Anatomy is the study of a plant’s internal structure. In a flowering plant, cells form tissues, and tissues are arranged into roots, stems and leaves. Studying a transverse section (T.S.) helps us identify how these organs are built and how dicot and monocot plants differ.
Table of Contents
Tissue Systems in Flowering Plants
Plant tissues are organised into three tissue systems: epidermal, ground and vascular.
1. Epidermal Tissue System
The epidermis is the outer covering of the plant. Its cells usually form a single, closely packed layer.
- Cuticle: A waxy layer on many above-ground parts that reduces water loss. Roots do not have a cuticle.
- Stomata: Openings in the leaf epidermis that allow gas exchange and regulate transpiration. Each opening is controlled by guard cells.
- Root hairs: Extensions of root epidermal cells that absorb water and minerals.
- Trichomes: Hairs on stems and other shoot parts that can help reduce water loss.
2. Ground Tissue System
Ground tissue includes tissues other than the epidermis and vascular bundles. It contains simple tissues such as parenchyma, collenchyma and sclerenchyma. Depending on the organ, ground tissue forms regions such as the cortex and pith. In a leaf, its photosynthetic tissue is called the mesophyll.
3. Vascular Tissue System
The vascular system contains two conducting tissues:
- Xylem transports water and minerals.
- Phloem transports food made by the plant.
Xylem and phloem together form a vascular bundle. In roots they occur on alternate radii, forming a radial arrangement. In typical stems they occur together in conjoint bundles.
A bundle is open when cambium is present between xylem and phloem, as in a typical dicot stem. It is closed when cambium is absent, as in a typical monocot stem.
Anatomy of Dicot and Monocot Roots
Dicot Root
From outside to inside, a typical dicot root has:
- Epiblema: The outer layer; some cells form root hairs.
- Cortex: Several layers of parenchyma cells.
- Endodermis: The innermost layer of the cortex. Its cells have suberin deposits called Casparian strips.
- Pericycle: A layer just inside the endodermis. Lateral roots arise from this region.
- Vascular tissues: Xylem and phloem occur alternately. A dicot root usually has two to four xylem patches.
- Pith: Small or inconspicuous.
Monocot Root
A monocot root has the same broad regions: outer layer, cortex, endodermis, pericycle, vascular tissues and pith. Its distinguishing features are numerous xylem bundles, usually more than six (polyarch), and a large, well-developed pith. Monocot roots do not undergo the usual secondary growth.
| Feature | Dicot root | Monocot root |
|---|---|---|
| Xylem bundles | Usually two to four | Usually more than six |
| Pith | Small or inconspicuous | Large and well developed |
| Secondary growth | May occur | Absent |
Anatomy of Dicot and Monocot Stems
Dicot Stem
A young dicot stem has an outer epidermis covered by a cuticle. Beneath it, a collenchymatous hypodermis helps support the stem. The cortex lies further inward, followed by an endodermis that is often called the starch sheath.
The vascular bundles form a ring. Each bundle is conjoint and open because cambium lies between its xylem and phloem. The centre of the stem contains a distinct pith.
Monocot Stem
A typical monocot stem has a sclerenchymatous hypodermis and a broad ground tissue. Its many vascular bundles are scattered through the ground tissue rather than arranged in a ring. Each bundle has a surrounding bundle sheath and is closed because it lacks cambium.
| Feature | Dicot stem | Monocot stem |
|---|---|---|
| Hypodermis | Collenchymatous | Sclerenchymatous |
| Vascular bundles | Arranged in a ring | Scattered |
| Cambium in bundles | Present; bundles open | Absent; bundles closed |
| Central pith | Distinct | Ground tissue is not divided into a distinct central pith |
Quick identification tip: If a stem T.S. shows vascular bundles arranged in a ring, identify it as a typical dicot stem. Scattered vascular bundles indicate a typical monocot stem.
Anatomy of Dicot and Monocot Leaves
Dorsiventral Dicot Leaf
A typical dicot leaf has different upper and lower surfaces, so it is called dorsiventral. It contains upper and lower epidermis, mesophyll and vascular bundles.
The lower epidermis generally has more stomata than the upper epidermis. The mesophyll has two regions:
- Palisade parenchyma: Closely arranged cells towards the upper surface.
- Spongy parenchyma: Loosely arranged cells with air spaces towards the lower surface.
Isobilateral Monocot Leaf
A typical monocot leaf is isobilateral. Stomata occur on both surfaces, and its mesophyll is not divided into separate palisade and spongy layers. In grass leaves, large bulliform cells on the upper epidermis help the leaf curl when water is scarce.
| Feature | Dicot leaf | Monocot leaf |
|---|---|---|
| Leaf type | Dorsiventral | Isobilateral |
| Stomata | Generally more on the lower surface | Present on both surfaces |
| Mesophyll | Palisade and spongy layers | Usually not differentiated into these layers |
| Venation | Typically reticulate | Typically parallel |
Key Terms to Remember
- T.S. (transverse section): A cut made across an organ to show its internal arrangement.
- Casparian strips: Suberin deposits in root endodermal cell walls.
- Cambium: Tissue between xylem and phloem in an open vascular bundle.
- Mesophyll: Photosynthetic ground tissue between the two leaf epidermal layers.
- Bulliform cells: Large cells in some grass leaves that help them respond to water stress.
Check Your Understanding
- Name the three tissue systems of a flowering plant.
- How can you distinguish a dicot root from a monocot root in T.S.?
- What does the arrangement of vascular bundles tell you about a stem?
- How does the mesophyll of a dicot leaf differ from that of a monocot leaf?
- What is the function of root hairs?
Answers: (1) Epidermal, ground and vascular. (2) Compare the number of xylem bundles and size of the pith. (3) A ring suggests a typical dicot stem; scattered bundles suggest a typical monocot stem. (4) Dicot mesophyll has palisade and spongy regions; monocot mesophyll is usually undifferentiated. (5) They absorb water and minerals.
For all chapters, visit the CBSE Class 11 Biology – Complete Study Guide.
Frequently Asked Questions
What is plant anatomy?
It is the study of the internal structure of plants.
What are the three tissue systems of a plant?
Epidermal, ground and vascular tissue systems.
What is the epidermal tissue system?
It is the outer protective covering, including epidermis and structures such as stomata and hairs.
What is the ground tissue system?
It includes most tissues other than epidermis and vascular bundles, such as cortex, pith and mesophyll.
What forms the vascular tissue system?
Xylem and phloem form the vascular tissue system.
What does xylem transport?
Xylem primarily transports water and dissolved minerals.
What does phloem transport?
Phloem distributes sugars and other organic substances through the plant.
What is a vascular bundle?
It is a strand of xylem and phloem within a plant organ.
What is a cambium?
Cambium is a lateral meristem that forms new vascular tissue during secondary growth.
What is the main difference between a dicot and monocot stem?
Dicot stem vascular bundles are generally arranged in a ring; monocot stem bundles are usually scattered.
How do dicot and monocot roots differ in xylem arrangement?
Dicot roots often have fewer xylem arms and a small or absent pith; monocot roots usually have many xylem arms and a large pith.
What is mesophyll?
Mesophyll is the photosynthetic ground tissue between a leaf’s upper and lower epidermis.
What are bulliform cells?
They are large epidermal cells found in many grass leaves that help the leaf roll under water stress.
What is the function of stomata?
Stomata allow gas exchange and regulate much of the leaf’s water vapour loss.
What is meant by secondary growth?
It is an increase in plant girth due mainly to the activity of lateral meristems.