Transport in Plants - Class XII

Roots concentrate minerals against their concentration gradient (from low concentration in soil to high concentration in the root) using active transport, which requires energy (ATP).

Water held tightly by soil particles around them is called as hygroscopic water. It is held in a very thin film and is not available to plants. Plants are able to absorb capillary water, which is present in the capillary spaces between soil particles. Run away water is also not available to plants. 

Absorption of mineral elements from the soil involves active transport by the cells. Minerals may also be absorbed as ions rather than salts.

Water transport is a physical process and not a physiological process. It does not require living cells and protoplasm. The driving force is the transpiration pull generated by loss of water through leaves. This is the reason why xylem tracheids and vessels are dead on maturity. Food transport is a physiological process and requires living cells similarly stomatal movement also is a physiological process and requires living cells.

The minerals are mainly absorbed by roots which are in direct contact with the soil. Absorption of water is known as water uptake. Short distance transport of water takes place from cell to cell  across the membranes involving physical processes such as diffusion, osmosis and water potential differences. Long distance transport involves complex processes such as root pressure and transpiration pull. transport There are two processes by which mineral absorption takes place:

Ion channels are special proteins through which ions flow along the concentration gradient. These channels are important, because the membrane is made up of bilayer of lipids and will not allow transport of water soluble ions. However lipid soluble components can dissolve in membrane lipids and can be transported across the membrane without special carrier or transport proteins.
But all ions cannot pass through same transport protein because volume of each ion will be different. There are different transport proteins for transport of different ions.

Active transport processes move substances against their concentration gradient, which requires energy in the form of ATP. Passive processes, such as diffusion or osmosis, occur spontaneously without the expenditure of metabolic energy.

The absorption of ions, involving use of metabolic energy is called active absorption. Energy is generally obtained from ATP.Therefore active absorption is linked to hydrolysis of ATP

Active transport moves molecules against their concentration gradient and requires an input of metabolic energy, typically in the form of ATP. In contrast, passive transport relies on existing concentration gradients to move substances across membranes without direct cellular energy expenditure.

Active transport is typically unidirectional because it involves specific pumps or carrier proteins that move solutes against a gradient in one specific direction. While some systems may have multiple transporters, the mechanism of a single active transport pump is inherently directional.

Active transport, which is the movement of ions or molecules across a cell membrane in the direction opposite that of diffusion, that is, from an area of lower concentration to one of higher concentration, requires the assistance of a type of protein called a carrier protein, using energy supplied by ATP. So, the correct option is 'ATP'.

Porins are beta barrel proteins that cross a cellular membrane and act as a pore, through which molecules can diffuse. Unlike other membrane transport proteins, porins are large enough to allow passive diffusion, i.e., they act as channels that are specific to different types of molecules. Porins from non-green plastids and from the outer mitochondrial membrane were re- constituted into planar lipid bi-layers. The proteins showed high pore-forming activities and similar single- channel conductance. So, the correct option is "Not associated with the inner membrane of plastids".

In facilitated diffusion ,special proteins help move substances across membranes without expenditure of  ATP energy. While in case of Active transport it uses energy to pump molecules against a concentration gradient .

Facilitated diffusion and active transport both involve membrane proteins and exhibit saturation kinetics, but facilitated diffusion moves molecules down their concentration gradient without cellular energy expenditure, making it a downhill process.

Diffusion is a slow process and is not dependent on a living system. Diffusion is very important to plants since it the only means for gaseous movement within the plant body. Intake of carbon dioxide and release of oxygen through stomata occurs through the process of diffusion. Diffusion rates are affected by the gradient of concentration, the permeability of the membrane separating them, temperature and pressure.

Gradient is the change in the value of a quantity with change in another variable. Example time, solute concentration, pressure potential, solute potential, etc.

Ions are small atoms or molecules carrying an electric charge. The core of plasma membrane is composed of nonpolar hydrophobic lipid tails and prevent simple diffusion of these charged particles. Thus, the correct answer is B. 

At 0 degree Celsius the respiration rate will be zero. At 20 degree Celsius only the respiration process will take place. Hence, the 5 gm initially absorbed is due to physical diffusion of mineral ions from a region of high to low concentration. Later on, respiration occurs, then extra 15 grams are actively absorbed.

• Facilitated transport or diffusion or passive-mediated transport can be defined as the process of spontaneous passive transport of molecules or ions across a cell membrane through the specific transmembrane integral proteins.
  
• It does not require the ATP molecules and is the diffusion is downhill.
• So, the correct answer is 'c and d only'.

Facilitated transport is the movement of molecules across a membrane through special transport proteins.

Facilitated diffusion is a passive transport process that uses specific membrane proteins to speed up the movement of molecules down their concentration gradient. It does not require ATP.

Carrier molecules in facilitated diffusion assist in moving solutes across a membrane down their concentration gradient, meaning they cannot build up a higher concentration on one side against the gradient without energy input.

Facilitated diffusion is the movement of water and other substances against the concentration gradient. The movement is through ions channels or membrane proteins which are present on the surface of the membrane. It requires the energy for the movement of substances. The movement is dependent upon the concentration gradient.

Substances having a hydrophilic moiety find it difficult to pass through the membrane. Their movement has to be facilitated. So, facilitated diffusion needs a 'carrier protein'. 

Facilitated diffusion is a passive process that does not require energy. While it is faster than simple diffusion, it is generally not faster than active transport, which can move substances against a gradient.

When a molecule moves across a membrane independent of other molecule, it is called uniport.

A uniporter is an integral membrane protein that transports a single type of substrate species (charged or uncharged) across a cell membrane. It may use either facilitated diffusion and transport along a diffusion gradient or transport against one with an active transport process. They can be either ion channels or carrier proteins. In facilitated diffusion, molecules diffuse across the plasma membrane with assistance from membrane proteins, such as channels and carriers.

In a resting neuron, the concentration of sodium ions (Na+) is much higher outside the cell than inside, while potassium ions (K+) are more concentrated inside. Therefore, concentration gradients alone would drive Na+ into the cell and K+ out of the cell.

Accumulating ions inside a vacuole at a concentration higher than the surrounding cytoplasm or medium requires moving them against their concentration gradient, which is an active process that relies on energy-dependent uptake (active transport).

Diffusion occurs in both liquids and gases and can take place over long distances. Diffusion in gases are much faster than in liquids the diffusion rate of oxygen in air is $1,00,000$ times more than diffusion rate of oxygen in water.

Diffusion is the movement of molecules or ions from the region of their higher concentration to the region of their low concentration. Diffusion is obvious in gases and liquids but rare in solids. Diffusion rates are affected by the concentration gradient, the permeability of the membrane separating different molecules, temperature and pressure. 

Diffusion keeps the cell walls of the internal plant tissues moist. It is a means of spreading of ions and other substances throughout the protoplast. Transpiration or loss of water in vapour forms is a diffusion process. Exchange of gases (CO2(CO2 and O2)O2) during photosynthesis and respiration between the plant interior and outside air also occurs through diffusion.

The movement of oxygen and carbon dioxide in and out of leaves during photosynthesis occurs by diffusion.

DPD is the difference in the diffusion pressure of the solution and a pure solvent when both are subjected to the same atmospheric pressure. When the increasing turgor pressure becomes equal to the decreasing osmotic pressure, the entry of the water into the cell would stop. This is called the turgid condition of the cell. This is when DPD equals zero.

Suction pressure or the DPD is given as the difference of osmotic pressure and the turgor pressure, $DPD = OP - TP$