Class 11 — Morphology of Flowering Plants

Chapter Overview & Weightage

Morphology of Flowering Plants is a memorisation-heavy chapter, but the marks are easy if you put in the diagram practice. CBSE asks straight terminology questions and floral diagram/formula questions in nearly every paper.

Year	Marks
2024	6
2023	5
2022	7
2021	5

Expect 1-2 mark questions on root/stem modifications, 3-mark short answers on inflorescence types or aestivation, and a 5-mark question that often combines a floral diagram with the floral formula.

Key Concepts You Must Know

Root system: tap root (dicots) vs fibrous root (monocots) vs adventitious root.
Root modifications: storage (carrot, turnip), respiratory (Rhizophora — pneumatophores), prop roots (banyan), stilt roots (sugarcane), nitrogen-fixing nodules (legumes).
Stem modifications: underground (rhizome — ginger, tuber — potato, bulb — onion, corm — Colocasia), sub-aerial (runner — grass, stolon — strawberry), aerial (tendrils, thorns — Bougainvillea, phylloclade — Opuntia).
Leaf: parts (petiole, lamina, leaf base, stipules), venation (reticulate vs parallel), simple vs compound leaves.
Phyllotaxy: alternate, opposite, whorled.
Inflorescence: racemose (continuous growth, e.g., mustard) vs cymose (terminal flower, e.g., Solanum).
Flower parts: calyx (sepals), corolla (petals), androecium (stamens), gynoecium (carpels).
Aestivation: arrangement of sepals/petals in bud — valvate, twisted, imbricate, vexillary.
Placentation: arrangement of ovules in ovary — marginal (pea), axile (lemon), parietal (mustard), free central (Dianthus), basal (sunflower).
Floral formula symbols: $\oplus$ actinomorphic, % zygomorphic, ⚥ bisexual, K = calyx, C = corolla, A = androecium, G = gynoecium.
Three families to memorise: Fabaceae (pea), Solanaceae (potato), Liliaceae (onion).

Important Formulas (Floral Formulas)

$\% \,⚥\, K_{(5)}\, C_{1+2+(2)}\, A_{(9)+1}\, \underline{G_1}$

Zygomorphic, bisexual, sepals fused (5), corolla papilionaceous (1 standard + 2 wings + 2 keels fused), androecium diadelphous (9 fused + 1 free), monocarpellary superior ovary.

$\oplus \,⚥\, K_{(5)}\, C_{(5)}\, A_5\, \underline{G_{(2)}}$

Actinomorphic, bisexual, sepals fused, petals fused, 5 free stamens, bicarpellary syncarpous superior ovary.

$\oplus \,⚥\, P_{3+3}\, A_{3+3}\, \underline{G_{(3)}}$

Actinomorphic, bisexual, perianth in two whorls of 3, stamens in two whorls of 3, tricarpellary syncarpous superior ovary.

Solved Previous Year Questions

PYQ 1 (CBSE 2023, 3 marks)

Differentiate between racemose and cymose inflorescence with one example each.

Solution:

Feature	Racemose	Cymose
Growth pattern	Indefinite (apex keeps growing)	Definite (apex ends in a flower)
Flower opening	Acropetal (bottom-up)	Basipetal (top-down)
Example	Mustard (Brassica)	Solanum

PYQ 2 (CBSE 2024, 5 marks)

Draw a labelled diagram of a typical dicot leaf and write the floral formula of Solanum nigrum.

Solution: [Diagram description] Lamina with reticulate venation, midrib running centrally, lateral veins branching out, petiole connecting to leaf base with no stipules.

Floral formula of Solanum nigrum: $\oplus \,⚥\, K_{(5)}\, C_{(5)}\, A_5\, \underline{G_{(2)}}$

PYQ 3 (CBSE 2022, 2 marks)

Name two underground stem modifications and the function they perform.

Solution:

Rhizome (ginger) — food storage and vegetative propagation.
Tuber (potato) — food storage; bears axillary buds (eyes).

Difficulty Distribution

Easy (60%): Direct terminology, naming examples for each modification type.
Medium (30%): Floral formulas, comparing inflorescence types, distinguishing modifications.
Hard (10%): Multi-part questions combining floral formula + diagram + family characteristics.

Expert Strategy

For the three families (Fabaceae, Solanaceae, Liliaceae), make a one-page comparison table covering: habit, root, stem, leaf, inflorescence, flower symmetry, perianth/calyx-corolla, androecium, gynoecium, fruit, seed, family example, economic importance. Memorise the table cold.

When drawing a floral diagram, use mother axis as a dot at the top, bract at the bottom, and arrange whorls concentrically: calyx (outermost) → corolla → androecium → gynoecium (innermost). Mark cohesion with arcs and adhesion with lines connecting whorls.

Common Traps

Trap 1: Confusing tendril vs thorn vs spine. Tendril = thin coiling structure for climbing (modified leaf or stem). Thorn = hard pointed stem modification. Spine = modified leaf (e.g., cactus). Examiners love this distinction.

Trap 2: Marginal placentation vs parietal. Marginal: ovules attached to one margin of a single carpel (Pea). Parietal: ovules on the inner walls of a multi-carpel ovary (Mustard). Look at the carpel count.

Trap 3: Bulb vs corm vs tuber. Bulb (onion) = condensed stem with fleshy scale leaves. Corm (Colocasia) = condensed solid stem. Tuber (potato) = swollen tip of underground stem with eyes. Different anatomy, different examples.

CBSE never asks more than the three families listed in the syllabus. Don’t waste time on Asteraceae or Poaceae — they’re not in the prescribed list.