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B2 R) Plant Transport Systems
B2 R) Plant Transport Systems
Plants need to transport substances from one place to another place. Plants have two transport systems; phloem and xylem. Phloem tubes transport cell sap around the plant – this process is known as translocation. Xylem tubes transport water and dissolved mineral ions from the roots to the leaves – this process is known as transpiration. The xylem tubes and phloem tubes in a leaf are shown below; they are on the left.
Phloem – Food
Phloem tubes are responsible for transporting cell sap around the plant. Cell sap is a solution of food substances (it contains sugars, amino acids and other soluble food molecules that have been produced during photosynthesis in the leaves). The cell sap/ food substances are transported through the phloem tubes from where they are produced in the leaves to growing tissue (tips of the shoots and roots), storage tissue and for the development of seeds. The cell sap can move in both directions in the phloem tubes. The process of moving dissolved food molecules around a plant is known as translocation. Translocation requires energy, which is obtained from respiration. Phloem tubes are made from living phloem cells. The phloem cells are joined by perforated ends that allow certain substances to pass through from one phloem cell to the next phloem cell.
Phloem tubes are responsible for transporting cell sap around the plant. Cell sap is a solution of food substances (it contains sugars, amino acids and other soluble food molecules that have been produced during photosynthesis in the leaves). The cell sap/ food substances are transported through the phloem tubes from where they are produced in the leaves to growing tissue (tips of the shoots and roots), storage tissue and for the development of seeds. The cell sap can move in both directions in the phloem tubes. The process of moving dissolved food molecules around a plant is known as translocation. Translocation requires energy, which is obtained from respiration. Phloem tubes are made from living phloem cells. The phloem cells are joined by perforated ends that allow certain substances to pass through from one phloem cell to the next phloem cell.
Xylem – Water
Xylem tubes are responsible for transporting water and dissolved mineral ions from the roots to the stems and then the leaves. Water and dissolved mineral ions only travel in one direction – from the roots to the leaves. No energy is required for water to move up the xylem tubes; the movement of water up the xylem tubes is a physical process. The process of water and dissolved mineral ions moving from the roots to the leaves is known as transpiration.
Xylem tubes are made from elongated dead xylem cells. Xylem cells contain a substance called lignin, which strengthens the walls of the xylem cells. There are no ends between the xylem cells that make up the xylem tubes.
Xylem tubes are responsible for transporting water and dissolved mineral ions from the roots to the stems and then the leaves. Water and dissolved mineral ions only travel in one direction – from the roots to the leaves. No energy is required for water to move up the xylem tubes; the movement of water up the xylem tubes is a physical process. The process of water and dissolved mineral ions moving from the roots to the leaves is known as transpiration.
Xylem tubes are made from elongated dead xylem cells. Xylem cells contain a substance called lignin, which strengthens the walls of the xylem cells. There are no ends between the xylem cells that make up the xylem tubes.
Comparison Between Phloem & Xylem
The table below shows a comparison between phloem and xylem tubes. It’s definitely worth copying this table down on a revision card.
The table below shows a comparison between phloem and xylem tubes. It’s definitely worth copying this table down on a revision card.