Anatomy of Flowering Plants — Biology Class 11 Notes (CBSE & HBSE)
Free NCERT Biology notes for Anatomy of Flowering Plants (Class 11) on Siksha Sarovar, aligned to CBSE and Haryana Board (HBSE). This chapter is broken into 3 topics with clear explanations, formulas, solved examples and board-pattern practice — free to read, no sign-up required.
Board exam focus — Anatomy of Flowering Plants (CBSE & HBSE)
This chapter explores the internal structure (anatomy) of angiosperms — the plant tissues (meristematic and permanent), the tissue systems (epidermal, ground and vascular), the internal organisation of dicot and monocot roots, stems and leaves, and the process of secondary growth that increases girth in dicots through the activity of the vascular and cork cambium.
The Tissues — Meristematic and Permanent
What is a Tissue?
A tissue is a group of cells having a common origin and usually performing a common function. Plant tissues are broadly meristematic (dividing) or permanent (non-dividing).
Meristematic Tissues
Meristems are groups of actively dividing cells responsible for growth.
| Meristem | Position | Function |
|---|---|---|
| Apical meristem | At root and shoot tips | Increase in length (primary growth) |
| Intercalary meristem | At the base of internodes/leaves | Elongation (common in grasses) |
| Lateral meristem | Along the sides (vascular & cork cambium) | Increase in girth (secondary growth) |
Apical and intercalary meristems are primary meristems (form the primary plant body); lateral meristems are secondary meristems.
Permanent Tissues
Cells derived from meristems that have lost the capacity to divide form permanent tissues.
A. Simple Permanent Tissues (one cell type)
| Tissue | Wall | Function |
|---|---|---|
| Parenchyma | Thin cellulose walls | Storage, photosynthesis (chlorenchyma), buoyancy (aerenchyma) |
| Collenchyma | Thickened at corners (pectin/cellulose) | Mechanical support to young/growing parts |
| Sclerenchyma | Thick, lignified walls; dead | Rigid mechanical support (fibres, sclereids) |
B. Complex Permanent Tissues (more than one cell type)
Xylem (conducts water and minerals upward):
- Tracheids, vessels, xylem fibres, xylem parenchyma.
- In gymnosperms vessels are usually absent.
Phloem (conducts food, mainly downward):
- Sieve tube elements, companion cells, phloem fibres, phloem parenchyma.
- Companion cells are absent in gymnosperms (replaced by albuminous cells).
NEET trap: Tracheids and vessels are dead at maturity; sieve tube elements are living but enucleate, depending on companion cells. The first-formed xylem is protoxylem and later-formed is metaxylem.
The Tissue System — Epidermal, Ground and Vascular
Tissue Systems
Based on structure and location, mature tissues are grouped into three tissue systems.
1. Epidermal Tissue System
Forms the outermost protective covering of the plant body.
- Epidermis: usually a single layer of compactly arranged cells; outer wall often cutinised.
- Stomata: pores in the epidermis (mainly leaves) bordered by two guard cells; regulate transpiration and gaseous exchange. In dicots guard cells are bean-shaped; in grasses they are dumb-bell shaped.
- Epidermal appendages: trichomes (on the stem, often multicellular) and root hairs (unicellular elongations of root epidermal cells for absorption).
2. Ground Tissue System
All tissues except the epidermis and the vascular bundles make up the ground tissue.
- Consists mainly of parenchyma, with collenchyma and sclerenchyma.
- In the stem, ground tissue is differentiated into cortex, pericycle, pith and medullary rays.
- In the leaf, ground tissue is the mesophyll (palisade + spongy parenchyma) containing chloroplasts.
3. Vascular Tissue System
Made up of vascular bundles (xylem + phloem). Their arrangement is a key identification feature.
| Vascular bundle type | Xylem–phloem relationship | Example |
|---|---|---|
| Radial | Xylem and phloem on different radii, alternating | Roots |
| Conjoint | Xylem and phloem on the same radius | Stems and leaves |
| Open conjoint | Cambium present between xylem and phloem (can form secondary tissue) | Dicot stem |
| Closed conjoint | Cambium absent (no secondary growth) | Monocot stem |
- Endarch xylem: protoxylem towards the centre (stems).
- Exarch xylem: protoxylem towards the periphery (roots).
NEET trap: In roots vascular bundles are radial and exarch; in stems they are conjoint and endarch. Memorising this pair resolves most 'identify the section' questions.
Anatomy of Dicot & Monocot Organs and Secondary Growth
Anatomy of the Root
| Feature | Dicot root | Monocot root |
|---|---|---|
| Vascular bundles | Radial, exarch; usually 2–4 xylem groups (di to tetrarch) | Radial, exarch; many xylem groups (polyarch) |
| Pith | Small or absent | Large and well developed |
| Cambium | Appears later (secondary growth occurs) | Absent (no secondary growth) |
From outside in, both have: epidermis (epiblema with root hairs) → cortex → endodermis (with Casparian strips) → pericycle → vascular tissue → pith.
Anatomy of the Stem
| Feature | Dicot stem | Monocot stem |
|---|---|---|
| Vascular bundles | Conjoint, open, endarch; arranged in a ring | Conjoint, closed, endarch; scattered |
| Cambium | Present (secondary growth) | Absent (no secondary growth) |
| Ground tissue | Differentiated into cortex, endodermis, pericycle, pith | Not differentiated; common ground parenchyma |
| Bundle sheath | Absent | Present (sclerenchymatous) |
Anatomy of the Leaf
- Dorsiventral (dicot) leaf: mesophyll differentiated into upper palisade and lower spongy parenchyma; stomata mostly on the lower surface.
- Isobilateral (monocot) leaf: mesophyll not differentiated; stomata on both surfaces; large, empty bulliform cells in the upper epidermis help roll the leaf to reduce water loss.
Secondary Growth
The increase in the girth (thickness) of the plant due to the activity of lateral meristems is secondary growth. It occurs in dicot stems and roots but not in monocots.
1. Vascular Cambium
- In the dicot stem, the intrafascicular cambium (inside the bundle) joins the newly formed interfascicular cambium to make a complete cambial ring.
- The cambium cuts off secondary xylem (wood) towards the inside and secondary phloem (bast) towards the outside. Far more xylem is produced, so the bulk of a tree trunk is wood.
- Spring/early wood (wide vessels, light) and autumn/late wood (narrow vessels, dark) together make one annual ring, used to estimate the age of a tree.
- Heartwood (dark, dead, non-conducting central wood; provides mechanical support) and sapwood (lighter, outer, conducting wood).
2. Cork Cambium (Phellogen)
As girth increases, the epidermis is replaced by a secondary protective layer:
- Phellogen (cork cambium) cuts off cork (phellem) outside and secondary cortex (phelloderm) inside.
- Together phellem + phellogen + phelloderm = periderm.
- Lenticels are pores in the periderm that allow gaseous exchange.
NEET trap: A single annual ring = one year's spring wood plus the following autumn wood; counting the rings gives the tree's age (dendrochronology). Monocots like palms do not form annual rings because they lack vascular cambium.
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