Plant Morphology — Set 4

Correct Answer: D. Phloem

• **Phloem** = the vascular tissue that transports photosynthetically produced organic food (mainly sucrose) from leaves to all non-photosynthetic parts — roots, stems, fruits — in both upward and downward directions. • **Sieve tube elements** — the main conducting cells of phloem lack a nucleus at maturity and are assisted by companion cells that regulate loading and unloading of sugars. • This bidirectional flow of food through phloem is called translocation, powered by a pressure gradient (source-to-sink movement). • 💡 Option A (Xylem) is wrong because xylem transports only water and minerals from roots upward; Option B (Epidermis) is wrong because it is the outermost protective layer with no transport function; Option C (Cambium) is wrong because it is a lateral meristem that generates new xylem and phloem cells, not a transport tissue.

Correct Answer: C. Stipules

• **Stipules** = small paired appendages arising at the base of the petiole in many dicot leaves, protecting the axillary bud when young and helping in photosynthesis or defence in some species. • **Diverse forms** — stipules can be leaf-like (pea), spiny (Acacia), scale-like, tendril-like, or completely absent; their presence or absence is a useful taxonomic character. • In roses, stipules are adnate (fused) to the petiole and are clearly visible as small flanges on either side. • 💡 Option A (Ligules) is wrong because ligules are membranous or hair-like projections found at the leaf-sheath junction in grasses; Option B (Bracts) is wrong because bracts are modified leaves associated with flower clusters, not leaf bases; Option D (Lamina) is wrong because lamina is the broad, flat blade of the leaf itself.

Correct Answer: B. Carrot

• **Carrot** = a classic biennial plant that completes its life cycle in exactly two growing seasons — in the first year it stores food in its swollen taproot, and in the second year it uses that stored energy to produce flowers, seeds, and then dies. • **Two-year strategy** — the first-year vegetative phase builds reserves (the edible carrot root we harvest), while the second-year reproductive phase ensures seed dispersal and propagation. • Other common biennials include beetroot, radish, cabbage, and turnip — many of which are root-vegetables humans harvest at the end of year one. • 💡 Option A (Pea) is wrong because pea is an annual that completes its life cycle — germination to seed production — within a single growing season; Option C (Mango) is wrong because mango is a perennial woody tree that lives and fruits for decades; Option D (Rice) is wrong because rice is an annual crop harvested within 3–6 months of sowing.

Correct Answer: D. Pedicel

• **Pedicel** = the individual stalk that attaches each single flower to the main axis (rachis) of an inflorescence, holding the flower in the correct position for pollination. • **Peduncle vs. pedicel** — the peduncle is the primary stalk of the entire inflorescence or of a solitary flower, while the pedicel is the secondary stalk of each individual flower within a multi-flowered inflorescence. • When a flower lacks a pedicel it is called sessile (e.g., flowers in a spike inflorescence sit directly on the rachis). • 💡 Option A (Thalamus) is wrong because thalamus (receptacle) is the swollen tip of the pedicel on which floral whorls are inserted; Option B (Petiole) is wrong because petiole is the stalk of a leaf, not a flower; Option C (Peduncle) is wrong because peduncle is the main stalk bearing the entire inflorescence, not an individual flower.

Correct Answer: B. Mangrove plants

• **Mangrove plants** = grow in oxygen-deficient, waterlogged, saline coastal mud and develop pneumatophores — pencil-like, negatively geotropic (upward-growing) roots that project above the mud surface to absorb atmospheric oxygen for underground root respiration. • **Lenticels** — the surface of pneumatophores is covered with tiny pores called lenticels through which gaseous exchange occurs; Avicennia and Rhizophora are classic examples. • Pneumatophores solve the anaerobic problem of tidal mudflats and are a remarkable adaptation to one of the harshest root environments on Earth. • 💡 Option A (Desert plants) is wrong because desert plants develop deep taproots or shallow, wide-spreading roots to maximise water absorption, not aerial respiratory roots; Option C (Parasitic plants) is wrong because parasitic plants develop haustoria — specialised roots that penetrate host tissue to absorb nutrients; Option D (Submerged plants) is wrong because fully submerged aquatic plants have reduced, weakly developed roots and absorb gases directly through the leaf surface.

Correct Answer: B. Aestivation

• **Aestivation** = the specific pattern in which sepals or petals are folded, rolled, or arranged relative to one another within an unopened floral bud — it is studied by botanists to classify plant families. • **Major types** — valvate (edges just touch, e.g., Calotropis), twisted/contorted (each member overlaps the next on one side, e.g., China rose), imbricate (irregular overlapping, e.g., Cassia), and vexillary/papilionate (unequal overlapping, e.g., pea). • Aestivation is one of the key characters used in writing a floral formula and floral diagram for plant taxonomy. • 💡 Option A (Venation) is wrong because venation refers to the pattern of veins in a leaf blade, not floral buds; Option C (Phyllotaxy) is wrong because phyllotaxy describes how leaves are arranged on the stem (alternate, opposite, whorled); Option D (Placentation) is wrong because placentation describes where ovules are attached inside the ovary.

Correct Answer: A. Leaf

• **Leaf** = in Pitcher plants (Nepenthes, Sarracenia), the leaf lamina is modified into a deep pitcher-shaped trap with a lid (operculum) and a slippery inner wall; insects that fall in are digested by enzymes secreted by glands on the inner surface. • **Nitrogen acquisition** — pitcher plants are carnivorous because they grow in nitrogen-poor, waterlogged soils (bogs, swamps); digesting insects supplements their nitrogen supply where the soil cannot. • The green petiole still photosynthesises normally — only the leaf blade is transformed into the trap, showing that plant organs can be partially modified for dual functions. • 💡 Option B (Stem) is wrong because the stem of pitcher plants remains a normal, non-modified supporting axis; Option C (Root) is wrong because roots remain functional for anchoring and water uptake but are not modified into traps; Option D (Fruit) is wrong because the fruit develops only after pollination and plays no role in carnivory.

Correct Answer: D. Thalamus

• **Thalamus** = the condensed, swollen receptacle at the tip of the pedicel on which all four floral whorls — calyx (sepals), corolla (petals), androecium (stamens), and gynoecium (carpels) — are inserted in a specific arrangement. • **Floral position types** — the relative position of the ovary on the thalamus determines whether a flower is hypogynous (superior ovary), perigynous (half-inferior), or epigynous (inferior ovary), which is a key classification character. • In strawberry, the fleshy part we eat is actually the enlarged, juicy thalamus — not the ovary — making it a false fruit (pseudocarp). • 💡 Option A (Style) is wrong because style is the elongated stalk of the pistil connecting ovary to stigma; Option B (Pedicel) is wrong because pedicel is the thin stalk below the thalamus that connects the flower to the inflorescence axis; Option C (Stigma) is wrong because stigma is the sticky surface at the top of the style that receives pollen during pollination.

Correct Answer: D. Cotyledon

• **Cotyledon** = the embryonic seed leaf (or leaves) that stores or absorbs food reserves — mainly starch, proteins, and fats — to nourish the seedling until it develops true leaves and becomes capable of independent photosynthesis. • **Mono vs. dicot** — monocots (e.g., wheat, rice, maize) have one cotyledon called the scutellum that absorbs endosperm; dicots (e.g., pea, bean, groundnut) have two fleshy cotyledons that directly store food, making endosperm absent or scanty at maturity. • In castor, the cotyledons are thin and absorb food from a persistent endosperm; in pea, the cotyledons are thick and fleshy because they are the actual food store. • 💡 Option A (Seed coat) is wrong because the seed coat (testa) is a tough, protective outer covering that shields the embryo from desiccation, mechanical damage, and pathogens — it stores no food; Option B (Radicle) is wrong because the radicle is the embryonic root that grows downward to anchor the seedling and absorb water; Option C (Plumule) is wrong because the plumule is the embryonic shoot tip that grows upward and forms the first true leaves.

Correct Answer: B. Pistil

• **Pistil** = the female reproductive unit of a flower, composed of three parts: the ovary (basal swollen part containing ovules), the style (elongated stalk), and the stigma (receptive sticky surface at the top that traps pollen). • **Carpels** — a pistil may be simple (single carpel, e.g., pea) or compound (multiple fused carpels, e.g., tomato); the number of carpels and their fusion pattern are key taxonomic characters. • After fertilisation, the ovary develops into the fruit while each ovule inside develops into a seed — making the pistil the origin of the plant's entire reproductive output. • 💡 Option A (Stamen) is wrong because stamen is the male reproductive organ made of a filament and anther that produces pollen — it has no ovary or stigma; Option C (Anther) is wrong because anther is only the pollen-producing head of the stamen, a part of the male organ; Option D (Sepal) is wrong because sepal is the green, leaf-like outermost whorl of the flower that encloses and protects the bud before it opens.