Exercises
How is a pinnately compound leaf different from a palmately compound leaf?
Answer
Pinnately compound leaf: The leaflets are arranged on both sides of a central axis called the rachis (which represents the midrib of the leaf). The leaflets arise laterally along the rachis like the arrangement of a feather. Example: Neem (Azadirachta indica), Cassia, Mimosa.
Palmately compound leaf: The leaflets are attached at a common point – the tip of the petiole – and spread out like the fingers of a palm. There is no rachis. Example: Silk cotton (Bombax), Cannabis, Cleome.
The key difference is that pinnately compound leaves have a rachis (central axis), while palmately compound leaves lack a rachis and have leaflets radiating from a single point.
Explain with suitable examples the different types of phyllotaxy.
Answer
Phyllotaxy is the pattern of arrangement of leaves on the stem or branch. There are three main types:
(i) Alternate phyllotaxy: A single leaf arises at each node, alternately on opposite sides of the stem. Example: China rose (Hibiscus), Mustard, Sunflower.
(ii) Opposite phyllotaxy: Two leaves arise at each node, opposite to each other. If successive pairs are at right angles to each other, it is called decussate. Example: Guava, Calotropis.
(iii) Whorled phyllotaxy: Three or more leaves arise at each node and form a whorl around the stem. Example: Alstonia, Nerium (oleander).
Define the following terms: (a) aestivation (b) placentation (c) actinomorphic (d) zygomorphic (e) superior ovary (f) perigynous flower (g) epipetalous stamen
Answer
(a) Aestivation: The mode of arrangement of sepals or petals in the floral bud with respect to the other members of the same whorl. Types include valvate, twisted, imbricate, and vexillary.
(b) Placentation: The arrangement of ovules within the ovary on the placenta. Types include marginal, axile, parietal, basal, central, and free central placentation.
(c) Actinomorphic: A flower that can be divided into two equal halves by any vertical plane passing through the centre – radially symmetrical. Example: Mustard, Datura, Chilli.
(d) Zygomorphic: A flower that can be divided into two equal halves only by one specific vertical plane – bilaterally symmetrical. Example: Pea, Bean, Gulmohar, Cassia.
(e) Superior ovary: The ovary is situated above the level of attachment of other floral parts (sepals, petals, stamens) on the thalamus (hypogynous condition). The flower is said to be hypogynous. Example: Mustard, Brinjal.
(f) Perigynous flower: The thalamus becomes cup-shaped (floral cup or hypanthium) and the sepals, petals, and stamens are inserted on the rim of this cup, around or surrounding the ovary (which is in the centre). The ovary is half-inferior. Example: Rose, Peach, Plum.
(g) Epipetalous stamen: Stamens that are attached to the petals (or fused with the corolla). Example: In Brinjal (Solanum melongena), the stamens are attached to the petals.
Q4. Differentiate between
(a) Racemose and cymose inflorescence
(b) Apocarpous and syncarpous ovary
Ans.
(a) Racemose vs Cymose inflorescence:
Racemose: The main axis continues to grow indefinitely and flowers are borne laterally in acropetal succession (older flowers at base, younger towards tip). The main axis does not terminate in a flower. Examples: Raceme (mustard), spike (Adhatoda), corymb (Iberis), umbel (coriander), head/capitulum (sunflower).
Cymose: The main axis terminates in a flower (limited growth). Subsequent flowers develop from lateral branches in basipetal succession (older flowers at top, younger below). Examples: Uniparous cyme/monochasium (Heliotropium), biparous cyme/dichasium (Jasmine, Teak).
(b) Apocarpous vs Syncarpous ovary:
Apocarpous: The gynoecium has more than one carpel, and the carpels are free (not fused) from each other. Example: Lotus, Rose.
Syncarpous: The gynoecium has more than one carpel and all the carpels are fused together. Example: Mustard, Tomato.
Draw the labelled diagram of the following: (i) gram seed (ii) V.S. of maize seed
Answer
(This question requires diagrams. Below are the key labelled structures.)
Gram seed (dicot): The gram seed has a tough seed coat (testa) with a hilum, micropyle, and raphe visible. Inside are two fleshy cotyledons that store food. The embryo axis has a plumule (future shoot) and a radicle (future root). The epicotyl is the part of embryo axis above the cotyledon attachment; hypocotyl is below.
V.S. of Maize seed (monocot): The maize grain (technically a fruit – caryopsis) consists of a seed coat fused with the fruit wall (pericarp). The large endosperm (starchy, white portion) stores food. The embryo is at the lower end and consists of: scutellum (single large cotyledon that absorbs food from endosperm), plumule enclosed in a protective sheath called coleoptile, radicle enclosed in coleorhiza. A hard layer called the aleurone layer borders the endosperm.
Take one flower of the family Solanaceae and write its semi-technical description. Also draw their floral diagram.
Answer
Flower: Solanum melongena (Brinjal)
Semi-technical description
Vegetative characters: Herb; stem erect, branched, hairy; leaves simple, alternate, exstipulate, petiolate, with entire or lobed margin.
Floral characters: Flower bisexual, actinomorphic, hypogynous, pentamerous.
Calyx: Sepals 5, gamosepalous (fused), persistent.
Corolla: Petals 5, gamopetalous (fused), rotate/stellate, purple or white.
Androecium: Stamens 5, epipetalous (attached to petals), polyandrous (free), with large yellow anthers dehiscing by pores.
Gynoecium: Bicarpellary, syncarpous; ovary superior, bilocular (sometimes falsely multilocular); placentation axile; style single; stigma capitate.
Fruit: Berry. Seeds many.
Floral formula: ⊕ K(5) C(5) A5 G(2)
Describe the various types of placentations found in flowering plants.
Answer
Placentation is the arrangement of ovules within the ovary. Types:
(i) Marginal: Placenta forms a ridge along the ventral suture of the ovary; ovules are in two rows along this ridge. Ovary is monocarpellary and unilocular. Example: Pea (legumes).
(ii) Axile: The margins of carpels fuse to form a central axis (septum) in a multilocular ovary; ovules are attached to the central axis. Example: China rose, Tomato, Lemon.
(iii) Parietal: Ovules develop on the inner wall of the ovary or on peripheral placentae in a unilocular ovary; carpels meet in the centre but ovary wall is the placenta. Example: Mustard, Argemone.
(iv) Free central: Ovules are borne on a central axis in a unilocular ovary but there are no septa. Example: Dianthus, Primrose.
(v) Basal: A single ovule is attached to the base of the ovary. Example: Sunflower, Marigold.
(vi) Superficial: Ovules are attached over the entire inner surface of the ovary wall. Example: Nymphaea (water lily).
What is a flower? Describe the parts of a typical angiosperm flower.
Answer
A flower is a modified shoot specialised for sexual reproduction in angiosperms. It bears the reproductive organs (stamens and carpels) and usually also accessory organs (sepals and petals). A typical flower is borne on a pedicel (stalk) and has an enlarged tip, the thalamus (receptacle), which bears all the floral parts.
Parts of a typical flower:
(i) Calyx: Outermost whorl of floral leaves called sepals. Usually green and leaf-like; protect the bud. May be free (polysepalous) or fused (gamosepalous).
(ii) Corolla: Whorl of petals, usually brightly coloured to attract pollinators. May be free (polypetalous) or fused (gamopetalous). Arrangement of petals in the bud is called aestivation.
(iii) Androecium: Male reproductive whorl; consists of stamens. Each stamen has a filament (stalk) and an anther (which produces pollen grains). May be free or fused in various ways.
(iv) Gynoecium (Pistil): Female reproductive whorl; consists of one or more carpels. Each carpel has three parts: stigma (receptive surface for pollen), style (slender stalk), and ovary (contains ovules). The ovary matures into fruit; ovules become seeds.
Define the term inflorescence. Explain the basis for the different types of inflorescence in flowering plants.
Answer
Inflorescence is the arrangement of flowers on the floral axis (the specialised stem bearing flowers). When a plant bears many flowers, they may be arranged in different ways on the stem.
The basis for classification of inflorescences is:
(i) Whether the floral axis is limited or unlimited in growth:
• If the main axis continues to grow indefinitely and bears flowers laterally
⇒ Racemose (indefinite/indeterminate) inflorescence. Flowers open from base to apex (acropetal succession). Examples: raceme, spike, corymb, umbel, capitulum (head).
• If the main axis terminates in a flower (limited growth)
⇒ Cymose (definite/determinate) inflorescence. Flowers open from apex to base (basipetal succession). Examples: monochasium, dichasium.
(ii) Nature of the floral axis: Whether it elongates, remains flat, or forms a disc also determines the type (e.g., the flat/convex/concave receptacle in capitulum).
Describe the arrangement of floral members in relation to their insertion on thalamus.
Answer
Based on the position of gynoecium (ovary) in relation to other floral parts on the thalamus, flowers are of three types:
(i) Hypogynous flower: Thalamus is convex; sepals, petals, and stamens are attached below the ovary. The ovary is at the top and is called superior ovary. Example: Mustard, China rose, Brinjal.
(ii) Perigynous flower: Thalamus grows into a cup-shaped structure (hypanthium) surrounding the ovary but not fused with it; sepals, petals, and stamens are inserted on the rim of this cup. The ovary is half-inferior. Example: Rose, Peach.
(iii) Epigynous flower: Thalamus grows up and completely encloses the ovary; the ovary is fused with the thalamus. Sepals, petals, and stamens appear to arise above the ovary. The ovary is called inferior. Example: Guava, Cucumber, flowers of Compositae (sunflower family).
Important Extra Questions
What is venation? Distinguish between reticulate and parallel venation.
Answer
Venation is the pattern of arrangement of veins and veinlets in the leaf blade. In reticulate venation, the veinlets form a network; this is characteristic of dicots (e.g., mango, peepal). In parallel venation, the veins run parallel to each other; this is characteristic of monocots (e.g., grass, banana).
What is a tap root system? How does it differ from a fibrous root system?
Answer
A tap root system develops from the primary root (radicle) which grows vertically downward, bearing lateral roots. It is found in dicots. A fibrous root system develops when the primary root is short-lived and is replaced by numerous thread-like adventitious roots arising from the base of the stem. It is found in monocots. Tap roots penetrate deep soil; fibrous roots spread widely in the upper soil and prevent soil erosion.
What are adventitious roots? Give examples of their modifications.
Answer
Adventitious roots arise from parts of the plant other than the radicle (from stem, leaves, etc.). Modifications include: prop roots (Ficus, banyan) for mechanical support; stilt roots (maize, Pandanus); pneumatophores/breathing roots (Rhizophora, mangroves) for aeration; storage roots (sweet potato); climbing roots (money plant).
What is a node? Distinguish between a node and an internode.
Answer
A node is the point on a stem where leaves, buds, or branches arise. The region between two successive nodes is called an internode. Nodes are solid and have an axillary bud in the leaf axil; internodes are hollow or solid spaces of elongation with no buds. Together, nodes and internodes make up the stem's structural units.
Describe the different types of aestivation.
Answer
Aestivation is the arrangement of sepals/petals in a floral bud. (i) Valvate: petals/sepals just touch at margins without overlapping (e.g., Calotropis). (ii) Twisted (contorted): each petal overlaps the next on one side and is overlapped on the other side (e.g., china rose, cotton). (iii) Imbricate: petals overlap in an irregular manner (e.g., Cassia). (iv) Vexillary (papilionaceous): the largest petal (standard) overlaps two lateral petals (wings), which in turn overlap two smallest petals (keel) – characteristic of pea family (Fabaceae).