Transport of food, water and minerals - class-XI

Active transport is a process that is required to move molecules against a concentration gradient.
For plants to take up mineral ions, ions are moved into root hairs, where they are in a higher concentration than in the dilute solutions in the soil. So, the correct answer is "Active Transport".

Translocation of organic nutrients from the region of source or supply to the region of sink or utilisation is mostly in the form of sucrose. Phloem (sieve tubes or sieve cells) is the pathway for this translocation, as found put by stem girdling, sieve tube puncturing, radioautography and chemical analysis of sieve tube sap.

• The cohesion-tension theory is a theory of intermolecular attraction that explains the process of water flow upwards (against the force of gravity) through the xylem of plants. 
• Transpiration pull, utilizing capillary action and the inherent surface tension of water, is the primary mechanism of water movement in plants. 
• Hence, The cohesion transpiration pull theory operates only in Conditions favouring transpiration.
• So, the correct answer is 'Conditions favouring transpiration'.

In vascular plants, water and minerals move through xylem, whereas sugars move through phloem. Ringing experiments prove that sugars move through phloem. If the phloem tissue is removed in a ring or girdle, the sugars cannot be transported to roots from aerial parts and plant dies. 

Dixon explained ascent of sap in trees based on transpiration, cohesion, adhesion theory. Mac Dougal supported transpiration pull theory through experimental proof. Cohesive force and adhesive force works continuously in the cavity (lumen) of xylem. Both the forces are responsible for maintaining unbroken continuity of water column from the roots to the leaves.

Cohesion-Tension or Cohesion Transpiration pull theory was put forward by Dixon and Jolly in 1894. It is also known as Dixon's theory of Ascent of Sap. The important points are: 

(A) Mass flow theory proposes the transportation of food in the plants.

Munch hypothesis is also called the pressure flow hypothesis, it explains the movement of sap through the phloem. It proposed by Ernest Munch in 1930. High concentration of organic substance inside the cell of the cells of the phloem at a source that creates the diffusion gradient drawing water from the adjacent xylem resulting into the turgor pressure.

Mass flow or pressure flow hypothesis was put forward by Munch $(1927, 1930)$. According to this hypothesis, organic substances move from the region of higher osmotic pressure to the region of lower osmotic pressure in a mass flow due to the development of a gradient.

Translocation of prepared food occurs through the phloem. Bicollateral vascular bundles have two patches of phloem. Bicollateral vascular bundles show following arrangement of vascular tissue, outer phloem, outer cambium, xylem, inner cambium, inner phloem. These vascular bundles can transport much more amount of sugars than collateral vascular bundles having only a single patch of phloem. Bicollateral vascular bundles are common in Family Cucurbitaceae with large leaves, large fruits called Pepo and thin weak stems. 

One atmospheric pressure of transpiration pull is enough to pull the water unto the height of 20 feet or so; but normally, the transpiration pull that develops runs to about 20-100 atm (it can be as high as 200 atms in case of rapidly transpiring tall trees in tropics), which is enough to pull the water to the height of 400 to 1000 ft and the tallest plant known to mankind is just about 400 ft. 

Dixon and Joly gave the theory that ascent of water in the plant through pored tracheary elements of xylem which uses cohesion-tension, transpiration pull and suction pressure developed in the leaf cells.

Cohesion transpiration pull theory was proposed by Dixon and Jolly. They proved that cohesion and adhesion support continuity of water columns and provide strength like a steel wire, transpiration pulls water columns towards leaves which causes ascent of sap.

Cohesion tension theory was proposed by John Joly and Henry Horatio Dixon in the year 1894. The theory has two fundamental features such as (i) cohesion of water and adhesion between water and xylem tiusses, (ii) Transpiration pull. This theory explains plants which is responsible for the movement of water column upward.

Mass flow hypothesis is also known as pressure flow hypothesis it is the best-supported theory to explain the movement of sap through the phloem. It was discovered by the scientist by Ernst Munch in 1930, He was the German plant physiologist. This creates the hydrostatic pressure in the phloem of the plant.

Cell membrane, also known as plasmalemma, is the innermost membrane of a plant cell. It is surrounded by a cell wall. The cell membrane is a selectively permeable membrane that allows only some type of compounds to pass through. The membrane has a phospholipid structure that contributes to this property.

Xylem tissue is comprised of dead cells involved in the process of transport of water and minerals. Transport of water is under the influence of transpiration pull and is a physical process. 

Phloem is involved in transport of sugars. Phloem cells are living cells, which carry out the physiological process of sugar transport in higher plants.

Movement of food takes place through phloem tissue. This can be demonstrated through ringing experiment in which, if ring of vascular tissue including phloem is removed in a dicot tree. The plant parts located below the point of ringing will die because these parts do not get food.

The Dixon and Jolly model (Cohesion-Tension theory) relies on cohesion, adhesion, surface tension, and transpiration pull. Pushing by root pressure is not part of this specific model.