Biology · Morphology of Flowering Plants · NEET
Because the shoot apical meristem changes into a floral meristem. In a normal shoot the apex makes leaves at nodes with long internodes in between. In a flower the internodes do not elongate, so the axis becomes condensed, and the apex makes floral appendages (sepals, petals, stamens, carpels) laterally at successive nodes instead of leaves. Same shoot plan, but modified for reproduction. For NEET, remember it is a determinate modified shoot.
From outside to the centre: calyx, corolla, androecium, gynoecium. Calyx (sepals) is the outermost. Then corolla (petals). Then androecium (stamens, the male part). Gynoecium (carpels, the female part) is in the centre. NEET loves this order, so learn it outside-to-in.
The thalamus, also called the receptacle, is the swollen end of the flower stalk (pedicel). All four whorls are arranged one after another on this thalamus. So the thalamus is the condensed axis of the modified shoot that carries the whorls. NCERT uses both names, thalamus and receptacle, for the same part.
Calyx and corolla are the accessory (non-essential) whorls, because they do not make gametes. Androecium and gynoecium are the reproductive (essential) whorls, because they make the male and female gametes. If a flower has both androecium and gynoecium it is bisexual. NEET often frames this as accessory vs essential organs.
No. In a flower the internodes do NOT elongate; the axis gets condensed. This condensation is exactly why the floral parts appear crowded in tight whorls instead of being spread out like leaves on a stem. This point is the reason the flower counts as a modified shoot, and it is a common Assertion-Reason line in NEET.
When a single shoot tip transforms into one flower, that flower is always solitary. When many flowers are arranged on a common floral axis, that arrangement is called an inflorescence (racemose or cymose). So one shoot apex to one flower means solitary; a branched or extended axis carrying many flowers means an inflorescence.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
A flower is the reproductive unit of angiosperms; it is a modified shoot with four whorls (calyx, corolla, androecium, gynoecium) borne on the thalamus.
Calyx is the outermost whorl and gynoecium is the innermost (central) whorl.
A flower is a determinate modified shoot, because once the apex becomes a flower it stops growing further.
The shoot apical meristem changes into a floral meristem, the internodes stop elongating so the axis condenses, and the apex makes floral appendages instead of leaves.
The pedicel is the flower stalk; the thalamus (receptacle) is the swollen tip of that stalk on which the four whorls are arranged.
