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Wednesday, February 22, 2012

Transportation System for the Continuation of Living Organisms Part I

The water and minerals absorbed by the roots should be transported to all the cells of the plant. Transportation in plants occurs in two ways

Dormant Transportation

The transportation that occurs without spending metabolism energy called dormant transportation. This occurs by
  • Mass flow
  • Diffusion
  • Osmosis
  • Evaporation

Mass Flow

When water and minerals are able to flow due to the difference of pressure at two points. water flows along xylem conducting tissue and through the cell wall in this manner. The cell wall is made up of tiny fibers. There are small spaces in between these fibers. Water flows along these spaces by this process. The dissolved salts in water are also carried with it.

Diffusion

When nyctanthes flowers bloom at night and when a joss stick is lit or a bottle of perfume is opened in a small room you get the pleasant smell spread all over the room. The smell spreads in particles. Matter is made up of particles and these particles continuously vibrate. When the particles are clustered together, each particle is surrounded by other particles, and they tend to get released from the other particles around. The process of spreading particles from a place with a higher particle concentration to a place with lower particle concentration is known as Diffusion. The particles of perfume spread into the air particles. The air particles as well as perfume particles are both vibrating. The gases can spread through liquid particles, solid particles and through gas particles.

As a example take a small bottle which filled with some color and release it under a water bath. Then the color spreads to the water outside from the small bottle. This is due to diffusion of the color particles in the water. After some time - a longer time the color of the water in the vessel and the small bottle will be the same. The concentration of the particles of the colored solution in the bottle decreases while the concentration of particles in the vessel of water increases. At one stage the spreading of particles inside the water is even. Then you can say that the system is balanced. When water enters a plant, diffusion takes place.

Osmosis

Osmosis is a process of diffusion taking place through tissues. If a certain substance can pass through a tissue, you can call it a permeable tissue for that substance. Some tissues are permeable to certain substances and non-permeable to others. Such tissues are known as selectively permeable membranes. The process of water flowing from a place with a lesser concentration to a place with high particle concentration through selectively permeable membrane - Permeable only to water is known as Osmosis.

Root Hairs

A special structure formed by a cell on the epidermis of the absorbing region of the root is called root hairs. Root hairs are inside the soil. The concentration of the cell liquid of the root hair is higher than the concentration of the water outside. Hence water diffuses into the root hairs. Then the water particles move into the xylem cells through the other cells in contact and move through the entire plant. Some particles can enter through the plasma membrane. Some mineral particles too enter through the root hairs.

Evaporation

Water boils at its boiling point. Then water particles enter the vapor state from the liquid state. Water can get evaporated without reaching its boiling point. But the rate of evaporation is less than the evaporation at its boiling point. The entering of water particles into the vapor state from the liquid state without reaching its boiling point is known as evaporation. A cloth hanging on a clothes line or a wet floor dries up due to evaporation. The water passing to the central cells of the leaf along the xylem cells of the leaf veins enter the intercellular spaces by evaporation.

I'll meet you up in the next post about Active Transportation which is part II of this post.
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