Vascular plants contain conducting elements such as xylem and phloem for the transport of water and food respectively in plants. Phloem is the conducting element that transports food produced in the plant from their source to the sink. They are composed of sieve elements, companion cells, phloem fibres and phloem parenchyma. Sieve cells and sieve tubes are two types of sieve elements found in phloem, let us differentiate between them.
What Are Sieve Cells?
Sieve cells are long, conducting cells with narrow diameter that do not have sieve plates. They are associated with albuminous cells that help in the transportation of organic materials. Albuminous cells have long unspecialised ends that overlap with other sieve tubes; they store food and nutrients for tissue nourishment. The albuminous cells connect the sieve cells to parenchyma which enables easy transportation of food and nutrients.
Because they lack companion cells, sieve cells are mostly associated with gymnosperms and other seedless vascular plants. They are evenly distributed throughout the sieve area. Sieve cells have narrow pores called sieve pores at their ends that ensures proper transportation of food.
What Are Sieve Tubes?
Sieve tubes, found in angiosperms, are living cells that are associated with companion cells. The association with companion cells helps in distant transportation within the plant cells. The sieve tubes are made up of longitudinal arrangement of sieve tube members from end to end. The sieve tube members do not have ribosomes and nucleus and thus need the help of companion cells.
The sieve tubes are largely dispersed with plasmodesmata in groups in their walls that later develop into sieve plates. The sieve tubes are very long and have horizontal end walls. The sieve plates contain sieve pores that help in regulating the size of the opening and thus the exchange of nutrients in the plant. The multiple vertical connections of the sieve tube members direct the transport of nutrients with minimum resistance.
Sieve Cells vs Sieve Tubes
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Sieve cells are long elongated cells found in gymnosperms and other seedless vascular plants. |
Sieve tubes are short specialised cells that are found only in angiosperms. |
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Long cells with narrow pores. |
Short cells with wider pores. |
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Gymnosperms and other seedless vascular plants. |
Only in angiosperms. |
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Sieve cells are associated with albuminous cells. |
Sieve tubes are associated with companion cells. |
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No |
Yes |
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Sieve cells are single cells. |
Sieve tubes are longitudinal arrangements of sieve tube members. |
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The sieve pores are present on both lateral and end walls. |
Sieve pores are present only on the sieve plates. |
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Less specialised cells. |
Much specialised cells. |
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Also see:
- Protophloem vs Metaphloem
- Difference between Xylem and Phloem
- Difference between Ascent of Sap and Translocation