Hormone Harvest

Hormone Harvest [Higher tier]

The same hormones that bend a shoot to the light are big business. Farmers and growers use them to kill weeds, clone plants, and put ripe fruit on the shelf all year round. This module is the commercial toolkit: **auxins**, **gibberellins** and **ethene** at work. (All of it is **Higher tier**.)

The commercial toolkit

Three plant hormones, each with its own set of commercial jobs. The Higher-tier question almost always wants the **specific hormone matched to the specific use**, so learn them in these three columns.

What auxins are used for

Pick the TWO commercial uses of **auxins**.

• As a selective weedkiller against broad-leaved weeds
• In rooting powder, so stem cuttings grow roots quickly
• To ripen hard fruit once it reaches the warehouse
• To end seed dormancy so seeds germinate early
• To bring a crop into flower ahead of its natural season
• To increase the size of the fruit on the plant

Selective weedkillers

Weedkiller is the auxin use examiners push hardest on, because **selective** has a precise meaning here.

Why the crop survives

A farmer sprays a synthetic auxin across a whole field of wheat. The broad-leaved weeds die, but the wheat is unharmed. Why is that possible?

• The weedkiller is selective: it disrupts broad-leaved plants but not narrow-leaved ones like wheat
• The dose is small enough that no established plant is affected by it
• The auxin washes off the wheat leaves but sticks to the broad weed leaves
• Wheat has no roots for the auxin to reach, so it cannot be taken up

Name the hormone

A grower dips cuttings in a powder containing _____ so that they grow roots. Weeks later they use _____ to bring another crop's seeds out of dormancy. At harvest, the picked fruit is exposed to _____ to ripen it.

Out of season

A grower needs a batch of seeds to germinate in January, months before they naturally would. Which hormone, and what does it do to the seeds?

• Gibberellins, which end the seeds' dormancy so they germinate on demand
• Ethene, which ripens the seeds until they are ready to sprout
• Auxins, which make the seeds grow roots before they germinate
• No hormone will do it, because dormancy can only be broken by cold weather

Ethene and the supply chain

**Ethene** is a **gas** released by ripening fruit. It controls **cell division** and the **ripening of fruit**. Growers turn that into logistics. Fruit is picked while **unripe and hard**, so it survives transport without bruising, then exposed to **ethene** to ripen it just before it reaches the shops.

From orchard to shelf

Put the stages of a commercial fruit journey into the order a grower uses them.

• Pick the fruit while it is still unripe and hard
• Transport it a long distance without bruising
• Hold it in a store and add ethene gas
• The fruit ripens on schedule
• It reaches the shop shelf ripe and undamaged

Read the grower's diary

Tap the entry that describes a use of **gibberellins**.

• March:
• dipped 200 cuttings in rooting powder
• . April:
• treated the stored seed so it would germinate ahead of season
• . July:
• sprayed the cereal field to clear the broad-leaved weeds
• . September:
• gassed the picked pears in the ripening store

Match the job to the hormone

A year at the nursery

You run a plant nursery and fruit farm. Choose the right hormone at each point in the year.

• February. You want 300 identical copies of one prize shrub, and you have taken stem cuttings. What do you treat them with?
• April. Your cereal field is full of broad-leaved weeds, and you cannot afford to lose the crop. What do you spray?
• June. A second crop has to flower six weeks early for you to hit a contract. What do you use?
• September. Your pears must travel 300 miles and arrive ripe but unbruised. What is the plan?

In the exam

Harvest gathered. The Higher-tier hormone-use question almost always wants the **specific hormone matched to the specific use**: learn them as three clean pairs: • **Auxins** → **weedkillers** and **rooting powders**. • **Gibberellins** → **ending seed dormancy**, plus flowering and fruit size. • **Ethene** → controlling **fruit ripening** in storage and transport.

Explain the grower's year

A fruit and cereal grower uses plant hormones at three points in the year: rooting cuttings, clearing weeds from a cereal field, and getting picked fruit to the shops ripe. Name the hormone used for each and explain how each one works.

• Name a hormone for all three jobs, not just the one you remember best.
• For the weedkiller, explain what selective means, which plants die and which survive.
• For the cuttings, say what the auxin makes each cutting produce.
• For the fruit, say why it is picked unripe and what the ethene is added for.
• This is a Higher-tier topic, so match the specific hormone to the specific use.