Major plant hormones (& how to remember) | Control & Coordination | class 10| Biology | Khan Academy

Summary

This video breaks down the five major plant hormones—auxin, gibberellin, cytokinin, abscisic acid, and ethylene—explaining their functions through vivid, memorable stories. Auxin drives cell elongation and phototropism, gibberellin promotes stem and fruit growth, and cytokinin triggers cell division and branching. Abscisic acid acts as a growth inhibitor, helping plants survive drought and regulating seed germination, while ethylene is the key gas responsible for fruit ripening. By linking each hormone to quirky visual mnemonics, the video helps students easily recall their roles for exams.

Takeaways

• 😀 Auxin is a growth hormone responsible for **cell elongation** and is concentrated in the **growing regions** of the plant, such as the tips of shoots and leaves.
• 😀 Auxin plays a key role in **phototropism**, where plants bend toward light due to auxin accumulating more on the shaded side.
• 😀 Visualization for remembering auxin: Picture an **ox with an elongated head** to remember that auxin promotes **cell elongation** and is concentrated at the **tip** of the plant.
• 😀 Gibberellin also promotes **cell elongation** but is specifically responsible for **stem elongation**, and is crucial for the **growth of new leaves** and **fruit development**.
• 😀 Gibberellin can be used to make dwarf plants **grow taller**, and it also plays a role in **seed germination**.
• 😀 Visualization for remembering gibberellin: Picture people talking **gibberish** to a rice plant, causing it to grow taller, which helps recall its function in **stem elongation**.
• 😀 Cytokinin is a growth hormone that promotes **cell division** and is essential for the formation of new cells, leaves, and branches in plants.
• 😀 Cytokinin is also involved in **branching** and ensures that plants can grow new cells and new parts.
• 😀 Visualization for remembering cytokinin: Break down **cytokinin** into **'cyto' (cell)** and **'kinin' (division)**, and imagine a **key entering your eyes**, causing them to split in two.
• 😀 Abscisic acid is a **growth inhibitor** that prevents plant growth and is responsible for **wilting of leaves**, especially during drought conditions when it helps close the stomata to conserve water.
• 😀 Ethylene is a **gas hormone** involved in **fruit ripening**. It breaks down the cell walls, making fruits softer and sweeter, and accelerates ripening in surrounding fruits.
• 😀 Visualization for remembering ethylene: Imagine eating **spicy Thai food** (which causes **gas**), and that gas causes **bananas to ripen**, helping to associate ethylene with **fruit ripening**.

Q & A

What is the primary function of auxin in plants?

Auxin is a growth hormone responsible for cell elongation, especially in the tips of plant shoots, leaves, and roots. It also plays a role in phototropism, where plants bend toward light.

How does auxin contribute to phototropism?

When light shines on a plant, auxins move away from the light, accumulating on the shaded side. This results in greater elongation on the shaded side, causing the plant to bend toward the light.

What is the memory trick associated with auxin and how does it help with retention?

The memory trick involves imagining an ox with an elongated head. The elongated head helps remember that auxin causes cell elongation, particularly at the tip of the plant, and its connection to phototropism.

What does gibberellin primarily affect in plants?

Gibberellin is a growth hormone that primarily affects **stem elongation**. It promotes the growth of plant stems, making them taller, and is also involved in fruit enlargement and seed germination.

How does gibberellin impact fruit growth and seed germination?

Gibberellin helps fruit grow larger by promoting elongation of cells within the fruit. It also triggers seed germination by accumulating in the seed, signaling the start of growth.

What is the memory trick for remembering gibberellin's role in stem elongation?

The memory trick involves associating the word 'gibberellin' with 'gibberish.' Picture people talking gibberish to a rice plant, causing it to grow tall, which helps remember gibberellin’s role in stem elongation.

What role does cytokinin play in plant growth?

Cytokinin is responsible for cell division, which is essential for producing new cells in plants. This hormone is critical for the growth of new leaves, fruits, and branches.

How can cytokinin's function be remembered?

To remember cytokinin’s function, associate 'cyto' with 'cells' and 'kinin' with 'key.' Imagine a key entering your eyes (representing sight), causing your eyes to split into two, symbolizing cell division.

What does abscisic acid (ABA) primarily do in plants?

Abscisic acid is a growth inhibitor. It plays a critical role in preventing growth during stressful conditions, such as drought, by closing the stomata to conserve water. It also inhibits seed germination under unfavorable conditions.

How does abscisic acid help during drought conditions?

During drought, abscisic acid causes the stomata to close, reducing water loss from the plant. This helps the plant conserve water until better conditions are available.

What is the memory trick for remembering abscisic acid's role in wilting leaves?

The memory trick involves splitting 'abscisic' into 'abs' and 'sick.' Imagine a person with great abs getting seasick and throwing up leaves, which helps remember that ABA is associated with leaf wilting.

What is ethylene and how does it affect fruit ripening?

Ethylene is a gas that accelerates fruit ripening by breaking down cell walls and converting stored starches into sugars, making the fruit softer and sweeter. It also triggers a chain reaction, where one ripe fruit causes others nearby to ripen faster.

What is the memory trick to remember ethylene's role in fruit ripening?

The memory trick involves the phrase 'eat Thai.' Imagine eating spicy Thai food, causing stomach issues and releasing gas, which ripens a banana. This quirky visualization helps remember that ethylene is a gas involved in fruit ripening.