Anatomy of Flowering Plants — NEET notes

Meristematic Tissues — The Growth Factories

Undifferentiated plant tissues that actively divide to produce new cells. Found at root tips, shoot tips, and lateral regions. They are the reason plants keep growing throughout their life.

Characteristics of Meristems

Meristematic cells have unique features that set them apart from all other plant cells — they are the perpetual 'stem cells' of the plant world.

Meristematic cells are actively dividing cells found in specific growth regions. They are the only cells in a plant that retain the ability to divide throughout the plant's life. This is why plants show open growth — they never stop growing.

• Cells are thin-walled with dense cytoplasm
• Nucleus is large and prominent — actively making DNA
• Vacuoles are absent or very small (no storage needed, just division)
• No intercellular spaces — cells are tightly packed
• Cells are isodiametric (equal dimensions in all directions)
• No ergastic substances (starch grains, crystals, etc.) — purely functional

Apical Meristem

Present at root tips and shoot tips, responsible for increasing the length of the plant body (primary growth).

Apical meristems are located at the tips of roots and shoots. They are responsible for primary growth — the increase in length of the plant. When your bean seedling grows taller day by day, thank the apical meristem.

• Found at root apex and shoot apex
• Responsible for primary growth (increase in length)
• Present in all plants — monocots, dicots, gymnosperms
• The shoot apical meristem also produces leaf primordia and axillary buds
• Root apical meristem is protected by the root cap

Lateral Meristem

Present along the sides of stems and roots, responsible for increasing the diameter (secondary growth).

Lateral meristems are positioned parallel to the sides (lateral surfaces) of stems and roots. They divide periclinally (parallel to the surface), adding new layers and increasing the girth (thickness) of the plant. This is called secondary growth.

• Two types: Vascular cambium (produces secondary xylem & phloem) and Cork cambium/Phellogen (produces bark)
• Responsible for secondary growth (increase in girth/diameter)
• Found mainly in dicots and gymnosperms — mostly absent in monocots
• Cells are elongated and flattened (not isodiametric like apical meristem)

Intercalary Meristem

Found at the base of internodes and leaf bases, especially in grasses. Helps plants regrow after grazing or mowing.

Intercalary meristems are located between regions of mature tissue — typically at the base of internodes, base of leaves, or near nodes. They are derived from the apical meristem and are separated from it by mature tissues.

• Found at base of internodes and leaf bases (especially in monocots/grasses)
• Contribute to primary growth — increase in length of internodes
• Temporary — eventually become permanent tissue
• Particularly prominent in grasses, bamboo, wheat, sugarcane
• Help plants regenerate after cutting or grazing

Simple Permanent Tissues — One cell type, one team

Tissues made of a single type of cell that has lost the ability to divide. The three types — parenchyma, collenchyma, and sclerenchyma — form the bulk of the plant body and handle storage, support, and protection.

Parenchyma

The most common and versatile plant tissue. Thin-walled, living cells that handle storage, photosynthesis, gas exchange, and even wound healing.

Parenchyma forms the bulk of the plant body. These are thin-walled, living cells with a large central vacuole. They are the 'default' tissue — found everywhere from cortex to pith to mesophyll.

• Cells are isodiametric (roughly spherical or oval)
• Cell walls are thin, made of cellulose
• Living cells with large central vacuole
• Intercellular spaces present — loosely packed
• Functions: storage (starch, fats), photosynthesis, gas exchange, wound healing
• Can dedifferentiate back to meristematic tissue (important for wound repair and tissue culture)

Collenchyma

Living cells with unevenly thickened walls that provide mechanical support while still allowing growth. Found in young stems and leaf stalks.

Collenchyma provides mechanical support to young, growing organs that need flexibility. The walls are thickened at the corners (or at tangential surfaces) with extra cellulose and pectin — thick enough for support, thin enough to allow growth.

• Living cells — can photosynthesize if chloroplasts present
• Cell walls thickened unevenly (at corners or tangential walls)
• Thickening material: cellulose + pectin (NOT lignin)
• Very few or no intercellular spaces
• Found in hypodermis of dicot stems, petioles, leaf margins
• Absent in monocot stems and roots (important NEET fact)

Based on the pattern of thickening, collenchyma is classified into: Angular (thickening at corners — most common), Lamellar/Plate (thickening on tangential walls), and Lacunar (thickening near intercellular spaces).

Sclerenchyma

Dead cells with thick, lignified walls that provide the strongest mechanical support. Two types: fibres (long) and sclereids (short/irregular).

Sclerenchyma cells are dead at maturity — their walls are so heavily thickened with lignin that nutrients can't pass through, and the cells die. But their rigid walls remain, providing maximum mechanical strength.

• Dead cells at maturity — lumen (cell cavity) is very narrow or absent
• Walls are uniformly thickened with lignin (secondary wall deposition)
• No intercellular spaces
• Two types: Fibres (long, narrow, pointed ends) and Sclereids/Stone cells (short, irregular, very thick walls)
• Fibres found in: vascular bundles, pericycle, hypodermis of monocot stems
• Sclereids found in: seed coats, nut shells, fruit walls (e.g., pear fruit grit)

Quick recall

Why are sclerenchyma cells dead at maturity?

Because lignin deposits in the secondary wall make it impermeable to water and nutrients. The protoplasm dies, but the rigid wall remains and continues providing structural support — like a building's steel framework that works without any living component.

Comparison Table

A side-by-side comparison of the three simple tissues — the most common table asked in NEET from this chapter.

This comparison table is a NEET goldmine. Almost every year, at least one MCQ tests a specific row from this table. Master it completely.

NCERT says 'collenchyma is found either as a homogeneous layer below the epidermis or in patches.' The patchy arrangement is seen at the ridges of stems like celery stalks — the 'strings' in celery are collenchyma.

Complex Permanent Tissues — Xylem & Phloem teamwork

Tissues made of MORE than one type of cell, all working together for a common function. Xylem transports water upward; Phloem transports food (sucrose) both ways. Together they form the plant's circulatory system.

Xylem

Xylem conducts water and minerals from roots to leaves. Made of tracheids, vessels, xylem fibres, and xylem parenchyma. Mostly dead cells — a pipeline that works without living power.

Xylem is the water-conducting complex tissue. It transports water and dissolved minerals unidirectionally upward (roots → leaves). It also provides mechanical support due to lignified walls.

• Tracheids — Long, narrow, spindle-shaped cells with tapering ends. Water moves through pits (thin areas in wall). Found in ALL vascular plants. Dead at maturity
• Vessels (Trachea) — Shorter, wider, tube-like. End walls dissolved → continuous pipe. More efficient than tracheids. Found mainly in angiosperms. Dead at maturity
• Xylem fibres — Long cells with thick lignified walls and narrow lumen. Mainly mechanical support. Dead at maturity
• Xylem parenchyma — Only living component of xylem. Thin-walled. Stores starch, fat. Helps in lateral conduction of water

Quick recall

Which is the only living component of xylem?

Xylem parenchyma. Tracheids, vessels, and xylem fibres are all dead at maturity. This is the most frequently asked NEET question from this topic.

Phloem

Phloem transports organic food (sucrose) from source (leaves) to sink (roots, fruits, growing tips). Made of sieve tubes, companion cells, phloem fibres, and phloem parenchyma.

Phloem is the food-conducting complex tissue. It transports sucrose and other organic solutes bidirectionally — from leaves (where food is made) to roots, fruits, seeds, and growing tips. This process is called translocation.

• Sieve tube elements — Long, tube-like cells. End walls form sieve plates (perforated). Nucleus absent at maturity but cell is LIVING (cytoplasm present). Connected end-to-end forming sieve tubes
• Companion cells — Small cells connected to sieve tubes by plasmodesmata. Have dense cytoplasm and prominent nucleus. Control the function of sieve tubes. Found ONLY in angiosperms
• Phloem fibres (Bast fibres) — Sclerenchyma fibres in phloem. Dead at maturity. Provide mechanical support. Used commercially (jute, flax, hemp)
• Phloem parenchyma — Living, thin-walled cells. Store food (starch, fat, resin). Absent in monocots

Xylem vs Phloem

Side-by-side comparison of xylem and phloem — a guaranteed NEET table.

• Together, xylem + phloem = vascular bundle
• Primary xylem & phloem form from procambium (during primary growth)
• Secondary xylem & phloem form from vascular cambium (during secondary growth)
• Xylem forms the bulk of wood in trees; phloem forms the inner bark

NCERT specifically mentions: in gymnosperms, the companion cells of phloem are replaced by albuminous cells (Strasburger cells). This is a classic one-liner NEET question.

Tissue Systems — Epidermal, Ground & Vascular

All tissues in a plant are organized into three systems: Epidermal (outer protection), Ground (bulk of the body), and Vascular (transport network). Each system has a distinct role and location.

Epidermal Tissue System

The outermost covering of the plant body. Includes epidermis, stomata, trichomes, and root hairs. First line of defense against water loss, pathogens, and mechanical injury.

The epidermis is a single layer of tightly packed cells covering the entire plant body. It is the plant's first line of defense. The outer wall of epidermal cells has a waxy coating called cuticle (made of cutin) that prevents water loss.

• Single-layered parenchymatous cells — tightly packed, no intercellular spaces
• Outer wall covered by cuticle (waxy layer of cutin) — prevents transpiration
• Cuticle is absent in roots (roots need to absorb water, not block it!)
• Stomata — pores on epidermis of leaves/young stems; each bounded by 2 guard cells
• Guard cells are bean-shaped in dicots, dumbbell-shaped in grasses (monocots)
• Trichomes — hair-like outgrowths on epidermis; can be multicellular, branched/unbranched
• Root hairs — unicellular extensions of epidermal cells in the root hair zone

Quick recall

What is the difference between trichomes and root hairs?

Trichomes are on aerial parts, can be multicellular, branched, and serve protection/reducing water loss. Root hairs are on roots, always unicellular, unbranched, and absorb water/minerals.

Ground Tissue System

All tissues except epidermis and vascular bundles. Includes cortex, pith, medullary rays, and mesophyll. The 'filling' of the plant body.

The ground tissue system includes all tissues except the epidermis and vascular bundles. It forms the bulk of the plant body and is mainly made of parenchyma, with some collenchyma and sclerenchyma.

• Cortex — region between epidermis and vascular bundles (parenchyma, collenchyma)
• Endodermis — innermost layer of cortex; cells have Casparian strips (waxy bands of suberin) in roots
• Pericycle — just inside endodermis; gives rise to lateral roots and contributes to vascular cambium
• Pith (Medulla) — central region of stem; made of parenchyma; stores starch
• Medullary rays (Pith rays) — parenchyma between vascular bundles; connect pith to cortex; lateral transport
• Mesophyll — ground tissue in leaves; contains chlorenchyma for photosynthesis

Vascular Tissue System

Xylem + phloem organized into vascular bundles. Arrangement varies between dicots and monocots, and between root, stem, and leaf.

The vascular tissue system consists of xylem and phloem organized into vascular bundles. The arrangement, number, and type of vascular bundles differ between organs (root vs stem vs leaf) and between plant groups (dicot vs monocot).

• Open vascular bundle — cambium present between xylem and phloem → can undergo secondary growth. Found in dicot stems
• Closed vascular bundle — cambium absent → NO secondary growth. Found in monocot stems
• Radial arrangement — xylem and phloem on alternate radii (separated). Found in roots
• Conjoint arrangement — xylem and phloem on the same radius (together). Found in stems and leaves
• Conjoint bundles can be collateral (phloem on outer side of xylem — most common) or bicollateral (phloem on both sides of xylem — Cucurbitaceae family)

Quick recall

What is a bicollateral vascular bundle?

A conjoint bundle with phloem on both sides of the xylem (outer phloem + inner phloem). Found in members of Cucurbitaceae (pumpkin family) and Solanaceae. Two strips of cambium may also be present.

Anatomy of Root — Dicot vs Monocot cross-sections

A transverse section of root shows concentric layers: epidermis → cortex → endodermis → pericycle → vascular bundles → pith. Dicot and monocot roots differ in the number of xylem arms, pith size, and secondary growth potential.

Dicot Root (TS)

A typical dicot root (e.g., gram, sunflower) shows a well-organized internal anatomy. Learn the layers in order — NEET diagrams test this directly.

When you cut a dicot root transversely and look under a microscope, you see a series of concentric rings. The outermost layer is the epidermis, and the innermost part is a small pith. Let's go layer by layer.

• Epiblema (Rhizodermis) — Outermost single layer. Thin-walled. Some cells extend as root hairs. No cuticle (needs to absorb water!)
• Cortex — Multiple layers of parenchyma. Large, with intercellular spaces. Stores starch. Major bulk of the root
• Endodermis — Single innermost cortical layer. Cells have Casparian strips (suberin bands). Some cells lack suberin → passage cells (allow water into vascular tissue)
• Pericycle — Single to few layers of parenchyma inside endodermis. Gives rise to lateral roots and contributes to vascular cambium during secondary growth
• Vascular bundles — Radial arrangement. Xylem and phloem alternate on different radii. Usually 2-6 xylem arms (diarch to hexarch). Xylem is exarch (protoxylem toward outside)
• Pith — Small or inconspicuous. May be absent in older roots. Parenchymatous

Monocot Root (TS)

A monocot root (e.g., maize) has a similar basic plan as dicot root but differs in number of xylem arms, pith size, and inability to show secondary growth.

Monocot roots follow the same general plan as dicot roots — epidermis, cortex, endodermis, pericycle, vascular bundles, pith. But there are key quantitative and qualitative differences.

• Xylem arms: Many (polyarch) — usually more than 6 (compared to 2-6 in dicots)
• Pith: Large and well-developed — conspicuous parenchymatous center
• No secondary growth — pericycle does not form vascular cambium
• Casparian strips present in endodermis (same as dicots)
• Xylem is exarch (same as dicots — ALL roots are exarch)
• Passage cells present in endodermis (same as dicots)

Universal Root Features

Regardless of dicot or monocot, all roots share certain fundamental features. Knowing these prevents confusion on tricky MCQs.

Some features are universal to ALL roots. NEET often tests whether you know what's root-specific vs. stem-specific. These never change between dicot and monocot roots.

• Vascular bundles are ALWAYS radial — xylem and phloem alternate on separate radii
• Xylem is ALWAYS exarch — protoxylem faces outside, metaxylem faces center
• Endodermis ALWAYS has Casparian strips (suberin deposition)
• No cuticle on the outermost layer (epiblema) — roots absorb water
• Pericycle is ALWAYS present — source of lateral roots
• No stomata — roots are underground, no gas exchange via stomata needed
• No trichomes — root hairs serve the absorption function instead

Quick recall

How do you instantly identify a root TS vs. a stem TS under a microscope?

Look for these root markers: (1) Radial vascular bundles (xylem and phloem alternating), (2) Exarch xylem (protoxylem outside), (3) Endodermis with Casparian strips, (4) No cuticle on the surface. If xylem and phloem are together (conjoint) and xylem is endarch — it's a stem.

Anatomy of Stem — Dicot vs Monocot cross-sections

A transverse section of stem shows: epidermis → hypodermis → cortex → endodermis (starch sheath) → pericycle → vascular bundles → pith. Dicot stems have bundles in a ring with cambium; monocot stems have scattered bundles without cambium.

Dicot Stem (TS)

A typical dicot stem (e.g., sunflower) shows vascular bundles arranged in a ring with cambium between xylem and phloem. This arrangement allows secondary growth.

A dicot stem cross-section reveals a highly organized structure with a clear distinction between cortex, vascular ring, and pith. The vascular bundles are arranged in a ring pattern.

• Epidermis — Single outermost layer. Has cuticle (waxy layer) on the outside. May bear trichomes (multicellular hairs). Stomata present in young stems
• Hypodermis — Just below epidermis. Made of collenchyma (provides flexible support). A few layers thick
• Cortex — Several layers of parenchyma with intercellular spaces. May contain chloroplasts in outer layers
• Endodermis (Starch sheath) — Innermost layer of cortex. Called starch sheath because cells are rich in starch grains. Not as distinct as root endodermis (no Casparian strips)
• Pericycle — Above the vascular bundles. Made of sclerenchyma patches (hard caps) alternating with parenchyma. Called bundle caps
• Vascular bundles — Conjoint, collateral, open (with cambium). Arranged in a ring. Xylem is endarch (protoxylem towards center/pith)
• Pith — Large, central, parenchymatous. Well-developed
• Medullary rays — Parenchyma between vascular bundles connecting pith to cortex

Monocot Stem (TS)

A monocot stem (e.g., maize) has vascular bundles scattered throughout the ground tissue, with no distinction between cortex and pith. No secondary growth occurs.

Monocot stems look dramatically different from dicot stems in cross-section. Instead of a neat ring of bundles, the vascular bundles are scattered throughout the ground tissue. There is no clear boundary between cortex and pith.

• Epidermis — Single layer with thick cuticle. No trichomes (unlike dicot)
• Hypodermis — Made of sclerenchyma (NOT collenchyma like dicot). Provides rigid support
• Ground tissue — Not differentiated into cortex, endodermis, pericycle, or pith. It's all one mass of parenchyma with scattered vascular bundles
• Vascular bundles — Conjoint, collateral, closed (NO cambium). Scattered throughout. Smaller bundles near periphery, larger bundles toward center
• Bundle sheath — Each bundle surrounded by a sclerenchymatous sheath (hard outer covering)
• Xylem is endarch (same as dicot stem — protoxylem toward center)
• Xylem vessels arranged in a Y-shape or V-shape — with 2 metaxylem vessels at top and protoxylem + lysigenous cavity (water-filled space) at the bottom

Dicot vs Monocot Stem

Every difference at a glance. This table alone can answer 3-4 NEET questions.

Quick recall

How do you tell apart root TS vs stem TS at a glance?

Stem markers: Conjoint vascular bundles (xylem & phloem together), endarch xylem (protoxylem toward pith), cuticle on epidermis, trichomes. Root markers: Radial vascular bundles (xylem & phloem alternate), exarch xylem (protoxylem outward), no cuticle.

Secondary Growth — How trees get thicker every year

Increase in girth of stems and roots due to the activity of lateral meristems — vascular cambium and cork cambium. Forms secondary xylem (wood), secondary phloem, and bark. Produces annual rings that reveal a tree's age.

Vascular Cambium

A lateral meristem that forms a complete ring between xylem and phloem. Produces secondary xylem (wood) toward the inside and secondary phloem toward the outside.

Vascular cambium is a lateral meristem that forms a continuous ring in dicot stems and roots. It is the main driver of secondary growth. It produces cells in two directions: secondary xylem (wood) toward the center and secondary phloem toward the outside.

• Fascicular cambium — cambium present within vascular bundles (between primary xylem and phloem)
• Interfascicular cambium — forms from parenchyma cells of medullary rays between bundles (dedifferentiation!)
• Together they form a complete cambial ring
• Cuts off MORE secondary xylem than secondary phloem (ratio roughly 8:1 to 10:1)
• Cambium is made of two types of initials: Fusiform initials (elongated → form axial system) and Ray initials (small → form radial system/medullary rays)
• Activity is seasonal — more active in spring (large vessels) and less in autumn (small vessels)

Cork Cambium (Phellogen)

A secondary lateral meristem that forms in the outer cortex. Produces cork (phellem) outward and secondary cortex (phelloderm) inward. Together = periderm.

As secondary growth increases the stem's girth, the outer epidermis and cortex rupture. A new protective layer is needed. The cork cambium (phellogen) arises in the outer cortex and takes over the protective function.

• Cork cambium (Phellogen) — arises from cortical parenchyma or epidermis (by dedifferentiation)
• Cuts off cork/phellem toward the outside — dead cells with walls impregnated with suberin (waterproof)
• Cuts off secondary cortex/phelloderm toward the inside — living parenchyma
• Phellogen + Phellem + Phelloderm = PERIDERM (the complete replacement for epidermis)
• Lenticels — lens-shaped openings in the bark for gas exchange. Loosely arranged complementary cells replace the tight cork

Quick recall

What is bark?

Bark includes ALL tissues outside the vascular cambium — secondary phloem + periderm. It can be further divided: Soft/inner bark = secondary phloem (living, functional). Hard/outer bark = periderm + dead phloem (protective, non-functional). Technically, bark = everything you see when you look at a tree trunk.

Annual Rings

Alternating bands of spring wood (wide vessels) and autumn wood (narrow vessels) visible in a cross-section of a tree trunk. Each pair = one year of growth.

In temperate regions, the vascular cambium is more active in spring (favorable conditions → large vessels, low density) and less active in autumn (harsh conditions → small vessels, high density). This creates alternating light and dark bands visible in cross-section.

• Spring wood (Early wood) — formed in favorable season. Large vessels, thin walls, light colored, low density
• Autumn wood (Late wood) — formed in unfavorable season. Small vessels, thick walls, dark colored, high density
• One annual ring = one band of spring wood + one band of autumn wood = one year of growth
• Dendrochronology = science of counting annual rings to determine tree age
• Annual rings are distinct in temperate regions (marked seasons) but indistinct in tropical regions (uniform climate)

Quick recall

Why are annual rings absent or indistinct in tropical trees?

Tropical regions have a relatively uniform climate throughout the year — no harsh winter to slow growth. The cambium produces similar-sized vessels year-round, so distinct bands don't form.

Heartwood vs Sapwood

The inner dark wood (heartwood) is dead and provides only structural support. The outer light wood (sapwood) is living and actively conducts water. Both are secondary xylem.

As a tree grows, the older, inner secondary xylem loses its conducting function. Its vessels get blocked by tyloses (balloon-like ingrowths) and filled with tannins, resins, oils, gums. This dark, non-functional wood is heartwood (duramen). The outer, younger, functional secondary xylem is sapwood (alburnum).

• Heartwood is NOT dead at formation — it BECOMES dead as vessels get blocked
• The proportion of heartwood increases with tree age
• Some trees (e.g., Populus, Salix) have very little heartwood
• Heartwood's durability comes from the organic deposits that are toxic to microbes and insects