NCERT Solutions Class 11 Biology Chapter 5

Q.1 What is meant by modification of root? What type of modification of root is found in the:

(a) Banyan tree
(b) Turnip
(c) Mangrove trees

Ans-

The root performs two major functions in a plant:

1. Absorption of nutrients and water from the soil for proper growth of the plants, and
2. Providing mechanical support to plant by anchoring it tightly with the soil

However, in some cases, depending on the environmental conditions and physiological needs of the plants, the roots get modified to perform the functions apart from the ones mentioned above. This change in the root structure and function is known as root modification. The types of root modification in different plants/trees are listed below:

Q.2 Justify the following statements on the basis of external features:

(i) Underground parts of a plant are not always roots.

(ii) Flower is a modified shoot.

(i) Underground parts of a plant are not always roots.

Ans-

During the course of evolution, plants modified their external morphologies according to the environmental conditions of their ecological niches for better adaptability. There are several examples where the stem, which is generally the aerial part of a plant, gets modified in a way that it remains under the soil. Such stem modifications can easily be recognized by the presence of nodes and internodes on them. The main reason for such modifications is to protect the plant from unfavourable environmental conditions. For example, the underground part of ginger, turmeric, zaminkand, and Colocasia all have distinct node and internodes, thus they are stem modifications. Similarly, in banana, pineapple and Chrysanthemum, the stem remains underground and grows beneath the soil. In case of onion and garlic, the leaves remain underground, become fleshy, and store food. Therefore, from the above examples, it is clear that underground parts of plants are not always roots as both stem and leaves in some cases have modified themselves to grow beneath the ground.

(ii) The flower is a modified shoot.

During the flowering season, the apical shoot meristem gets transformed to floral meristem. The close anatomical study of a flower reveals the presence of nodes and internodes. The main axis gets highly condensed and the internodes do not undergo further elongation. From the apex, instead of leaves, various floral appendages such as calyx, corolla, androecium and gynoecium arise. Thus, it can be said that a flower is a modified shoot.

Q.3 How is a pinnately compound leaf different from a palmately compound leaf?

Ans-

Q.4 Explain with suitable examples the different types of phyllotaxy.

Ans-

The term phyllotaxy originated from the Greek words ‘phyllon’ which stands for “leaf” and “taxis” which stands for arrangement. Thus, the pattern of arrangement or organization of leaves on a branch or stem is called phyllotaxy.

Broadly, it is of three types:

(i) Alternate: When each node of the axis bears a single leaf, it is called alternate phyllotaxy. Example: China rose, mustard and sunflower plants.

(ii) Opposite: When each node of the axis bears a pair of leaf facing in the opposite direction, it is called opposite phyllotaxy. Example: Calotropis and guava plants.

(iii) Whorled: When more than two leaves arise from each node, it is called whorled phyllotaxy. Example: Alstonia.

Q.5 Define the following terms:
(a) aestivation
(b) placentation
(c) actinomorphic
(d) zygomorphic
(e) superior ovary
(f) perigynous flower
(g) epipetalous stamen

Ans-

(a) Aestivation: The positional arrangement of sepals or petals in the floral bud with respect to other sepals or petals in the same whorl is called aestivation. The four different types of aestivation are twisted, valvate, imbricate and vexillary.

(b) Placentation: The arrangement of ovules in the ovary is called placentation. Depending on the pattern of arrangement, placentation is categorized into different types, namely marginal, parietal, axile, basal, central and free central.

(c) Actinomorphic: The flowers that can be divided into equal halves in any of the radial plane passing through the centre of the flower are called actinomorphic. Thus, these flowers show radial symmetry. Example: flowers of chilli and Datura are actinomorphic.

(d) Zygomorphic: The flowers that can be divided into two equal halves only in one particular vertical plane are called zygomorphic. These flowers show bilateral symmetry. Example: flowers of Gulmohar, bean and Cassia are zygomorphic.

(e) Superior ovary: The flowers in which the gynoecium is present at the highest position, that is, above calyx, corolla and androecium, the ovary in such flowers is called the superior ovary. Example: mustard, china rose and brinjal.

(f) Perigynous flower: The flower in which the ovary (gynoecium) is located at the centre of the thalamus while other floral appendages are located at the rim of the thalamus, such flower is called perigynous flower. Example: plum, rose, and peach.

(g) Epipetalous stamen: When the stamen is connected to the petals of a flower, it is known as the epipetalous stamen. Example: Brinjal

Q.6 Differentiate between

(a) Racemose and cymose inflorescence

(b) Fibrous root and adventitious root

(c) Apocarpous and syncarpous ovary

Ans-

(a) Racemose and cymose inflorescence

(b) Fibrous root and adventitious root

(c) Apocarpous and syncarpous ovary

Q.7 Draw the labelled diagram of the following:

(i) gram seed

(ii) V.S. of maize seed

(i) Gram seed

(ii) Vertical section (V.S.) of maize seed

Q.8 Describe modifications of stem with suitable examples.

Ans-

The stem is the aerial part of a plant which originates from the plumule of the embryo and bear branches, leaves, flowers and fruits. In certain cases, it gets modified into tendrils, thorns, fleshy, or flattened structures. The main functions of stem are as follows:

(i) It forms an axis to support the lateral branches, flower and fruits.

(ii) It conducts water and nutrients through vascular tissue.

(iii) It bears leaves.

Apart from the above-mentioned functions, the stems sometimes get structurally modified to perform the following specialized functions:

(i) Storage: In the case of potato, zaminkand, Colocasia, ginger, and turmeric the stem gets modified to form an underground structure that protects the plant from unfavourable conditions and also acts as a storage organ.

(ii) Support: In some creepers such as cucumber, pumpkin and watermelon, the stem gets modified to form a slender and spirally coiled structure, called tendril, that coils around the wall or rope and helps the plant in climbing up.

(iii) Protection: In Bougainvillea and Citrus plants, the axillary bud of stem gets modified to a straight and pointed woody structure called a thorn, which protects the plants from being eaten up by herbivorous animals.

(iv) Photosynthesis: In arid regions, to prevent high water loss through transpiration, plants modify their stem into a flattened or fleshy cylindrical structure. These structures have chlorophyll and perform photosynthesis. Examples: Opuntia and Euphorbia.

(v) Vegetative propagation: In plants like grasses and strawberry, the underground stem spreads to new niche and develops into new plants. In mint and jasmine, the lateral branches after growing for certain length, arch down to the ground and form a new plant. In some aquatic plants like Pistia and Eichhornia, each node bears the rosette of leaves and tuff of roots, which give rise to a new plant once it gets detached from the parent plant.

Q.9 Take one flower each of the families Fabaceae and Solanaceae and write its semi-technical description. Also draw their floral diagram after studying them.

Ans-

	Fabaceae	Solanaceae
Name of Plant	Pea plant (Pisum sativum)	Makoi plant (Solanum nigrum)
Vegetative Characters	Herbaceous climber	Annual herb
Root	Contains root nodules	Tap root without nodules
Stem	Erect, branched, solid, possesses tendrils	Herbaceous, erect, smooth and branched
Leaves	Alternate, pinnately compound, reticulate venation, pulvinate base, terminal leaflet modifies into tendrils	Alternate, simple, estipulate with reticulate venation
Inflorescence	Racemose	Cymose
Flower	Bisexual, zygomorphic	Bisexual, actinomorphic
Calyx	Five sepals, gamosepalous; imbricate aestivation	Five sepals, united, persistent; valvate aestivation
Corolla	Five petals, polypetalous, vexillary aestivation	Five petals, united, valvate aestivation
Androecium	Ten stamens, diadelphous, anther dithecous	Five epipetalous stamens
Gynoecium	Superior ovary, mono carpellary, unilocular with many ovules, single style	Bicarpellary, syncarpous, superior ovary, bilocular, swollen placenta with many ovules.
Fruits	Legume	Berry
Seeds	Several, non-endospermic	Many, endospermic
Floral diagram

Q.10 Describe the various types of placentations found in flowering plants.

Ans-

The arrangement of ovules in the ovary is called placentation. Depending on the mode of arrangement, placentation is of following types:

1. Marginal placentation: It is observed in the flowers where gynoecium is monocarpellary, apocarpous and unilocular as in pea. At the ventral surface of the ovary, a ridge is formed by the placenta and ovules are borne in the ridge.
2. Axile placentation: It is observed when gynoecium is multicarpellary, syncarpous and multilocular. Here, the placenta is axial and ovules are attached to it in the multilocular ovary. Example: China rose, tomato and lemon.
3. Parietal placentation: It is observed when gynoecium is multicarpellary, syncarpous and unilocular. Here, ovules develop on the periphery of the ovary. Example: mustard and Argemone.
4. Free central placentation: In this, the gynoecium is multicarpellary, syncarpous and unilocular and the ovules are borne on the central axis without any septa. Example: Dianthus and Primrose.
5. Basal placentation: In this, the gynoecium is unilocular with placenta developing at the base of the ovary and single ovule attaches to it. Example: Sunflower and marigold.

Q.11 What is a flower? Describe the parts of a typical angiosperm flower.

Ans-

The reproductive unit of the angiosperm plant, bearing male or female or both reproductive parts that are responsible for sexual reproduction is called flower. A flower is a modified stem with a highly condensed axis.

A typical angiosperm flower consists of four whorls, namely calyx, corolla, androecium and gynoecium. The flower, having all these four whorls, is known as a complete flower. The complete flower is a bisexual flower as both male and female gamete forming organs are present in it. The various parts of a typical angiosperm flower are described below:

(i) Calyx: It is the outermost whorl of the flower. It consists of individual units called sepals. Generally, sepals are green in colour. Its main function is to protect the bud of the plant from adverse environmental conditions. If the sepals are free, it is called polysepalous but sometimes sepals are fused giving rise to the gamosepalous condition.

(ii) Corolla: Next to calyx is corolla, which consists of individual petals. Petals are beautiful coloured structures that play a key role in attracting insects to increase the chances of pollination.

(iii) Androecium: The male gamete producing part of the plant is called androecium. Its individual units are called the stamen. An individual stamen consists of filament and anther.

(iv) Gynoecium: It is the female reproductive organ of a plant. It consists of carpels. Each carpel is made up of three parts, namely; ovary, style and stigma.

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

Ans-

Leaves are the photosynthetic sites of the plant; however, in some cases, they get modified to provide support, protection, storage or nutrients to the plants.

1. Support: In case of plants like pea, the leaves get converted to a spiral structure called tendrils that help the plant to climb up on the support structure like a wall.
2. Protection: In cactus, the leaves get reduced to spins to protect the plant from animals as well as to reduce water loss through stomata.
3. Storage: The fleshy underground leaves of garlic and onion help in the storage of food and ensure the survival of plant under unfavourable conditions.
4. Nutrients: In the carnivorous plants such as venus-fly trap that grows in the nitrogen-deficient soil, the leaves get modified into a pitcher to capture the insect and thus provide required nutrients to the plant.

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

Ans-

The arrangement of flowers on the floral axis is called inflorescence.

During the flowering season of a fully developed plant, the apical meristem gives rise to floral meristem which in turn develops the floral axis. Floral axis contains laterally developed flowers. On the basis of the type of growth of the floral axis, the inflorescence is of two types:

(i) Cymose inflorescence or determinate inflorescence: When the main axis terminates in a flower, it is known as cymose inflorescence. This type of inflorescence limits the growth.

(ii) Racemose or indeterminate inflorescence: When the main axis keeps on growing without terminating in a flower bud, it is known as racemose inflorescence.

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

Ans-

Keys:

Terms	Symbol used in the floral formula
Actinomorphic
Bisexual
Five united sepals	K(5)
Five free petals	C5
Five free stamens	A5
Two united carpels with superior ovary and axile placentation	G(2)

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

Ans-

The floral appendages are arranged on the thalamus. On the basis of the location of the ovary with respect to other floral appendages (calyx, corolla and androecium), the flower can be broadly classified into three categories:

(a) Hypogynous flower: In some plants like mustard, china rose and brinjal, gynoecium occupies the highest position compared to calyx, corolla and androecium. Such flowers are called hypogynous flowers. Here, the ovary is located at the uppermost part of the thalamus. Such an ovary is called the superior ovary.

(b) Perigynous flower: In the flowers like rose, the gynoecium is at the centre of the thalamus and other floral whorls are at the rim of the thalamus with ovary situated at the same level. Such flowers are called perigynous flowers.

(c) Epigynous flower: In the flowers like guava, the margin of thalamus completely covers the ovary and other floral whorls arise above the ovary. Such flowers are called epigynous flowers.