Plant Regulation and Control Flashcards
how do plants compensate for their relative immobility ?
by modifying their growth in response to stimuli from the environment
what are Internal factors ?
known as Phytohormones, these are hormones found in plants.
what are External factors ?
environmental factors such as light intensity, temperature, day length & gravity.
how do hormones affect growth by causing as change in?
- Changes in cell division and elongation.
- Death in some parts of the plant.
A hormone’s influence growth is by?
– Changing enzyme activity or permeability of membranes.
– Inhibiting the synthesis of proteins.
What is positive tropism?
– Growth towards a stimulus
What is negative tropism?
– Growth away from a stimulus
Types of Tropisms?
– Phototropism ( towards light)
– Geotropism (roots go down towards gravity)
– Thigmotropism (touch)
– Photoperiodism (flowering)
what is Phototropism?
– is when a plant moves in response to light.
– Stem grows towards light – positive phototropism.
– Roots grow away from light – negative phototropism
what is geotropism?
– is the growth response of a plant in response to gravity.
– Roots exhibit positive geotropism
– while stems and leaves exhibit negative geotropism.
what is Thigmotropism?
is the response of a plant to physical contact (touch).
• Plants that cling to physical structures such as walls exhibit positive thigmotropism.
• Ex. Tendrils of vines wrapping around things, venus fly traps
Hormones are Classified into 5 Groups which are?
– Auxins – Cytokinins – Gibberellins – Abscisic acid – Ethylene
What is the role of Auxin?
– Controls stretching of plant cells
– Stimulate growth of roots that grow out of a stem
– At high concentrations auxins inhibits root growth.
– Inhibits side branch growth – Apical dominance
what happens when there is a Removal of Apical Bud ?
, the lateral buds grow and the plants become thicker.
– If you cut off the tip of a seedling, there will not be any growth or bending of the plant.
what is the role of Cytokinins?
– Responsible for increase in cell division
– Breaks dormancy
– Produced in the roots
– Promotes cell division
what is the role of gibberellins?
Responsible for cell division and growth in cell size
what is ethylene?
is a gas that is released by ripening fruits that encourage the aging processes .
what is the role of Abscisic acid ?
– Responsible for dormancy of various types
– Causes the falling of leaves and fruits – ‘Abscission’
– Produced in older leaves, root cap and stem.
– Occurs in Autumn
what is Photoperiodism?
– When plants may respond to the length of daylight and dark.
– This can have an effect on the timing of flowering in a plant.
what are the 3 types of plants?
- short day
- long day
- day neutral
what do short day plants require?
– require an uninterrupted long period of darkness (long, dark nights) in order to flower.
– They typically flower in early spring.
Even just a flash of light during the long dark may be enough to stop the flowering
what do long day plants require?
- require short periods of darkness to flower (i.e. shorter nights).
- They usually flower in Summer.
what do day neutral plants require?
flowering does not depend on length of day or night
Circadian Rhythm?
- is any activity that follows a 24 hour cycle.
* For example, Mimosa pudica leaves are horizontal during the day but fall into a sleeping position at night
Nastic Movement?
• a response of plants and flowers to a stimulus which is not connected with the direction from which the stimulus comes, e.g. the closing of flowers at night
Trigger Plant?
When an insect lands on the centre of the flower, the tube jumps up to strike the insect, covering it with pollen which it then takes to another flower.
The “trigger” usually reset itself within about 20 minutes.
Vernalisation
?
In some plants the young plant cannot flower unless it has been exposed to a period of cold before spring growth.
A ‘cold naps’ or frost is needed to stimulate flowering.
This is why bulbs are often stored in the fridge before they are planted.
