Plant Physiology: Cytoplasm & Solutions

• Course title is Principles of Plant Physiology.
• Course Code: B103
• First Level
• Biotechnology and its applications Students
• Instructor: Mustafa Ismaeil Elnajar, lecturer of plant physiology at Mansoura University.
• Plant physiology is the science that studies plant functions, processes, and behavior.
• The text will discuss cytoplasm and it's physical and chemical properties.
• Colloids are also called colloidal state, colloidal system or colloidal solution.
• Solution = Solute + Solvent

Types of Solutions

• True solutions include substances (solutes) that separate into free molecules or ions.
• Colloidal solutions (Colloids)
• Suspensions & Emulsions
• Diameter of solute in true solutions is less than 0.001 micron.
• The solute in true solutions cannot be seen by any optical system and are homogenous and stable, with examples including salt and sugar in water.
• The diameter of solute in colloidal solution is 0.001-0.1 micron.
• The solute in colloidal solutions can be seen by ultra-microscope and the solutions are heterogenous and stable, with examples including clay in water and cytoplasm.
• The diameter of solute in suspensions and emulsions is more than 0.1 micron.
• The solute in suspensions and emulsions can be seen by an ordinary microscope and the solutions are heterogenous and unstable.
• Suspension (solid in liquid), example sand in water.
• Emulsion (liquid in liquid), example Oil in water.

Colloids vs Solutions vs Suspensions and Emulsions

• Stable mixtures do not separate over time, while unstable mixtures do.
• Homogenous mixtures are evenly mixed.
• Heterogeneous mixtures are uneven.
• Ordinary microscopes are for big particles and ultra-microscopes are for tiny ones.
• All colloids have two components: Dispersed particles (Solute) and Dispersion medium (Solvent).
• Dispersed particles are small particles spread throughout a mixture that are not connected and are scattered throughout (Discontinuous phase).
• Dispersion medium is the substance in which the small particles are spread that forms a connected and unbroken phase (Continuous phase).
• Condensation/Association entails the collection of small particles until they reach colloidal size.
• Dispersion/Dissociation entails the disintegration/break down of coarse particles until they reach colloidal size.
• Colloidal solutions are an intermediate stage between suspensions and true solutions.

Types of Colloids

• There are eight types based on the state of dispersed particles and the dispersion medium.
• Liquid in Liquid
• Liquid in Solid
• Liquid in Gas
• Solid in Liquid
• Solid in Solid
• Solid in Gas
• Gas in Liquid
• Gas in Solid
• Liquid in liquid colloid is the most important type in biology.
• Gas-gas mixtures are generally not classified as colloids.
• In colloids, the dispersed particles have to remain separate from the dispersion medium and not dissolve completely.
• Gases mix homogeneously without forming separate phases.
• Gas-gas systems have no dispersed particles or dispersion medium, and are a single uniform phase.
• Air is a gas-gas mixture of nitrogen, oxygen, carbon dioxide, and other trace gases and the gases mix uniformly at the molecular level, making it a solution.

Classification of Colloids

• There are two types according to the affinity between the dispersed particles and the dispersion medium.
• Lyophobic Colloid (Dispersion medium-hating)
• Lyophilic Colloid (Dispersion medium-loving)
• There is no affinity between the dispersed particles and the dispersion medium in Lyophobic colloids.
• There is a great affinity between the dispersed particles and the dispersion medium in Lyophilic colloids.
• Affinity is how much two things are attracted to each other and how well particles stick to or interact with the medium.
• If particles and the medium have a high affinity, they mix well together.
• If the affinity is low, the particles might not mix as easily or separate over time.
• If the dispersion medium is water, the colloids can be hydrophobic (water-hating) or hydrophilic (water-loving).
• Hydrophobic example: Clay solution
• Hydrophilic example: Starch solution
• Stability of hydrophobic colloids is due to the presence of similar electrical charges on all the dispersed particles.
• Stability of hydrophilic colloids is due to the presence of similar electrical charges on all the dispersed particles and the presence of water shell around each particle.
• A reddish brown color indicates a hydrophobic colloid.
• Colloids are heterogeneous and stable systems with solutes ranging from 0.001 to 0.1 micron.
• Stability of hydrophobic colloids is characterized by particles carrying the same electrical charges.
• Fe(OH)3 have particles of small size that condense together to form particles of colloidal nature (0.001-0.1 micron).
• The particles of small size will disperse in water with all particles carrying the same electrical charges, forming a stable hydrophobic colloid.
• Hot water dissociates the starch paste particles in to particles of colloidal nature (0.001-0.1micron).
• The particles will disperse in water and the particles carry the same electrical charges, forming a stable hydrophilic colloid.
• Solid in Liquid is Sol.
• Liquid is Water is Hydrosol.
• Hydrosols (Solid in water) can be hydrophobic or hydrophilic.
• Temperature, concentration of dispersed particles, hydrogen ion concentration (pH), and electrolytes, can change a hydrophilic sol into a rigid and elastic get.
• Sol can transform to rigid and elastic Gel (reversed phases).
• The conversion of a sol to a gel through cooling is gelation.
• The conversion of a gel to a sol through heating is solation.
• Gelatin in warm water -> Sol
• Sol -> Cooling -> Gel
• Gel -> Heating -> Sol.
• Most of the dispersion medium (water) is in the free state separating the gelatin particles in Sol.
• Most of the dispersion medium (water) is still present but is not easily withdrawn (bound water) and few molecules of water are free in Gel.

Properties of Colloids

• Tyndall phenomenon
• Brownian movement
• Diffusion
• Dialysis
• Electrical charges property
• Flocculation or Precipitation
• Adsorptive power or Adsorption
• Viscosity
• Imbibition

Tyndall Phenomenon

• Differentiation from true solutions depends on the optical properties of colloids.
• This is the scattering of light by colloidal particles and the development of the ultra microscope depends on it.
• John Tyndall discovered the Tyndall phenomenon.
• In colloid sols, the dispersed particles are large enough to scatter the light and appear as a beam of light.
• In true solution, the particles are very small and no scattering occurs.
• Robert Brown discovered Brownian movement (pollen grain in water).
• Colloidal particles can be observed under the ultra microscope in a continuous irregular motion.
• Brownian movement is attributed to bombardment through liquid medium, and moving back & forth, up & down.
• Brownian movement depends on temperature.
• An increase in temperature increases Brownian movement.
• Due to increase in the kinetic energy of the colloidal particles and the molecules of the liquid medium.
• Due to decrease in the viscosity of the liquid medium.
• Diffusion is defined as the Movement (Migration) of solute particles from the side of high concentration to the side of low concentration.
• Diffusion of colloidal particles is slower than those of true solutions.
• Dialysis is defined as the separation of colloids from true solutions through semi-permeable membranes.
• The apparatus used for this process is called a dialyser, and this property provided the first rough differentiation between true solutions and colloids.
• Used in industry for purification of enzymes from impurities.
• Used in medicine for purification of blood in renal failure patients.