Question

$\left(a\right)$ How water is transported to various parts of the plant. Is the water movement active, or is it still passive?

$\left(b\right)$ Since the water has to be moved up a stem against gravity, what provides the energy for this?

Answer 1

1)Transportation in plants:
Transportation is defined as the movement of the water and essential nutrients, minerals from the roots to the other plant parts.

Types of transport:
Transportation in plants takes place by three ways:
1.Passive transport
a.Diffusion and osmosis
b.Facilitated diffusion
2.Active transport

Passive transport:
Diffusion is a passive process in which molecules move from a region of their higher concentration to a region of their lower concentration. It is a slow process which does not require energy expenditure. The molecules in diffusion move in a random fashion from cell to cell or from one part of the plant cell to the other. It generally depends upon the temperature, pressure, concentration gradient etc.

Osmosis ensures the diffusion of water through a semipermeable membrane.

Facilitated diffusion is a type of passive process where molecules move from a region of their higher concentration to a region of their lower concentration with the help of certain transport molecules.

Passive transport occurs in leaves, roots etc. For example, the influx of water from xylem into the phloem sieve tube cells when the latter get loaded with photosynthates. It also occurs in the process of water absorption and transportation across apoplast pathway till endodermis.

Active transport:
When molecules are pumped against the concentration gradient with the utilisation of ATP, it is termed as active transport.

Active transport takes place across the roots of the plants for the absorption of minerals and ions. This further leads to entry of water into those cells.

2) Transpirational pull:
Transpirational pull helps to move the water against the gravitational force. During transpiration, the generation of negative suction inside the mesophyll cells pulls up the water from the roots to the leaves. This water is used up by the leaves during the process of photosynthesis and the excess water escapes from the surface of the leaves. As more and more water escapes due to transpiration, it creates a pulling effect due to which the water column ascends.

Root pressure:
Root pressure is defined as the osmotic pressure generated inside the cell of the roots due to the influx of water after absorption of minerals and ions. This causes the sap to rise through the stem upto small heights.