NCERT Book Class 11 Biology Anatomy of Flowering Plants

ANATOMY OF FLOWERING PLANTS

6.1 THE TISSUES

A tissue is a group of cells having a common origin and usually performing a common function. A plant is made up of different kinds of tissues. Tissues are classified into two main groups, namely, meristematic and permanent tissues based on whether the cells being formed are capable of dividing or not.

6.1.1 Meristematic Tissues

Growth in plants is largely restricted to specialised regions of active cell division called meristems (Gk. meristos: divided). Plants have different kinds of meristems. The meristems which occur at the tips of roots and shoots and  produce primary tissues are called apical meristems (Figure 6.1). Root apical meristem occupies the tip of a root while the shoot apicalmeristem occupies the distant most region of the stem axis. During the formation of leaves and elongation of stem, some cells ‘left behind’ from shoot apical meristem, constitute the axillary bud. Such buds are present in the axils of leaves and are capable of forming a branch or a flower. The meristem which occurs between mature tissues is known as intercalary meristem. They occur in grasses and regenerate parts removed by the grazing herbivores. Both apical meristems and intercalary meristems are primary meristems because they appear early in life of a plant and contribute to the formation of the primary plant body.

The meristem that occurs in the mature regions of roots and shoots of many plants, particularly those that produce woody axis and appear later than primary meristem is called the secondary or lateral meristem. They are cylindrical meristems. Fascicular vascular cambium, interfascicular cambium and cork-cambium are examples of lateral meristems. These are responsible for producing the secondary tissues. Following divisions of cells in both primary and as well as secondary meristems, the newly formed cells become structurally and functionally specialised and lose the ability to divide. Such cells are termed permanent or mature cells and constitute the permanent tissues. During the formation of the primary plant body, specific regions of the apical meristem produce dermal tissues, ground tissues and vascular tissues.

6.1.2 Permanent Tissues

The cells of the permanent tissues do not generally

divide further. Permanent tissues having all cells

similar in structure and function are called simple

tissues. Permanent tissues having many different

types of cells are called complex tissues.

6.1.2.1 Simple Tissues A simple tissue is made of only one type of cells. The various simple tissues in plants are parenchyma, collenchyma and sclerenchyma (Figure 6.2). Parenchyma forms the major component within organs. The cells of the parenchyma are generally isodiametric. They may be spherical, oval, round, polygonal or  elongated in shape. Their walls are thin and madeup of cellulose. They may either be closely packed or have small intercellular spaces. The parenchyma performs various functions like photosynthesis, storage, secretion.

EXERCISES

1. State the location and function of different types of meristems.

2. Cork cambium forms tissues that form the cork. Do you agree with this statement? Explain.

3. Explain the process of secondary growth in the stems of woody angiosperms with the help of schematic diagrams. What is its significance?

4. Draw illustrations to bring out the anatomical difference between

(a) Monocot root and Dicot root

(b) Monocot stem and Dicot stem

5. Cut a transverse section of young stem of a plant from your school garden and observe it under the microscope. How would you ascertain whether it is a monocot stem or a dicot stem? Give reasons.

6. The transverse section of a plant material shows the following anatomical features - (a) the vascular bundles are conjoint, scattered and surrounded by a sclerenchymatous bundle sheaths. (b) phloem parenchyma is absent. What will you identify it as?

7. Why are xylem and phloem called complex tissues?

8. What is stomatal apparatus? Explain the structure of stomata with a labelled diagram.

9. Name the three basic tissue systems in the flowering plants. Give the tissue names under each system.

10. How is the study of plant anatomy useful to us?

11, What is periderm? How does periderm formation take place in the dicot stems?

12. Describe the internal structure of a dorsiventral leaf with the help of labelled diagrams.

Please refer to attached file for NCERT Class 11 Biology - Anatomy of Flowering Plants