NCERT Class 11-Biology: Chapter – 5 Morphology of Flowering Plants Part 7 (For CBSE, ICSE, IAS, NET, NRA 2022)

Get unlimited access to the best preparation resource for IMO-Level-2 : Get full length tests using official NTA interface: all topics with exact weightage, real exam experience, detailed analytics, comparison and rankings, & questions with full solutions.

Question 4:

The mode of arrangements of sepals or petals in a floral bud is known as aestivation. Draw the various types of aestivation possible for a typical pentamerous flower.


The mode of arrangements of sepals or petals in a floral bud is known as aestivation.

There are 4 types of aestivations, namely –

i. Valvate –

When sepals or petals in a whorl just touch one another at the margin, without overlapping, as in Calotropis, it is said to be valvate.


ii. Twisted –

If one margin of the appendage overlaps that of the next one and so on as in China rose, lady՚s finger and cotton, it is called twisted.


iii. Imbricate –

If the margins of sepals or petals overlap one another but not in any particular direction as in Cassia and gulmohur, the aestivation is called imbricate.


iv. Vexillary –

In pea and bean flowers, there are five petals, the largest (standard) overlaps the two lateral petals (wings) which in turn overlap the two smallest anterior petals (keel) ; this type of aestivation is known as vexillary.


Question 5:

The arrangements of ovules within the ovary is known as placentation. What does the term placenta refer to? Name and draw various types of placentations in the flower as seen in T. S. or V. S …


Each ovary bears one or more ovules attached to a flattened, cushion-like structure called placenta.

The arrangement of ovules within the ovary is known as placentation. There are various types of placentations, namely:

(a) Marginal - In marginal placentation, the placenta forms a ridge along the ventral suture of the ovary and the ovules are borne on this ridge forming two rows. Example - pea.


(b) Axile - When the placenta is axial and the ovules are attached to it in a multilocular ovary, the placentaion is said to be axile. Examples - china rose, tomato and lemon.


(c) Parietal - In parietal placentation, the ovules develop on the inner wall of the ovary or on peripheral part. Ovary is one-chambered but it becomes two-chambered due to the formation of the false septum, e. g. , mustard and Argemone.


(d) Free – Central - When the ovules are borne on central axis and septa are absent, the placentation is called free central. Examples - Dianthus and Primrose


(e) Basal - In basal placentation, the placenta develops at the base of ovary and a single ovule is attached to it. Examples - sunflower, marigold.