quiz 4 mod 6 Flashcards
Define the terms phototropism, photoreceptors, and photomorphogenesis
Phototropism: The directional growth response of plants to light.
Photoreceptors: Molecules that absorb light within plant cells, like chlorophylls and phytochromes.
Photomorphogenesis: Light-triggered development in plants.
What lights are the most important colors in regulating a plant’s development?
Red and blue light are the most important colors in regulating a plant’s development.
What are the two major classes of light receptors, what light do they absorb, what plant processes do they regulate?
Blue-light photoreceptors: Absorb blue light, regulate phototropism and stomatal opening.
Phytochromes: Absorb red and far-red light, regulate seed germination, shade avoidance, chlorophyll synthesis, and leaf expansion.
Why are Lactuca sativa (lettuce seeds) excellent models for examining the effects of light on germination?
Because of their limited nutrient reserves, many lettuce seeds germinate only when light conditions are optimal, making them ideal for studying light-induced germination.
Explain the process of light-induced germination of lettuce seeds
Effect of far-red light: Inhibits germination compared to dark controls.
Effect of red light: Increases germination percentage maximally.
Effect of dark: Seeds remain dormant with phytochrome in the Pr form.
How does light absorption break seed dormancy in lettuce seeds?
Light causes the conversion of phytochrome from Pr to Pfr, which triggers germination processes.
Do all seeds require light to germinate?
No, not all seeds require light to germinate. Some germinate in darkness.
What is the effect of light on phytochrome isoforms?
Red light activates phytochrome (Pfr), while far-red light or darkness deactivates it (Pr).
The ultimate physiological effect induced by the phytochrome depends on which wavelengths (the one absorbed first or last)?
The ultimate physiological effect depends on the wavelengths absorbed last by the phytochrome.
Phytochromes and gene transcription: How does phytochrome Pfr work?
When phytochrome absorbs red light, it converts to the active Pfr isoform, which moves to the nucleus and stimulates gene transcription involved in photomorphogenesis
Effect of Pfr on genes for gibberellin (hormone) synthesis in Arabidopsis plants
Pfr activates genes for gibberellin synthesis during seed germination, leading to the breakdown of seed dormancy.
Understand the experimental design, variables, and controls
Experimental Design: Studying the effects of different light wavelengths (red, far-red, and darkness) on lettuce seed germination.
Variables:
Independent: Light wavelength (red, far-red, darkness).
Dependent: Germination percentage or rate.
Controls: Seeds kept in complete darkness as a control group to compare germination rates and conditions.
