The epidermal resistance to diffusion of water vapour: an ...
05 water and diffusion
description
Transcript of 05 water and diffusion
The Chemistry
of Life
Water and Diffusion
Objectives Relate water’s unique features to polarity
Identify how the process of diffusion occurs and why it is important to cells
Read section 6.2
Water’s Importance
Most life processes occur only when molecules and ions are free to move and collide with one another When does this condition exist?
Transport Ex/ blood and plant sap
Makes up 70% - 95% of most organisms
Water’s Importance
Water is polar
Water resists temperature change
Water expands when it freezes
Water is Polar Sometimes, when atoms form covalent
bonds they do not share the electrons equally. This is a polar bond.
Water is Polar A polar molecule has an unequal
distribution of charge
A polar molecule has a positive and and a negative end
A polar solvent (like water) dissolves ionic compounds and other polar molecules
Like dissolves like
Water is Polar
Water is Polar The weak bond formed between the
positively charged hydrogen atom and the negatively charged oxygen atom is called a hydrogen bond
Hydrogen bonds help hold biomolecules such as protein together
Water is Polar
Because water is polar, it has a couple more unique properties Capillary action Surface tension
Water resists temperature
change Water requires more heat to increase its
temperature than most other common liquids
Thus, water also loses a lot of heat when it cools
Why is this beneficial to an organism?
Water expands when it freezes
Thus, ice is less dense than water
Why does water expand when in cools if almost all other substances contract? Hydrogen bonds are stabilized!
Diffusion
Brownian motion: The random motion of atoms and molecules Characteristic of gases, liquids and some
solids
Diffusion The net movement of particles from an area
of high concentration to an area of low concentration due to the random movement of particles (Brownian motion) is called diffusion
3 factors affect diffusion rate: Concentration Temperature Pressure
The results of diffusion
Dynamic equilibrium: Materials move into
and out of the cell at equal rates
No net change in concentration inside or outside the cell
Diffusion in living systems
The difference in concentration of a substance across space is called a concentration gradient
Ions and molecules diffuse from an area of high concentration to an area of lower concentration The ions and molecules are said to be
‘moving with the gradient’ If no other processes interfere, diffusion will
continue until there is no concentration gradient (dynamic equilibrium)