Transport System In Living Things

In this article, the following are the objectives that will be discussed.

• Understand systems.
• Describe unicellular and multicellular organisms and the use of systems in these organisms.
• Describe the processes that take place in the transport system of living things.

What are “systems”?

A system is defined by placing boundaries around interrelated entities. 

The behaviours and functions of systems can be understood through observation and measurement.

Unicellular Organisms

Unicellular organisms are simple organisms made up of only one cell.

Examples of unicellular organisms are bacteria and amoeba.

Unicellular organisms do not have transport systems as they are able to absorb nutrients and release the wastes through osmosis and diffusion. 

Multicellular Organisms

Multicellular organisms are complex organisms made up of more than one cell.

Multicellular organisms require systems to survive as they are often made up of billions of cells, to which most of these cells lie far from the source of essential substances. Hence, a transport system is required to ensure that all the cells in the organism receive these essential substances.

There are many different systems in human beings.

• human circulatory system
• human respiratory system
• human digestive system
• human nervous system
• human reproduction system
• human muscular system
• human skeletal system

Processes in Transport Systems

The two processes that take place in transport systems are diffusion and osmosis.                  

Diffusion

Diffusion is a net movement of particles from a region of higher concentration to a region of lower concentration until the concentration reaches equilibrium.

Image Credits: unsplash - Laura Chouette

For example, what happens when perfume is sprayed in a corner of a room? What happens when an individual is standing at the opposite corner to which the perfume was sprayed?

Hence, diffusion happens in fluids, such as liquids and gases, but not in solids. The particles of solids are held in their fixed position and therefore, the particles cannot move from one place to another.

What affects the rate of diffusion?

The two factors that affect the rate of diffusion are related to the Particular Nature of Matter, which states that all matter is made up of tiny particles, to which these particles are always in a constant and random motion.

1. Temperature 

The higher the temperature, the faster the rate of diffusion.

2. Concentration Gradient

The steeper the concentration gradient, the faster the rate of diffusion.

Where does diffusion take place in living things?

Diffusion also takes place in plants and animals.

• In plants, the movement of oxygen and carbon dioxide into and out of the leaves through the stomata is an example of diffusion. 
• In humans, the movement of oxygen and carbon dioxide between the alveoli and blood capillaries in the lungs is an example of diffusion.  

Osmosis

Osmosis is a net movement of water molecules from a region of higher water potential to a region of lower water potential through a partially permeable membrane.
A partially permeable membrane is a membrane that allows selected molecules to pass through but not other substances.
Examples of partially permeable membranes are the cell membrane, Visking tubing and cellophane paper.

What affects the rate of osmosis?

The rate of osmosis is affected by the term called water potential. Water potential is very similar to the concentration gradient in diffusion. Water potential refers to the tendency for water molecules to move.

Where does osmosis take place in living things?

• In plants, osmosis occurs in the roots of plants, where water is absorbed from the soil and into the roots.
• In humans, the absorption of water in the large intestine is an example of osmosis.

Compare and contrast between Diffusion and Osmosis

Similarities:

• In diffusion and osmosis, the substance moves from a region of higher concentration to a region of lower concentration.
• No energy is required in order for diffusion and osmosis to occur.

Differences:

• Diffusion refers to the movement of all substances while osmosis refers to the movement of only water molecules.
• Diffusion may or may not require the presence of a partially permeable membrane while osmosis requires the presence of a partially permeable membrane.

Revision Questions

Here are some questions for us to look into on the objectives of this article.

Question 1: 

Which is not an example of a system in living things?

1. human digestive system
2. human circulatory system
3. human respiratory system
4. human heart system

Solution: 

(D) human heart system

Explanation:

The heart belongs to the human circulatory system.

Question 2:

What is the definition of diffusion?
 

1. Diffusion is the net movement of particles from a region of lower concentration to a region of higher concentration.
2. Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration.
3. Diffusion is the net movement of particles around an area in circles.
4. Diffusion is the net movement of particles due to the smell of the particles.

Solution:

(B) Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration.

Question 3:

What affects the rate of diffusion?

1. temperature and smell
2. temperature and colour of the particles
3. concentration gradient and smell
4. concentration gradient and temperature

Solution:

(D) concentration gradient and temperature

Explanation:

The rate of diffusion is affected by the concentration gradient and temperature. The steeper the concentration gradient, the faster the rate of diffusion. The higher the temperature, the faster the rate of diffusion.

Question 4:

A piece of Visking tubing, filled with water, was placed in a concentrated salt solution. Which of the following describes what happens to the Visking tubing?

1. The Visking tubing will enlarge as water moves into the tubing.
2. The Visking tubing will shrink as water moves out of the tubing.
3. The Visking tubing will shrink as salt moves into the salt solution.
4. The Visking tubing will enlarge as salt moves into the tubing.

Solution:

(B) The Visking tubing will shrink as water moves out of the tubing.

Explanation: 

Due to a higher water potential in the Visking tubing as compared to the concentrated salt solution, water molecules move out of the Visking tubing and into the concentrated salt solution, through the partially permeable membrane, via osmosis.

Question 5:

What is one of the differences between diffusion and osmosis?

1. Diffusion applies to water molecules only and osmosis applies to all particles.
2. Diffusion occurs only when a partially permeable membrane is present while osmosis can occur without a partially permeable membrane.
3. Diffusion applies to all particles while osmosis applies to water molecules only.
4. Diffusion is the movement of particles from a region of higher concentration to a region of lower concentration while osmosis is the movement of particles of all concentrations.

Solution:

(C) Diffusion applies to all particles while osmosis applies to water molecules only.

Explanation: 

Diffusion refers to the movement of all substances while osmosis refers to the movement of only water molecules.
Diffusion may or may not require the presence of a partially permeable membrane while osmosis requires the presence of a partially permeable membrane.
In diffusion and osmosis, the substance moves from a region of higher concentration to a region of lower concentration.