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- Internal Structure of a dicot and monocot root
The cross-section of a dicot root shows the following:
- Epiblema/Piliferous layer. It is a single outer most layer of thin walled cells. The outer walls of these cells extents to form unicellular hairs. The epiblema has not cuticle.
- It has many layers of thin walled rounded cells with many inter-cellular spaces. These cells have leucoplasts to store starch grains.
- It has a ring like barrel-shaped layer which are closely packed without intercellular spaces. The radial wall of this layer is thickened. It is the inner most layer of the cortex and surrounds the stele as a cylinder.
- Inner to the endodermis is a single ring like layer called pericycle. The cells have abandoned protoplasm.
- Conjunctive tissue. These are parenchyma cells lying between xylem and phloem bundles.
- It occupies within the centre of the root.
- Vascular bundles. These are arranged in ring. Xylem and phloem are equal number of separate bundles and the arrangement is called radial. Its number varies from 2 to 6. Cambium is present. Xylem bundles consist of protoxylem towards the circumference abutting on the pericycle and metaxylem towards the centre. So it is called exarch. Xylem contains vessels and phloem consists of sieve tubes, companion cells and phloem parenchyma.
The Cross-section fo a monocot root shows the following:
- It is similar to that of dicot root.
- It is wider than dicot root.
- Their radial walls are often thickened. Endodermises without thickenings are called passage cells.
- It lies internal to endoderms. The cells are small and thin.
- It is well-developed and made up of parenchyma cells.
- Vascular bundles. It consists of alternate radial bundles of xylem and phloem. These are numerous Phloem consists of sieve tube, companion cells and phloem parenchyma. Xylem consists of protoxylem, which lies abutting on the pericycle and metaxylem towards the centre (exarch). Protoxylem consists of reticulate vessels.
- Conjunctive tissue. These are sclerenchyma cells.
- Internal Structure of a dicot and monocot leaf
The cross-section of a dicot leaf (dorsiventral leaf) shows the following:
- Both the surfaces are covered by epidermis. The cells are tightly packed and are parenchymatous.
- Cuticle occurs on the outside over the lower epidermis. It is thin or less developed. It checks excessive evaporation of water form the surface. The lower epidermis contains numerous stomata, which contain two guard cells. The guard cells contain chloroplasts. Expansion of guard cells forms a pore in between the two, while their contraction closes the pore.
- The ground tissue lying between the upper and lower epidermis is mesophyll. It is differentiated into (a) palisade parenchyma and (b) spongy parenchyma.
- Palisade parenchyma-Consists of one to three layers of elongated, cylindrical cells and are closely packed. The cells contain numerous chloroplasts. Their function is photosynthesis.
- Spoagy parenchyma-Cells are oval, rounded, irregular and are loosely arranged towards the lower epidermis with large inter-cellular spaces. The cells contain a few chloroplast. These help in diffusion of gases.
- Vascular bundles. Each vascular bundles is covered by a layer of parenchyma cells called bundle sheath. Xylem lies towards the upper side and phloem towards the lower side. Above the xylem few sclerenchyma occur. Vascular bundles are conjoint, collateral but closed.
The cross-section of a monocot leaf (Isobilateral) shows the following:
- Epidermis. Both the surfaces are covered by the layer of parenchyma cells.
- Cuticle. It is distributed equally on both the upper and lower epidermis. Stomata are equally distributed.
- Mesophyll. It is not differentiated into palisade and spongy parenchyma, but contains spongy cells only. Chloroplasts are evenly distributed.
- Vascular bundles. These are conjoint, collateral and closed. Xylem lies towards the upper side and phloem towards the lower side. The midrib contains vascular bundles embedded in sclerenchyma patches.
Differences between dicot and monocot leaves:
|Dicot leaf||Monocot leaf|
|(i) Culticle is present more on upper epidermis.(ii) Mesophyll is differentiated into palisade and spongy parenchyma.
(iii) Stomata are mostly present on the lower epidermis.
(iv) Guanl cells are bean-shaped.
|(i) Cuticle is equally distributed on both epidermises.(ii) It is not differentiated, but consists of spongy parenchyma with chloroplasts.
(iii) Stomata are equally distributed in upper and lower epidermis.
(iv) They are dump-bell shaped.
State the difference:
- Dicot and monocot leaf.
- Dicot and monocot root.
- Lenticels and stomata.
- Closed and open vascular bundles.
- Endrach and exarch xylem.
- Palisade and spongy cells.
- Dorsiventral and isobilateral leaf.
- Radial vascular bundle and collateral vascular bundle.
- Xyle and phloem.
- Conjoint and concentric vascular bundle.
|Sr. No.||Dicot leaf||Monocot leaf|
|1.||(i) Mesophyll tissue is differentiated into palisade and spongy cells.(ii) Stomata are more numersous on the lower epidermis.
(iii) Guard cells are kidney-shaped.
|(i) Mesophyll is not differentiated but consists of spongy cells with chloroplasts.(ii) Stomata are equally distributed.
(iii) Guard cells are dum-bell shaped.
|2.||Dicot root||Monocot root|
|(i) Xylem bundles varies form 2 to 6.(ii) Pericycle gives rise to lateral roots, cambium and cork cambium.
(iii) Cambium appears later.
(iv) Pit is small or absent.
|(i) Xylem bvundles are numerous.
(ii) Pericycle gives rise to lateral roots only.
(iii) Cambium is absent.
(iv) Pith is large and well-developed.
|(i) Do not contain guard cells.(ii) Located in older stems.
(iii) Always open.
|(i) Contain guard cells.(ii) Located in younger stems.
(iii) Open and closes.
|4.||Closed vascular bundles||Open vascular bundles|
|(i) Cambium is absent between xylem phloem.||(i) Cambium is present between xylem and phloem.|
|5.||Endarch xylem||Exarch xylem|
|(i) Mainly present in stem.(ii) Protoxylem lies towards the centre.
(iii) Metaxylem lies towards the periphery.
|(i) Mainly present in root.(ii) Protoxylem lies towards the periphery.
(iii) Metaxylem lies towards the centre.
|6.||Palisade cells||Spongy cells|
|(i) Cells are elongated and cylindrical.(ii) They are closely packed and contain numerous chloroplasts.
(iii) They help in photosynthesis.
|(i) Cells are oval or rounded.
(ii) They are loosely packed and contain less chloroplasts.
(iii) They help in diffusion of gases.
|7.||Dorsiventral leaf||Isobilateral leaf|
|(i) It has distinct upper and lower surfaces.(ii) Stomata are more on the lower epidermis.
(iii) Bulliform cells are absent.
|(i) Both the surfaces are uniform.
(ii) Stomata are more or less equal in number on both the epidermis.
(iii) Bulliform cells are present.
|8.||Radial vascular bundles||Collateral vascular bundles|
|(i) Xylem and phloem are located separately on different radii.(ii) Xylem is exarch.
(iii) These are present in root.
|(i) Xylem and phloem are located on same radii.(ii) Xylem is endarch.
(iii) Sieve plate is present.
|(i) It conducts water and minerals.(ii) It is dead.
(iii) Sieve plate is absent.
|(i) It conducts food.(ii) It is living.
(iii) Sieve plate is present.
|10.||Conjoint vascular bundles||Concentric vascular bundles|
|(i) It may or may not contains cambium.(ii) Xylem and phloem are bound together in and the same bundle occurring side by side on the same radius.||(i) Combium is absent.
(ii) Xylem completely surrounds the phloem or vice-versa.