All about Tonicity

 Tonicity and Osmosis are closely related. It is a comparative term which describes the concentration of one solution as compared to another solution. Its the capability of one solution to modify the volume of cells by altering their water content. But what is a concentration?

Concentration describes the amount of solutes dissolved in a solution 

Solutions are made up of two parts

(A) Solute- the solid part e.g. salt

(B) Solvent- the liquid part e.g. Water 

Solute+ Solvent= Solution 

There are three types of tonicity, 

Hypertonic

This when a solution has a higher concentration of solutes (more dissolved particles) than another. 80%+20% = 100%

Hypotonic 

This is when a solution has less solutes and more solvents than another.

20%+80% =100%

Isotonic

This is when a solution has equal amounts of solvents and solutes as another.

50%+50% =100%

Tonicity helps us determine how and where particles move! The following video explains how tonicity work, after watching complete table 1.0 with your observations and explanations.

 

Hypertonic Solution

Blood cells placed in an hypertonic solution will have a lower concentration of solutes (dissolved particles) than the solution itself. This means that water would be greatest within the blood cell and will therefore leave the cell to where its lower. The cell will therefore become flaccid and can be compared to a deflated balloon that was once filled with water. 

Hypotonic Solution

Blood cells placed in an hypotonic solution will have a higher concentration of solutes (dissolved particles) than the solution. Water is therefore lesser in the blood cell and will take in water to where there's less. The cell will therefore become larger or swell (turgid) and can be compared to a balloon filled with water. 

Isotonic Solution

Blood cells placed in an isotonic solution will have the same concentration of solutes (dissolved particles) to that of the solution. Water will therefore be of similar volume inside and outside the cell making the cell normal. 

Table 1.0 observe and explain the changes seen in each raisins

                          

Transport Across Cells-A Comparison

 

There are two major ways molecules can be transported across cells. This can be either Passive or Active and while active requires the use of energy, passive does not. Passive transport requires the movement of particles from high to low concentration such as diffusion and osmosis, active transport in contrast requires the movement of particles from low to high concentration hence why energy is needed.  

Fig 1.0 Passive transport can be described as rolling a ball downhill needing less energy and active transport is pushing the ball uphill requiring hard work.

Diffusion: The movement of particles down a concentration gradient from an area of high                                       concentration to an area of low concentration until evenly distributed. A solution is required                    which includes a solute + solvent. Water is a universal solvent and sugar or salt is a good                         example of a solute.

Fig 1.1 Diffusion down a concentration gradient 

Osmosis: This is the movement of water particles in a solution from an area of  high concentration to    an area of low concentration across a selectively permeable membrane. A selectively permeable membrane or partially permeable membrane only allows  certain molecules or ions to cross it. It can be described as a sieve or filter. 

Fig 1.2 Osmosis across a selectively permeable membrane

What are some example of osmosis in living things?

Active Transport: Movement of molecules or ions across a cell membrane from a  region of lower      concentration to a region of higher concentration against the concentration gradient. This process is most seen in the sodium-potassium pump (Na+/K+ ATPase) that helps to create a resting potential in the cell using ATP.

Fig1.3 Sodium potassium pump allowing ions to flow down gradient 

 Below is a table of comparison between each processes, what are two reasons why transport processes   are important to living organisms?