Plants need water, minerals, and food for their growth and survival. Water and minerals are taken up by roots and leaves prepare the food. These are then transported to the other parts of the plants. When we talk about transport, there should be some means of transportation. Diffusion is the main pathway of transportation in plants. Let us study about the different means of transport in detail.
Diffusion: Means of Transport
- Diffusion – It includes the movement of particles of a medium from the region of its higher concentration to the region of its lower concentration without the expenditure of energy. This process is slow and occurs mostly in gases and liquids. The rate of diffusion is affected by the concentration gradient, permeability of the separating membrane, temperature, and pressure.
- Facilitated Diffusion – In this, substances move across membranes with the help of special proteins without the expenditure of energy. These proteins are embedded in the membranes. The transport rate reaches to maximum when the transporter molecules get saturated. This type of transport is extremely specific. The protein molecules from a channel in the membrane for molecules to pass. Huge pores are formed on the outer membranes of some organelles like plastids, mitochondria etc. by proteins called porins. Sometimes an extracellular molecule is bound to the transport protein; this protein rotates and releases the molecule inside the cell. For example, water channels which are made up of eight different types of aquaporins.
There are some proteins which allow diffusion only when two types of molecules move together. When both the molecules cross the membrane in the same direction, the movement is called symport. In antiport, they move in opposite directions and in uniport, a molecule moves across a membrane independent of other molecules.
- Active Transport – In this, molecules move against the concentration gradient. i.e. from the region of their lower concentration to the region of their higher concentration. Energy is used in the process. In this process also, membrane proteins are involved and the rate of transportation reaches to maximum when all the protein molecules are used. The carrier proteins are sensitive to inhibitors and are very specific.
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