NCERT Class 11 Biology Chapter 6 Anatomy of Plants

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NCERT Class 11 Biology Chapter 6 Anatomy of Plants

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Anatomy of Plants

Chapter: 6

BIOLOGY

TEXTUAL QUESTIONS ANSWERS

Q.1. State the location and function of different types of meristem.

Ans. Primary Meristems-

(i) They are derived directly from the meristems of the embryo.

(ii) Depending upon their position, primary meristems are of three types: apical, intercalary and lateral.

1. Apical Meristems-

(a) The apical meristems are present at the tips of stem, root and their branches.

(b) They cause growth in length.

2. Intercalary Meristems-

(a) They are meristematic regions derived from apical meristems and separated from them by the formation of permanent tissues in between.

(b) Intercalary meristems cause localized elongation of the organ.

(c) Intercalary meristems are found at the bases of leaves [eg Pinus], above the nodes (eg grasses) or below the nodes (eg mint).

(d) Intercalary meristems get fully used in the formation of permanent tissues.

3. Lateral Meristem–

(a) Lateral meristem occurs on the sides.

(b) It takes part in increasing girth of the plant.

(c) Only one Primary lateral meristem is found in plants — It is Intrafascicular cambium [It lies in vascular bundles of dicot and gymnosperm stems].

Q.2. Cork cambium forms tissues that form the cork. Do you agree with this statement? Explain.

Ans. The pericycle layer forms a secondary meristem called cork cambium or phellogen. The cells of phellogen divide towards the outside and inside. The tissue formed towards the inner side is parenchymatous and called secondary cortex or phelloderm. Tissues formed by phellogen on outside become dead with suberized walls and tannin in cavities. These are known as cork cells or phellem.

Q.3. Explain the process of secondary growth in stems of woody angiosperm with help of schematic diagrams. What is the significance?

Ans. Secondary Growth in dicot stem-

(a) Secondary tissues are formed by two types of lateral meristems — vascular cambium and cork cambium / phellogen.

(b) Vascular cambium produces secondary vascular tissues and phellogen forms periderm.

(c) Formation of secondary vascular tissues-

They are formed by the vascular cambium. Vascular cambium is produced by two types of meristems – fascicular / intrafascicular and interfascicular cambium. Intrafascicular cambium is a primary meristem which occurs as strip in vascular bundles. Interfascicular cambium arises secondarily from the cells of medullary rays which occur at the level of intrafascicular strips. Both connect to form a ring of vascular cambium. Vascular cambium is single layered.

The cells of vascular cambium are of two types – elongated fusiform initials and shorter ray initials.Ray initials form vascular rays having two parts xylem ray and phloem ray. Fusiform initials divide to form secondary phloem on the outer side and secondary xylem on the inner side.Secondary phloem is differentiated into soft bast (secondary phloem without fibres) and hard bast (secondary phloem with abundant fibres). Secondary phloem is formed inner to the primary phloem and has more fibres.

Secondary Xylem – It forms the bulk of the stem and is called wood. It occurs toward the outer side of primary xylem and forms annual rings. It has more fibres.

Q.4. Draw illustrations to bring out anatomical difference between

(a) Monocot root and dicot root.

Ans. Monocot root and dicot root:

(b) Monocot stem and dicot stem.

Ans. Monocot stem and dicot stem:

Q.5. Cut a transverse section of young stem of a plant from your school garden and observe it under the microscope. How would you ascertain whether it is a monocot stem or dicot stem? Give reasons.

Ans. Primary Dicot Stem Structure-

Tissues present in dicot stem (from outside to inside) are as follows-

1. Epidermis-

(i) It is made up of elongated barrel shaped parenchymatous cells.

(ii) The cells are transparent and devoid of chloroplasts.

(iii) Outer side of epidermis has a layer of cuticle.

(iv) The epidermis contains minute pores called stomata.

2. Cortex-It Has three parts: hypodermis, general cortex and endodermis.

(a) Hypodermis-

(i) It is made of 3-4 layered collenchyma tissue.

(ii) Its cell possess extra cellulose thickening in various regions.

(b) General Cortex-

(i) It is made up of thin walled parenchymatous cells.

(ii) They enclose intercellular spaces.

(c) Endodermis-

(i) It is wavy layer of one cell in thickness.

(ii) It is innermost boundary of cortex.

(iii) It is made up of barrel shaped cells which do not enclose intercellular spaces.

3. Pericycle-

(i) The pericycle is heterogenous — made up of parenchyma and sclerenchyma fibres.

(ii) Sclerenchyma lies in patches called bundle caps and is also called hard bast.

4. Vascular Strand-

(i) It is in form of eustele or ring of vascular bundles around central pith.

(ii) Each vascular bundle has phloem on the outside, xylem on inner side and strip of Cambium in between the two — conjoint, collateral, and open.

(iii) Xylem is Endarch.

5. Medullary or Pith rays-

(i) They are radial strips of parenchyma between adjacent vascular bundles.

(ii) They connect the pith with pericycle and cortex.

6. Medulla or Pith-

(i) It forms the center of stem.

(ii) It is made of parenchyma cells.

Monocot Stem Structure-

(i) It lacks secondary growth.

(ii) Tissues present in monocot stem (from outside to inside) are as follows-

1. Epidermis –

(i) It is made up of elongated barrel shaped parenchymatous cells.

(ii) The cells are transparent and devoid of chloroplasts.

(ii) Outer wall of epidermis has deposits of silica and cutin.

(iii) The epidermis contains minute pores called stomata.

2. Hypodermis-

(i) It is made of thick walled lignified sclerenchyma fibres.

3. Ground tissue-

(i) It does not show distinction into cortex, endodermis, pericycle, pith and pith rays.

(ii) It is parenchymatous and occupies the interior of whole stem.

4. Vascular Strand-

(i) It is in form of atactostele or large number of vascular bundles scattered in the ground tissue.

(ii) Vascular Bundles are smaller and more numerous towards outside than center.

(iii) Each vascular bundle has phloem on the outside, xylem on inner side.

(iv) Cambium is absent.

(v) Vascular bundles are conjoint, collateral, and closed.

(vi) Vascular Bundle is surrounded by sheath of sclerenchyma called bundle sheath.

Q.6. The transverse section of a plant material shows the following anatomical features,

(a) the vascular bundles are conjoint, scattered and surrounded by sclerenchymatous bundle sheath

(b) phloem parenchyma is absent. What will you identify it as?

Ans. The monocot stem.

Q.7. Why are xylem and phloem called complex tissues?

Ans. Xylem and phloem are known as complex tissues as they are permanent tissues which contain more than one type of cells. All types of cells of a complex tissue work as a unit.

Q.8. What is stomatal apparatus? Explain the structure of stomata with a labelled diagram.

Ans. Stomatal aperture, guard cells and subsidiary cells together form a complex called stomatal apparatus.

Q.9. Name the three basic tissue systems in the flowering plants. Give the tissue names under each system.

Ans. Three basic tissue systems are —

1. Epidermal tissue system: It consists of epidermis and epidermal appendages.

2. Ground tissue system: It consists of simple permanent tissues like parenchyma, collenchyma and sclerenchyma.

3. Vascular tissue system: It consists of xylem, phloem, cambium.

Q.10. How is the study of plant anatomy useful to us?

Ans. The study of plant anatomy helps us to study taxonomy. It also helps us to distinguish between monocots, dicots, and gymnosperms. It helps in the improvement of food crops. The study of plant anatomy helps to differentiate the type of wood. It is also useful in the study of various plant fibres like jute, flax, etc.

Q.11. What is periderm? How does periderm formation take place in dicot stem?

Ans. Periderm is composed of the phellogen, phellem, and phelloderm.

Periderm formation in dicot stem:

(i) Cortical cells produce cork cambium or phellogen.

(ii) Phellogen divides on inner side to form parenchymatous or collenchymatous secondary cortex or phelloderm. Its cell show radial arrangement.

(iii) Phellogen produces cork / phellem on the outer side. It consists of dead cells with suberized cell walls.

Q.12. Describe the internal structure of a dorsiventral leaf with the help of labelled diagrams.

Ans. Dorsiventral leaves are found in dicots. The vertical section of a dorsiventral leaf contains three distinct parts:

1. Upper Epidermis-

(i) Epidermis of upper surface.

(ii) It has a layer of cuticle on the outer side of epidermis.

(iii) Epidermis has single layer of transparent parenchymatous cells devoid of chloroplasts.

2. Lower Epidermis-

(i) Epidermis of lower surface.

(ii) It has a layer of cuticle on the outer side of epidermis.

(iii) Epidermis has single layer of transparent parenchymatous cells.

(iv) It contains a large number of pores called stomata, guard cells and subsidiary cells.

3. Mesophyll-

(i) The interior of the leaf between the upper and the lower epidermis has parenchymatous green tissue or Chlorenchyma.

(ii) Chlorenchyma of leaf is called mesophyll.

(iii) Mesophyll has two regions – upper palisade and lower spongy.

4. Vascular System / Strand-

(i) The vascular bundles are rounded, conjoint and collateral.