Question

The main photoreceptor that triggers phototropism is a ________.

a. phytochrome

b. cryptochrome

c. phototropin

d. Carotenoid

Short answer

C. Photoropin

Step-by-step solution

Step-1 Introduction 

Plants are rooted in a place and are unable to move from one place to another. These plants must respond to the environmental factors that surround them. Plants generally possess sophisticated systems to detect physical factors such as light, temperature, gravity, and physical touch. Receptors present in plant cells sense environmental factors, and the effectors receive the information generally through some chemical messengers which result in plant responses.

Step-2 Explanation

Phototropism is a process of response to light that is seen in plants. It is defined as a directional response that allows the plants to incline towards the light or away from the light. Light is important for every plant species on land for photosynthesis and so is the sensing of light.

The phototropin is the receptor (protein-based) that is mainly responsible for regulating the phototropic response. Photoreceptors usually consist of two parts that are a protein part and a light-absorbing portion. Flavin is the protein whereas chromophore acts as the light-absorbing portion. Phototropin belongs to the class of flavoprotein because the chromophore is bound to flavin protein covalently.

Phytochromes are the receptors that help the plants to absorb light.

Cryptochromes are the protein that helps to absorb light from the blue and ultraviolet region of the spectrum.

Carotenoid (a pigment) gives the characteristic colors to the fruits and vegetables.

Step-3 Final Answer

Therefore, option ‘C’ is the correct answer.

Phototropins are the receptor molecules that mediate the process of phototropism.