Transport Systems, Biology tutorial

Introduction to Transport Systems:

All living organisms require being able to move (transport) particles like molecules or ions, into themselves that is in body of organism and to be able to move such particles around within organism. They also need to be able to eradicate unwanted substances from their bodies. This is essential in order for organisms to breathe, feed, and maintain internal environment of organism within satisfactory limits (homeostasis) that is to continue to live.

Different kinds of organisms, like - but not only - plants and animals, have various kinds of internal transport systems through which fluids having substances essential for life of their cells are moved around organism.

Due to huge diversity of different kinds of animals and plants it is helpful to specify some categories of organisms to compare transport systems in plants and animals. 

In biology, mass flow is the movement of the fluid in one direction, generally through the system of tube-like vessels. The mass transport system is a transport system that is means through which materials are moved from exchange surface/s that form part of the organism to all other locations within organism where materials from exchange surfaces are needed by cells which involves mass flow.

Transport systems in several different organisms contain lots of common features. Has transport medium in which materials, comprising different sizes and shapes of molecules, can be conveyed. This medium is generally water-based. Water acts as the solvent for the wide range of substances and flows easily at temperatures of living organisms. Examples of transport media in animal transport systems comprise blood, lymph and hemolymph. Although gas exchange surfaces are important due to the need for respiration, they aren't the only kinds of exchange surfaces. Another instance in humans is wall of the small intestine where digested (food) material is transported into the blood stream for distribution to cells throughout the body. Though gas exchange surfaces are significant because of the need for respiration, they are not only kinds of exchange surfaces. Another example in humans is wall of small intestine where digested (food) material is transported in blood stream for distribution to cells throughout body.

Transport Systems in plants:

Plants contain two systems for transportation of substances - employing two different kinds of transport tissue. Xylem transports water and solutes from roots to leaves, whereas phloem transports food from leaves to rest of plant. Transpiration is a procedure by which water evaporates from leaves that result in more water being drawn up from roots. Plants have adaptations to decrease excessive water loss.


Xylem vessels are involved in movement of water through plant - from its roots to its leaves through stem.

During this procedure:

  • Water is absorbed by root hair cells from soil.
  • Water moves by osmosis from root cell to root cell until it reaches xylem.
  • It is transported through xylem vessels up stem to leaves.
  • It evaporates from leaves (transpiration).

Xylem tubes are composed from dead xylem cells that have cell walls removed at the end of cells, forming tubes by which water and dissolved mineral ions can flow. Rest of the xylem cell has thick, reinforced cell wall that gives strength.


Phloem vessels are engaged in translocation. Dissolved sugars, generated in photosynthesis, and other soluble food molecules are moved from leaves to growing tissues (like tips of roots and shoots) and storage tissues (likein the roots).

In contrast to xylem, phloem comprises of columns of living cells. Cell walls of these cells don't entirely break down, but instead form small holes at the ends of cell. Ends of the cell are stated to as sieve plates. Connection of phloem cells efficiently forms the tube that permits dissolved sugars to be transported.

Transport system in Animals:

Simplest animals to have transport systems are annelids i.e. segmented worms. Simpler animals like flatworms and Cnidarians utilize simple diffusion and thin body design to provide all cells with nutrients; foods and gases directly diffuse from outside to inside with no internal fluid transport. More complex animals having thick bodies use internal fluid transport to move food and/or nutrients between outside and inside. Hearts pump blood from arteries to capillaries where gas exchange occurs. Veins get blood from capillaries and return it to heart.

Among unicellular protists, oxygen and nutrients are attained directly from aqueous external environment through simple diffusion. Body wall is only 2 cell layers thick in cnidarians, like Hydra, and flatworms, like Planaria. Every cell layer is in direct contact with either external environment or gastrovascular cavity. Gastrovascular cavity of Hydra expands from body cavity in tentacles, and that of Planaria branches widely to supply every cell with oxygen and nutrients.

Larger animals, though, have tissues which are several cell layers thick, so that several cells are also far away from body surface or digestive cavity to exchange materials directly with environment. In its place, oxygen and nutrients are transported from environment and digestive cavity to body cells by the internal fluid within the circulatory system.

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