Control and Coordination 4 Flashcards
what is tropism
tropism can be defined as the movement of a plant in response to a stimuli. Plants show tropic movements to help them to adapt to different conditions and survive. So when a plant shows some growth movement, towards or away from a stimulus it is called tropism
The directional growth movement of plants due to external stimuli is called a tropic
movement. It can be either towards the stimulus, or away from it. For example, in case of
phototropic movement, shoots respond by bending towards. light while roots respond by
bending away from it.
what are nastic movements
nastic movements are fast, non directional response in plants to an external stimulus. Nastic movements are not growth related and do not involve hormones. These are caused due to changes in turgor pressure. They are temporary and reversible.
give an example of nastic and tropic movements
Nastic:
- Touch me not plant
When we touch the leaves of the sensitive plant, they begin to fold up droop. This is the immediate response to the external stimulus which is touch.
Tropic:
When a seed germinates, the
root goes down, the stem comes up into the air. This is dependent on the growth of the plant.
how do plants show these nastic movements?
(or)
How does the sensitive plant detect the touch, and how do the leaves move
in response?
The leaves of sensitive plant( mimosa pudica) is extremely sensitive to touch.
These leaves have a swollen base which is filled with water called pulvini. this base provides stiffness to the base and allows it to stand upright.
When the leaf is stimulated by touch, the water moves from one side of the pulvini to the other side. Cells from the lower half of pulvini lose water and become flaccid while the upper half of pulvini become turgid due to accumulation of water.This shifting of water from one side to the other causes the leaf to lose its stiffness and hence folds up and droops.
So the shifting of water is the actual cause of the folding up of leaf. It is a nastic movement
what is phototropism
Phototropism refers to the tropic movements as response of plants towards of away from the stimulus of light.
Which parts show phototropism(+ve/-ve)
The shoot shows positively phototropic movements towards light.
The root shows negatively phototropic movements away from light.
what is geotropism
The tropic upward and downward movement of plants,as a response, away or towards the earth’s gravitational pull as a stimulus is called geotropism.
The shoot is negatively geotrophic movement.
The root shows positively geotropic movement.
what is hydrotropism
The tropic movement of plants as a response towards or away from the stimulus of water is called hydrotropism. The shoot is negatively geotropic movement. The root shows positively geotropic movement.
What is thigmotropism
The tropic movement of plants as a response to the stimulus of touch/contact is called thigmotropism. The sweet pea plant’s tendrils grow show positive geotropic movements.
how does sweet pea show positive thigmotropism
Sweet-pea tendrils and other tendrils in other climbers show positively thigmotropic movements/ sensitive to touch. When the tendril comes in the contact with the support, the auxins shift to the portion of the tendril that is not in contact with the support. The growth-promoting auxins, as it is concentrated in the part away from the tendril, this part grows more than the part in contact with support. This causes the tendril to coil around the support
What is chemotropism. give example
The plants tropic movements in response to a chemical stimulus is called chemotropism.
The growth of pollen tubes towards ovules. The ovules secrete certain substances that the pollen tube senses and grows towards it.
what is negative and positive tropism?
When the plant part shows tropism in the same direction as that of the stimulus, then it is called positive tropism.
When the plant part shows tropism in the direction opposite to that of the stimulus, then it is called negative tropism.
what is the difference between tropic and nastic movements
tropic movements
-it is slow
- it is directional
-it is growth related
- it regulated by hormone action
-growth under the influence of auxins is the cause of movement
nastic movements
-it is fast
- it is non directional
- it is not growth related
- it not regulated by hormone
-the shifting of water is cause of movement
