Plant transport tissues - Xylem and phloem
Xylem
The Narrow, hollow, dead tubes with lignin, responsible for the transport of water and minerals in plants. is a tissue which transports water and minerals from the roots up the plant stem and into the leaves.
Xylem consists of dead cells. The cells that make up the xylem are adapted to their function:
- They lose their end walls so the xylem forms a continuous, hollow tube.
- They become strengthened by a substance called Carbohydrate material lining the xylem vessels providing strength and support.. Lignin gives strength and support to the plant. We call lignified cells wood.
Transport in the xylem is a physical process. It does not require energy.
Phloem
The The tissue in plants that transports the products of photosynthesis, including sugars and amino acids. moves food substances that the plant has produced by photosynthesis to where they are needed for processes such as:
- growing parts of the plant for immediate use
- storage organs such as An underground food store able to grow into a new plant. A natural method of asexual reproduction in plants. and A swollen, fleshy underground stem of a plant, such as the potato, bearing buds from which new plant shoots arise.
- developing seeds
Transport in the phloem is therefore both up and down the stem. A disaccharide made from glucose and fructose. It is used as table sugar. is the transport sugar in the phloem. Transport of substances in the phloem is called The transport of dissolved material within a plant.. Translocation requires energy as it is an active process.
Phloem consists of living cells. The cells that make up the phloem are adapted to their function:
- Cells that have no nuclei and are connected to each other by their cytoplasm. - specialised for transport and have no The nucleus controls what happens inside the cell. Chromosomes are structures found in the nucleus of most cells. The plural of nucleus is nuclei.. Each sieve tube has a perforated end so its The living substance inside a cell (not including the nucleus). connects one cell to the next. Sucrose and amino acids are translocated within the living cytoplasm of the sieve tubes.
- Companion cells - transport of substances in the phloem requires energy. One or more companion cells attached to each sieve tube provide this energy. A sieve tube is completely dependent on its companion cell(s).
Comparison of transport in the xylem and phloem
| Xylem | Phloem | |
| Type of transport | Physical process | Requires energy |
| Substances transported | Water and minerals | Products of photosynthesis; includes sucrose and amino acids dissolved in water |
| Direction of transport | Upwards from roots to leaves | Upwards and downwards |
| Type of transport | |
| Xylem | Physical process |
| Phloem | Requires energy |
| Substances transported | |
| Xylem | Water and minerals |
| Phloem | Products of photosynthesis; includes sucrose and amino acids dissolved in water |
| Direction of transport | |
| Xylem | Upwards from roots to leaves |
| Phloem | Upwards and downwards |
