Plants obtain minerals from soil, water and fertilisers. Need for transportation in plants is to distribute water and nutrients to various parts. Transportation in a plant is a method of circulation of water and minerals from soil throughout the body of a plant.
Vascular tissues in transport
Vascular tissues like the xylem and phloem help in the conduction of water, minerals and nutrients throughout a plant’s body.
a) Xylem is the vascular tissue extending from top to bottom of the plant.
- Xylem tissue is present in the roots, stems and leaves.
- It helps in the transport of water molecules and dissolved substances from the root hairs to aerial parts of the plant.
- Xylem mainly comprises of tracheids, vessels, xylem parenchyma and xylem sclerenchyma.
- The transport in xylem is unidirectional.
- Xylem mostly occupies the centre of the vascular bundle.
- The xylem transports water and minerals from the roots to the leaves.
- Tracheids and vessels are interconnected to form a continuous system of water-conducting channels that reach all parts of a plant.
- Cells in the roots take up ions to create a high ion concentration. This causes water to move into the roots.
b) Phloem is the vascular tissue which transports food molecules to the place of necessity in the plant.
- The elements in the phloem are sieve elements, fibres, phloem parenchyma and companion cells.
- The transport in the phloem tissue is bidirectional.
- It forms vascular bundles in association with xylem.
- Phloem occupies the edges of the vascular bundle.
Transpiration is the evaporation of water from the leaves in the form of water vapour. Transpiration occurs in leaves through special structures present on them called as stomata.Transpiration is the process which helps the plant in many ways.
- Transpiration always occurs against the gravity.
- Transpiration involves mainly the xylem cells which become active during absorption process by the roots.
- Excess water is removed from the cells of the plant to prevent plant decay.
- Osmotic balance of the cell is maintained by the process of transpiration.
- Transpiration is the process which helps all the parts of the plant to cool them.
- Transpiration helps in the distribution of dissolved substances to all parts of the plant.
Translocation is the process of the movement of synthesised products from the leaves to the roots and other parts of a plant’s body through the phloem.
Types of transport
- The phloem is a conducting tissue for nutrients from the leaves to the other parts of a plant’s body. Translocation does not always occur against gravity.
- Translocation involves both xylem and phloem cells to carry the synthesized food materials within the plant.
- As sugar is synthesised in the leaves by the process of photosynthesis, a high concentration of organic substance inside the phloem cells of the leaf creates a diffusion gradient by which more water is sucked into the cells.
- Translocation takes place in the sieve tubes, with the help of adjacent companion cells.
a) Passive transport can be explained by diffusion. Diffusion is the movement of molecules in a random manner that is from a region of higher concentration to a region of lower concentration. Diffusion involves no expenditure of energy as it does not involve any semi-permeable mebrane.Diffusion is a process which can occur in all media which involve solid, liquid and gaseous molecules. Diffusion is a passive process which occurs in the transportation of substances in plants.
b) Active transport involves the movement of ions against concentration gradient through membranes. It is carried out with expenditure of energy. Active transport requires carriers for transport across the cell membrane. Active transport is involved in translocation os minerals in the plant body and accumulation in the plant cells. e.g Glucose molecules in the leaves are transferred to the phloem tissue using energy from ATP.
c) Osmosis is the process of diffusion of solvent particles from the region of less solute concentration to a region of high solute concentration through semi-permeable membrane. Osmosis can be observed in human beings in the phenomenon of membrane transport. Cells possess cell membranes. These cell membranes are selectively permeable and many molecules move in and out of the cell by the process of osmosis.
Types of solutions
Osmosis can occur in hypertonic solutions, hypotonic solutions and isotonic solutions. Sometimes cell can even undergo the phenomenon called as plasmolysis.
- Hypotonic solutions are the ones which have a lower concentration of solute than the cell. Water diffuses into the cell to balance the solute concentration on either side (outside and inside) equal. Here the cell swells up due to entry of water.
- Hypertonic solutions are the ones which have higher solute concentration than the cell. Water moves out of the cell through cell membrane to balance the concentration of the solute on either side. It results in cell shrinking .This may also lead to desiccation of the cell.
- Isotonic solutions have the same concentration of the solute as the cell. Water moves in and out of the cell with no net change.