Coordination in Plants Questions in English

(A) Plant tendrils exhibit $Thigmotropism$.
$Thigmotropism$ is the directional growth movement of a plant part in response to touch or physical contact with a solid object.
When tendrils come in contact with a support,the side in contact with the object grows slower than the side away from it,causing the tendril to coil around the support.

(C) When a potted plant is placed horizontally,the stem exhibits negative geotropism (or negative gravitropism).
This means the stem grows away from the pull of gravity.
Due to the redistribution of auxin,which accumulates on the lower side of the stem,the cells on the lower side grow faster than those on the upper side.
As a result,the stem bends and grows upwards,away from the ground.

(D) The shoot of a plant exhibits positive phototropism because it grows towards the light source.
It also exhibits negative geotropism (or negative gravitropism) because it grows away from the pull of gravity (upwards against the gravitational force).
Therefore,the correct combination is positive phototropism and negative geotropism.

(B) Phototropism is the growth of an organism in response to a light stimulus.
Positive phototropism is growth towards the light source,which is observed in the stem of the plant.
Negative phototropism is growth away from the light source.
The roots of a plant exhibit negative phototropism because they grow away from light and towards the soil (geotropism).

(A) Photonastic movement is a type of nastic movement in plants where the movement of plant parts,such as the opening and closing of flowers,occurs in response to changes in light intensity.
Jasmine $(Jasminum)$ flowers exhibit photonastic movement,as they typically open in response to the light conditions of the evening or night.
Sunflower exhibits heliotropism (solar tracking),not photonasty.
Therefore,the correct option is $A$.

(C) The movement shown by $Mimosa$ $pudica$ (touch-me-not plant) in response to touch is known as thigmonasty or seismonasty.
This is a non-directional movement where the plant leaves fold inward upon being touched.
Unlike tropisms,which are directional growth movements,thigmonastic movements are independent of the direction of the stimulus.
Therefore,the correct option is $C$.

(C) The movement of a plant part in response to light is known as $phototropism$.
Sunflower flowers exhibit a directional growth movement towards the Sun,which is a classic example of $phototropism$.
$Chemotropism$ is movement in response to chemicals.
$Hydrotropism$ is movement in response to water.
$Photonasty$ is a non-directional movement in response to light,which is not the case for the directional tracking of the Sun by sunflowers.

(C) The movement of plant parts in response to temperature is known as $Thermonasty$.
$Photonasty$ is the movement in response to light.
$Thigmonasty$ is the movement in response to touch.
$Tropism$ is a directional growth movement in response to a stimulus.

(A) The opening of a lotus flower in response to light is known as $Photonasty$.
$Photonasty$ is a nastic movement in which a plant part moves in response to light intensity.
Since the lotus flower opens in the morning due to the presence of sunlight,it is a classic example of $Photonasty$.

(A) The opening of a tulip flower is a response to changes in temperature.
When the temperature rises,the flower opens,and when the temperature drops,it closes.
This type of non-directional movement in plants in response to temperature is known as $Thermonasty$.