Botany lecture notes

Difference between Sieve Tubes and Sieve Cells- A Comparison Table

sieve cells and sieve tubes differences

Sieve Tubes vs Sieve Cells
(Similarities and Differences between Sieve Tubes and Sieve Cells)

Phloem is a permanent vascular tissue system associated with the conduction of food materials in plants. It is a complex tissue composed of more than one type of cells namely sieve elements, companion cells, phloem fibres and phloem parenchyma. Among these cells, the sieve elements are the most specialized cells in the phloem performing the conduction of food materials.

There are two types of sieve elements are described among vascular plants based on structural complexity and evolutionary significance. They are (1) Sieve Cells and (2) Sieve Tubes.

The present post describes the similarities and differences between sieve cells and sieve tubes as a comparison table.

Similarities between Sieve Cells and Sieve Tubes

Ø  Both sieve cells and sieve tubes components of phloem.

Ø  Both are the sieve elements (a category of phloem cells).

Ø  Both sieve cells and sieve tubes transport food materials.

Ø  Both are living cells.

Ø  Both cells have thin primary cell wall (secondary thickening absent).

Ø  Both contain dense granular protoplasm.

Ø  Nucleus is absent in both sieve cells and sieve tubes.

Ø  Both present in primary and secondary phloem.

Difference between Sieve Cells and Sieve Tubes

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Botany lecture notes

P Protein (Phloem Protein): Structure, Classifications and Functions

forisomes definition

P – Protein (Phloem Protein)
(Structure, Classification and Functions of Phloem Proteins)

What are P Proteins? 

Ø  P Proteins (Phloem Proteins) are a category of proteins found in the sap of the sieve tubes of the phloem of Angiospermic plants.

Ø  P-proteins were also as called ‘slime bodies’ of ‘slime’ in the old literature.

Ø  P proteins are usually found in the phloem of dicot plants.

Ø  They are very rarely reported in monocots.

Ø  P proteins are completely absent in the phloem of Pteridophytes and Gymnosperms.

Ø  P proteins occur in different forms in the different developmental stages of sieve tubes.

Ø  P proteins can exist in the sieve tubes as tubular, globular, fibrillar, granular and crystalline forms.

Ø  P proteins are highly polar molecules and they can form gel like substance in the presence of water.

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Botany lecture notes

Complex Tissue System in Plants: Part 2 – Phloem – Structure, Components and Classification (with PPT)

cell types in phloem

Structure, Composition & Classification of Primary and Secondary Phloem

What is phloem?

Phloem is a complex tissue system in plants. It is the food conducting tissue of vascular plants. Together with xylem, they form the vascular tissue system. The phloem composed of several types of cells among which some are living cells and some are dead. The term ‘phloem’ was introduced Nageli (1853) from a Greek word ‘phloios’ meaning ‘bark’. The ‘bark’ is a non-technical term describing all tissue outside the secondary xylem of the plant. Botanically the bark includes secondary phloem, cortex, primary phloem and periderm. The current post describes the structure, composition and classification of phloem.

Location of phloem in plants:

Ø  Usually, the phloem is situated external to xylem.

Ø  In leaves, the phloem is located on the abaxial side (lower side).

Ø  In some plants (members of Cucurbitaceae and Convolvulaceae), the phloem is present on both external and internal to xylem. Such a vascular bundle is called bicollateral vascular bundle.

Ø  Phloem present internal to the xylem is called ‘internal phloem’ or intra-xylary phloem.

Ø  Phloem located external to the xylem is called ‘external phloem’.

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