Chapter 13: Plant hormones Flashcards
What is positive phototropism?
The ability of a plant stem to grow towards the light
What is positive gravitropism?
The ability of a plant stem to grow downwards
What is an auxin?
A type of plant hormone responsible for cell elongation
How do plants grow towards light or water?
Auxins concentrate on the side of the stem opposite to the direction the stem needs to curve in, causing cells there to elongate and the stem to curve
Where are auxins produced?
Tips of shoots and roots
How do selective weedkillers work?
They can be sprayed on a lawn and only kill broadleaved plants because they have a higher surface area to absorb the weedkiller. They cause some cells to grow uncontrollably and some to stop growing, killing the plant
How does rooting powder work?
Plant cuttings are dipped into rooting powder and placed into the soil. Rooting powder contains auxins, which help the cutting form roots. This is essentially artificial asexual reproduction
How does tissue culturing work?
Small numbers of cells are removed from the parent plant. They are then placed into a growth medium and grow into cloned copies
How does fruit ripening work?
Fruits are picked in the tropics when they are unripe, stopping them from rotting on the boat journey. They are sprayed with ethene (a chemical that causes fruits to ripen faster) a short time before arriving so that the fruit is beginning to ripen when it reaches supermarkets.
How do gibberellins work?
Gibberellins are used by plants for stem elongation, seed dormancy and germination. They are used in agriculture to begin germination and help plants flower and increase the size of their fruit
What is the effect of removing the tip of a plant’s shoot?
The plant does not bend towards the light, showing that auxins are produced in the tip
What is the effect of covering up the tip of a plant’s shoot?
The plant does not bend towards the light, showing that the light-sensitive cells are in the tip of the shoot
What is the effect of inserting an impermeable barrier into one side of the shoot?
If the barrier is inserted on the light side, the plant will grow towards the light; if it’s inserted on the dark side, the plant will not. This shows us that auxins diffuse down the dark side of the shoot
What is the effect of inserting a permeable gelatine barrier into the dark side of the shoot?
The plant still bends towards the light, showing that auxins can diffuse through gelatine
What is hydrotropism?
A plant’s ability to grow roots towards water. This can overpower gravitropism
