Introduction

A vertical take-off and landing (VTOL) aircraft is one that can hover, take off, and land vertically. This classification can include a variety of types of aircraft including fixed-wing aircraft

Objective


The main objectives of e-content are to :

a) Enable the students to define transportation.

b) Enable the students to identify means of transportation.

c) Enable the students to understand the mechanism of transportation.

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Water Absorption


The way in which water from the soil enter roots, particularly to the root xylem, is called water absorption in plants. It is also called as Transportation. In plants water can be transported over short distances as well as long distances. Based on the distance travelled transportation is classified into two categories :-

a) Short Distance Transport

The transport of water that occurs within a cell or from one cell to other in a tissue is called short distance transport. It is further of two types-

i) Passive Transport : Transportation that occurs according to the concentration qradient i.e. from high concentration to low concentration without consumption of ATP is called passive transport. It is facilitated by two ways-

Diffusion -

Movement of an atom, molecule or ion of a material from an area of high concentration to low concentration is called diffusion.

Diffusion is continued till dynamic equilibrium is achieved. At this point the movement of molecule is equal in both directions. So net movement of molecule is zero.

Diffusion is very important in plants because it is the only medium for gaseous exchange in plants.

Diffusion of one substance is independent to diffusion of other substance.

Diffusion is a slow process.

The rate of diffusion is Gas>Liquid>Solid.

The rate of diffusion is affected by concentration gradient, membrane permeability, temperature and pressure.

The pressure exerted by the diffused molecule or ion on the medium in which diffusion takes place is known as Diffusion Pressure.

Facilitated Diffusion -

Facilitated means "facility" and diffusion means from high to low concentration gradient. So the movement of an atom, molecule or ion of a material high to low concentration gradient across the membrane via specific protein molecules is called facilitated diffusion.

Proteins molecules may be carrier proteins and channel proteins.

Carrier proteins are present on the membrane and are always open.

Channel proteins are gated passage for movement of selective molecules or ions across the membrane.

Some proteins are large that allow variety of molecules to pass. These forms large pores in the membrane and are called as porins.

It is a selective process.

It is faster than simple diffusion.

When a molecule moves across a membrane independent of other molecules, the process is called Uniport.

Some carrier or transport proteins allow diffusion only if two types of molecules move together or in opposite directions. In a Symport, both molecules cross the membrane in the same direction; in an Antiport, they move in opposite directions.

ii) Active Transport : Transportation that occurs against the concentration qradient i.e. from low concentration to high concentration with consumption of ATP is called active transport.

b) Long Distance Transport

The transport of water that occurs through vascular system (xylem and phloem) is called long distance transport. It is also called as Translocation.

Transport through the xylem is unidirectional i.e from root to the tip.

Transport through the phloem is bidirectional i.e. from leaf to storage organ of plant and from storage organ to other growing organs of plant.

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