Biology Class 11 NCERT Solutions: Chapter 5 Morphology of Flowering Plants Part 5

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Q: 12. How do the various leaf modifications help plants?

Answer

The main function of the leaves is to carry out the process of photosynthesis.

However, in a few plants, leaves are modified to perform different functions.

Image of the various leaf modifications

Image of the Various Leaf Modifications

Image of the various leaf modifications

(A) Tendrils: The leaves of a pea plant are modified into tendrils that help the plant in climbing.

(B) Spines: The leaves in cactus are modified into sharp spines that act as an organ of defense.

(C) Phyllode: The leaves of some Australian acacia are short-lived and soon replaced by flattened, green structures called phyllodes that arise from the petiole of the leaves. The petioles in these plants synthesize food.

(D) Pitcher: The leaves of the pitcher plant are modified into pitcher-like structures, which contain digestive juices and help in trapping and digesting insects.

Q: 13. Define the term inflorescence. Explain the basis for the different types of inflorescence in flowering plants.

Answer

Inflorescence is the manner in which the flowers are arranged on the flowering axis. During the flowering season, the vegetative apex of the stem gets converted into a floral meristem. Based on whether the floral axis continues to grow or end in a flower, inflorescence is classified into racemose and cymose. In racemose inflorescence, the floral axis continues to grow and produces flowers laterally. On the other hand, in cymose inflorescence, the main axis terminates into a flower. Hence, it is limited in growth.

Image of the different types of inflorescence

Image of the Different Types of Inflorescence

Image of the different types of inflorescence

Q: 14. Write the floral formula of an actinomorphic bisexual, hypogynous flower with five united sepals, five free petals. Five free stamens and two united carpals with superior ovary and axile placentation.

Answer

The floral formula of the described flower is represented as:

Actinomorphic flowers are represented by the symbol .

A bisexual flower is indicated by .

The calyx contains five united sepals which can be represented as .

The corolla consists of five free petals and it represented as

The androecium consists of five free stamens and is represented by .

The gynoecium consists of a superior ovary with two united carpels and axile placentation’s, which can be represented as ,

Q: 15. Describe the arrangement of floral members in relation to their insertion on thalamus?

Answer

Based on the position of the calyx, corolla, and androecium (with respect to the ovary on the thalamus), the flowers are described as hypogynous, perigynous, and epigynous. In hypogynous flowers, the ovary occupies the highest position on the thalamus while other floral parts are situated below it. In such flowers, the ovary is superior e.g., China rose, mustard etc.

In perigynous flowers, the ovary is situated at the centre and other floral parts are arranged on the rim of the thalamus. The ovary here is said to be half inferior e.g., plum, rose, peach.

In epigynous flowers, the thalamus grows around the ovary fusing with its wall. The other floral parts are present above the ovary. Hence, the ovary is said to be inferior

e.g., flowers of guava and cucumber.