Chapter-6 ANATOMY OF FLOWERING PLANTS

 Chapter-6

ANATOMY OF FLOWERING PLANTS

POINTS TO REMEMBER

Anatomy : Anatomy is the study of internal structure of organisms. Plant

anatomy includes organisation and structure of tissues.

Tissue : A group of similar cells along with intercellular substance which

perform a specific function.

Meristematic tissues : The meristematic tissue is made up of the cells which

have the capability to divide. Meristems in plants are restricted to a specialised

regions and responsible to the growth of plants.

Meristems

Apical meristem Intercalary meristem Lateral meristem

• Occurs at the tips of roots and • Occurs between mature tissue •Occurs in the mature

shoots regions of roots and

shoots

• Primary meristem • Primary meristem • Secondary meristem

• Increase the length of plant • Capable of forming branch •Appears later than pri-

and flower mary meristem and res-

ponsible for secondary

growth

Axillary bud : The buds which are present in the axils of leaves and are

responsible for forming branches or flowers.

Permanent tissues : The permanent tissues are derived from meristematic

tissue and are composed of cells, which have lost the ability to divide.

Types of Permanent Tissue

Simple Complex

Parenchyma Collenchyma Sclerenchyma Xylem Phloem

Parenchyma : Thin walled cells, with intercellular spaces, cell wall is made

up of cellulose. It performs the function like photosynthesis, storage, secretion.

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Collenchyma : It is formed of living, closely packed isodimetric cells. It’s

cells are thickened at the corners due to deposition of cellulose and pectin. It

provides mechanic support to the growing parts of the plant.

Sclerenchyma : It is formed of dead cells with thick and lignified walls.

They have two types of cells : fibres and sclereids.

Xylem : Xylem consists of tracheids, vessels, xylem fibres and xylem pa-

renchyma. It conducts water and minerals from roots to other parts of plant.

Protoxylem : The first formed primary xylem elements.

Metaxylem : The later formed primary xylem.

Endarch : Protoxylem lies towards the centre and metaxylem towards the

periphery of the organ.

Phloem : Phloem consists of sieve tube elements, companion cells, phloem

fibres and phloem parenchyma. Phloem transports the food material from leaves

to various parts of the plant.

Protophloem : First formed phloem with narrow sieve tubes.

Metaxylem : Later formed phloem with bigger sieve tubes.

The Tissue System :

1. Epidermal tissue system : It includes cuticle, epidermis, epidermal hairs,

root hairs, trichomes and stomata.

2. The ground tissue system : It is made up of parenchyma, collenchyma,

sclerenchyma. In dicot stems and roots the ground tissue is divided into

hypodermis cortex, endodermis, pericycle, medullary rays and pith.

3. The vascular tissue system : It includes vascular bundles which are

made up of xylem and phloem.

Vascular Bundles

Radial bundles Conjoint bundles

(Xylem and phloem occur (Xylem and phloem are situated at

on different radii) the same radius of vascular bundle)

Collateral bundles Bicolateral bundles Concentric bundles

Open Closed

(with cambium) (without cambium)

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Anatomy of Root

Dicot Root Monocot Root

1. Cortex is comparatively narrow. 1. Cortex is very wide.

2. Endodermis is less thickened 2. Endodermal cells are highly thickened

casparian stripes are more prominent. Casparian strips are visible only

in young roots.

3. The xylem and phloem bundles 3. Xylem and phloem are more than 6

varies from 2 to 5. (polyarch).

4. Pith is absent or very small. 4. Well developed pith is present.

5. Secondary growth takes place with 5. Secondary growth is absent.

the help of vascular cambium and

cork cambium

Anatomy of Stem

Dicot Stem Monocot Stem

1. The ground tissue is differentiated 1. The ground tissue is made up of

into cortex, endodermis, similar cells.

pericy and pith.

2. The vascular bundles are 2. The vascular bundles are scat

arranged in a ring. tered throughout the ground tissue.

3. Vascular bundles are open, without 3. Vascular bundles are closed,

bundle sheath and wedge-shaped surrounded by sclerenchymatous bundle

outline. sheath, oval or rounded in shape.

4. The stem shows secondary growth 4. Secondary growth is absent.

due to presence of cambium between

xylem and phloem.

5. Stomata have kidney-shaped 5. Stomata have dumb bell-shaped guard

guard cells. cells.

Secondary growth in dicot stem : An increase in the girth (diameter) in

plants. Vascular cambium and cork cambium (lateral meristems) are involved in

secondary growth.

1. Formation of cambial ring : Intrafascicular cambium + interfascicular

cambium.

2. Formation of secondary xylem and secondary phloem from cambial ring.

3. Formation of spring wood and autumn wood.

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4. Development of cork cambium (phellogen)

Cork Cambium Cork (phellem) - From outer cells

Sec. cortex (phelloderm) - From inner cells

(Phellogen + Phellem + Phelloderm) = Periderm

Secondary growth in dicot roots : Secondary growth in dicot root occurs

with the activity of secondary meristems (vascular cambium). This cambium is

produced in the stele and cortex, and results in increasing the girth of dicot roots.

Anatomy of Leaf

Dorsiventral (Dicot) Leaf Isobilateral (monocot) Leaf

1. Stomata are absent or less abundant on the 1. The stomata are equally distributed

upper side. on both sides.

2. Mesophyll is differentiated into two 2. Mesophyll is undifferentitated.

partsupper palisade parenchyma and

lower spongy parenchyma.

3. Bundle sheath is single layered and formed 3. Bundle sheath may be single or

of colourless cells. double layered.

4. Hypodermis of the mid-rib region is collen- 4. Hypodermis of the mid-rib region

chymatous. is sclerenchymatous.

QUESTIONS

Very Short Answer Questions (1 mark each)

1. Name the tissue represented by the jute fibres used for making the ropes.

2. Which kind of roots have polyarch vascular bundles ?

3. What is heart wood ?

4. State the role of pith in stem.

5. Where are bulliform cells found in leaves ?

6. Which meristem does produce growth in length ?

7. What forms the cambial ring in a dicot stem during the secondary growth ?

8. Name the anatomical layer in the root from which the lateral branches of

root originate.

9. Which tissue of the leaf contains chloroplast ?

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a

b

10. A plant tissue when stained, showed the presence of hemicellulose and pec-

tin in cell wall of its cells. Name the tissue.

Short Answer Question-II (2 marks each)

11. Why is cambium considered to be lateral meristem ?

12. Give any four differences between tracheids and vessels.

13. How are open vascular bundles differ from closed vascular bundles ?

14. What are trichomes ? State their functions.

15. Given below are the various types of tissue and their functions. Which out

of these is not a matching pair and why :

(a) Collenchyma : provides mechanical support to the growing parts

of plant.

(b) Sclerenchyma : photosynthesis, storage and secretion.

(c) Chlorenchyma : perform the function of photosynthesis.

(d) Xylem : conduction of water and minerals.

Short Answer Question-I (3 marks each)

16. If you are provided with microscopic preparation of transverse section of a

meristemic tissue and permanent tissue, how would you distinguish them ?

17. Differentiate between arenchyma and collenchyma on the basis of their struc-

ture and function.

18. Are there any tissue elements of phloem which are comparable to those of

xylem ? Explain.

19. Palm is a monocotyledonous plant, yet it increases in girth. How is it pos-

sible ?

20. Observe the figure and answer the following questions :

(i) Name parts (a) and (b).

(ii) Are these types of stomata observed in monocot or in dicot plants ?

(iii) Which parts of stomata constitute the stomatal apparatus ?

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Long Answer Questions (5 marks each)

21. (i) What are meristems ?

(ii) Name the various kinds of meristems in plants.

(iii) State the location and function of meristems.

22. (i) Suppose you are examining a cross section of a stem under compound

microscope, how would you determine whether it is monocot stem or

dicot stem ?

(ii) Write the characterstics of collenchyma.

23. What is secondary growth in plants ? Describe various steps of secondary

growth in dicot stem with the help of diagrams.

ANSWERS

Very Short Answers (1 mark)

1. Sclerenchyma.

2. Monocotyledonous roots.

3. The hard central region of tree trunk made up of xylem vessels.

4. Pith stores the food material.

5. Bulliform cells are found in the upper epidermis of monocot leaves.

6. Primary meristem.

7. Fascicular and intrafascicular strips of meristem.

8. Pericycle of mature zone.

9. Mesophyll tissue.

10. Chollenchyma.

Short Answers-II (2 marks)

11. The cambium is considered as a lateral meristem because it occurs along the

lateral sides of the stem and roots and appear later than primary meristem.

Cells of this meristem divide periclinally and increase the thickness of the

plant body.

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12. Tracheid Vessel

1. A tracheid is formed from 1. A vessel is made of a number

a single cell. of cells.

2. The ends are rounded or transverse. 2. The ends are generally oblique

and tapering.

3. They are comparatively narrower. 3. They are comparatively wider.

4. The lumen is narrower. 4. The lumen is wide.

13. Open Vascular bundles : These vascular bundles contain a strip of cam-

bium in between phloem and xylem. Open vascular bundles are collateral

and bicollateral.

Closed Vascular bundles : Intrafascicular cambium is absent. Closed vas-

cular bundles can be collateral or concentric.

14. Trichomes are multicellular epidermal hairs on the stem, seeds or fruits.

Trichomes help in protection, dispersal of fruits and seeds and reduction in

water loss.

15. (b) Sclerenchyma : photosynthesis, storage and secretion is not a matching

pair. The function of sclerenchyma is to provide mechanical support to or-

gans.

Short Answers-I (3 marks)

16. Meristematic tissues are composed of cells that have the capability to di-

vide. These cells are exist in different shapes without intercellular space.

Cells are thin walled, rich in protoplasm, without vacuoles.

Permanent tissues are derived from meristematic tissue and are composed

of cells have their definite shape, size and function. These cells may be thin

walled (living) or thick walled (dead).

17. Arenchyma Collenchyma

(a) Parenchymatous tissue (a) Tissue contains deposits of

containing space large air cellulose and large pectin7 at

space. the corner of cells.

(b) Thin walled cells, isodiametric (b) Consists of oval and polygonal

in shape with intercellular cells without intercellular

space. space.

(c) Provides buoyancy to the plant.(c) Provides elasticity and mechanical

strength.

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18. (a) The sieve elements of phloem is comparable to the vessel of the xylem

because both lack nucleus.

(b) Phloem fibre is similar to the xylem fibre because both provide tensile

strength to the tissue.

(c) Phloem parenchyma and xylem parenchyma is the living components

of phloem and xylem respectively.

19. A palm tree is monotcotyledonous plant, hence do not have primary cam-

bium in the vascular bundles of stem. However, with age the tree grows in

diameter. A secondary cambium may be formed in the hypodermal region of

the stem. The later forms the conjuctive tissue and patches of meristematic

cells. The activity of meristematic cells results in the formation of second-

ary vascular bundles.

20. (i) a : epidermal cell

b : guard cell

(ii) In dicot plants.

(iii) The stomatal apparatus includes the stomatal aperture, guard cells and

the surrounding subsidiary cells.

Long Answers (5 marks)

21. (i), (ii) and (iii) : Refer ‘Points to remember’

22. (i) and (ii) : Refer. ‘Points to remember’

23. • Secondary growth : Refer notes.

• Steps of secondary growth : Refer page 94-97, NCERT, Text Book of

Biology for Class XI.

• Figure 6.9, page 95 NCERT, Text Book of Biology for Class XI.