Question

Autumn colouration of leaves appear only in
A. Tropical regions
B. Evergreen forests
C. Temperate deciduous plants
D. Deserts

Answer 1

Hint: Autumn marks a transition of change of summer to winter, it occurs outside the tropical regions. It occurs when days become short and nights get longer. Plants get less sunlight and therefore there is transition in the colour of leaves in this season. Marked as the season named as autumn.

Complete Answer:
Let us find the correct answer:
Option -A- Tropical regions: Most of the tropical regions are located close to the equator. They get more exposure to the sunlight as compared to the other forest regions. Due to more sunlight exposure, it is not possible to cause the transition of summer to winter in plants by changing the colour of leaves.

Option -B- Evergreen forests: Evergreen forests are known to have needles in their plants which have a special coat, a protective coat which helps to save more water during summer and winter. They have more water stored in them and they remain attached to the plants for longer duration and therefore leaves do not shed. Therefore autumn is not seen in evergreen forests. This is an incorrect option.

Option -C- Temperate deciduous forests: In temperate forests, there is a marked transition from summer to winters which is known as autumn and is marked by the change of colouration of leaves and leaves fall from the trees.
- Plants in the temperate region in the growing season produce a hormone named auxin which prevents the formation of an abscission layer.
- When the days get shorter and darkness is elongated there is a decline in the production of auxin which leads to the formation of this layer at the base of leaves which cuts off the supply of water, nutrients and carbohydrates to leaves. This leads to a decrease in the chlorophyll pigment and therefore change in the colour of leaves to red, orange, yellow etc. So in temperate regions, autumn is seen.

Option -D- Deserts: In deserts plants get enough sunlight, the days are very long and each plant gets enough sunlight throughout the day. There is no such fall of leaves and therefore autumn is seen in deserts. So this is an incorrect option.

So, the correct option to this question is the option"C".

Note: The chlorophyll pigment is responsible for the green colouration of leaves in plants. During autumn chlorophyll pigment is decreased in the leaves due to increased darkness and this gives a signal which leads to shedding of leaves. The autumn is a beautiful season changing transition which is marked in plants.