NCERT Class 11 Biology Chapter 5 Morphology of Flowering Plants

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NCERT Class 11 Biology Chapter 5 Morphology of Flowering Plants

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Morphology of Flowering Plants

Chapter: 5

BIOLOGY

TEXTUAL QUESTIONS ANSWERS

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. Roots mainly absorb water and min-erals from the soil. Roots modify their shape and structure to perform various functions and act as storage sites for food, support to plant, respiration etc. Type of Root modifications found in:

(a) Banyan tree — prop roots.

(b) Turnip — fleshy tap roots.

(c) Mangrove tree — pneumatophores.

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

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

Ans. Underground parts of a plant are not always roots: Stems are also modified to underground structures to do differ-ent functions like storage of food, vege-tative propagation, perennation etc. Underground modifications of stem are rhizomes, corm, tuber and bulb.

(ii) Flower is a modified shoot.

Ans. During the flowering season, apical meristem forms floral meristem. The axis of the stem gets condensed, while the internodes lie near each other and various floral appendages arise from the node. Therefore, flower is a modi-fied shoot.

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

Ans. Pinnate Compound Leaf:

(i) Leaflets are borne laterally on an elongated axis [midrib/lateral vein] like a feather.

(ii) Leaflets occur in two rows. e.g. Neem.

Palmate Compound Leaf:

(i) Petiole bears leaflets at the tip like the fingers of the palm.

(ii) Leaflets are clustered together. eg Bombax (Silk Cotton), Citrus

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

Ans. Phyllotaxy:

(i) It is the arrangement of leaves on the stem or its branches.

(ii) The purpose is to get proper expo- sure to sunlight.

(iii) It is of three types –

1. Spiral/Alternate-

• Only one leaf is borne on a node and leaves of the adjacent nodes lie towards the opposite sides e.g. Mustard, sun- flower, china rose (shoe flower), grass.

2. Opposite-

• Two leaves are borne on the opposite sides of a single node e.g. Calotropis, Tulsi, Guava.

3. Whorled/Verticllate-

• Three or more than three leaves develop from a single node e.g. Alstonia, Oleander.

Q.5. Define the following terms:

(a) Aestivation.

Ans. Aestivation is the mode in which sepals or petals are arranged in a floral bud with respect to other floral members. There are four types of aestivation –val-vate, twisted, imbricate, and vexillary.

(b) Placentation.

Ans. Placentation is the arrangement of ovules within the ovary of a flower.It is of five types marginal, basal, pari-etal, axile, and free central.

(c) Actino- morphic.

Ans. Actinomorphic flowers are those flowers which can be divided into two radial halves by any radial plane passing through its centre e.g. chilly and mustard.

(d) Zygomorphic.

Ans. Zygomorphic flowers are those flowers which can be divided into two similar halves by asingle vertical planee.g. pea and beans.

(e) Superior ovary.

Ans. Superior ovary:

(i) Gynaecium or Ovary is superior: They develop at its tops while sta- mens, petals, sepals are born below.

(ii) e.g. Mustard, Shoe Flower (China Rose), brinjal.

(f) Perigynous flower.

Ans. Perigynous flower:

(i) Thalamus forms an expanded structure called hypanthium (Floral Cup).

(ii) Ovary is superior (eg Pea, Cassia) or half inferior (eg Plum, Peach, Rose).

(iii) Gynaecium lies in center while other floral parts occur on periphery at around or above the level of ovary.

(g) Epipe- talous Stamen

Ans. Epipetalous Stamen:

Epipetalous stamens are stamens attached to the petals. They are found in brinjal.

Q.6. Differentiate between-

(a) Racemose and cymose inflorescence.

Ans. Racemose Inflorescence:

(i) It shows indefinite growth and bears a number of flowers due to the presence of active growing point.

(ii) The arrangement of flower is either acropetal (older towards base and younger towards apex) or centripetal (older towards periphery and younger towards centre). Types —

Cymose Inflorescence-

(i) It is definite inflorescence in which the tip of the main axis terminates in a flower and further growth continues by one or more lateral branches.

(ii) The arrangement of flowers is either basipetal or centrifugal.

(iii) e.g. Solanum, Bougainvillea.

(b) Fibrous roots and adventitious roots.

Ans. Fibrous Root System-

(i) It is a root system found in many monocots e.g. Wheat, Barley

(ii) Number of thin, thread like branched roots develop from the base of the stem.

(iii) They form a bunch which helps in holding the soil firmly. It gives good anchorage to the plant, helps in proper absorption of water and min-erals.

Adventitious Root System-

(i) It is found in both dicots and monocots.

(ii) Roots that grow from any part of plant other the radicle or its branches are called adventitious roots. They develop from stem nodes, internodes, leaves etc

(i) It may be underground or aerial.

(c) Apocarpous and syncarpous ovary.

Ans. Gynaecium may be apocarpous (with free carpels) as in lotus, rose or syn. carpous (with fused carpels) as in mus. tard and tomato.

Q.7. Describe modifications of stem with suitable examples

Ans. Modifications of stem with examples are:

(A) Modifications of Prostrate / Sub aerial weak stems-

(i) Runners – e.g. Grass

(ii) Stolons – e.g. Jasmine, Peppermint.

(iii) Offset – e.g. Pistia, Eichhornia.

(B) Modification of Underground Stems-

Sucker – e.g. Chrysanthemum (Mint), Banana, Pineapple.

Rhizome – e.g. fernDryopetris, Banana (Musa), Water lily, Lotus (Nelumbo), Ginger (Zingiber).

Corn – e.g. Gladiolus, Colocasia, Crocus.

Tuber – e.g Potato (Solanum tuberosum).

Bulb – e.g Tulip, Garlic, Onion, Lily.

(C) Modification of Aerial Stems-

Stem Tendrils – e.g. Grape Vine, Gourds (water melon, pumpkin, cucumber).

Stem Thorns – e.g. Citrus, Bougainvillea.

Phylloclades – e.g. Opuntia, Euphorbia.

Q.8. Draw the labelled diagram of the following:

(i) Gram seed.

Ans.

(ii) V.S. of maize seed.

Ans.

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

Ans. Family Fabaceae [Flowers of Pisum sativum] Climbing herbaceous plant.

Leaves: Pinnately compound, leaf tendrils with the pulvinus present at the leaf base, venation reticulate.

Root: Tap root system with root nodules.

Floral features:

Inflorescence: Racemose.

Flower: Zygomorphic and bisexual flowers.

Calyx: It contains five sepals, imbricate aestivation.

Corolla: It contains five petals, vexillary aestivation.

Androecium: It consists of ten anthers that are diadelphous with dithecous anthers.

Gynoecium: Monocarpellary superior ovary which is unilocular with marginal placentation.

Fruit: Legume pod with non-endosper- mic seeds

Floral formula:

Family Solanaceae [Flowers of Solanum nigrum] Erect, herbaceous plant

Leaves: Simple, exstipulate leaves with reticulate venation.

Stem: Erect stem with numerous branches.

Floral features:

Inflorescence: Cymose.

Flowers: Actinomorphic, bisexual flowers

Calyx: Calyx is composed of five sepals with valvate aestivation.

Corolla: Corolla consists of five united petals with valvate aestivation.

Androecium: It consists of five epipetalous stamens.

Gynoecium: It consists of bicarpellary syncarpous superior ovary with axile placentation.

Fruits: Berry with numerous, endospermous seeds.

Floral formula:

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

Ans. Placentation:

(i) Placentation is arrangement of placentae and ovules inside an ovary. Types —

(ii) Marginal – Ovary is unilocular. Placenta forms a ridge along the two margins or ventral suture of ovary and ovules are born on ridge in two rows e.g. family leguminosae (Pea, Cassia)

(iii) Parietal – It is seen in syncarpous /fused carpels.

Two or more placentae or ovules develop on the inner wall of ovary.

A false septum called replum develops between placentae eg family Brassicaceae [mustard], Cucurbits, Argemone.

(i) Axile Ovary is multilocular and ovules are attached to axial placenta. egg, tomato, lemon, china rose.

(ii) Free central – Ovary is unilocular and ovules are born on central axis which is not connected with ovary wall by any septum e.g. Primrose, Dianthus.

(iii) Basal – Ovary is unilocular. It bears a single placenta at the base of ovary with a single ovule e.g. Sun flower, Mari gold.

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

Ans. Flower:

(i) Flowers Condensed Shoot Of Angiosperms to carry sexual reproduction.

(ii) It may develop in axil of small leaf like structure called bract.

(iii) Floral organs are of four types – sepals, petals, stamens and carpels.

(iv) A typical flower has floral organs arranged on the swollen end of G stalk or pedicle called thalamus or receptacle

(v) Sepal and petal are nonessential or accessory floral organs which do not take part in sexual reproduction.

(vi) Stamens and carpels are essential floral organs as they are sporophylls which take part directly in sexual reproduction.

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

Ans. Modifications of Leaves-

1. Leaf Tendrils – are thread like sensitive structures which can coil around a support to help the plant in climbing eg Pea [Pisum].

2. Leaf Spines – The leaf parts change into spines to protect the plant from grazing animals and excessive transpiration eg Aloe, Opuntia [Cactus].

3. Phyllodes – Petiole and rachis become flat structure for performing the function of food synthesis eg Acacia.

4. Leaf Pitchers –

(i) Leaf lamina forms a large pitcher eg Nepenthes, Dischidia.

(ii) Leaf is changed into an open pitcher for storing rain water.

(iii) Pitchers are meant for catching and digesting insects for nitrogen deficiency in plants.

5. Succulent Leaves-

(i) The leaves are fleshy or swollen.

(ii) They store water, mucilage or food materials.

(iii) Succulent leaves occur in plants of saline and xerophytic habitats eg Aloe, Agave, Bryophyllum, Portulaca.

(iv) Scaly storage leaves are seen in Onion.

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

Ans. INFLORESCENCE

(i) Inflorescence is the arrangement and distribution of flowers over a plant.

(ii) Inflorescence is the modified shoot that is specialized to bear flowers.

(iii) The axis of the inflorescence is called peduncle. A flattened peduncle is known as receptacle.

(iv) Inflorescence is of five types solitary, racemose, cymose, mixed and specialized.

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.

Ans. The floral formula of the described flower is represented as:

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

Ans. Forms of Thalamus-

(a) Hypogyny-

(i) Thalamus is convex or conical

(ii) Gynaecium or Ovary is superior: They develop at its tops while stamens, petals, sepals are born below.

(iii) e.g. Mustard, Shoe Flower (China Rose), brinjal.

(b) Perigyny-

(i) Thalamus forms an expanded structure called hypanthium (Floral Cup).

(ii) Ovary is superior (eg Pea, Cassia) or half inferior (eg Plum, Peach, Rose).

(iii) Gynaecium lies in center while other floral parts occur on periphery at around or above the level of ovary.

(c) Epigyny-

(i) Thalamus is in the form of flask but with its internal wall fused with wall of ovary.

(ii) Ovary is inferior.

(iii) Eg Apple, Guava, Sunflower.