Chapter 29.5- The environmental context of growth and development Flashcards
What is tropism?
tropism is the bending of an organism in response to light or gravity
Plant stems are described as positively photrophic and negatively gravitropic. Define these terms.
Positively phototrophic: they bend towards light
Negatively gravitrophic: they grow against gravity
How did Charles Darwin experiment: How do plants detect light? and what was the conclusion of the experiment?
Experiment 1: the tip of the plant was cut off and placed on a glean block to absorb chemicals when gelatin block placed on the plant, the plant grew upwards.
Experiment 2: When the gelatin block was placed on an angle the plant bent
Conclusions: A signal is produced at the tip of the plant and travels down to the roots Auxin.
What is auxins relationship to exposure to light?
The angle from which light hits a plant, effects the concentration of auxin which determines the direction of plant growth.
The area of the plant more exposed to light leads to the increase of auxin. The auxin then moves to an area of low auxin (shaded area). Causing the plant to grow in that area.
What is auxin relationship to gravity?
Higher concentrations of auxin in lower areas of plant stem causes the stem to grow upwardly and roots to grow downwards
How does high concentration of auxin effect plant roots?
it decreases cell elongation and triggers hormone ethylene
How are plants able to detech what is up and what is down?
statoliths are starch filled organelles that detech gravity from applied pressure
How does red light vs. far red light effect seed germination?
red light: stimulations germination
far red light: inhibits germination.
The effects of far red light can be overcomed by more exposure to red light. Experimentation shows that lettuce seeds exposed to far light last inhibited.
What is phytochrome? when is it in a active form? How does it aid germination?
Def: a photoreceptor that switches between two forms depending on light exposure.
It is in active from when its exposed to red light and changes into form (Pfr) which absorbs far-light
When in its active form it moves to the nucleus altering gene expression then seed germination occurs.
How does phytochrome allow dormant seeds to detect the presence of another plant overhead?
the production of active phytochrome in is dependent on the ratio of red light and far red light. When the ratio is off phytochrome becomes in active.
Why are seedlings produced in the dark taller and produce less leaves than ones produced in light?
Because they are less exposed to light the plant focuses energy on growing the length of the plant in order to reach light instead of leaves.
How do roots respond to scarcity of water?
When a plant is in a drough roots grow further into the ground and branch less in order to dry to hit moisture.
How does the root cap help detect water drought in plants?
In the absence of water root caps produce abscisic acid a hormone that stimulates enlongation and triggers the stomata to close.
How does wind effect the growth pattern of plants ?
results in shorter but stronger stems
