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The phloem is the most important tissue in the plant which helps in the translocation of food that is glucose to various parts of the plant. The components of phloem are companion cells, sieve tubes, phloem fibres and phloem parenchyma. The only living component in the phloem is the phloem parenchyma.

Found- Sieve tubes are the important component of the vascular tissue in the plant called the phloem. Phloem is associated with the transport of food from leaves to various parts of the plants. Sieve tube cells function in association with other components of the phloem.

Let us discuss the structure and function of sieve tubes.

Sieve elements are the conducting element in the phloem. It works in association with the companion cells and brings about conduction. It is made up of sieve cells and sieve tubes.

Structure- It is the highly organised tissue which lacks nucleus. It comprises elongated cells and lie parallelly to the tissue they are present in. whose walls are perforated like a sieve called the sieve plates. These pores help in connecting with the adjacent cells and thus bring about transportation of the organic molecules. The sieve tubes lack ribosomes. Sieve tubes are shorter and wider so as to provide greater surface area for transport. It is found in the angiosperms.

Function: It is the major conducting component in the phloem. The main function is to transport the product formed by the photosynthesis that is the glucose. The sieve tube works in association with the companion cells which are nucleated.

Note: All the organelles are absent in the sieve tube element. It resembles a prokaryotic cell. The gymnosperms and nonvascular plants have sieve cells which are similar in function but are longer and narrower as compared to sieve tubes.

Sieve cells found in phloem helps in the transportation of materials.

B) Sieve tube

Any tissue which contain vessels through which fluids are passed is called a vascular tissue.

C) i false, ii true

Correct option is C) Tracheid

Correct option is B) Vessel

D) Collenchyma

C) Sclerenchyma

D) 3, 4, 1, 2, 5

C) 1 – b, 2 – a, 3 – c

A) Chlorenchyma

Correct option is C) 330 ft

C) Storage tissue

C) Sclerenchyma

B) Water storage tissue

Oil glands are found in Lemon.

C) Intercalary meristematic tissue

C) a – 2, b – 3, c – 1

D) Cells in root tip

a) Parenchyma 

b) Collenchyma 

c) Scierenchyma 

d) Xylem, Phloem

Meristematic cells. is the cells which divide continuously.

Airpores is the other name for stomata?

A) epidermis

D) 1 – c, 2 – a, 3 – b

Water plants like Pistia, Eichornia.

Located in growing aspects of main and lateral shoots and roots.

C) Ground tissue

B) Dermal tissue

D) Cells with similar structures and functions

C) b, d, c, a

Correct option is D) Tissues

Correct option is D) Lignin

D) Tissue Organ System

(d) calyptrogen

Forms central portion in apex.

Tunica cells divide by anticlinal division and corpus divide in all planes.

B) Collenchyma

A) Intercalary meristems

1. In fern rachis, the number of vascular bundles is less as compared to number of vascular bundles in monocot stem. In monocot stem, vascular bundles are numerous. 

2. In fern rachis, xylem consists of only tracheids whereas in monocot stem, xylem consists of vessels (protoxylem and metaxylem) as well as tracheids. Monocot stem shows presence of lysigenous cavity just below protoxylem.

3. In fern rachis, phloem consists of only sieve cells whereas in monocot stem, phloem consists of sieve tubes and companion cells. Thus, a student must hav e observed these differences in the given section and agreed to teacher’s statement that the given section is of fern rachis and not of monocot stem.

Concentric vascular bundle: 

a. When one vascular tissue is completely encircling the other, it is called as concentric vascular bundle. 

b. When phloem is encircled by xylem, it is called as leptocentric vascular bundle, whereas when xylem is encircled by phloem, it is called as hadrocentric vascular bundle. 

c. When xylem is encircled by phloem on both faces, it is called as amphicribral vascular bundle. When phloem is encircled by xylem on both faces it is called as amphivasal vascular bundle.

Secondary growth: 

1. Dicotyledonous plants and gymnosperms exhibit increase in girth of root and stem. 

2. In dicot stem, secondary growth begins with the formation of a continuous cambium ring. 

3. The cambium present between the primary xylem and primary phloem of a vascular bundle is called intrafascicular cambium. 

4. The cells of medullary rays adjoining these intrafascicular cambium strips become meristematic (regain the capacity to divide) and form the interfascicular cambium. 

5. Thus, a complete and continuous ring of vascular cambium is formed.

6. The cambium ring cuts off new cells, towards both inner and outer sides. 

7. The cells that are cut-off towards pith (inner side) mature into secondary xylem and cells that are cut-off towards periphery mature into secondary phloem. 8. Generally, amount of secondary xylem is more than the secondary phloem.

Cell is the component that brings about important processes in the living organisms.

Peculiarity of a sclerenchyma cell wall: 

1. Cell wall of sclerenchyma is evenly thickened due to uniform deposition of lignin. 

2. Cell wall of sclereids is extremely thick and strongly lignified.

Organism → Organ system → Organs → Tissue system → Tissue → Cells

Location or position of meristematic regions is divided into three types.

T.S. of phloem tissue: 

Structure of phloem: 

1. Phloem is a living tissue. It is also called as bast. 

2. It is responsible for conduction of organic food material from source (generally leaf) to a sink (other plant parts). 

3. On the basis of origin, it can be protophloem (first formed) and metaphloem (latterly formed).

4. It is composed of sieve elements (sieve cells and sieve tubes), companion cells, phloem parenchyma and phloem fibres. 

2. Sieve elements:

a. Sieve tubes are long tubular conducting channel of phloem. 

b. These are placed end to end with bulging at end walls. 

c. The sieve tube has sieve plate formed by septa with small pores. 

d. The sieve plates connect protoplast of adjacent sieve tube cells. 

e. The sieve tube cell is a living cell with a thin layer of cytoplasm, but loses its nucleus at maturity. 

f. The sieve tube cell is connected to companion cell through phloem parenchyma by plasmodesmata. 

g. Sieve cells are found in lower plants like pteridophytes and gymnosperms and sieve tubes are found in angiosperms.

h. The cells are narrow, elongated with tapering ends and sieve area located laterally. 

3. Companion cells: 

a. These are narrow elongated and living. 

b. Companion cells are laterally associated with sieve tube elements. 

c. Companion cells have dense cytoplasm and prominent nucleus. 

d. Nucleus of companion cell regulates functions of sieve tube cells through simple pits. 

e. From origin point of view, sieve tube cells and companion cell are derived from same cell. Death of the one result in death of the other type. 

4. Phloem parenchyma: 

a. Cells of phloem parenchyma are living, elongated found associated with sieve tube and companion cells. 

b. Their chief function is to store food, latex, resins, mucilage, etc.

c. The cells carry out lateral conduction of food material. 

d. These cells are absent in most of the monocots. 

5. Phloem fibres (Bast fibres): 

a. Phloem fibres are the only dead tissue among this unit. 

b. They are sclerenchymatous. 

c. They are generally absent in primary phloem, but present in secondary phloem. 

d. These cells have with lignified walls and provide mechanical support. 

e. They are used in making ropes and rough clothes.

Characteristics of meristematic tissue: 

1. It is a group of young, immature cells. 

2. These are living cells with ability to divide in the regions where they are present. 

3. These are polyhedral or isodiametric in shape without intercellular spaces. 

4. Cell wall is thin, elastic and mainly composed of cellulose. 

5. Protoplasm is dense with distinct nucleus at the centre and vacuoles if present, are very small. 

6. Cells show high rate of metabolism.

Sclerenchyma fibres: 

1. Fibres are thread-like, elongated and narrow structures with tapering and interlocking end walls. 

2. Fibres are mostly in bundles. Pits are narrow, unbranched and oblique. They provide mechanical strength.