Question

Plants grown in total darkness lack chlorophyll and thus appear white or yellow. What is this type of growth known as?
A. Etiolation
B. Heterotrophic
C. Stuntism
D. Euploid growth

Answer 1

Chlorophyll is one of the main pigments that is needed by the plants for the process of photosynthesis, the process of making their food. Plants that grow in absence of sunlight have retarded growth, long internodes, weak stem and premature fall of leaves and flowers.

Complete answer:
Growth is regarded as one of the most fundamental and conspicuous characteristics of living growth. It can be defined as an irreversible permanent increase in the size of an organ or its parts or even of individual cells. Sunlight, water, oxygen and nutrients are essential for growth.

Lack of sufficient light retards chlorophyll formation in the plant. It promotes slender growth with long internodes, leading to pale green leases due to the absence of chlorophyll pigment in them, spindle growth and premature drop of leaves and flowers cause etiolation condition.

Etiolated plants are mainly found outside only when plants are spaced too close to each other or when these plants are grown under tall plants. However, it is rather common in houseplants and also in plants that are grown in a greenhouse or in cold frames. These are usually deprived of sunlight. These plants are usually thin and tall and are susceptible to lodging.

The development of seedlings in the dark is known as "skotomorphogenesis" which leads to etiolated seedlings. Some of the changes that occur include:
1. elongation of leaves and stem
2. weakening of cell walls in stems and leaves
3. presence of longer internodes with few leaves per unit length of the stem
4. chlorosis

Etiolation can be controlled by the plant hormone named auxin, which is produces by the growing tip to maintain apical dominance. Auxin is active in light, when they are active they stimulate proton pumps in the cell wall and helps in the activation of expansin that usually weaken the cell wall and allow the cell to expand. Chloroplasts that have not been exposed to light are termed "etioplasts".

Therefore the correct answer is option ‘A’.

Note: De- etiolation is a series of physiological and biochemical changes that takes place in plant shoot when it is emerging from the ground or in response to sunlight after a period of sufficient exposure to light. It is also called greening.