Answer the following questions

Plant Anatomy (Structural Organisation)

Tissue and Tissue System

6. Why the cells of sclerenchyma and tracheids become dead?

(i) Sclerenchyma and tracheids are cells which have nucleus and cytoplasm (protoplasm) initially but it soon degenerates. They become to the plant.

(ii) Both give mechanical strength to the plant.

(iii) Tracheids being a part of xylem help to conduct water.

7. Explain sclereids with their types.

1. Sclereids-dead cells Isodiametric-but some elongated.

2. Cell wall is very thick due to lignification

3. Lumen - much reduced

4. Pits - may be simple or branched.

TYPE NAME & NATURE

1. BRACHY SCLEREID OR STONE CELLS:

Isodiametric, with hard cell wall - due to lignindepostion lumen very much reduced

Occurrence & Function :

Found in the park, pith cortex , hard endeosperm and fleshy portion of some fruits.

Mechanical – suppot

2. MACROSCLEREID OR ROD CELLS

Cells - elongated, rod shaped

Occurrence & Function :

Found in outer seed coat of leguminous plants

Mechanical support

3. OSTEOSCLEREID OR BONE CELLS:

cells - rod shaped with dilated ends, so look like bone

Occurrence & Function : occur in leaves and seed coats

4. ASTROSCLEREID OR STAR CELLS:

cells with lobes diverging from a central body

Occurrence & Function : occur in petioles

5. TR1CHOSCLEREID OR HAIR CELLS:

Hair like then walled cells - Numerous small angular crystals are embedded in the wall

Occurrence & Function : Occur in stem and leaves hydrophyes

6. FILIFORM SCLEREIDS FIBRE CELLS

They are very much elongated fibre like and about 1 mm length

Occurrence & Function : Occur in the leaf lamina of some plants

8. What are sieve tubes ?explain.

i) Sieve tubes are long tube like conducting elements in the pholem formed from a series of cells called sieve tube elements.

ii) The sieve tube elements are arranged one above the other and form vertical sieve tube.

iii) The end wall contains sieve plate.

iv) The sieve elements show nacreous thickenings on their lateral walls.

v) They may possess simple or compound sieve plates.

vi) The function of sieve are believed to be controlled by companion cells.

vii) In mature sieve tube, Nucleus is absent, it contains a lining layer of cytoplasm. A special protein (P. Protein= Pholem Protein) called slime body is seen in it.

viii) In mature sieve tubes, the pores in the sieve plate are blocked by a substance called callose (callose plug). The conduction of food material takes place through cytoplasmic strands. Sieve tubes occur only in Angiosperm. 

9. Distinguish the anatomy of dicot root from monocot root.

10. Distinguish the anatomy of dicot stem from monocot stem.