EDEXCEL UNIT

2 PLANT STRUCTURE  AND FUNCTION 

 

XYLEM

​

1. A vascular bundle is a part of the transport system in vascular plants.

2. The transport itself happens in vascular tissue,

3. which exists in two forms: xylem and phloem.

4. Both these tissues are present in a vascular bundle,

5. which in addition will include supporting and protective tissues

6. xylem is a term applied to woody (lignin-impregnated) walls of certain cells of plants.

7. lignin-  waterproofing and support / to prevent (inward) collapse

8. cellulose for -  adhesion of water / formation of hydrogen bonds with water

9. xylem cells tend to conduct water and minerals from roots to leaves.

10. pits for lateral movement of water

11. rings / spirals, for, extension / growth

12. xylem consists of four different types of cells:

    1. sclerenchyma  (xylem fiber cells)

    2. vessel elements

    3. Adaptation

1. long cells / tubes with no end walls;

2. continuous water columns;

3. no cytoplasm / no organelles/named organelle;

4. to impede/obstruct flow / allows easier water flow;

5. thickening/lignin;

6. support / withstand tension / waterproof / keeps water in cells;

7. pits in walls; - allow lateral movement / get round blocked vessels;

 

 

Sclerenchyma fibres structure (Outer edge particularly)

1. Bundles of dead cells running vertically;

2. Hollow lumen;

3. No end walls;

4. Thickening/lignin;

5. support / withstand tension;

6. More cellulose than other plant cells;

Similarities in the structures of sclerenchyma fibres and xylem vessels.

1. (both) have {cellulose / microfibrils} ;

2. (both) have secondary thickening ;

3. (both) contain lignin ;

4. (both) contain pits ;

5. (both) are composed of dead cells ;

6. (both) are {hollow / have no cytoplasm / eq} ;

 

PHLOEM

 

1. Phloem is composed of several cell types including

   1. sieve elements

   2. companion cells

2. The sieve element and companion cell are found closely associated with each other in what is referred to as the sieve element/companion cell complex.

3. One or more companion cells may be associated with a single sieve element.

4. The so called sieve element may be more specifically referred to as a sieve tube member (angiosperms) or sieve cell (gymnosperms and ferns).

5. The sieve cells of gymnosperms lack a sieve plate and instead have sieve pores throughout the cell wall which allow flow between adjacent cells.

6. The sieve tube members found in flowering plants are generally wider than sieve cells and have sieve plates connecting the ends of adjacent cells.

7. These sieve plates are areas with many pores through which adjacent cells are connected by a continuous cytoplasm.

​

​