transportation of nutrients and water
Nutrients and water are transported through the plant via two transport tissues: the xylem and phloem.
The xylem is responsible for transporting water and dissolved minerals from the roots to the leaves. It is made up of long tubes made of dead cells and is hydraulically driven. This means that water is constantly being pulled up through the plant due to a process called transpiration, where water evaporates from the leaves. The water molecules at the top of the plant create a negative pressure that pulls up the water from the roots.
The phloem, on the other hand, is responsible for transporting sugars and other organic compounds from the leaves to other parts of the plant, such as the fruits and roots. It is made up of living cells and is controlled by the source-sink relationship. The source is where the sugars and other organic compounds are produced, which are usually the leaves, and the sink is where they are needed, such as the fruits or roots. The phloem moves these compounds by creating a pressure gradient, where it pushes the sugars from the source to the sink.
In summary, the xylem transports water and dissolved minerals from the roots to the leaves, and the phloem transports sugars and other organic compounds from the leaves to other parts of the plant.
Transportation of nutrients and water in plants occurs through two main systems: the xylem and the phloem.
1. Xylem: The xylem transports water and minerals from the roots to the rest of the plant.
- Water absorption: Water is absorbed by the root hairs through osmosis. It moves into the root cortex and then enters the xylem vessels.
- Transpiration: Water is pulled upwards from the roots to the shoots due to transpiration. Transpiration is the loss of water vapor through the stomata in leaves. It creates a negative pressure, resulting in the upward movement of water in the xylem.
- Cohesion-Tension Theory: This theory describes how water molecules stick together (cohesion) and how the transpiration pull creates tension, allowing water to move upwards against gravity.
- Root pressure: In certain circumstances, root pressure can push water up in smaller plants. This occurs when the active transport of minerals into the xylem causes osmosis, resulting in water uptake.
2. Phloem: The phloem transports organic compounds, such as sugars, from the leaves to other parts of the plant.
- Source to sink movement: The source is the area where sugar molecules are produced (like leaves during photosynthesis), while the sink is the area where sugars are needed for growth or storage. Sugars move from the source to the sink through the phloem.
- Pressure flow hypothesis: According to this hypothesis, sugars are actively loaded into the phloem at the source, creating a high concentration. This causes water to enter the phloem through osmosis, increasing the pressure. The pressure pushes the sugar-water solution through the phloem to the sink, where the sugar concentration is lower, allowing the sugars to be unloaded and used.
Overall, the xylem transports water and minerals upwards, while the phloem transports sugars and other organic compounds in any direction needed by the plant. Both systems work together to ensure proper nutrition and hydration throughout the plant.