Problem 15 - Biology Today and Tomorrow with Physiology

Question

Match the observation with the hormone. $$ \text { ethylene } \quad \quad\quad\quad\quad \text { a. Your cabbage plants bolt (they form elongated flowering stalks.} $$ $$ \text { cytokinin } \quad \quad\quad\quad\quad \text { b. The potted plant in your room is leaning toward the window. } $$ $$ \text { auxin } \quad \quad\quad\quad\quad \text { c. The last of your apples is getting really mushy. } $$ $$ \text { gibberellin } \quad \quad\quad\quad\quad \text { d. The seeds of your roommate's marijuana plant do not germinate no matter what he does to them.} $$ $$ \text { abscisic acid } \quad \quad\quad\quad\quad \text { e. Lateral buds are sprouting. } $$

Step-by-Step Solution

Answer

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

Step 1: Matching Ethylene

Ethylene is a plant hormone that promotes fruit ripening and is involved in the aging of plants. It is famously known for its role in turning green bananas yellow. Therefore, ethylene would be responsible for observation c: "The last of your apples is getting really mushy."

Step 2: Matching Cytokinin

Cytokinins are a class of plant hormones that promote cell division in plant roots and shoots and also play a role in promoting lateral bud growth. So, cytokinin would be associated with observation e: "Lateral buds are sprouting."

Step 3: Matching Auxin

Auxin is a plant hormone involved in the regulation of plant growth, particularly in response to light (phototropism). This causes plants to lean towards light sources. Therefore, auxin corresponds to observation b: "The potted plant in your room is leaning toward the window."

Step 4: Matching Gibberellin

Gibberellins are plant hormones that regulate growth and influence various developmental processes, including stem elongation, germination, and flowering. Hence, gibberellin is related to observation a: "Your cabbage plants bolt (they form elongated flowering stalks)."

Step 5: Matching Abscisic Acid

Abscisic acid is known for its role in inhibiting growth and promoting seed dormancy. It prevents seeds from germinating under inappropriate conditions. Therefore, abscisic acid matches observation d: "The seeds of your roommate's marijuana plant do not germinate no matter what he does to them."

Key Concepts

Ethylene

Ethylene is a gaseous plant hormone that plays a crucial role in the lifecycle of a plant, particularly during fruit ripening and aging. Often referred to as the "fruit ripening hormone," ethylene is responsible for the softening of fruits, turning them from hard to mushy.

• It also influences leaf abscission, which is the shedding of leaves, flowers, or fruits.
• Ethylene is unique because it acts as a gas, allowing it to easily diffuse throughout the plant and even into the air around it.

In practical terms, when you leave a banana next to an apple, the ethylene emitted by the banana will hasten the ripening of the apple. This is why, in the exercise, observation c is associated with ethylene.

Cytokinin

Cytokinins are a group of plant hormones that primarily encourage cell division, which subsequently leads to plant growth. These hormones are instrumental in promoting branching by encouraging the growth of lateral buds.

• They work in coordination with auxins to determine the balance of root and shoot development.
• Cytokinins can delay aging processes in plant tissues, extending the life of leaves and fruits.

The sprouting of lateral buds, as highlighted in the exercise (observation e), showcases how cytokinins are hard at work, turning potential growth regions into actual plants.

Auxin

Auxin is essential for the directional growth of plants. It facilitates phototropism, which is the plant's response to light, enabling them to grow towards a light source.

• This hormone is produced in the stem's tip, and its concentration can be uneven on different sides of the plant, causing it to bend.
• Auxin also plays a role in the elongation of cells, mostly found in young shoots and leaves.

This ability to steer plant growth towards light is captured in observation b of the exercise, where the potted plant leans toward the window.

Gibberellin

Gibberellins are involved in various developmental processes, significantly impacting stem elongation and flowering. They are particularly famous for their ability to make "dwarfed" plants grow taller.

• These hormones can break seed dormancy, prompting seeds to sprout under the right conditions.
• Gibberellins also aid in bolting, which is the rapid growth of stems before a plant flowers.

Observation a from the exercise where cabbage plants bolt exemplifies gibberellin's effect in action.

Abscisic Acid

Abscisic acid, often abbreviated as ABA, acts as a growth inhibitor in plants. It plays a pivotal role in maintaining seed dormancy, ensuring that seeds do not germinate until conditions are favorable.

• This hormone helps the plant respond to stress, such as drought, by closing stomata to prevent water loss.
• It counteracts the growth-promoting effects of other hormones like gibberellin.

Observation d in the exercise, where seeds fail to germinate, highlights the role of abscisic acid in regulating plant growth and ensuring survival under suboptimal conditions.