Study Of Different Modifications In Roots, Stems, And Leaves

Aim Of The Experiment

To study different modifications in roots, stems and leaves.

Theory

Angiosperms or flowering plants are differentiated into flowers, stem, roots, and leaves. These plants bear seeds that enclose the fruit. On the basis of seed type they can be classified into:

  • Monocotyledonous – They have seeds with a single cotyledon
  • Dicotyledonous – They have two cotyledons

Materials Required

  • Dissecting microscope
  • Glass slides
  • Forceps
  • Hand lens
  • Scissors
  • Onion/paddy/wheat/maize plant (complete monocot plant)
  • Sunflower/pea/mustard (complete dicot plant)

See Also: Leaves: Morphology, Types & Modification

Procedure

  • Select a monocot plant. Dissect the plant for different parts such as stem, root, flower and leaves of this plant using scissors. Set up these different parts on separate slides with the help of forceps
  • Repeat the same process for a dicot plant
  • Make observations compare different external features of stem, root, leaves and flower of the dicot and monocot plants with the help of a hand lens and afterwards by dissecting microscope.

Observation

1) Root

Distinguish the root features:

  • The root is the part of the plant that typically emerges from the embryo’s radicle
  • It renders rigidity against water and wind and firmly fixes the plant to the ground
  • Absorption of minerals and water from the soil
  • It is positively geotropic, it grows towards the centre of the gravity
  • It has unicellular root hairs
  • Normally, it grows away from light. It is negatively phototropic
  • It does not yield leaves, buds and flowers that do not have internodes and nodes.

Regions of the root

 

 

 

 

 

 

 

 

 

 

 

 

 

  • The root consists of four regions up till the base from the apex.
  • Apical meristem – cell division region
  • Root cap
  • Elongation region
  • Maturation region
  • The root cap renders protection to the developing root apex. The main growing part of the root is found just behind the root cap.

External features of plant

 

Monocot Root

  • Primary roots do not sustain for long, they are replaced by a group of elongates, thread-like roots that emerge from stem foundation which is known as fibrous roots
  • Adventitious roots are the roots that emerge from different plant parts other than the radicle
  • One type of adventitious root is the fibrous root
  • The root thickness is slender due to the absence of secondary growth

Types of root

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Dicot Root

  • Root directly emerge from the radicle
  • They develop into long, thick primary roots
  • They form the tap root as a result of persisting and turning stronger
  • It yields lateral branches known as secondary roots
  • The tertiary roots are the branches of the secondary roots
  • Along with the taproot, the branch system is referred to as the taproot system.

2) Stem

Distinguish the stem features:

  • It emerges from the plumule of the embryo
  • It is the ascended plant part and results in the formation of the axis
  • It is distinguished into the nodes and internodes
  • At the nodes, the stem yields the branches and the leaves. The internodes is that section of the stem that is found between two nodes
  • As they grow towards the light they are positively phototropic
  • As they grow away from gravity, they are negatively geotropic
  • The stem and the branches form the shoot of the plant and are green in colour, hence are photosynthetic
  • The stem apex is known as the shoot tip. It yields the apical bud that accounts for the plant elongation. The shoot apex does not have a cap
  • They possess trichomes or multicellular or unicellular hair.
  • Function: Renders support to the branches and leaves and fixes them in their position in order to receive light to the maximum. Hence, they form the main skeleton of the plants.

Monocot Stem

  • It is erect, aerial, woody or herbaceous and branched usually.
  • They are typically distinguished into hollow internodes and solid nodes. The internodes in maize are solid
  • The stem in some plants is altered into underground structures such as rhizome (example: ginger), bulb(example: onion)

Dicot Stem

  • Typically erect, long, woody or herbaceous, branched and cylindrical.
  • It has discrete and solid internodes and nodes
  • In some plants, they are altered into tendril
  • They can be five-angled or four-angled
  • The underground stem in potato is altered into tubers

3) Leaf

  • The leaf is the lateral appendage which emerges at the node
  • The axil yields the bud
  • They are appended to the stem through the leaf base
  • The petiole is a stalk that emerges from the base of the leaf and yields the lamina which is the green flattened structure
  • The leaf blade or the lamina bears the veins, midrib, leaf margin and the leaf apex
  • The leaves can be categorized into compound and simple, depending on the incision. Simple leaves possess only one lamina. A compound leaf has many leaflets(multiple leaf segments) which are as a result when the lamina incision reaches the midrib.
  • Function – Food synthesis, gas exchange through stomata, transpiration
  • Leaves are altered for defence, storage, reproduction, support and to trap insects.

Monocot Leaf

  • Isobilateral arrangement of leaves – Similar surfaces on both sides
  • Parallel venation – arrangement of veins on the lamina). The veins are parallel that arise from the base to the lamina tip.
  • They are narrow, long and parallel to the stem
  • Simple
  • Typically leaf sheath is observed(leaf base is expanded into a broad sheath)

Venation In Leaves

Dicot Leaf

  • Dorsoventral arrangement of leaves – lower and upper surface are discrete
  • Reticulate ventation – Irregular distribution resulting in the formation of a network.
  • The base of the leaf has stipules which are two lateral appendages
  • They are either pinnately compound or simple
  • The leaf sheath is not observed

4) Flower

Distinguishing features of a flower:

  • The flower is the reproductive part, observed in higher plants(angiosperms). It develops from floral buds
  • It is assumed to be the altered shoot
  • The pedicel is the flower stalk. The pedicel tip persists as an extended axis known as receptacle or thalamus.
  • The floral parts are ordered in a definite sequence on the thalamus
  • A flower typically has 4 floral whorls or components, such as:
  • Sepals(calyx)
  • Petals(corolla)
  • Stamens(androecium)
  • Carpels(gynoecium)
  • The corolla and calyx are not responsible directly for reproduction. They are known as accessory whorls
  • The gynoecium and the androecium(inner two whorls) are involved in sexual reproduction. They are referred to as essential whorls.
  • The outermost whorl formed by the sepal is known as calyx. It is green in colour and has a leaf-like structure and emerge from the flower base.
  • Corolla is formed by the petals. They are fragrant, bright coloured.
  • The androecium is the third whorl and forms the male reproductive part of the flower. It comprises of the stamens. Each stamen has a slim filament and the tip, there is an anther.
  • The pistil or the gynoecium is the fourth whorl that is centrally present. It yields the female reproductive structure known as carpel. Every pistil has a basal swelled ovary, a tapered stalk-like style, and stigma at the top. The ovary comprises of one or multiple ovules.

Monocot Flower

  • Corolla and calyx are not discrete. The perianth is observed and consists of tepals.
  • Flowers appear in a group
  • The flower is usually trimerous – every whorl is found in multiples of three
  • Typically, stamens are versatile. The filament is fastened to the anther’s back at one point.

Parts Of A Flower

Dicot Flower

  • They have discrete floral parts – corolla, calyx, gynoecium and androecium.
  • Calyx consists of sepals and Corolla consist of petals
  • Flowers are usually pentamerous(whorls in multiples of 5), a few other times they are tetramerous(whorls in multiples of 4).
  • Flowers, apparently are separate
  • Stamens are typically basified – the filament is fastened to the anther’s base.

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