Transport in Plants Test - 23

• Ion channels are special proteins through which ions flow along the concentration gradient. These channels are important because the membrane is made up of a bilayer of lipids and will not allow the 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 the same transport protein because the volume of each ion will be different. There are different transport proteins for the transport of different ions.

Solution

Correct answer is option B.
Explanation for correct option:

• Root pressure is the positive pressure that develops in the roots of the plants by the active absorption of nutrients from the soil.
• The active absorption depends on the active accumulation of solute in xylem sap.
• Root pressure is maximum when transpiration is very low and absorption is high because transpiration is the output of water from a plant, and absorption is the input of water into a plant.
• If the output is low and the input is high, the pressure will be at its greatest. 
  So, the correct answer is 'Transpiration is very low and absorption is high'.

In ringing experiment, the bark ring is scraped away which also removes the phloem causing xylem exposure. In this experiment, sugar moves downwards in the stem but the movement is stopped by the ring. As as result sugar bulge forms above the ring. This suggest that sugar transports down in the stem in the phloem.

Water is an essential component of protoplasm and forms 80-90% of the fresh weight of actively growing tissues. Water acts as a solvent for the solutes, take part in photosynthesis and maintain turgidity of the cells and tissues.
Therefore, the correct answer is option D.

The innermost cortical layer of the dicot root is called the endodermis. Many cells get suberized on their radial and inner walls. The cells are barrel-shaped and are closely packed, such thickenings are called casparian strips which contain lignin and suberin. 
Thus, the correct answer is option C.

• Hydathodes are a type of secretory tissue in leaves of angiosperms that secrete water through pores in the epidermis or margin of leaves. 
• They are modified stomata and are involved in guttation. Hydathodes are connected to the plant vascular system by the vascular bundle.

Protoplasmic streaming: Rapid movement of cytoplasm inside the cell. It is an autonomic movement of locomotion. Autonomic movements are the movements which occur due to factors are inherent in plant body.

Phloem transports food from leaf to other parts of the plant. In vascular plants, phloem is the living tissue that carries organic nutrients (known as photosynthate), particularly sucrose; a sugar, to all parts of the plant. The phloem is concerned mainly with the transport of soluble organic material made during photosynthesis.  Therefore, the correct answer is option A.

Active transport is the movement of a substance against its concentration gradient i.e., from a region of low concentration to high concentration. As the transport is against the concentration gradient, ATP or adenosine triphosphate is required to facilitate this transport. So, the correct answer is option A.