(Paper 2) 5.5 Homeostasis: Plant hormones Flashcards
(22 cards)
What is a tropism?
A growth response of a plant to a stimulus.
What is phototropism?
A plant’s growth response to light.
What is a positive tropism?
When a plant grows towards a stimulus (e.g., stem grows towards light).
What is a negative tropism?
When a plant grows away from a stimulus (e.g., root grows away from light).
What part of the plant shows positive phototropism?
The stem – it grows towards the light.
What part of the plant shows negative phototropism?
The root – it grows away from the light.
What are auxins?
A group of plant hormones that control growth, made in the tips of stems and roots.
How do auxins cause growth?
By promoting cell division and causing cell elongation (cells get longer).
How do stems and roots respond differently to high auxin concentrations?
In stems, cells grow more.
In roots, cells grow less.
What causes a stem to grow towards the light?
More auxin accumulates on the shaded side, making cells elongate more there, so the stem bends toward the light.
What causes a root to grow away from the light?
More auxin on the shaded side inhibits growth, so the root bends away from the light.
What happens when the tip is removed from a seedling?
No auxin is produced → no growth.
What happens when equal light reaches both sides of a seedling tip?
Auxin is evenly distributed → even growth on both sides.
What happens when light reaches one side of a seedling tip?
More auxin builds up on the shaded side → that side grows more → the stem bends toward the light.
What is geotropism (also called gravitropism)?
A plant’s growth response to gravity.
What is positive geotropism?
Growth towards gravity (e.g., roots growing downwards).
What is negative geotropism?
Growth against gravity (e.g., stems growing upwards).
What causes geotropism in plants?
An unequal distribution of auxin in response to gravity.
What happens to auxin in a horizontally placed root?
Auxin builds up on the bottom side, causing those cells to grow less, so the root bends downward.
What happens to auxin in a horizontally placed stem?
Auxin builds up on the bottom side, causing those cells to grow more, so the stem bends upward.
Why do roots grow downward in geotropism?
More auxin on the bottom side inhibits cell growth, causing the root to bend toward gravity.
Why do stems grow upward in geotropism?
More auxin on the bottom side stimulates cell growth, causing the stem to bend upward, away from gravity.
