CBSE Class 11 Biology Chapter 7: Morphology of Flowering Plants NCERT Solutions

Solution:

Modification of root refers to the process where roots undergo structural changes to perform functions other than their primary roles of anchorage and absorption of water and minerals. These specialized functions can include storage of food reserves, mechanical support, or gas exchange.

The types of root modifications found in the given examples are:

1. Banyan tree: The massive, pillar-like structures seen hanging from the branches of a banyan tree are adventitious roots that grow downwards to provide additional support to the heavy branches. These are known as prop roots.
2. Turnip: The turnip is a classic example of a root modified for food storage. It has a swollen taproot that stores a significant amount of nutrients. Other examples of such storage roots include carrots and radishes.
3. Mangrove trees: Mangroves grow in waterlogged, saline environments with poorly aerated soil. To overcome this, their roots develop specialized structures called pneumatophores. These are negatively geotropic roots that grow vertically upwards, emerging from the soil surface to facilitate gaseous exchange (uptake of oxygen) through numerous pores called lenticels.

Solution:

1. Underground parts of a plant are not always roots: Many plant parts that grow underground are not roots but modified stems or leaves, adapted for various functions like storage, vegetative propagation, or perennation. For instance:
   • Rhizomes: Underground stems like those found in ginger and banana are swollen and store food.
   • Corms: Underground stems such as those in Colocasia and 'Zamin-khand' are also modified for storage.
   • Tubers: The potato is a classic example of a tuber, which is a swollen underground stem tip bearing 'eyes' (nodes with buds).
   • Fleshy leaves: In plants like onions, the underground leaves become fleshy and store food.
   • Geocarpy: In groundnuts, the ovary or flower stalk elongates after fertilization and pushes the developing fruit into the soil.
2. Flower is a modified shoot: A flower develops from the apical meristem of a plant's stem. During the reproductive phase, the shoot apical meristem transforms into a floral meristem. The stem axis (which is typically elongated) becomes condensed, and the internodes become very short, bringing the nodes closer together. Instead of leaves, various floral appendages (sepals, petals, stamens, and carpels) arise in a specific sequence from these nodes. This organization and development pattern are analogous to that of a shoot, leading to the conclusion that a flower is essentially a highly modified reproductive shoot.

Solution:

Pinnately compound and palmately compound leaves differ in the arrangement and attachment of their leaflets:

• Pinnately Compound Leaf: In this type of leaf, the leaflets are attached along a common axis, which is an extension of the petiole and is called the rachis. The leaflets are arranged feather-like along this central axis. Examples include the leaves of neem (Azadirachta indica) and Cassia fistula (Golden Shower tree).
• Palmately Compound Leaf: In this type, all the leaflets are attached at a single point, which is the tip of the petiole. The leaflets radiate outwards from this common point, resembling the fingers of a palm. Examples include the leaves of silk cotton (Bombax) and Cannabis.

Solution:

Phyllotaxy refers to the specific pattern or arrangement of leaves on the stem of a plant. This arrangement is crucial for maximizing sunlight exposure for photosynthesis. There are three main types of phyllotaxy:

1. Alternate Phyllotaxy: In this arrangement, a single leaf arises from each node, and the leaves are positioned alternately along the stem. This is a very common type of phyllotaxy. Examples include plants like sunflower (Helianthus annuus), mustard (Brassica juncea), and peepal (Ficus religiosa).
2. Opposite Phyllotaxy: Here, two leaves arise from each node, positioned on opposite sides of the stem. This arrangement can be further classified into 'decussate' if successive pairs of leaves are at right angles to the previous pair. Examples include plants like guava (Psidium guajava) and jamun (Syzygium cumini).
3. Whorled Phyllotaxy: In this type, three or more leaves arise from a single node, forming a whorl around the stem. This arrangement is less common than alternate or opposite. An example is the Alstonia plant.