening. When fruits, such as apples or bananas, emit ethylene, it acts as a signal to other parts of the plant to initiate the ripening process.
During ripening, ethylene triggers several biochemical changes:

• Conversion of starches to sugars, making the fruit sweet.
• Softening of the fruit as cell walls break down.
• Degradation of chlorophyll, leading to color changes.

Farmers sometimes utilize ethylene to control the ripening of fruits, ensuring they reach markets at the perfect stage for consumption.

Cytokinin

Cytokinins are a group of plant hormones that primarily promote cell division and growth. They play a pivotal role in the growth of lateral buds and the modulation of apical dominance. When cytokinins are present in higher concentrations, they encourage the growth of shoots and the development of lateral buds.
This hormone also works in tandem with auxin to regulate cell differentiation and organ formation in plants. In practical applications, cytokinin levels are manipulated to produce bushier plants through the stimulation of auxiliary sprout growth.

Auxin

Auxin is a fundamental plant hormone known for its role in regulating plant growth and facilitating phototropism. Phototropism is the process where plants grow towards a light source, optimizing their ability to capture sunlight for photosynthesis.
Auxins help by accumulating on the shaded side of the plant, causing cells there to elongate more than those on the light-exposed side. This uneven growth pushes the plant towards the light.
Additionally, auxins are involved in:

• Root development.
• Fruit development.
• Maintaining apical dominance, which suppresses lateral bud growth.

Gibberellin

Gibberellins are important plant hormones that affect various developmental processes, including seed germination and stem elongation. They promote the transition of seedlings from dormancy to active growth and are essential for the bolting of rosette plants, such as cabbages, which involves the rapid elongation of flowering stalks.
In particular, gibberellins help:

• Break seed dormancy and stimulate germination.
• Regulate flowering.
• Increase the size of fruit.

In agriculture, gibberellins are sometimes used to improve crop yields and control plant growth.

Abscisic Acid

Abscisic acid (ABA) is a plant hormone that primarily functions to inhibit growth and promote dormancy, especially in seeds and buds. It is a critical component in regulating plant responses to environmental stress, such as drought or extreme temperatures.
When seeds do not germinate despite favorable conditions, abscisic acid is often the inhibiting factor. This hormone ensures seeds remain dormant until conditions are optimal for germination, thus enhancing the seed's survival chances.

• It helps close stomata to reduce water loss during drought.
• Promotes leaf abscission in adverse conditions.
• Inhibits gibberellin activity to delay germination.

Nitric Oxide

Nitric oxide (NO) is a versatile molecule that acts as a signaling compound in plants, influencing various physiological processes. It plays a critical role in plant stress responses, which can include inducing cell death in leaves under certain stress conditions.
Nitric oxide can lead to oxidative stress, which manifests as browning in leaves or other plant tissues.
This molecule is involved in:

• Defense mechanisms against pathogens.
• Modulation of plant hormone signaling.
• Regulation of stomatal closure.

Given its role, nitric oxide is crucial in helping plants adapt to changing environments and stress conditions.

Phototropism

Phototropism is the growth response of a plant in relation to light direction. Thanks to the hormone auxin, plants exhibit positive phototropism by bending towards light sources. This behavior ensures that the leaves receive optimal sunlight for photosynthesis, leading to energy production for growth and development.
During this process, auxins migrate to the plant's shaded side, causing those cells to elongate more. This results in the plant bending towards the light.
Phototropism is crucial for plant adaptation and survival, allowing them to efficiently utilize their surroundings for maximum energy intake.

Seed Germination

Seed germination is the process by which a seed develops into a new plant. It requires specific environmental conditions, such as adequate moisture, a suitable temperature, and oxygen. Hormones like gibberellin and abscisic acid play significant roles in regulating this process.
Gibberellin stimulates the transition from seed dormancy to active growth by activating enzymes that facilitate embryo growth. Conversely, abscisic acid acts as an inhibitor, ensuring seeds remain dormant during unfavorable conditions.
Farmers and gardeners manipulate these hormones to optimize germination rates and improve plant yields.

Fruit Ripening

Fruit ripening is a complex physiological process heavily influenced by ethylene. It involves a series of changes making the fruit palatable and ready for seed dispersal.
During ripening:

• Fruits soften due to the breakdown of cell walls.
• Acidity decreases, sweetening the fruit.
• Colors change as chlorophyll degrades and other pigments form.

Ethylene acts both as a hormone to trigger ripening in individual fruits and as a signal between fruits to synchronize ripening within clusters or baskets.
This knowledge aids in controlling post-harvest handling of fruits to prolong shelf life and reduce spoilage.