Question

An apparatus used to demonstrate phototropism is
a. Heliotropic chamber
b. Clinostat
c. Arc auxanometer
d. Potometer

Answer 1

Hint: The seedling stem held in this would be bent towards the light source, while the seedling kept open under sunlight in a pot grows straight. It indicates that the stem is phototrophic in a positive way and demonstrates bending to unidirectional light.

Complete answer:
Phototropism was first studied by Charles Darwin in 1880 in Canary Grass and oat coleoptiles. Later on F.W. The role of auxins in this phenomenon was proposed by Went in 1923. Experimental method to show positive phototropism in shoot tips is a darkened black box. The black box is getting a tiny window at one side. A well-watered potted plant is located inside the box. This is known as a heliotropic chamber or a phototrophic chamber. For about 24 hours, the window is kept locked and the plant shows normal growth. When the window is kept open, it is noticed after two days, that the shoot tip bends and develops towards light demonstrating that it is positively phototropic.

Hence, the correct answer is option (A).

Additional information:
From east to west, heliotropic flowers watch the sun's motion through the sky. At night, Daisies or Bellis perennis close their petals but expand in the light of the morning and then follow the sun as the day advances. The flowers can assume a random orientation during the night, while they turn eastward again at dawn, where the sun rises. Motor cells in a flexible section just below the flower, called a pulvinus, perform the motion. The motor cells are specialised in pumping potassium ions, changing their turgor strength, into neighbouring tissues. The segment flexes and due to a turgor rise, the motor cells at the shadow side elongate. Turgor-mediated heliotropism is deemed to be this. Heliotropism may occur by irreversible cell expansion that generates unique growth patterns in plant organs that lack pulvini. It is considered that this type of heliotropism is growth-mediated. A reaction to light from the sun is heliotropism.

Note: In specific, by raising pollination, fertilisation success, or perhaps seed growth, particularly in the spring flowers, flower heliotropism may increase reproductive success. A few solar tracking plants are not strictly heliotropic: the shift of orientation in those plants is an intrinsic circadian motion caused by light that, if the light cycle is disturbed, persists for one or more cycles.