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MHT-CET : Biology Entrance Exam

MHT - CET : Biology - Conquest of Land Page 3

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27.

Characters of Jowar Plant (Sorghum)

 

  • Jowar is an example of monocotyledons. It has fibrous root system, unbranched stem, parallel venation of leaf, trimerous symmetry of flower and single cotyledon in seed.
  • The non-essential whorls, i.e., calyx and corolla are not differentiated here. They show a fused structure called perianth.
  • Secondary growth is absent.

 

 

 

 

28.

Systematic Position of Jowar

 

 

Classification of Jowar, i.e., sorghum vulgare is as follows:

 

Kingdom        

:

Plantae

:

Multicellular autotroph

 

Division       

:

Spermatophyta

:

Seeds produced during sexual reproduction.

 

Subdivision

:

Angiospermae

:

Seeds inside fruits

 

Class       

:

Monocotyledonae

:

Single cotyledon in the embryo

 

Order      

:

Glumae

:

Flowers arranged in spikes and presence of glumes.

 

Family      

:

Graminae

:

Caryopsis type of fruit

 

Genus      

:

Sorghum

 

 

 

Species   

:

Vulgare

 

 

 

 

 

 

29.

Root System, Stem and Leaf of Jowar

 

 

  • In addition to fibrous root system, jowar shows presence of additional roots arising from basal nodes. These are called stilt roots which give additional support.
  • Stem called culm is unbranched with nodes and internodes.
  • Leaves are simple, sessile, arranged in alternate fashion on the stem. Each leaf has entire margin, acute apex and parallel venation. Each leaf shows a sheathing leaf base having hairy ligule.

 

 

 

 

30.

Inflorescence in Jowar

 

 

  • In Jowar, many minute flowers are produced on a special branch called inflorescence which is produced at the tip of the stem. In Jowar, panicle type of inflorescence is produced.
  • Flowers produced in the inflorescence are called spikelets.
  • In Jowar, two types of spikelets are produced in a pair.
  • One pair is with stalk called pedicellate while the other is without stalk called sessile. Sessile spikelet is fertile and produces grains while the pedicellate spikelet has only stamens thus called staminate. This produces only pollen grains and cannot form grains.

 

 

 

 

31.

Structure of Sessile Spikelet of Jowar

 

 

  • Presence of two protective bracts called glumes.
  • Lemma and palea are the delicate bracts present inside glume.
  • Perianth is in the form of two minute, membranous structures called lodicules.
  • Presence of three stamens each having versatile anthers which hang outside.
  • Gynoecium is made up of ovary, style, stigma.
  • Ovary contains single ovule, two styles with feathery stigmas.

 

 

 

 

32.

Pollinations and Adaptations for Wind Pollination in Jowar

 

 


In Jowar, wind pollination takes place. The flower is adapted to wind pollination,
because of following characters.

  1. Pollen grains are light in weight thus easily carried by wind.
  2. As the chances of wastage are more, great quantities of pollen grains are produced.
  3. Versatile anthers swing in the breeze and release pollen grains.
  4. Feathery stigma hangs out to catch pollen grains in the air.

 

 

 

 

33.

Post fertilization Changes and Fruit Formation in Jowar

 

 

  • After pollination, the process of double fertilization and fruit formation takes place.
  • The type of fruit is Caryopsis. It is a single-seeded fruit which has fused testa and pericarp to form a hull. Starchy endosperm forms the major part of fruit.
  • The embryo contains plumule, radicle and single cotyledon which is shield-shaped. This cotyledon is called scutellum.

 

 

 

 

34.

Alternation of Generations in Jowar

 

 

  • Jowar plant itself is a sporophyte.
  • Bicelled pollen grain represents male gametophyte while embryo sac represents female gametophyte.
  • Zygote is the beginning of sporophytic generation.
  • Gametophytic generations are dependent on sporophyte.
  • Since in the entire life cycle, sporophytic and gametophytic generations alternate with each other, the process is called alternation of generations.

 

 

35.

Vascularisation

 

  • Main vascular tissues in plants are xylem and phloem.
  • Xylem helps in conduction of water while phloem helps in conduction of prepared food.
  • The cylinder or core of vascular tissues surrounded by an endodermis is called a 'stele'.
  • The stele consists of xylem, phloem and pericycle and in some cases even pith and medullary rays.
  • The elaboration of vascular tissues was with increasing complexity of plants.
  • The two main types of stele are protostele and siphonostele.

 

 

 

 

36.

Protostele

 

 

  • It is the most simple and primitive type of stele.
  • Here central xylem is surrounded by phloem.
  • Protostele is observed in stems of ferns and roots of most of the plants.
  • Three different types of protostele are - haplostele, actinostele and plectostele.

 

 

 

 

37.

Siphonostele

 

 

  • In this type, there is presence of a central parenchymatous pith.
  • Pith is surrounded by xylem ring and phloem ring in a concentric manner.
  • There are two types of siphonosteles, viz,Ectophloic and amphiphloic.
  • Ectophloic Siphonostele: Here, phloem cylinder lies outside xylem cylinder.
  • Amphiphloic Siphonostele: Here, one cylinder of phloem is outside xylem ring while another cylinder of phloem is on the inner side of xylem.
  • Ectophloic siphonostele resulted in 'eustele' which is a ring of dissected vascular bundles.
  • In atactostele, ectophloic vascular bundles are scattered in the ground tissue.

 

 

38.

Development of Seed Habit

 

  • Seed is fertilized ovule which contains embryo.
  • Seed habit did not appear suddenly but a number of evolutionary stages are involved in the development of seed habit. Such as:
    1. Homosporous Condition: In primitive plants like most of the pteridophytes, only one type of spores were produced.
    2. Heterosporous Condition: Microspores and megaspores were produced which gave rise to male and female gametophyte respectively.
    3. Megaspore Number was Reduced: Out of four megaspores only one develops in a megasporangium.
    4. Retention of female gametophyte on parent plant.
    5. Reduction in male gametophyte.
    6. Development of seed.

 

 

39.

Development of Flower

 

  • Development of flower is from an apical bud.
  • The apical bud divides repeatedly and gives rise to a flower bud with characteristic changes in the arrangement of cells.
  • The physiological changes taking place within the dividing meristematic cells arrest the formation of vegetative leaves.
  • Thus, development of floral leaves takes place. All the floral leaves are developed from individual meristematic cells and give rise to calyx, corolla, androecium and gynoecium.
  • Calyx and corolla are accessory whorls while androecium and gynoecium are essential whorls.

 

 

 

 

40.

Development of Fruit

 

 

  • Development of fruit mainly includes post fertilization changes in ovule and ovary.
  • After completion of fertilization, some changes take place in the wall of the ovary as a result of which it becomes the wall of the fruit.
  • The fruit wall is called pericarp.
  • Seeds are formed from ovules.
  • The funicle of ovule gets converted into stalk of the seed.
  • Nucellus forms the nutritive tissue of the seed.
  • Integuments develop into seed coat, i.e., testa and tegmen.
  • Auxins are produced after fertilization which are responsible for post fertilization changes.

 

 

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