Lesson 1 of 13 · 6 min

Growth and why it never stops in plants

NCERT §13 (opening text) and §13.1–§13.1.1

Kavya's mango tree was planted by her grandfather and it is still getting taller and thicker. Her goat stopped growing years ago. Why does a plant never seem to finish?

The story this chapter follows: Kavya's farm through a growing season

From the rice nursery to the sugarcane rows, Kavya's farm is full of plants that never stop growing. Some of her rice seedlings shoot up thin and pale, the tea bushes nearby are plucked flat on top, and hard green bananas ripen in the store room within days. This chapter explains how plants grow, how that growth is measured, and which chemical messengers are behind each of these sights.

The lesson in notes

In short

Every plant cell descends from one zygote, yet a mature plant has roots, stems, leaves, flowers, fruits and seeds. Getting there takes two things working together, growth and differentiation, in a precise, ordered run of events; together they make up development.

The first step is seed germination. A seed germinates only when conditions in the environment favour growth; otherwise it stays in a period of suspended growth or rest, and resumes metabolism once conditions improve.

Growth is an irreversible, permanent increase in the size of an organ, its parts or even a single cell. It is usually accompanied by metabolic processes, both anabolic and catabolic, that consume energy. A leaf expanding is growth; wood swelling in water is not, because it is reversible and not driven by metabolism.

Plants keep the capacity for unlimited growth throughout their life because they have meristems at certain places. Meristem cells divide and perpetuate themselves; their products soon stop dividing and make up the plant body.

This form of growth, in which the meristem keeps adding new cells to the body, is called the open form of growth.

The root apical meristem and shoot apical meristem cause primary growth, lengthening the plant along its axis.

Later in life, dicots and gymnosperms add lateral meristems, the vascular cambium and the cork cambium. These thicken the organs where they work, so the plant widens as well as lengthens. This is secondary growth.