8 - RESPONSES IN PLANTS Flashcards
What is a tropism?
The response of a plant to a directional stimulus
How do plants respond to directional stimuli?
By regulating their growth
What is a positive tropism?
Growth towards a stimulus
What is a negative tropism?
Growth away from the stimulus
What is phototropism?
The growth of a plant in response to light
Are shoots positively or negatively phototrophic?
They are positively phototropic as they grow towards the light
Are roots positively or negatively phototrophic?
They are negatively phototropic as they grow away from the light
What makes the plants respond to stimuli?
Growth factors
What are growth factors?
Chemicals that speed up or slow down plant growth
Where are growth factors produced?
In the growing regions of the plant
Which growth factors stimulate the growth of the shoots and how?
Auxins stimulate the growth of the plant by cell elongation which is where the cell walls become loose and stretchy and the cells become longer.
Which type of auxin do we need to know about, where is it produced and what does it do?
Indoleacetic Acid (IAA) is an important auxin produced in the tips of the shoots, and when it enters the nucleus of a cell its able to regulate the transcription of genes related to cell elongation and growth
How is IAA moved around the plant?
diffusion and active transport - short distances
through the phloem - long distances
What does an uneven distribution of IAA mean?
Uneven growth of the plant
How does the IAA work in the shoots?
It moves towards the more shaded parts of the shoots and roots, so there’s uneven growth. (It moves to the side of the shoot and the cells elongate and the shoot bends towards the light)
How does the IAA work in the roots?
IAA moves to the side of the root and the growth is inhibited so the root bends away from the light
How do plants detect light?
Using photoreceptors called phytochromes
What are phytochromes?
Molecules that absorb light
What are the two states of phytochromes?
Pr absorbs red light at 660nm, and Pfr absorbs far-red light at 730nm
Which states do the phytochromes convert into?
- Pr is quickly converted into Pfr when exposed to red light
- Pfr is quickly converted into Pr when exposed to far-red light
- Pfr is slowly converted into Pr when it’s darkness
Does daylight contain more red or far light
Red so more Pr is converted into Pfr
How do the differing amounts of Pr and Pfr control the responses to light?
By regulating the transcription of genes involved in these responses.
How does flowering occur?
high levels of Pfr stimulates
