Class 9, Science, Chapter-6, Lecture-3, Xylem & Phloem (Notes)
Xylem:
The connective tissue consisting of tracheids, vessels, xylem parenchyma and xylem fibre which transport water and minerals from the roots to the leaves of a plant is called xylem.
Elements of xylem:
- Tracheids -
long tubular dead cells. - Vessels -
long tubular dead cells. - Xylem Parenchyma -
living cells
Contains nucleus
Stores food
helps in lateral movement of water. - Xylem Fibre -
Dead cells
provide mechanical strength.
Phloem:
The connective tissue consisting of sieve tubes, companion cells, phloem parenchyma and phloem fibre which transport food from leaves to the different parts of plant is called phloem.
Elements of phloem:
- Sieve tubes -
long tubular living cells with perforated transverse walls.
Nucleus is not present
Transports food in upward and downward directions. - Companion cells -
living cells adjacent to sieve tubes.
contains nucleus. - Phloem Parenchyma -
living cells
Contains nucleus
Stores food
helps in lateral movement of food. - Phloem Fibre -
Elongated dead cells
provide mechanical strength.
Differences Between:
Tracheid | Vessel |
1. It is formed by a single cell. | 1. A vessel is formed by a large number of cells. |
2. The ends of individual cells remain intact. | 2. The ends or transverse walls of cells get dissolved to from a vessel. |
3. Tracheid ends are tapering. | 3. Vessel ends are rounded. |
4. Wall is comparatively thick while the lumen is narrow. | 4. The wall is comparatively less thickened while the lumen is wide. |
5. It is less efficient in conduction of water. | 5. It is more efficient in conduction of water. |
Differences Between:
Xylem | Phloem |
1. It conducts water and minerals. | 1. Phloem conducts organic solutes or food materials. |
2. Conduction is mostly unidirectional. | 2. Conduction can be bidirectional. |
3. Conducting channels are tracheids and vessels. | 3. Conducting channels are sieve tubes. |
4. Xylem consists of tracheids, vessels, xylem parenchyma and xylem fibres. | 4. Phloem consists of sieve tubes, companion cells, phloem parenchyma and phloem fibres. |
5. Three of the four elements of xylem are dead. Only xylem parenchyma is living. | 5. Three of the four elements are living. Only phloem fibres are dead. |
6. Xylem also provides mechanical strength to plants. | 6. There is no mechanical function of phloem. |