Plant Hormones Flashcards

All 14 cards in this deck

Where in a plant shoot is auxin produced?

In the tip of the shoot. It then moves down the shoot to the region where cells elongate.

What are the steps that make a shoot bend towards light?

e.g. a shoot lit from the left only

1. Auxin from the shoot tip moves to the shaded side — here, the right side.
2. Auxin makes those cells elongate more — the right-side cells get longer.
3. The shoot bends towards the light — it bends to the left (positive phototropism).

What are the steps that make a root grow downwards?

e.g. a seedling laid on its side

1. Auxin collects on the lower side of the root.
2. In roots auxin inhibits cell elongation, so the lower cells stay short and the upper cells elongate.
3. The root bends downwards, in the direction of gravity (positive gravitropism).

A shoot tip is cut off and the shoot stops growing; when the tip is placed back on, the shoot grows again. What conclusion can be made?

Auxin (the substance that causes shoot growth) is produced in the tip of the shoot, and the tip controls growth.

True or false? On a graph of auxin concentration against growth, the more auxin there is, the more a plant grows.

False. Growth increases up to an optimum concentration; higher concentrations slow or inhibit growth, and very high concentrations (as in weedkillers) kill the plant.

What is a selective weedkiller?

A weedkiller containing auxins that kills broad-leaved weeds but leaves narrow-leaved crops and grasses unharmed.

How do auxin-based weedkillers kill weeds?

They make the weeds grow too fast (uncontrolled growth), so the weeds overgrow and die, reducing competition for the crop.

What is rooting powder and which hormone does it contain?

A powder containing auxins, dipped onto cuttings so they grow roots and develop into new plants.

Give three commercial uses of gibberellins.

To make seeds germinate (end dormancy), to control fruit and flower formation, and to produce seedless fruit.

Which plant hormone is used commercially to ripen fruit?

Ethene.

Why do growers pick fruit unripe and treat it with ethene later?

Unripe fruit is firm, so it is damaged less during transport and storage; ethene then ripens it just before it is sold.

True or false? Seedless fruit is produced by spraying plants with ethene.

False. Seedless fruit is produced using gibberellins; ethene is used to ripen fruit.

In an investigation where several shoots are each lit from one side, name two variables that must be controlled.

Same light intensity (lamp at the same distance) for each shoot, and same temperature.
Also accept same volume of water, same species/age of shoot.

True or false? Repeating an investigation into shoot growth using more shoots makes the results more reliable.

True. A mean can be calculated and anomalous results identified.