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Name the two general classes of cells in the human body

Sex cells
Somatic cells


Define somatic cell

any cell of a living organism other than the reproductive cells.


Define Sex cells

Sperm of males or oocytes of females
(Also called germ cells or reproductive cells)


Name the three major parts of a cell

Cell membrane


Cell membrane is also called?

Plasma membrane


Functions of cell membrane

The cell membrane is selectively permeable to ions and organic molecules and controls the movement of substances in and out of cells. The basic function of the cell membrane is to protect the cell from its surroundings.
Allows selective communication between intracellular and extracellular compartments.
Gives form to the cell.


Define semipermeable

allowing certain substances to pass through it but not others, especially allowing the passage of a solvent but not of certain solutes.


Two types of selective permeability

Differentially permeable


Cell membranes are made of?

Lipids and proteins. Usually a double layer of phospholipid molecules. (Phospholipid bilayer)
Phosphate outer surface
Fatty acid inner surface


Passive cell mechanisms



Explain the passive cell mechanism: diffusion

Spontaneous movement of substances from regions of higher concentration to regions of lower concentration (concentration gradient). Until evenly distributed throughout a substance, achieving equilibrium.
Two types: simple and facilitated diffusion


Explain the passive cell mechanism: simple diffusion

Diffusion of very small or lipid soluble particles.
Non polar and lipid-soluble substances are diffused through the lipid bilayer. Including carbon dioxide, fat soluble vitamins and oxygen.


Explain the passive cell mechanism: facilitated diffusion (assisted diffusion)

Its a passive transport process.
Some substances cannot pass through the lipid bilayer, requiring proteins in the cell membrane to assist them. E.g. Certain amino acids, ions and glucose.
Two types: channel mediated and carrier mediated
Facilitated diffusion rate is controllable: membrane permeability may be regulated by altering the number or activity of individual channels (or carriers).


The two types of facilitated diffusion are called?

Carrier mediated
Channel mediated


Carrier mediated facilitated diffusion

Is when a peripheral protein (transmembrane integral) envelopes a polar molecule, sugar or amino acid. protecting it from the non polar lipid bilayer and transports it to the other side of the cell membrane. Always moves down the concentration gradient like in simple diffusion.


Channel mediated facilitated diffusion

Transmembrane proteins that move ions, water and other substances through aqueous channels from one side of the cell membrane to another.
Because of pore size and amino acid charges in the lining of the channel they act selectively.
Gated channels - opened and closed by electrical or chemical signals
Leakage channels - open constantly
Allows water or ions movement through based on concentration gradients.
facilitated diffusion rate is controllable because membrane permeability may be altered by regulating the number or activity of individual channels (or carriers)


define: Osmosis

Osmosis is a special type of diffusion where water molecules diffuse from an area of higher water concentration to an area of lower water concentration. This requires a selectively permeable membrane like a cell membrane.


Define: Osmosis

Osmosis is a special type of diffusion that occurs when water molecules diffuse form an area of higher concentration to an area of lower water concentration.
This requires a selectively permeable membrane, such as a cell membrane.
Solutions containing higher concentrations of solutes have a lower concentration of water and vica versa.
Osmosis continues until Osmotic and Hydrostatic pressures acting upon the cell membrane are equal.


define: Osmotic Pressure

The ability of osmosis to create enough pressure to raise a volume of water is called osmotic pressure.
Water always diffuses towards solutions of greater osmotic pressure.
the higher the amount of non-penetrating (non-diffusible) solutes in a cell, the higher the Osmotic pressure.


where does Osmosis take place

Through the lipid bilayer of the cell.
Via osmosis water equilibrates throughout the body so the concentration of water and solutes in both intracellular and extracellular fluids is nearly the same.
Distributes water in the cells, blood and fluid containing body compartments.


define: Aquaporins

Aquaporins are transmembrane proteins that construct water-specific channels that allow water to move freely and reversibly and water molecules to be diffused in a single file manner.
Believed to exist in all cell types they are most prevalent in red blood cells and cells involved in water balance (kidney tubule cells and others).


Define: Osmolarity

The total concentration of all solute particles in a solution.
Net diffusion of both solute and water occurs, moving down their concentration gradients, when the same volumes of aqueous solutions of different osmolarity are separated by a membrane that is permeable to all molecules in the system. When the water and solute concentration on both sides of the membrane is the same, equilibrium is reached.
Osmolarity is based only on a solutions total solute concentration. It is expressed as osmoles per litre (osmol/L). One osmol is equal to one mole of nonionizing molecules.


Define: Hydrostatic pressure

Hydrostatic pressure pushes water out, Osmotic pressure pulls water in.


Define: Isotonic

Any solution with the same osmotic pressure as body fluids. When a cell is exposed to an isotonic solution, it retains normal shape, with no net gain or loss of water.
The body's extracellular fluids and most intravenous solutions are isotonic.


define: Hypertonic

Any solution with a higher osmotic pressure than body fluids.
Has a higher concentration of non-penetrating solutes than in the cells. Cells that receive hypertonic solutions loose water and crenate (shrink).


define: Hypotonic

Any solution with a lower osmotic pressure than body fluids.
Hypotonic solutions are more dilute with a lower concentration of non-penetrating solutes, than cells.
Cells receiving hypotonic solutions swell quickly and eventually lyse (burst).


define: Active cell mechanisms

Particle movement from a region of lower concentration to a region of higher concentration. When this occurs, energy is required. This energy comes from the cellular metabolism, specifically from the molecule known as ATP, which is created in the mitochondria of cells.


Types of active cell mechanism's

Active transport


define: Active transport

the movement of particles through membranes from regions of lower concentrations to regions of higher concentrations (moves solutes, mostly ions, against the concentration gradient, requiring energy).
Requires carrier proteins similar to facilitated diffusion, but active transport also requires ATP.
In primary active transport hydrolyzed ATP causes phosphorylation of the transport protein, changing its shape so it pumps the bound solute accross the membrane.


the two types of active transport

primary active transport
secondary active transport