Maharashtra Board Class 12 Biology Chapter 7 Plant Growth and Mineral Nutrition PDF Download

Plant Growth and Mineral Nutrition

Do you think that the growth is property of living beings only?

Is there any difference between plant growth and animal growth?

7.1 Plant Growth

Growth is one of the characteristic features of living organisms. Growth as a phenomenon has two aspects viz. quantitative and qualitative. Quantitative aspect speaks for an increase in the length, breadth, size, volume, body mass or dry weight and number of cells. Growth as a quantitative change is a final end product of successive metabolism.

Qualitative aspect talks about the change in the nature of growth where development is an ordered change or progress while differentiation leads to higher and more complex state. Growth thus can be defined as permanent, irreversible increase in the bulk of an organism, accompanied by the change of form.

In multicellular (vascular) plants, growth is indeterminate and occurs throughout the life indefinitely. It is restricted to some specific region called meristems which are the regions where new cells are constantly and continuously produced. Meristems are of three types based on location viz. Apical, Intercalary and Lateral.

Apical Meristem: In vascular plants, growth is restricted to the apices of root and shoot. It is responsible for growth in length/height and the differentiation or cell types. It contributes to the primary growth.

Intercalary Meristem: It is located at the node or at the base of internode of stem. It is primarily responsible for increasing length of internodes and also for formation of leaf primordia and lateral buds.

Lateral Meristem: It is located laterally along the axis of dicotyledons and gymnosperms. It is located as strip in the vascular bundles of stem of dicots. It is called vascular cambium. It is responsible for increase in the girth of the stem due to addition of secondary vascular tissues.

Teacher's Note

Meristems are special parts of plants where new cells are always made. Think of it like a factory in your school that makes new uniforms every day. The root tip and stem tip are meristems that help the plant grow taller.

Exam Trick

Remember: Apical = top, Lateral = side, Intercalary = middle. Apical meristem makes plants tall. Lateral meristem makes them fat/thick. Use "ALI" to remember all three.

Points to Remember

Meristems are regions where new cells are made.
Apical meristem is at the tip of roots and stems.
Lateral meristem makes the stem thicker.
Intercalary meristem is between the nodes.
Growth in plants never stops throughout their life.

7.2 Phases of Growth

The cells in the meristem divide, enlarge and get differentiated. Corresponding to these three stages, there are three phases of growth:

A. Phase of Cell Division/Formation: Cells of meristem are thin walled, non-vacuolated having prominent nucleus and granular cytoplasm. Meristematic cell undergoes mitotic division to form two new cells. One cell remains meristematic and the other cell undergoes enlargement and differentiation. In this phase, rate of growth occurs at a slower pace (Lag phase).

B. Phase of Cell Enlargement/Elongation: The newly formed cell becomes vacuolated, osmotically active and turgid due to absorption of water. The turgidity results in the enlargement of cell both lengthwise and breadthwise. In this phase new wall materials and other materials are synthesized to cope up with the enlargement. The growth rate in this phase occurs at an accelerated pace (exponential or Log phase).

C. Phase of Cell Maturation/Differentiation: The enlarged cell now becomes specialized to perform specific function and attains maturity both morphological and physiological. In this phase, rate of growth slows down and comes to a steady state (stationary phase).

Teacher's Note

Plants grow in three steps like making a cup from clay. First you make the clay pieces, then you stretch and shape them, and finally you polish and decorate them to make them special. Each step takes different time.

Exam Trick

Remember the three phases: Division = slow, Elongation = fast, Maturation = stop. Think "Slow-Fast-Stop" like a traffic light cycle. This is "Lag-Log-Stationary" phase.

Points to Remember

Phase 1 is cell division where growth is slow.
Phase 2 is cell elongation where growth is fastest.
Phase 3 is maturation where growth slows down again.
All three phases happen one after another in growing plants.
Each cell in a meristem goes through all three phases.

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