Biology
Class Notes
Lesson 2 Homeostasis and Cell Transport
Objective: 1.1.1, 1.2.1, 4.2.2
Maintenance of Homeostatis
Homeostasis: The ability of a cell or organism to regulate its internal conditions despite changes to the
environment.

Maintaining homeostasis involves regulating conditions like pH and temperature with voluntary
and involuntary response.
Means of Obtaining Energy for Metabolism
Autotroph: Organisms that obtain their energy by making their own foods (plants).
Heterotroph: Organisms that must take in food to meet their energy needs (animals, fungi, bacteria).
Thermoregulation: The control of body temperature.
Ectotherm: Organisms who warm their bodies by absorbing heat from their surroundings.
Ex: Reptiles, fish and amphibians
Endotherm: Organisms that have a rapid metabolism and generate the heat needed to warm their body.
Ex: Mammals and birds
Regulating Movement of Materials Into and Out of Cells to Maintain Homeostasis
Passive Transport: Some substances can cross the membrane without any input of energy by the cell.
1) Diffusion

The simplest type of passive transport.

The movement of molecules from an area of higher concentration to an area of lower concentration.

Driven by kinetic energy of particles. Diffusion stops when kinetic E is equal among particles.
Equilibrium: When the concentration of the molecules of a substance is the same throughout a space.
2) Osmosis: The process by which water molecules move across a semipermeable membrane from an
area of high concentration to low.
Concentration gradient: The difference in the concentration of molecules from one area to another that
drives osmosis.
Possible States:
Isotonic: When the concentration of solute (e.g. salt) is equal inside and outside the cell.
Hypotonic: When the concentration of solute inside the cytoplasm is higher than the concentration
outside the cell.

Hypo = too low

Water moves into the cell to establish equilibrium and causes it to swell.
Hypertonic: When the concentration of solute outside the cell is higher than the concentration in
the cytoplasm.

Hyper = too high

Water moves out of the cell to establish equilibrium and causes it to shrink.
http://www.youtube.com/watch?v=H6N1IiJTmnc
http://www.youtube.com/watch?v=nHWUAdkYq4Q
http://www.youtube.com/watch?feature=fvwp&v=xC5zRkUqZso&NR=1
3) Facilitated diffusion: A process used for molecules that cannot diffuse rapidly across a membrane, even
when there is a concentration gradient.

The movement of these molecules across the membrane is facilitated by “helper” proteins in the
membrane called carrier proteins.
Active Transport: Movement of materials across the cell membrane from an area of lower concentration to an
area of higher concentration (i.e. against the concentration gradient).
*Active transport requires a cell to expend energy.
Acids and Bases
Acid: Produce hydronium ions H+ in water solution.
 Taste sour
 Turn litmus paper red
 Because acids ionize to produce positive hydrogen ions (H+), they are referred to as proton donors.
 Because acids remove hydrogen and oxygen (i.e. H2O) from other compounds, they are referred to as
dehydrating agents.
*Intense dehydration causes skin burns.
Base: Produces hydroxide ions (OH-) in water solution.
 Taste bitter
 Slippery
 Turns litmus paper blue
 Because all bases contain a hydroxide ion (OH-), they will react with hydrogen ions (H+) to form water.
Hence, bases are referred to as proton acceptors.
*Intense proton acceptance causes skin burns.
Acids/Bases In Solution
*Both form ions. Strong acids and bases produce many ions while weak acids and bases produce a few
ions.
pH: The measure of the number of hydronium ion concentration for a given substance. Substances with a
pH < 7 are acids and substances with a pH > 7 are bases.
Buffers
A weak acid or base that can react with strong acids or bases to prevent sudden changes in pH.

Buffers help to resist changes in pH
Regulating Temperature to Maintain Homeostatis- Metabolism
Metabolism: The sum total of the body’s chemical activities.

Changes in temperature cause the chemical reactions to speed up or slow down and affect the metabolic
rate.

The rate at which metabolism occurs affects how fast the body uses energy.
Key Words:
Homeostasis
Hypertonic
pH
Hypotonic
Buffer
Isotonic
Metabolism
Equilibrium
Diffusion
Passive Transport
Osmosis
Active Transport
Facilitated Diffusion
Observation
Concentration Gradient
Inference
SelectivelyPermeable