Homeostasis *All living things must maintain a balance

regardless of internal and external conditions

Homeostasis• The process of maintaining equilibrium in the cell’s

internal environment, a resistance to change

*This is similar to a thermostat in your home

Important terms to know:

• Solute: substance being dissolved in another substance (often the lesser quantity)

• Solvent: substance that dissolves another substance

Example: Kool-Aid, Which is the solute and which the solvent?

Mixture vs. Compound

• Compound: cannot be easily separated by physical methods

• The chemical/physical properties are totally different than the properties of the parts

•NaCl–Na-very reactive, whitish, Cl-poisonous, green

gas• We know this compound as table salt.

•H2O2 –H2- explosive gas, O2-flammable gas• We know this compound as hydrogen peroxide.

• Mixture: can be easily separated by physical methods

• The chemical/physical properties remain the same

Three types of mixtures:1. Solution: two or more substances in a single

phase, does not settle out, it is mixed evenly – *solute molecules are smaller than in the solvent– ex. Sugar water

Three types of mixtures:

2. Suspension: solute larger than solvent will settle out over time, unless the mixture is constantly stirred or agitated – ex. muddy water-mud

settles when not stirred, particles can be separated

Three types of mixtures:

3. Colloid: particles of solute and solvent are mainly the same size, gel-like– small particles remain

suspended• ex. types of emulsion-oils,

waxes• smoke, fog-liquid in gas

• Each of these mixtures is in our body:

–Solution: salt water–Suspension: blood–Colloid: Cytoplasm

Major part of cells that maintain homeostasis:

• 1. Plasma Membrane:– a. Function: boundary between cell and its environment,

allows steady supply of nutrients to come into the cell and excess wastes out-too much can be harmful

– Cells need nutrients-glucose, amino acids, lipids

• b. Selective permeability: allows some molecules in and keeps others out

• c. Structure: – phospholipid bilayer: two layers of phospholipids back to

back– glycerol, fatty acids, phosphate

• Nonpolar: phospholipids, no charge• Polar: phosphate can dissolve other substances

• (“like dissolves like”…so nonpolar can only dissolve nonpolar)

• Water is polar, so it can interact with phosphate (facing outside of the cell)

• Fatty acids avoid water (face middle of cell membrane)• Hydrophobic: water fearing• Hydrophilic: water loving

• d. Fluid mosaic model: membrane is flexible, proteins create a pattern on the membrane surface

• Transport proteins: allow needed material or wastes to move through the membrane, movement of substances in a mixture

Processes used to maintain homeostasis:

1. Diffusion: net movement of particles from an area of higher concentration to an area of lower concentration until it reaches equilibrium

*results due to the random movement of particles, a slow process

3 Key factors of diffusion1. Concentration: more concentrated, more rapid

diffusion 2. Temperature: increase in temp. speeds up the

movement of molecules and then diffusion 3. Pressure: increase in pressure, accelerate molecule

movement and diffusion

Goal of cell is to have:• Dynamic Equilibrium: continuous movement of

molecules, same rate in and out of the cell, but no overall concentration change

• Concentration gradient: difference in concentration across space

Processes used to maintain homeostasis continued…

2. Osmosis: diffusion of water across a semi-permeable membrane– water flows to side of cell with less water, where

water concentration is low

– *water continues to diffuse until it is in equal concentration on both sides of the membrane

3 types of solutions, osmosis in cells

1. Isotonic solution: The concentration of solute inside and outside the cell are the same, so water moves in and out of the cell at the same rate– *shape and size of the cell are normal, do not

experience osmosis, water concentration is the same in and out of the cell

3 types of solutions, osmosis in cells

2. Hypotonic: solute concentration is low outside the cell, water concentration or amount is lower inside the cell so water moves into the cell

• *shape and size of cell swells beyond normal

pressure increases, can cause cytolysis • Result: animal cells can burst, plant cells

become firm due to turgor pressure

3 types of solutions, osmosis in cells

3. Hypertonic: solute concentration outside the cell is higher than in the cell, so water concentration or amount is less outside the cell, so water moves out of the cell– *size of cell decrease for animal cells, causes

plasmolysis

Result: animal cell shrinks, vacuole in plant cell shrinks, plant wilts

Turgor pressure vs. plasmolysis vs. cytolysis

• Turgor pressure: in hypotonic cells, when water moves into cell the pressure increases and makes cell rigid

• Plasmolysis: water leaves cell and cell wilts

• Cytolysis: cells take in too much water and burst, only in animal cells

Water regulation in organisms1. Single celled: most found in hypotonic

environments, lakes and ponds*Want to avoid bursting, have contractile vacuoles that act as a pump and remove water by contracting

• 2. Higher level animals: cells in a hypertonic environment: no water, high-salt

– Small portion of cells in the brain shrink and cause thirst• Cells in hypotonic environment drink too much water, low salt

– *Small patch of cells in brain when they swell trigger nerves in kidney and cause kidney tubules to open up and produce more urine

• Passive transport: no energy is needed to move the particles across the membrane

– Ex. Diffusion and osmosis

• Facilitated diffusion: passive transport of materials with the help of proteins–Moves sugars and amino acids

• Active transport: movement of particles through a membrane

End of homeostasis notes