Question

Match the observation with the hormone. $$ \text {ethylene } \quad \quad \text {a. Homegrown seedless grapes are smaller than grocery store grapes.} $$ $$ \text {cytokinin} \quad \quad \text {b. The potted plant in your room is leaning toward the window.t} $$ $$ \text {auxin } \quad \quad \text {c. The last of your apples is getting really mushy.} $$ $$ \text {gibberellin } \quad \quad \text {d. The fresh seeds of your friend's marijuana plant do not germinate no matter what he does to them.} $$ $$ \text {abscisic acid } \quad \quad \text {e. Lateral buds are sprouting.} $$

Short answer

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

Step-by-step solution

Ethylene

Observe that ethylene is known for its role in fruit ripening and causing the aging process in plants. Match observation (c), where the apple is getting mushy, which indicates over-ripening, to ethylene.

Cytokinin

Cytokinins promote cell division and growth, particularly in shoots and lateral buds. Match observation (e), related to lateral bud sprouting, to cytokinin.

Auxin

Auxin is involved in plants' growth responses towards light, known as phototropism. Match observation (b), where the plant is leaning toward the window, to auxin.

Gibberellin

Gibberellins promote stem elongation and seed germination. Match observation (a), concerning the growth differences in grape size, to gibberellin.

Abscisic Acid

Abscisic acid is known for inhibiting seed germination and promoting dormancy. Match observation (d), where seeds do not germinate, to abscisic acid.

Key concepts

Ethylene

Ethylene is a unique plant hormone known for its role in the fruit ripening process. This gaseous hormone is crucial for triggering various physiological changes within the plant.
It accelerates the ripening of fruits by stimulating the production of enzymes that convert starches and acids in the fruit into sugars. This process is what makes the fruit softer and alters its color and taste.
Beyond ripening, ethylene also plays a role in the aging of plants, a process known as senescence. Its overproduction can cause fruits and flowers to mature rapidly and rot, as indicated when an apple becomes mushy if left for too long.

• Triggers fruit ripening.
• Promotes aging and senescence in plants.
• Can result in faster deterioration of harvested produce.

Auxin

Auxin is a vital plant hormone mainly responsible for growth in response to light, a phenomenon known as phototropism. This hormone is distributed unevenly in plants, causing cells on one side of the plant to grow faster than those on the opposite side.
This differential growth causes the plant to bend towards its light source, such as a window in a room. Auxins also facilitate cell elongation and are crucial for maintaining apical dominance, where the main, central stem of the plant grows more vigorously than the side stems.

• Promotes plant growth towards light (phototropism).
• Involved in cell elongation in stems and roots.
• Maintains apical dominance in plants.

Gibberellin

Gibberellins are a group of hormones that have critical roles in promoting plant growth, particularly in stem elongation, seed germination, and flowering.
These hormones can overcome seed dormancy, helping seeds to sprout by breaking down food reserves within the seed. Additionally, gibberellins influence the size of fruits, explaining why homegrown seedless grapes may be smaller compared to commercially grown ones where gibberellin sprays are used to boost fruit size.

• Promotes stem and fruit growth.
• Stimulates seed germination.
• Increases fruit size in commercial agriculture.

Cytokinin

Cytokinins are a class of plant hormones that facilitate cell division and growth, particularly in young plant tissues.
They are significant in promoting the growth of lateral buds, demonstrating their ability to influence the overall architecture of a plant. This leads to bushier plants as more side shoots are developed. Cytokinins also delay the process of senescence, making them important for the maintenance of plant health and longevity.

• Promote cell division and growth.
• Encourage lateral bud development.
• Delay leaf senescence, contributing to plant vitality.

Abscisic Acid

Abscisic acid (ABA) is often referred to as a "stress hormone" as it plays a key role in plant responses to stress and dormancy.
It functions primarily to inhibit growth and promote dormancy in seeds, ensuring that they only germinate under favorable conditions. By controlling stomatal closure on leaf surfaces, ABA helps plants conserve water during drought conditions.
The presence of abscisic acid in seeds is what typically hinders their germination when environmental conditions are unsuitable for growth.

• Inhibits seed germination and promotes dormancy.
• Induces stomatal closure for water conservation.
• Essential in plant stress responses to adverse conditions.